DOCUMENT RESUME

ED 325 324 SE 051 659

TITLE Science Framework for California Public Schools.Kindergarten through Grade Twelve.

INSTITUTION California State Dept. of Education, Sacramento.REPORT NO ISBN-0-8011-0870-5PUB DATE 90NOTE 238p.; For previous edition, see ED 164 358.

Developed by the Science Curriculum Framework andCriteria Cormaittee under the direction of theCurriculum Development and Supplemental MaterialsCommission.

AVAILABLE FROM Bureau of Publications, Sales Unit, California Dept.of Education, P.O. Box 271, Sacramento, CA 95802-0271($6.50 plus sales tax).

PUB TYPE Guides - Classroom Use - Guides (For Teachers) (052)-- Guides - Non-Classroom Use (055)

EMS PRICE MF01 Plus Postage. PC Not Available from EDRS.DESCRIPTORS Educational Improvement; *Educational Objectives;

*Elementary School Science; Elementary SecondaryEducation; Evolution; Professional Development;*Science Curriculum; Science Education; *ScienceInstruction; *Secondary School Science; StateCurriculum Guides

IDENTIFIERS *California

ABSTRACTThis science framework is about connections. Each

section draws on and contributes to those that precede and follow it.The framework opens with a discussion of the nature of science andthe need for science educators to model the attributes of scientificinvestigation including objectivity, testability, and consistency.The framework also calls for a thematic presentation of scienceconcepts so that students appreciate the connections across sciencedisciplines and learn how science relates to other subjects. Threechapters address the content of science. The repeated use of"sidebars" helps teachers appreciate zhe connections among thesciences. The final part of the framework demonstrates how scienceeducation might be implemented in the 1990's. There are specificrecommendations for the teaching of science and the restructuring ofscience education at the elementary, middle, and high school levels.There are also suggestions for attracting into science classesstudents who historically have been underrepresented in thoseclasses. "inally, the framework closes with ideas on how other facetsof the system, including staff development, assessment, and,especially, instructional materials, need to be changed to help allstudents achieve scientific literacy. Appendices include: (1)"Significant Court Decisions Regarding Evolution/Creation Issues";(2) "Education Code Sections of Special Relevance to ScienceEducators"; and a list of 33 selected refereaces. (CW)

Reproductions supplied by EDRS are the best that can be madefrom the original document.

****** ******* *******1. ********** ****** **T

1

SC ENCEFRAMEWORKfor California Public Schools

Kindergarten Through Grade Twelve

cr4

2

/,

U.S. DEPARTMENT Of EDUCATIONOnce el Educational Research and Impro.amantEDUCATIONAL RESOURCES INFORMATION

CENTER (ERIC)

This document has bean reoroduced asreceived Nom the gorsOn Or organizationongnating it

0 Minoz changes have been made to emproverploducnon Quality

Ram101y9.401 odmonsstatod in thd clocu-mint do not neCessargy represent otnoatOERI pc,soon or Doicy

"PERMISSION TO REPRODUCE THISMATERIAL IN MICROFICHE ONLYHAS BEEN GRANTED BY

T. Smith

TO THE EDUCATIONAL RESOURCESINFORMATION CENTER (ERIC)."

CALIFORNIA DEPARTMENT OF EDUCATIONBill Honig, State Superintendent of Public Instruction

Sacramento, 1990

SCIENCEFRAMEWORKfor California Public SchoolsKindergarten Through Grade Twelve

Developed by the

Science Curriculum Frameworkand Criteria Committeeunder the direction of theCurriculum Development andSupplemental MaterialsCommission

Adopted by the

California State Board of Education

Publishing InformationThe Science Frimework for California Public Schools was adopted by theCalifornia State Board of Education on Novemlzr 9, 1989, and themembers of the Board at that time warn Francis Laufenberg, President;Joseph D. Crerabino, Vice-President; Agnes Chan; Lee Manolakas; MarionMcDowell; Para: Mehta; Kenneth L Peters; David T. Romero; and JosephStein. The framework was developed by the Science Curriculum Frame-work and Criteria Ccmmittee and recommended to the State Board foradoption by the Curriculum Development and Supplemental MaterialsCommiision. (See pages ix and x for the membership of the full canmiuceand the. names of the principal writers and others who made significantcon-uibutions to the document.)

The Science FraMework was edited for publication by Marilyn Butts andStephanie Prescott, working in cooperaticn with Bill Andrews and ThomasP. Sachse of the Mathematics, Science, and Environmental Education Unit.The document was prepared for photo-offset productien by the staff of theDepaitment of Education's Bureau of Publications, under the direction ofTheodore R. Smith, Editor in Chief. Cheryl Shawver McDonald designedand prepared the layout for the framework, and Steve Yee prepared thecover, using a photo provided by the Naticnal Aeroniud= and SpaceAdministraticn (NASA). The typesetting was done by Merribeth Carlson,Jeanneue Huff, and Carey Johnson. The framework wxt published by theCalifornia Department of Education, 721 Capitol Mall. Sacramento,California (mailing address: P.O. Box 944272; Sacramento, CA 94244-2720). It was printed by the Office of State Printing snit distributed underthe provisions of Goyernmem Code Section 11096 Ind the LibraryDistributicn Act, which means that it is available through the publiclibraries in California.

et 1990 California Department of Education

Ordering InformationCopies of the Science Framework are available for 36.50 per copy, plussales tax for California residents, from the Bureau of Publications, SalesUnit, California Department of Education, P.O. Box 271, Sacramento, CA95802-0271 (pi: AC; 916-445-1260). A partial list. of other publications thatare available from the Department of Education appears at the end of thisdocument.

Cover Photo

The photo used for the cover was provided by courtesy of NASA. Itwasphotographed through the aft flight deck of is space shuttle and showsastronauts David C., Leestma (left) and Kathryn D. Sullivan prepare forextravehicular activity (EVA), the first suen feat for an Americanwoman.

ISBN 0-8011-0870-5

/7!" ,.'-'!!"^".7"m"'"'",'"T"17""...rry!".-"11.91117,

Contents

State Board's Message

Page

D. Energy: Sources and Transformations

Page

61

Foreword vii E. Energy: Heat 64Preface viii F. Energy: Electricity and Magnefism 67Acknowledgments ix G Energy: Light 72State Board of Education Policy on the Teaching H. Energy: Sound 75

of Natural SciencesExecutive Summary

xi1

Chapter 4. Earth Sciences 79

Part J. What Is Science9 1 A. Astronomy 79

Part II. The Content of Science 2 B Geology and Natural Resources 90Part III. Achieving the Desired Science C. Oceanography 98

Curriculum 3 D. Meteorology 106

Introduction 7 Chapter 5. Life Sciences 116

Part I. What Is Science? 11 A. Living Things 116

Chapter 1. The Nature of Science 12 B. Cells, Genetics, and Evolution 126

A. Introduction 12C. Ecosystems 136

B. The Joy of ScienceC. Teaching What Science IsD. Scientific Practice and Ethics

131418

Part III. Achieving the DesiredScience Curriculum 143

E. Social Issues in Science 19 Chapter 6. Science Processes and the Teaching

Chapter 2. The Major Themes of Science 26 of Science 144

A. Introduction 26 A. Scientific Thinking Processes 144

B. Why Themes Are Essential 27 B. The Processes in the Context of Child

C. Some Major Themes of Science 28 Development 152

D. Incorporating Themes 33 C. Developing Science Concepts 155D. The Role of Direct Experience in Science

Part II. The Content of f'..cience 37 Learning 156

Overview 38 E. Values and Ethics 157F. Science, Technology, and Society 158

Chapter 3. Physical Sciences 41 G. Elementary School Science 160

A. Matter 41 H. Middle School Science 161

B. Reactions and Interactions 48 I. High School Science 163

C. Force and Motion 53 J. Teaching All Students 167

5

Page

Chapter 7. Implementing a Strong ScienceProgram 172A. Introduction 172B. Implementation Planning 173C. Staff Development 175D. Assessment 176E. Resources 178F. An Implementation Model 180G. Relationship with Other Frameworks 195

Chapter 8. Instructional M nerials Criteria 198A. Introduction 198B. Content 200C. Presentation 203

List of FiguresFigure Page

I. Darwin's Conception of How Lineages ofOrganisms Diversify and Evolve 22

2. Reconstruction of Continents' RelativePositions 200 Million Years Ago 92

3. Geologists' Use of Rock Strata toReconstruct Ancient Environments 100

4. Amino Acid Sequences in the CytochromeC Molecules of 14 Organisms 117

List of Tables

Table

1. Matching Science Processes and Contentwith Children's Cognitive Development,Kindergarten Through Grade Twelve

2. A Matrix for Program Elements in ScienceEducation

3. A Pattern for a Content Matrix in ScienceEducationKindergarten ThroughGrade Six

4. Content Matrix: Example AKindergartenThrough Grade Six

5. Content Matrix: Example AEarthScience

Page

D, Pedagogy 207E. Local Considerations 211F. Conclusion: Putting Criteria into Practice 211

Appendix A

Significant Court Decisions RegardingEvolution/Creation Issues 214

Appendix B

Education Code Sections of Special Relevanceto Science Educators 215

Appendix C

Selected References 218

Figure Page

5. Cladogram 1246. Punctuational Evolution Contrasted with

Gradual Evolution 1317. The Carbon Cycle in the Ecosystem 1388. The Implementation Process 174

Page Table Page

6. Content Matrix: Example ASubconceptsin the Grade Four Curriculum Keyed

151 to Themes 1897. Content Matrix: Example BKindergarten

181 Through Grade Six 1918. Content Matrix: Exampk, BPhysical

Science 192183 9. Content Matrix: Example BSubconcepts

in the Grade One Com Curriculum186 Keyed to Themes 194

10. Weighting of Criteria for Adoption187 of Instructional Materials 199

lv

State Board'sMessage

THE 1990 Science Framework deals with the convic-tions of modern'science. More than any previousframework, this document addresses the scienceenterprise and the effects of this powerful force onour daily lives. Much has been written about the new"State-Board of Education Policy on the Teaching ofNatural Sciences." This new policy was drafted andapproved by the State Board of Education becauseour conviction that all science should be taughtnondogmatically needed clarification and amplifica-tion. As the State Board of Education, we needed togo on record in support of modern science. Wewanted to ensure that the ideas of science are madeclear to students and that they begin to learn andappreciate the distinctions between fact and theory,between belief and dogma. Students in today'sculture must routinely be reminded that skepticismand understanding are characteristics of a scientifi-cally literate mind.

There is much in this Science Framework for theState Board of Education to endorse. Beyond theBoard's resolve to support modern science is thepredisposition toward major reforms that can improvescience education significantly. We look forward to

impmvements in the way science is taught andlearned. Thematic teaching, coupled with activelearning, is the best way to provide students with thescience education they will need as voters, consum-ers, and parents in the future. As the State Board ofEducation, we join with science teachers, sciencespecialists, and the educational community in supportof science education in the 1990s that provides alifetime of learning and living in the year 2000 andbeyond.

California State Board of Education

FRANCIS LAUFENBERG, PRESIDENT

JOSEPH D. CARRABINO, VICE-PRESIDENT

AGNES CHAN

LEE MANOLAKAS

MARION MCDOWELL

PARAS MEHTA

KENNETH L. PETERS

DAVID T. Rommo

JOSEPH STEIN

7

THIS Science Framework calls for a new dynamic inscience learning. We want our students to be activelyengaged in learning about the natural and technologi-cal world in which they live. We want our students tograpple with the ideas of science as they learn theinner workings of the counterintuitive universe. Wewant students to enjoy learning science and to de-velop an interest in and responsibility for protectingthe environment. The expectation that students beactive learners is favored throughout the curriculum,but nowhere is it more demonstrable than in applyingthe five senses to the learning of science.

By active learning we mean instructional activitieswhere students take charge of learning the majorideas in science. There are many ways in whichstudents can be active learners. In science classes wetypically think of hands-on laboratory experiences,but there are many other forms of active learning,including active reading, listening, discoufse, andusing new learning technologies. The importantcommon denominator for active learning is thatstudents regularly make new associations betweennew ideas and their previous conceptions of how theworld works.

We are learning more each year about how studentsdevelop conceptual understanding in science. So far,we have learned that teachers must be cognizant ofthe conceptions students hold about how things work.And we know that students must create meaning forthemselves, which means we need to feature, ratherthan sterilize, the context in which science is pre-sented. We need to move beyond a simplistic dichot-omy that emphasizes just content or process. Instead,we need to merge the two in ways that students seethe meaning and utility of the scientific issues andideas.

vii

Just as we want students to be active learners, wealso want an active response to the challenges posedin how science education is organized. Testing andaccountability mechanisms must move toward moreauthentic assessment. Instructional materials mustexploit electronic technologie§ and refined pedagogy.The high school program must be reorganized tocompete with science education on an internationalscale. The middle school science program mustreflect the unique needs of students as they movethrough adolescence. The elementary school programmust be a well-organized effort in which teacherscollaborate to offer a sound science experience ateach grade level. Overall, we need to fashion scienceeducation to present students with the lively, engag-ing stories that science reveals.

This framework is designed to help science educa-tors at all levels understand and appreciate the neededreforms before us. Accordingly, this is a complex andchallenging manuscript. The reader is directed to theintroductory materials, which emphasize the appro-priate sections for each audience and purpose. I lookforward to a time when every student is involved inlearning science every year. California is technologi-cally advanced because of the ways we use science.We can perform no better service than helping allstudents share in the science-rich heritage that definesCalifornia.

8

State Superintendent of Public Instruction

THIS new Science Framework arrives at a time wheneducators throughout California and indeed theUnited States are grasping for a way to help allstudents achieve scientific literacy. Two previousframeworks, issued in 1978 and 1984, attempted toaddress the definition and development of scientificliteracy. Surely, those frameworksand the experi-ences learned in their implementationhave had an'important impact on the directions of the sciencereforms for the 1990s. There will likely be oneadditional framework before the close of the millen-nium, but for the students in the class of 2000, thisframework represents the best chancc to make thenecessary improvements systemwide. Therefore, theideas and strategies contained in this document areespecially important for addressing the crisis inscience education. We urge readers of this documentto reflect on how the efforts made by each student,teacher, school, and school district can contribute torefortning science education in California and in thenation.

This framework is about connections. As JamesBurke writes, "This interdependenc13 typical ofalmost every aspect of life in the modern world. Welive surrounded by objects and systems that we takefor granted, but which profoundly affect the way webehave, think, work, play, and, in general, conductour lives and those of our children."1'yhe frameworkembodiesihis sense of connections: Each sectiondraws on and contributes to those that precede andfollow it.

The framework oNns with a discussion of thenature of science and the need for science educatorsto model the attributes of scientific investigation,including objectivity, testability, and consistency. The

'James Burke, Connections. Boston: Little, Brown & Co., 1980.

framework also calls for the thematic presentation ofscience concepts so that students appreciate theconnections across science disciplines and learn howscience relates to other subjects.

Three chapters address the content of science. Therepeated use of "sidebarb" helps readers appreciatethe connections among the three branches of science.Part III of the framework demonstrates how scienceeducation might be implemented in the 1990s. Thereare specific recommendations for the teaching ofscience and the restructuring of science education atthe elementary, middle, and high school levels. Thereare also suggestions for attracting into science classesstudents who historically have been underrepresentedin those classes. Finally, the framework closes withideas on how other facets of the system, includingstaff development, assessment, and, especially, in-structional materials, need to be changed to help allstudents achieve scientific literacy.

Ultimately, the implementation of the ideas in thisframework rests with California's classroom teachers.To the extent that they make these connectionsmanifest for their students, teachers will be modelingthe spirit and practice of science in their classrooms.As we reach for scientific literacy by the year 2000,we salute California's science teachers in their questto make science basic for all students.

JAMES R. SMITHDeputySuper intendentCurriculum and InstructionalLeadership Branch

FRANCIE ALEXANDERAssociate SuperhuendetuandDirectorCurriculum, Instruction,and Assessment Division

9

WALTER DENHAMAdministrator

Office of Mathematics,Science,l1 calf 11,Nutrition,

and Physical Education

THOMAS P. SAC HSEAdministrator

Mat hematics,Scie nee, andEnvironmental EducationU nit

Acknowledgments

Contributing WritersThe following indiyiduals made significant contribu-

tions in the writing of the chapters or sectionsnoted for each:

Kathryn E. DiRanna, Executive nirector, CaliforniaScience Implementation Network, University ofCalifornia, Irvine (Implementation)

Peter Giddings, Meteorologist, KGO-Television, SanFrancisco (Meteorology)

Scott Hays, Teacher and Curriculum Coordinator,Coffee Creek Elementary School District (PhysicalSciences Implementation)

Arie R. Korporaal, Science Constultant, Office of theLos Angeles County Superintendent of Schools(Science Piocesses, Teaching'All Students)

Lawrence S. Lerner, Professor of Physics andAstronomy, California State University, LongBeach (Heat, Electricity and Magnetism, Light,Sound; Earth Sciences; The Nature of Science)

Larry Lowery, Professor of Education, University ofCalifornia, Berkeley (Science Processes)

George E. Miller, Senior Lecturer in Chemistry,University of California, Irvine (Physical Sciences,Secondary School Science)

Kevin Padian, Associate Professor of IntegrativeBiology and Curator, Museum of Paleontology,University of California, Berkeley (The Nature ofScience, Life Sciences, Earth Sciences.Instructional Materials Criteria)

Wendell Potter, Associate Professor of Physics,University of California, Davis (Physical Sciences)

Science Curriculum Frameworkand Criteria CommitteeDanielle A. Andrews, Teacher and Elementary

Science Specialist, Vacaville Unified SchoolDistrict

lx

Kathryn E. DiRanna, Executive Director, CaliforniaScience Implementation Network, University ofCalifornia, Irvine

Thomas C. Edholm, Science Teacher, Fresno UnifiedSchool District

Gary E. Estep, Science Teacher and Department Chair,Chico Unified School District

Philip D. Gay, Science Curriculum Coordinator, SanDiego Unified School District

Judith S. Gordon, Science Resource Teacher, LosAngeles Unified School District

Scott Hays, Teacher and Curriculum Coordinator,Coffee Creek Elementary School District

Helen E. Huey, Teacher, Ukiah Unified SchoolDistrict

Michael E. Jay, Product Analyst, Apple Computer, Inc.Arie R. Korporaal, Science Consultant, Office of the

Los Angeles County Superintendent of SchoolsLawrence S. Lerner, Professor of Physics and

Astronomy, Californizi State University, LongBeach

George E. Miller, Senior Lecturer in Chemistry,University of California, Irvine

Gary A. Nakagiri, Coordinator of Mathematics andScience Education, Office of the San Mateo CountySuperintendent of Schools

Kevin Padian, Associate Professor of IntegrativeBiology and Curator, Museum of Paleontology,University of California, Berkeley

Joe Alfonso Smith, Teacher, Ramona Unified SchoolDistrict

Dorothy J. T. Terman, Science CurriculumCoordinator, Irvine Unified School District

California Department of EducationBill Andrews, Consultant, Mathematics, Science, and

Environ-rtental Education Unit

10

Jerry Cummings, Consultant, Curriculum Frameworkand Textbook Developinent Unit

Gayland Jordan, Consultant, Mathematics, Science,and Environmental Education Unit

Thomas P. Sachse, Administrator, Mathematics,Science, and Environmental Education Unit

Zack Taylor, Consultant, Mathematics, Science, andEnvironmental Education Unit

Glen Thomas, Administrator, Curriculum Frameworkand Textbook Development Unit

Science Subject Matter Committee of theCurriculum Development and Supplemental'Materials Commission

Elizabeth K. Stage (Chair), Executive Director,California Science Project, University of

x

California (formerly Lawrence Hall of Science,University of California, Berkeley)

Ann Chlebicki, Assistant Superintendent, SaddlebackValley Unified School District

Charles Kocpke, Teacher, Upland Unified SchoolDistrict

Jesse Perry, Program Manager for English LanguageArts, San Diego Unified School District

Roger Tom, Director of Curriculum and StaffDevelopment, San Francisco Unified SchoolDistrict

Tom Vasta, Teacher and Science Resource Specialist,Elk Grove Unified School District

11

On January 13 , 1989, the State Board of Education adopted the following policy statement on the teaching of natural

sciences.This statemera supersedes the Board's 1972 Antidogmatism Policy that xas distributed statewide in 1981 and

printed in the 1984 Science Framework Addendum. To this newpolicy statement are appended standard scientific dictionary

definitions of several scientific terms to emphasize their meanings in scientific contexts.

State Board of Education Policy on theTeaching of Natural Sciences

The domain of the natural sciences is the naturalworld. Science is limited by its toolsobservablefacts and testable hypotheses.

Discussions of any scientific fact, hypothesis, ortheory related to the origins of the univeise, theearth, and of life (the how) arc appropriate to thescience curriculum. Discussions of divine crea-tion, ultimate purposes, or ultimate causes (thewhy) are appropriate to the historysocial scienceand Englishlanguage arts curricula.

Nothing in science or in any other iield ofknowledge shall be taught dogmatically. Adogma is a system of beliefs that is not subjectto scientific test and refutation. Compellingbelief is inconsistent with the goal of educa-tion; the goal is to encourage understanding.To be fully informed citizens, students do nothave to acpt everything that is taught in thenatural science curriculum, but they do have tounderstand the major strands of scientificthought, including its methods, facts, hypotheses,theories, and laws.

A scientific fact is an understanding based onconfirmable observations and is subject to testand rejection. A scientific hypothesis is anattempt to frame a question as a testable proposi-tion. A scientific theory is a logical constnictbased on facts and hypotheses that organizes andexplains a range of natural phenomena. Scientific

theories am constantly subject to testing, modifi-cation, and refutation as new evidence and newideas emerge. Because scientific theories havepredictive capabilities, they essentially guidefurther investigations.

From time to time natural science teachers arcasked to teach content that does not meet thecriteria of scientific fact, hypothesis, and theoryas these terms am used in natural science anddefined in this policy. As a matter of principle,science teachers are professionally bound to limittheir teaching to science and should resist pres-sure to do otherwise. Administrators shouldsupport teachers in this regard.

Philosophical and religious beliefs are based, atleast in part, on faith and arc not subject to scien-tific test and refutation. Such beliefs should bediscussed in the social science and language artscurricula. The Board's position has been stated inthe Board's adopted policy, Moral and CivicEducation and Teaching About Religion (1988),and in the HistorySocial Science Framework(1988). If a student should raise a question in anatural science class that the teacher determinesis outside the domain of science, the teachershould treat the question with respect. Theteacher should explain why the question isoutside the domain of natural science and encour-age the student to discuss ihe question furtherwith his or her family and clergy.

xl 1 2

Neither the California nor the United StatesConstitution requires, in order to accommodatethe religious views of those who object to certainmaterial or aztivities that art presented in scienceclasses, that time be given in the curriculum tothose particular religious views. It may be uncon-stitutional to grant time for that reason.

Nothing in the California Education Code allowsstudents (or their parents) to excuse class atten-dance based on disagreement with the curricu-lum, except as specified for certain topics dealingwith reproductive biology and for laboratorydis-

section of animals. (See California EducationCode sections 51550 and 32255.1 [Chapter 65,Statutes of 1988], respectively.) However, theUnited States Constitution guarantees the freeexerche of religion, and local governing boanisand districts are encouraged to develop state-ments like this one that recognize and respect thatfreedom in the teaching of science. Ultimately,students should be made aware of the differencebetween understanding, which is the goal ofeducation, and subscribing to ideas, which is not.

tiorn`ffOrriti*BaiOail Dictiologeienee. Mapleweed; If.I.:-Hamthond,irie., ©1986.

n on*

Ialivivsoccnis

"otfaisutheitistbaiis*)041:id

'044t5f,;..,-k".4_

11140:41,-, ..P11.694-0faideil?Os0 on _

yOneAli4lias' been tested and çonfiimed-is

-getier41.,pSineriPie **lig to eXplairrand predict#0141****:-_thetteOry-of EiAition.... . .Vt401%-h. terffiSifi science-titan a

It:oet4144O4 ctd by :..- *nee, ftonT, observed-P000140' aidpcbposed -as* eplanation .of their-044-- 161-Aids:a-' meOliicl.t greater degree. ..... _ _ _..._

ffypoUiesis designate:5 a merelytOtita*t 141g**100 of . *-04.zbithoo.4 or

_: Of0Yisi*Ally;offeti at-1114.baits.-Ofa'tl*ory4f it kg-tOck-gyfiliither obsivation oreV:dine/it,. ..

1 SxH

Executive Summary

Chapter 1The Nature el Science

Science is a field that is constantly adapting to newadvances in basic knowledge, medicine, and technol-ogy. An understanding of the nature of science and anappreciation of its methods and philosophy continueto be necessary parts of education. How the naturalworld works is important to everyone's education.Students need to understand the way of thinking andasking questions that is the essence of science.Science is also important for its own sake. A personcan carry an appreciation of science all through lifeand use it to learn more about the natural world.

Technology is based on fundamental science.Educators have the chance to prepare students for thetechnology of the finure by helping them develop adeeper knowledge of basic science. We must clearlypresent how science works, what processes andmethods expand scientific knowledge, and whatscience is and what it is not.

To be effective, science education should beenjoyable. Science is a source of enjoyment much asmusic is. The appreciation of science is likely toincrease as the audience becomes more knowledge-able about the workings of the discipline. Science isconcerned with all of nature, medicine, and technol-ogy; it can prepare students for decisions they mustmake as adultsdecisions that are increasinglydependent on a clear understanding of science.

14

Science is guided by a particular kind of theory thatcan be tested in the natural world, with methods thatany practitioner of science can and must follow. Thescientific method aims to be testable, objective, andconsistent. Science is opcn-ended, but scientistsoperate with expectations based on predictions oftheory. Scientists use a preexisting body of observa-tions, facts, inferences, hypotheses, and theories tobuild expectations of what will happen and to guidefurther inquiry. Teachers must strive to show studentshow expectation and openness both play importantroles in science. Scientific knowledge must bepresented as authoritative, not authoritarian. We candepend on scientific knowledge and theory, yet wecan always learn more and must constantly revisewhat we know in the light of new discoveries.

Science is based on observations set in a testableframework of ideas. To observe is to use the evidenceof our senses to obtain the information on whichscientific work is based. Scientific inquiry is guidedby theory, which is a logical construct of facts andhypotheses that attempts to explain a range of naturalphenomena. Theories are sometimes replaced whollyor in part by new theories. The new theory does thisby explaining everything that the old theory ex-plained, as well as other evidence that might not havefit very well in the old theory. This is how scienceproceeds. But science never commits itself irrevoca-bly to any fact or theory, no matter how firmly itappears to be established in the light of what is

known. This is not a weakness of uncertainty but astrength of self-correctability. Science is not a matterof belief; rather, it is a matter of conclusive evidencethat can be subjected to the tests of observation and

Execulive Summary

objective reasoning. The open competition of ideas isa major part of the excitement of science. Emphasisin the classroom should be placed not on coming upwith the right answers buton doing science the rightway.

There are scientific issues that arouse controversy.Some of these issues are ethical, some involveclarification of scientific methods and philosophy,awl some are not strictly within the realm of science.School boards, administrators, and parents mustsupport the teaching of rigorous science, a iationalapplication of science to scientific and technologicalactivities. Science instruction should respect theprivate beliefs of students; on the other hand, theteaching of science cannot be suppressed simplybecause some individuals disagree with findings onreligious or philosophical grounds.'

Chapter 2

The Major Themes of Science

This Science Framework differs from previousframeworks and addenda in its emphasis on the majorthemes of science.

Themes are the big ideas of science, 1' Tier thanfacts and concepts; they link the theoretical structuresof the various scientific disciplines. Themes am away to integrate the overarching concepts of scienceinto a curriculum, much as theories encompass andconnect the basic data and evidence of science.

Six major themes are developed in this framework:(1) energy, (2) evolution; (3) patterns of change; (4)scale and structure; (5) stability; and (6) systems andinteractions. Educators and developers of instruc-tional materials are encouraged to weave these oralternative thematic strands into science curricula.These major themes occur again and again in thesciences, whether one studies ecology, plate tecton-ics, meteorology, or organic chemistry.

Themes are necessary in the teaching of sciencebecause they are necessary in the doing of science. Inorder for science to be a philosophical discipline andnot merely a collection of facts, there must be athematic connection and integration. Themes providea framework to guide teachers in developing instruc-tional tools. If curricula and instructors are successfulin developing themes for students to use in connect-ing and integrating scientific concepts and facts, then

2 Science Framowork

this intellectual habit will carry over and enrich otherfields and disciplines.

Themes should be used to integrate concepts andfacts at all levels of the curriculum. Through the useof themes, such as those of scale and structure ands3 lems and interactions, students can see how theparts fit toge ,ther logically and how The informationthey are learning is used to describe other kinds ofphenomena.

Within individual disciplines, such as physicalsciences, earth sciences, and life sciences, themesneed to be instituted and developed throughout ayear's study and from one year to another.

Themes should be used to integrate the mainsubfields of scientific disciplines. The subfields oflife sciencegenetics, evolution, and paleontologyare connected by using the themes of evolution aswell as those of pattern. lf change and scale andstnicture.

Themes in science shou... direct the design ofclassroom activities. They can connect classroomactivities and provide them with a logical sequenceand scope of instruction.

Assessment should be thematically and conceptu-ally based. Instead of repeating facts learned in chap-ters and units, explaining the connections amongconcepts in the light of themes represents an improve-ment in assessment practices.

The use of conceptual themes will not by itselfsolve all the problems of science education. However,the incorporation of themes in thoughtful and judi-cious ways should improve the integration of factsand ideas, the interrelationships of theories anddisciplines, and the quality of instructional materials.

THE content of a science program is its heart. Thethematic approach described in this framework makesconnections among the scientific disciplines that havetraditionally been taught as separate subjects. Herewe illustrate one way that a conceptual approach canbe organized within the traditional content areas ofscience.

It is important to distinguish between theories,which are conceptnal and empirical entities within adiscipline that unify u`te content of that discipline, and

15

themes, which are pednogical tools to unify ideasamong different disciplines.

Some ideas, such as energy and evolution, appearas both theories and themes. Evolution, for instance,is the theory that unifies the content of biology.Evolution is also a theme that unifies the content ofvarious disciplines by observing evolution in bothgeological and biological history.

Within the traditional areas of physical sciences(Chapter 3), earth sciences (Chapter 4), and lifesciences (Chapter 5), we describe the underlyingtheories in the discipline. Then wc present a set ofquestions central to the content area. These arefollowed by a narrative description of content, writtenfrom the perspective of one or more of the majorthemes of science, appropriate to various gradelevels. The purpose of this approach is to avoid anemphasis on isolated facts and definitions that havelong dominated science instruction.

The choice of questions is not definitive nor exclu-sive; we did, however, concentrate on areas that havebeen poorly represented in the past. For instance, theframework may emphasize learning the causes ofweather, rather than how to read a weather map(though students will still learn this, but it is an activ-ity already well represented in traditional materials).

The intended audience for these descriptions is notstudents but educators and textbook publishers.

Part ni Actheving the'DesiredScience Curriculum

Chapter 6Science Processes and the Teachingof Science

Students should be helpcd to increase their knowl-edge of the natural world and to understand itsconnection to our technologically advanced society.A student-centered science program can be created byteachers who are free to design the types of experi-ence that best fit their-students.

The content of science consists of a highly strtic-lured, complex set of facts, hypotheses, and theoriesin a context where many observations have meaning.Th3ory development is progressive; theory suggestsfurther observations that often make possible furtherelaboration and testing of the theory. Scientists use

16

their senses and extensions of their senses to see,touch, and otherwise view the world, observing itscharacteristics and behaviors as objectively as pos-sible. Scientists describe and picture what theyobserve in various ways, thus communicating theirideas to others so that they can exchange views andinterpretations and pass along information. They testwhat they know against what they do not yet know,comparing features and behaviors for similarities anddifferences. Scientists organize their understandings,ordering and categorizing them into broader, moregeneral groupings and classifications. They study theinteractions among objects and describe the events,relating factors that reveal deeper insights into causesand effects. Scientists hypothesize and predict whatwill happen, based on accumulated knowledge and onthe events they expect to take place, inferring some-thing that they have not seen because it has not yethappened or because it cannot be observed directly.And as knowledge grows through the use of thesescientific thinking processes, scientists developexpertise, applying both knowledge and processes foruseful purposes, to make still further extensions ofthe explanatory power of theory and to perceive fresh

possibilities.In developing science concepts, a teacher should:

(1) pose questions to determine what ideas studentshold about a topic before beginning instruction; (2) besensitive to and capitalize on students' conceptionsaboutscience; (3) employ a variety of instructionaltechniques to help students achieve conceptualunderstanding; and (4) include all students in discus-sions and cooperative learning situations.

It is necessary to engage students in science activi-ties by placing them in a position of responsibility forthe learning task. Students should be provided withexperimental problcm-solving experiences where theresult has direct meaning for them.

As a human endeavor, science has a profoundimpact on society. Values and ethics arc importantcomponents of science teaching and must be consid-ered by teachers, textbook authors, and curriculumwriters. It is important to (1) identify thc commonlyshared values of the scientific community; (2) pro-mote scientific values in the classroom; and (3)develop rational decision-making skills applicable tomajor issues of personal and public concern.

Science is directed towards a progressively greaterunderstanding of the natural world. Technology is

Executive Summary 3

related to science as a human endeavor, but thedirection is toward using accumulated knowledgefrom science and other fields in order to control andalter the way things work. Teaching a Science,Technology, and Society (STS) approach is invari-ably interdisciplinary, with strong connections tohistorysocial science, mathematics, literature, andthe arts. Teaching science in the context of STS helpsreveal the situations in which science has meaning.

The elementary science program holds greatpotential for exploring natural phenomena andtechnological applications in science. At a time whenchildren are most curious about the world, teacherscan capitalize on this joy of learning in ways thatmake science enjoyable, interesting, and meaningful.

In most curricular areas, middle school programsare seen as transitions from a sound basis providedduring elementary grades to the specialization of highschool. For students in middle school, it is importantto provide a semester of health and relevant adoles-cent topics as well as electives for those interested.

The high school science curriculum is less subjectto mandate than that of die elementary school. Not allstudents take more than a minimum of sciencein highschool, and no textbook adoption process is usedbeyond grade eight. In spite of strong traditions re-garding what high school biology, chemistry, andphysics courses should be like, many excellentoptions for teachers and students have been devel-oped. The process of science as an aesthetic pursuitand an effective tool with the power to both createand solve problems must be apparent to graduatesfrom high school.

With concerns of domestic equity and internationalcompetitiveness, science educators must help ensurethat all studentsincluding the historically under-representedhave an equal opportunity to succeed inscience-related endeavors. By all reports and analy-ses, females,-minoritygroups, and persons withdisabilities are underrepresentedjriundergraduate andgraduate programs, research, industry, and otherscientific enterpriSes. Fortunately, there are individu-als and pilot progtams working to help youngstersovercome barriers that keep them from succeeding.

All children in California, including those whoseprimary langnage is other than English, should haveaccess to high-level science instruction. Students whoare limited-English proficient (LEP) can have imme-diate entry into science via their primary language

4 Science Framework

while acquiring English. The strategies describedhere can be used by teachers to lower the linguisticbarriers that prevent access to their disciplines.

Chapter 7

implementing a Strong Science Program

A well-formufated districtwide plan for scienceeducation provides the basic design for the establish-ment of an effective science program. Proof of theestablishment of a good science program lies instudent growth in understanding and enthusiasm forscience.

Implementation entails more than the disseminationof information, materials, and programs. To ensurethat an adopted science curriculum results in knowl-edge, experience, and understanding for students, theprogram must be challenging, stimulating, and useful,Students should be doing science in their classrooms,not merely readin About it.

The changes suggested by this framework build onthe preceding Science Framework and ScienceFramework Addendum and sirengthen the positionthat students should actively experience sciencerather than passively read about it. The changes inpractice that are requiml to implement thisframework faithfully involve a shift from instructionthat emphasizes accumulation of knowleige to aprogram that develops concepts and an understandingof the connections among the disciplines of science.

Effective implementation incorporates both adistrictwide plan and plans for individual schools. Awhole range of people should participate throughoutthe implementation processprincipals, governingboards, district and county personnel, and localcollege and university representatives.

An effective science program depends primarily onteachers who are enthusiastic, informed, and providedwith adequate resources. Teachers need the opportu-nity_toexperiencethe kind of instruction they arebeing asked to provide. While generic workshops onteaching techniques and classroom managementstrategies are of benefit to science teachers, it isimportant that substantial time and resources bedevoted to strategies for incorporating these tech-niques most effectively in the teaching ofscience.

If the goals of the science program are scientificliteracy and the ability to make sense of the world,then tests of vocabulary and knowledge will nct

17

measure their attainment. The design of an assess-ment program requires as much care and considera-tion as the design of the instructional program itself.There is a temptation to limit assessment of teachersto.what can be most easily observed: direct instruc-tion. This is as much to be avoided as limiting studentassessment to _what can be most easily measured:factual recall. The assessment of instruction mustmeet the challenge^of the wide range of instructionalstrategies Proposed in this framework in the sameway that teachers meerthese challenges in makingdecisions about instmction.

The physical resources of the entire school plantand the community should be taken into considera-tion in planning the science instructional program.Equipment and mato lals must be made available toall teacherselementary and secondary. Traditionalequipment, such as test tubes, scales, meter sticks,and microscopes, has always had a prominent role ineffective science programs. As newer products oftechnology, such as scientific calculators, computers,videotapes and videodisks, become less expensiveand more significant as mechanisms for teaching andlearning, their role should be constantly evaluated fortheir contribution to an effective science program.

Technology can provide conduits to new informa-tion, experiences, and an opportunity to experimentand fail in a safe environment. A likely result of theincreased use of technology in the classroom is theevolution of the role of the teacher from disseminatorof information to facilitator of the students' learning.Mechanisms for changing the way that teachers teachwill have to incorporate this view of technology'srole in instruction.

Parents and the community offer tremendouspotent;a1 for supporting and enhancing the school'sscience program.

The California Science Implementation Networkhas developed a school-based model that manyteachers and principals have found useful. Theplanning proms, which involves the entire schoolstaff, hasihree steps: (1) complete a matrix forprogram elements'and one for content; (2) conductindicated staff development; and (3) monitor individ-ual teacher progress. (Information about this networkcan be obtained from the California Department ofEducation's Mathematics, Science and Environ-mental Education Unit.)

The reforms in science education that are reflectedin this framework are part of an overall reform

1 8

strategy to transform education for all students so thatit promotes thinking and reasoning. The manifesta-tion of this attempt to cultivate higher-order thinkingtakes different forms in different subject areas. Ineach case, the details and mechanics of the disciplineare teing subordinated to the goal a a meaning-centered curriculum, with the aim of increasing thethinking and reasoning in which students engage.

Chapter 8Instructional Materials Criteria

The California State Board of Education has begunto use the adoption process as a way of supporting thecurriculum reform reflected in its recent frameworksand standards. More stringent criteria place additionaldemands on publishers and teachers alike. We feel,however, that fine instructional materials can them-selves instruct teachers while they support studentlearning.

The instructional materials criteria that followdiffer from past criteria in a number of ways. Theoverall weighting is as follows: content, 50 percent;presentation, 25 percent; and pedagogy 25 percent.(See Table 9 in Chapter 8 for the full list of weighted

criteria.)Content refers to the subject matterhow well it

represents what is currently known of science.Content should be treated dynamically, including athematic approach that makes connections amongideas, and it should value depth over breadth ofcoverage. Standards for evaluation include whether(1) the topics discussed in Part II of this frameworkare treated in the instructional materials under consid-eration; (2) content is treated accurately and cor-rectly; (3) instructional programs are organizedaround themes, not around facts; (4) instructionalmaterials in science emphasize depth of understand-ing, not encyclopedic breadth of coverage; and (5)explanations embroider the accumulation of knowl-edge, with a detailed description of how it is that wecame to know these facts and why this information isimportant.

Presentation means how science is described,organized, written, and illustrated. Standards forevaluation include whether (1) the prose style ofinstructional materials is considerate and engagingand the language and vocabulary of science are re-spected; (2) language is accessible to students; (3) the

Executive Summary 5

character of science is represented faithfully: that it isshown as open to inquiry, open to controversy, andnondogmatic by it&nature; and (4) science is pre-sented as an enterprise that does not operate inIsolation from-society and technology or from otherfields of.kpdivledge.

Pedagogy refers to the instmctional methods thatare emploYed. Standards for evaluation includewhether (1) instructional programs are connectedwitivexperience; (2) instructional materials recognizecultu.al diversity and reflect strategies that researchand practice have shown to be successful in meetingthe needs of all students; and (3) assessment isintegrative and oriented toward solving problems, notsimply recall-based.

The criteria pmviously described will guide theInstrudtional Materials Evaluation Panel (IMEP), agroup of approximately 40 teachers, curriculumspecialists, and scientists who review the materialssubmitted for adoption and submit its recommenda-tions to the Curriculum Development and Supple-mental Materials Commission (CDSMC), which willin turn make recommendations to the State Board ofEducation. This section concludes with some ex-

6 Science Framework

amples of what is andis not desirable in sciencewriting.

The most important points made in this section am(1) the desirability of thematic orientation in sciencecurricula; (2) the motivation andlearning that can begenerated by hands-on, experience-oriented activitiesand curricula; (3) the importance of "considerateprose" and the elimination of readability formulas asdetenniners of grade-level appropriateness of curricu-lar materials; and (4) the fundamental respect forscientific methods of inquiry and for the language andphilosophy of science that is absolutely necessary to ascience program.

Improvement in instructional materials must becoupled with support for more in-service training forteachers and reevaluation and change in criteriacommonly used in the adoption and selection ofinstructional materials. These improvements are theprincipal means by which the current system ofdeveloping, adopting, and using instructional materi-als can meet the challenges of educating studentsabout what science really is and how it matters totheir lives.

1 9

Introduction

IN1983 A Nation at Risk declared that Americaneducation had become victim to "a rising tide ofmediocrity." The National Science Board's Commis-sion on Precollege Education in Mathematics, Sci-enceand Teclriology confirmed that the situation inscience education was particularly critical. Recentstudies have placed America's students last amongtheir international counterparts in understandingscience. In 1988 the National Assessment of Educa-tional Progress of the Educational Testing Service(ETS) issued The Science Report Card. ETS notedthat although the responses in the years since 1983have resulted in some progress, "average scienceproficiency across the grades remains distressinglylow."

What are the major reasons for this state of affairs,and what can be done to improve it? A first wave ofeducational reform, stimulated by the early reports,prompted legislatures to regulate administrativestrategies. Both nationally and in California, theresults were raised standards, increased graduationrequirements, and a longer school day and year. Thesecond wave of reform addressed the teachingprofession and again raised standards while increas-invesponsibilities and roles.

BY establiSting R.stronger and more demandingapparatus, these reforms paved the way for a thirdwaVe of reform that focuses on what and how stu-dents learn. The 1990 Science Framework addressestwo.aspects of this focus: (1) What is important tolearn? and (2) How can we ensure that alisaidentshave the opportunity to learn it? It is natural torespond to these questions in terms of a common corecurriculum for all students. A core curriculum is notunique to science. But in a field in which proliferationof knowledge is so extensive and the exclusion of

20

certain students from access to that knowledge sopervasive, it is essential to develop a core curriculumthat is appropriate for all students.

Although it is founded on the 1978 Science Frame-work for California Public Schools and the 1984Science Framework Addendum, the 1990 ScienceFramework shifts the emphasis of science educationby centering on the answers to the questions raised in

the preceding paragraph. In recent years tremendousprogress has been made in response to those previousdoduments by making science instruction moreexperiential and engaging for students. Yet thegeneral trend has been to reduce and compartmental-ize science content and focus on isolated facts andconcepts. This fragmentation is especially detrimentalin the elementary grades. Rather than being encour-aged to attain a global and integrated understandingof the natural world, which the disciplines and thenature of science describe and define so beautifully,students have been encouraged to memorize isolatedfacts and concepts.

To.counteract this situation, this framework empha-sizes a thematic approach to science. Its approach isderived from the most current available thinking andcriticism of instructional practices. Science for AllAmericans, a report issued by Project 2061 of theAmerican Association for the Advancement ofScience in February, 1989, envisions an ideal contentfor future science courses. That report shows a needfor a thematic approach to science instruction todemonstrate the connections that exist among thevarious disciplines of science and enable students tounderstand the rapidly changing world.

The purposes of this framework are consistent withthose of the Instructional Materials and FrameworkAdoption Policies and Procedures developed by the

Introduction 7

Office of Curriculum Framework and TextbookDevelopment of the California Depaftment of Educa-tion and approved by the State, Board of Education inJune, 1988; that is, to (1) eFtahlish guidelines andprovide direction to help districts revise their curric-ula, evaluate their programs, assess their instruction,and develop instructional strategies; (2) serve as aresource for preservice and in-service education ofteachers and administrators; (3) provide direction topublishers for the development of textbooks andinstructional materials and to reviewers for selectinginstructional materials and testing programs; and(4) make information on curricula available to parentsand the general public.

Another primary audience for the frameworkincludes science curriculum specialists, sciencesupervisors, science staff developers, and those incurriculum development and leadership roles. Thecommittee, members of which are listed on page ix, isrepresentative of these roles, including faculty frompublic schools, kindergarten through grade twelve,and universities; science consultants from district andcounty offices; and other persons with responsibilityfor curriculum and staff development. This portion ofthe audience that the committee members had in inindwas very much like themselves but was operationallydefined as the teacher whom you would expect tofind on a district curriculum development committee.Therefote, what follows presumes some backgroundand interest in science. We do not expect teachers orothers who have no background or particular inteiestin science to use this framework as their first experi-ence in teaching science. This document is not atextbook or a curriculum guide, nor is it a substitutefor extensive staff development, in-service training,or professional preparation.

Different audiences will be interested in differentsections of this framework. Part I answers the ques-tion, What is science? and should be read by, thoseinterested in science and the science curriculum. Indescribing the nature and themes of science, itpromotes the conceptual teaching of science. Part IIoutlines the required content of physical, earth, andlife sciences programs. Part III has three chaptzrs:Chapter 6 is intended for teachers and supervisorswho are interested in the processes of teaching andthe processes of science; Chapter 7 is intended forsupervisors, department chairs, principals, and otheradministrators who have msponsibility for imple-

8 Science Framework

menting the science curriculum; and Chapter 8 isintended for publishers and other devulopers andreviewers of instructional materials who collectivelyform the other primary audience for the framework.

After the approval of a framework by the StateBoard of Education, the Department of Educationtakes several steps to provide a consistent sciencecurriculum. The Department will review and, ifnecessary, revise the Quality Criteria (for elementary,middle grades, and high schools), the Model Curricu-lum Standards, Grades Nine Through Twelve, and theScience Model Curriculum Guide, KindergartenThrough Grade Eight. The California AssessmentProgram will use this framework as the basis fordesigning assessment of students in grades three, six,eight, and twelve. State-supported professionaldevelopment programs, such as the California Sci-ence Implementation Network (for elementaryschools) and the California School LeadershipAcademy (for administrators), will review theircurricula and bring them into alignment. The In-tersegmental Committee of the Academic Senateswill consider the match with its Statement on Prepa-ration in Natural Science Expected of EnteringFreshmen. Of course, these changes will not takeplace immediately, but they should assist educators inpreparing for the changes embodied in this frame-work. And in 1992 the State Board of Education willadopt instructional materials that meet the criteriadelineated here.

To achieve scientific literacy for all of our students,we hold the following expectationswhich reflectthe main ideas in the frameworkfor science pro-gmms:

1. The major themes underlying science, such asenergy, evolution, pattems of change, scaleand structure, stability, and systems andinteractions, are developed and deepenedthrough a thematic approach.

2. The three basic scientific fields of studyphysical, earth, and life sciencesarcaddressed, ideally each year, and the connec-tions among them are developed.

3. The character of science is shown to be opento inquiry and controversy and free of dogma-tism; thc. curriculum promotes student under-standing of how we come to know what weknow and how we test and revise our thinking.

4. Science is presented in connection with itsapplications in technology andits implicationsforsociety.

5. Science iS presented in connectiOn withstudents' own experiences and interests,frequently using hands-on experiences that arcintegral to the instructional sequence.

6. Students am-given opportunities to consuuctthe important ideas of science, which are thendeveloped in depth, through inquiry and inves-tigation.

7. Instructionar strategies and materials allowseveratlevels and pathways of access so thatall students can experience both challenge andsuccess.

8. Printed materials are written in an interestingand engaging narrative style; in particular,vocabulary is used to facilitate understandingrather than as an end in itself.

22

9. Textbooks are not the sole source of thecwriculum; everyday materials and laboratoryequipment, yideotapes and software, and otherprinted materials such as reference booksprovide a substantial part of student experi-ence.

10. Assessment prograim are aligned with theinstrucLioaal program in both content andformat; student performance and investigationplay the same central role in assessment thatthey do in ingniction.

The 1990 Science Framework builds on previouswork and, much like science itself, is subject torevision. We trust that it represents a step forward forscience education in California, and we hope that ithelps to bring the joy and power of scientific inquiryand understanding to all of our students.

Introduction 9

Part I

What Is Science?

2311

Chapter 1

The Nature of Science

THis first chapter is about science itself: what it is,what itis not, what its philosophies and methods are,and how these differ from those of other intellectualactivities. Structured closely after the State Board ofEdutation's 1989 policy statement on the teaching ofscience (reproduced in the beginning of this docu-ment), it is meant to serve as a guide for teachers,administrators, and parents on the nature of scienceand what is and is not appropriateto teach in ascience classroom. Beyond these functions, thischapter also guides teachers on how to deal withsocially relevant and sensitive scientific issues andhow to ensure that the views and beliefs of all stu-dents are treated with respect. This chapter is instru-mental to the understanding of the rest of the frame-work.

Section, A Introduction

EDUCATING children for the future is one of theprincipal aims of any well-balanced curriculum. Thisis especiallyimportant in science education, a field

.that IS cOnSt011y adapting to new advances in basic,knoWledge, medicine, and technology. Though it isincreasingly difficult to anticipate the world that ourchildre141.face and shape, it is clear that a basicunderstanding Of science and an appreciation of its.Metliodkand.philosophy will continue to be a neces-sa4,0rt'of edtioationperhaps more than ever.

mindrthe State Board of Educationadopted,in January, 1989, new statement of policyon,the. teaching of tho-natural sciences. This policy,Which Supernedes previous statements, is reproduced

12 Part I-What Is Science?

in full in the front of this document. It delineates theresponsibilities of science educators in explainingwhat science is and how it differs from other intellec-tual endeavors. Instructional materials submitted foradoption in the State of California must confonn tothe letter and spirit of this policy in order to beconsidered.

This chapteris about science itself. What ate itsbasic operating principles and methods? What part ofscientific philosophy needs to be communicated toyoung students? Why study science at all? How canthe excitement of science be cOmmunicated? Andwhat are the educator's responsibilities in discussingmoral, ethical, and social issues on which scientificunderstanding has some bearing? Some basicthoughts in response to these questions follow. (For asimilar point of view, see Science for AU Americans[Project 2061, American Association for the Ad-vanc .nent of Science, Washington, D.C., 19891.)

How the natural world works Is important toeveryone's education.

The genetic code, the history of the universe andthe earth and its life, the structure of the atom, theforce that brings apples to the ground and moves thetides, and the logic of the periodic table of the ele-ments are more than just the facts and ideas ofscience: they are an integral part ofour culturalheritage. We need to understand the way of thinkingand asking questions that is the essence of science.

Science Is important for Its own sake.

The American poet Walt Whitman characterizedscience as a limitless voyage of joyous exploration. A

24

person can carry the appreciation of science allthrough life and use it to learn more about the naturalworld. There arc marry well-known stories of howfamous scientists became captivated by science at anearly age, but there are just as many stories of ordi-nary people--:the true "amateurs" (lovers) of sci-encewho went on to pursue other careers, butxemained fascinated by the endless possibilities fordiscoveries in the natural world. Enjoyment is asuperb motivator of understanding.

Technology IS based on fundamentalscience.

An understanding of the principles and practice ofscience is essential for students to cope successfullywith the world they will inherita wodd about whichwe can predict but little. Much of modem science isbased on technological development, largely ininstrumentation. Educators have the chance toprepare students for the technology of the future byhelping them to develop a deeper knowledge of basicscience and how science works. We cannot expectour democratic society to make intelligent decisionsabout science, technology, and public policy unlessits citizens are scientifically literate.

As educators we face a complex and difficult task.We cannot present the entire body of scientificknowledge because there is too much to teach. Wecan hope for best results if we clearly present howscience works and the processes and methods whichexpand scientific knowledge. A stimulating class-room environment can nurture natural curiosity toconvey the excitement of science. But we must alsofoster an understanding of what science is and what itis not. Because scientific knowledge figures in somany other aspects of life and culture, we have tohelp students to deal with this relationship. Natureitself is morally and ethically neutral, but those whodeal with science must make important moral andethical choices. We have the responsibility of con-fronting students with some of the political and socialissues that require an understanding of science. Afterall, science is universal; it engages people without

41111

regard to their sex, race, culture, or views on matters-mtside the realm of science, and its findings tran-scend cultural differences.

The remainder of this chapter is devoted to anexploration of these matters and how they can beincorporated in the daily use of any science textbook,classroom, and curriculum. This treatment should notbe regarded as exhaustive but merely as a basicintroduction.

To be effective, science education should beenjoyable. The enjoyment of science is open toeveryone of every age: as thrilling as the experienceof a five-year-old on seeing Tyrannosaurus rex forthe first time or as cerebral as the aestheticappreciation of a beautiful new idea set forth by amasterful physicist such as Stephen Hawking.Science is a source of enjoyment, much as music is. Itis not only virtuosos who enjoy and benefit fromplaying a musical instrumenteven those who do nmplay an instrument can enjoy listening to music. Theappreciation of science, like the appreciation ofmusic, is likely to increase as the audience becomesmole knowledgeable about the workings of thediscipline.

Science educators want their students to take thismessage to heart: If you like some aspcct of science,you should consider pursuing science as a career.Whether your taste nms to physics instead ofpharmacology does not matter any more than whetheryou prefer piccolos to pianos. The point is to becomeinvolved and to communicate your enthusiasm toothers. Science careers are delightfully varied; you donot have to be a professor, an engineer, or a chemistto be a successful scientist. You can be a wildlifemanager, a forester, a nature guide, a laboratorytechnician, orbest of alla science teacher. Buteven if you simply increase your appreciation ofscience and your regard for the natural world, yourlife will be enriched.

"Lffe is not easy for any of us. But what of that? We must have perseverance and, above all, confidencein ourselves." Marie Curie (1867-1934)

2r- Chapter IThe Nature of Science 13

The most personal message that a science teacher can bring to students is this: Science is concernedwith all of nature, medicine, and technology. These concerns are not simply empirical; they are ethicaland social. The responsibility of science educators and the function of science curricula are to preparestudents for the decisions they must make as adultsdecisions that daily become increasingly dependenton a clear understanding of science.

- t * a

As an intellectual activity science shares manycharacteristics with other fields of knowledge, but italso has its own unique characteristics. All fields ofknowledge benefit from open-minded, open-endedinvestigation ami an honest exchange of ideas. Morethan any other field, however, science is guided by aparticular kind of theory that can be tested in thenatural world, using particular methods and principlesthat any practitioner of science can and must follow.This is why progress in scientific research is soconsistent and so universaland why it is so rapid.Any investigator following the universal methods andprinciples of science can test, verify or reject, and useprevious discoveries to take scientific knowledge astep further.

In general, scientists plan investigations by workingalong the lines suggested by theories, which in turnare based on previous knowledge. This knowledge isformed from empirical observations; that is, observa-tions of the natural world, which are then organizedsystematically into logical frameworks called hy-potheses. Hypotheses must be testable by recourse toobservations of the natural world if they are to qualifyas scientific hypotheses. Thus, theory and observationinteract: each contributes to the other.

There is an important lesson in this for students.Any new scientific knowledge must be communi-cated fully and openly to others if it is to be of use.This basic obligation makes even the full-timeresearcher a teacher of his or her colleagues andstudents, and this obligation binds scientists toteachers at all levels. The process of teaching sciencerequires a precise, unambiguous use of language anda dear demarcation of the criteria, power, and limitsof scientific investigation. The following points

14 Part IWhat Is Science?

should be made clearly and integrated into sciencetextbooks, cunicula, and class discussions:

1. Science has its own character as anintellectual activity.

Science differs in several ways from other scholarlyinquiries, such as literary criticism, historical writing,or the development of a philosophical or religiousperspective. Science aims to be testable, objective,and consistent.

Testability. Observations and inferences aboutscience are based in the natural world. An explana-tion should suggest a crucial experiment, fact, orempirical observation that can settle the controversybetween it and alternative explanations. In the mosttheoretical fields, such experiments may be difficultor impossible at present, but it must be at leastpossible in practice to test them by recourse to naturalphenomena. If an idea cannot (even potentially) be sotested, then it is outside the realm of science.

Objectivity. We make observations through oursenses, which am necessarily subjective, and ap-proach each problem with certain explicit and im-plicit ideas about what we are looking for and thepossible outcomes of our investigation. We cannotchange this; we art human. Nevertheless, explana-tions of nature must be based on natural phenomenaand observations, not on opinions or subjectiveexperiences. One good control of scientific objectiv-ity is the repeatability of science; that is, any observa-tion ought to be repeatable and capable of beingconfirmed or rejected by other scientists. This appliesas much to the interpretation of the structure of afossil plant or animal as it does to the result of anexperiment in a chemistry lzb.

Consistency. A scientific explanation does morethan provide a plausible account, it must clearly agree

26

with all the observable facts better than alternativeexplanations do, and it must show an explicit connec-tion between cause and effect. Some observationsremain puzzling for years and do not seem to fit wellwithin established understanding. Many of these turnout to be incorrect, or the inferences based on themturn out to be erroneous in the light of other data.Some observations are highlyNalued because theysignal a need to alter theory to accommodate themusually with a better, more inclusive theory.

When we test forms of inquiry such as parapsychol-ogy, the study of unidentified flying objects, orastrology, we find that claims for their validity onscientific grounds fail repeatedly; thus, belief in themmug be based on other, nonscientific considerations.Such realms of inquiry cause confusion in students,and scientists raise objections when their pmponentsattempt to L.:A them forth as science. Teachers must becareful to separate science from pseudoscience and toexplain the criteria for the distinction. Excessive timeshould'not be spent in discussing pseudosciences;they should be treated only in passing, as examples ofsubjects that do not meet the criteria of sciencediscussed here.

As educators we have a responsibility to teachstudents what science is and how it differs from otherkinds of inquiry or knowledge, such as art history,literary criticism, or philosophy. We need to showstudents how to differentiate between scientificinquiry.and other kinds of inquiry that do not adhereto the methods and principles discussed in thissection.

2. Science Is open-ended, but scientistsoperate with expectations based on thepredictions of theory.

There are no preordained conclusions in science.However, along with the legendary open-endednessand semndipity of science goes another very impor-tant factor. Scientists build expectations of what willhappen on a tremendous preexisting body of observa-tions, facts, inferences, hypotheses, and theories.They use these expectations to guide further inquiry.If scientists did not base further inquiry on what hadgone before, if there were no reasonable base forscientific prediction, scientific research would bereduced to random trial-and-error experimentation.

Because science is open-ended, those who wouldpractice or understand it must be open-minded. To beopen-minded is to use our experience. For example, itis probable that futum discoveries may give us a moreprecise age for the earth than the currently acceptedrougn value of 4.54 billion years, a value that haschanged by only 0.01 billion years in over threedecades of research. But we know that the new valuewill not be 10,000 years or 100 billion years. Sciencebuilds on what has gone before and refine't its conclu-sions. The first scientific estimates of the age of theearth were based oh rates of erosion, estimates ofdeposition of sediments and of mountain building,and they ranged from several thousands to hundredsof millions of years. Ip the 1800s Lord Kelvin deriveda famous estimate of 100 million years, on the basisof his assumption that all the energy radiated by thesun was gravitational. When radioactive energy wasdiscovered, this assumption and the constraint that hiscalculation had put on the age of the carth provedfalse. As estimates of sedimentary rates and cycleswere refined and as radiometric dating of isotopes inrocks became a repeatedly mbust technique, the ageof the earth's various rock layers was confirmed froma variety of measures. Indeed, our understanding ofthe age of the various geological periods has notchanged markedly in 50 years.

Two examples may illustrate how experience andopen-mindedness are inseparable in science. Anaturalist exploring an uncharted tributary of theAmazon River would not expect to find polar bears,corals, and platypuses; it would be more logical toexpect lizards, cmcodiles, tapirs, and other membersof the South American jungle fauna. These reason-able expectations are based on our knowledge of ahost of biogeographical patterns and precessesthedistribution and spread of animals and plants andtheir ecological relationships. This does not mean thatit would be impassible for any of these exotic organ-isms to appear in the Amazon, only unexpected. Tofind them them would, of course, bc of extraordinary

"We are 'Ian age of discovery, we live in theworld of the unknown. That' s the only place tolive."

Lloyd Quarterman (1918-1982)

Chapter IThe Nature of Science 15

interestto see how they differed from their relativeselsewhere and what historical and adaptive featuresmight account for their unexpected presence.

Expectations in science, as this second exampleshows, also suggest possibilities and drive furtherinquiry. Most life science textbooks give accounts ofthe Miller-Urey experiments of the 1950s, which triedto synthesize amino acids, someof the simple mole-cules that are the building blocks of life. Otherscientists had suggested the possibility that on theprimordial earth, amino acids were first synthesizednaturally from simpler compounds such as ammonia,methane, and water. Miller and Urey decided to seewhether thesynthesis was possible. They assembled avariety of mixtures of the simpler compounds inclosed vessels. But they had clear expectations thatnothing would happen if they simply mixed thecompounds together. They knew from elementarychemical theory that they would need additionalenergy in the system, so they introduced an electricalspark through the vessel. Indeed, amino acids wereproduced. Miller and Urey did not know in advanceexactly which compounds would form, nor in whatproponions. But they knew fiem expectation thatenergy was needed in order to synthesize morecomplex compounds from simpler ones. This is agood example of how the open-endedness of scien-tific inquiry goes hand in hand with structuredscientific expectations based on previous knowledge.

What do these examples mean to science teaching?Simply that teachers must strive to show studentshow expectation and openness both have importantroles in science. The interplay between them confirmsboth the body of accumulated scientific knowledgeand the value of its open-ended philosophy. Scientificknowledge must be presented as authoritative, notauthoritarian; we can depend on scientific knowledgeand theory, yet we can always leam more and mustconstantly revise what we know in the light of newdiscovery.

3. Science Is based on observations set Ina testable framework of Ideas.

Scientific terms such as fact and theory, which wereoriginally nonscientific words but which have reen-tered our everyday vocabulary with the veneer ofscientific authority, are easy to misunderstand or useloosely. When these terms are used in a scientific

16 Part IWhat Is Science?

context and in science teaching, we must preservetheir proper meaning. In detective novels, the sleuthdiscovers the corpse and develops a "theory" as to"whodunit." At the end the murderer confesses, andthe "theory" becomes a "fact." These words havedifferent meanings to a scientist.

When we say that all science is based on observa-tions, we mean that we use the evidence of our senses(seeing, feeling, hearing, and so forth)sto.obtain theinformation on which scientific work is.based. Evenwhen we use an instrument to detect and measurethings too =alto be seen with an optical micro-scope, the output of the instrument must feed into oneof our senses before we Call interpret the data that itsupplies.

When our observations of a phenomenon have beenconfirmed or found to be repeatable, such observa-tions become fact. However, even though there islittledoubt about the observation, it cannot be ac-cepted as an absolute certainty without experimentalconfirmation.

For example, suppose a child comes into a class-room with wet, shiny rubber boots. Everyone canobserve these features, so they are facts. To explainwhy the boots are wet requires another level ofintellectual activity called inference. An inference isreasoning based on observation and experience. In thecase of the nibber boots, one could draw a rationalinference that it is raining outside or that the child hasrecently stepped in a puddle. It is easy to think that aninference is automatically a fact, but critical thinkingis required to maintain the distinction between thetwo. An inference can become a fact when it isconfirmed by other observations.

A hypothesis is an attempt to convert an explana-tion into a testable prediction. If we make the hy-pothesis that the child's boots are wet from rain, wecan test it by looking to see if it is rainhig. If it isclear outside, we reject the hypothesis. But even if itis raining, the rain may not have anything to do withthe wet boots. Perhaps the child has not been outsideat all but has been playing with the water fountain inthe hall. Further inquiry might be necessary.

There is still the possibility that we did not observewith sufficient care. Perhaps the boots were not wet atall but were shiny because they were new. Observa-tions may be mistaken and may legd to mistakeninferences. This is a weakness of human observationbecause humans tend to bee what they expect to see.

28

When a add wears rain boots, it is usually because itis raining.

We cannot ever expect to be completely free ofpreconditioned 'expectations. An important part of thescientific method is to maintain an awareness of thisfrailty and allow for it. To do this, it is essential tokeep an open mind and to test ideas systematicallyand thomughly.

4. Scientific inquiry Is guided by theory.

As already noted, the concept of theory is enor-mously important in science, but the term is oftenmisunderstood and misused by nonscientists. Atheory is a logical constnict of facts-and hypothesesthat attempts to explain a range of natural phenom-ena. Fôr example, gravitation is a fact, and it is also atheory. The principles that underlie the phenomenonof gravitational attraction are not fully understood.But no one doubts the fact of gravity; apples do notsuspend themselves in midair pending the happy daywhen a physicist observes an apple exchanginggravitons with the earth. Moreover, if some hypothe-sis concerning the gravitational behavior of objectsunder certain conditions is tested and shown to be inerror, the theory of gravitation does not becomeinvalid. Only the part of the theory that failed the testmust be modified and reevaluated.

Theories are replaced in their entirety infrequentlyand then only when a new theory is proposed thatsubsumes the old theory. The new theory does so byexplaining everything.that the old theory explained aswell as other evidence that mightnot have fit verywell in the old theory, In time the new theory mayitself be modified or replaced; this is how scienceproceeds. For example, in Columbus's time the earthwas generally thought to be the center of the cosmos,and the sun, moon, and planets were thought to circlethe earth. But in this cosmology, it was difficult toaccount for the irregular motion of many heavenlybodies:,planets.sloWed, sped up, and sometimesreversed their motion. With Copernicus's proposalthat the.sun, net the earth, was the center of thesysteth,.the -calculations of the motions of heavenlybodies were siMplified and made more sense. Helio-cefitrid theory, which better explained the knownobservations, replaced the geocentric theory. °

However, that was not the end of the story. Theshape of the planetary orbits was assumed to be

29

circular. Kepler proposed that the orbits were ellipti-cal, and this further simplified calculations of theirmotion and improved the accuracy of such predic-tions. Even this advance did not solve everything;there are "hitches" in the rates at which planets movethrough space, partly because they exert a physicalattraction on each other, as Newton showed. So theadvent of Newtonian mechanics further improved ourexplanatory power of these natural phenomena.Newtonian the6ry has now been superseded andembedded in a more general theory, the theory ofrelativity pioneered by Einstein. But Einstein's theoryis not the last word on the subject. It may one day bereplaced by an even more comprehensive theoryperhaps developed by a student now sitting in ascience classroom in.Californial

The lesson of the previous example of solar me-chanics is simple. Educators must be precise in theuse of scientific language because that language iscrucial to its teaching. A theory is not a half-bakedidea nor an uncertain fact but a large body of continu-ally refined observation, inference, and testablehypotheses. Terms such as fact and theory are useddifferently in scientific literature than they are insupermarket tabloids or even in the normal conversa-tion of well-educated people. For clear communica-tion scientists, teachers,, and students must communi-cate the definitions of scientific terms and use themwith consistency.

Notice that in the preceding discussions we haveavoided the word prove, the use of which should belimited to abstract mathematics. Most scientific workdoes not result in infallible propositions, such as theword proof seems to imply to the nonscientist. Wehave already explored the ways in which scientificideas are tested, observations made, facts gathered,and theories built. But science never commits itselfirrevocably to any fact or theory, no matter howfirmly it appears to be established in the light of whatis known. Science is never dogmatic; it is prag-maticalways subject to adjustment in the light ofsolid new observations like those of Joule, or new,strong explanations of nature like those of Einsteinand Darwin. This is a cardinal property of science. Itis not a weakness of uncertainty but a strength of self-correctability. Students shuuld be carefully taught thisintrinsic value.

A similar issue is very closely related to the use ofterms. Language used to describe science must

Chapter IThe Nature of Science 17

represent science accurately as an intellectual andsocial process. Fpr example, in discussing a particularscientific issue, students should never be told that"many scientists" think this or that. Science is de-cided not by vote but by evidence. Nor shouldstudents be told that "scientists believe." Science isnot a matter of belief; rather, it is.ra matter of evidencethat can be subjected to the tests of observation andobjective reasoning. A phrase such as "Many scien-tists believe . .." misrepresents scientific inquiry. Italso obscures for students what scientists really doand hOw they come to their understandings. Educa-tors should be encouraged to stretch their pedagogicalvocabularies. Say instead that scientists reach conclu-sions based on evidence and that all conclusions arealways subject to modificationbased on new knowl-edge. Students should be told about evidence andhow scientists reach their conclusions, not whetherscientists believesomething or how many do or donot. Scientists no more believe in their findings than asuperior court judge believes in a vetrliet.

How certain or uncertain is science? What are itslimits? And how should these issues be presented tostudents? Science should be presented in the spiritevoked in the previous discussions. Detractors ofscience deride the idea that science can be authorita-tive on the grounds that it cannot be omniscient.Since scientists cannot know everything, how can wedepend on what they say they know now? Studentscan be misled into seeing a contradiction here:Science seems to know so much, yet changes its mindconstantly and has more to know the more it discov-ers. Educators should show clearly how this uniquecombination of reliability and tentativeness is thecentral characteristic and fundamental strength ofscience. Show students that nothing in science isdecided just because someone important says it is so(authority) or because that is the way it has alwaysbeen done (tradition). In the free marketplace of

Science is never dogmatic; it is pragmaticalways subject to adjustment in the light of solidnew observations like those of Joule, or new,strong explanations of nature like those ofEinstein and Darwin. This is a cardinal propertyof science.

18 Part IWhat Is Science?

ideas, the better new idea supersedes or absorbs theprevious ones. This open competition of ideas is amajor part of the excitement of science.

Sect,on Sdientific Practice.and_Efffics

SCM1117STS have responsibilities to their colleaguesand to the public. Because all observations are basedon human senses and expectations, results must bereported as fully and openly as possible. Scientistsalso have a responsibility to limit the scope and theimplicatiOns of their results, not to overgeneralizetheir findings. Negative resultsthose that do notagree with the hypothesismust be reported alongwith those that do agree. (Trivial results are notnormally reported, although what seems initiallytrivial can turn out to be important. Therefore, recordsmust be kept carefully and made available to otherqualified researchers.)

Students, especially younger ones, often feel underpressure to come up with the right answer whendoing hands-on science activities. Older studentssometimes falsify results, usually because they justassume that they have made an error in observing,measuring, or recording data. This conduct simplyreflects human nature. To relieve this problem,teachers and writers of instructional materials shouldencourage students to report the results they get. Theyshould also use open-ended experiments, not "cook-book" ones and not even good ones that have as theironly aim to duplicate a known result. In a well-designed instmctional activity, there is no single rightanswer, and students' results may reveal problemswith the experiment, the apparatus, or the conclusion.Even if their data are incorrect for some reason,repeated trials and independent observations made byothers will uncover error. Emphasis should be placednot on coming up with the right answer but on doingscience the right way. Teachers should emphasizediscussion that revals how the errors crept in andwhether and how anomalous observations revealfeatures of interest in the experimental design, theequipment, or the results.

For students famous cases of scientific error orfraud perpetrated on the scientific community can beconfusing. Some such cases, notably the "Piltdown

30

man" hoax, have been used to suggest that science issomehow unreliable or dishonest. Piltdown man,discovered in rural England in the early 1900s,appeared to be a very interesting but anomalousspecimen of early hominid that altered the prevailingunderstanding of human ancestry and evolution.Eventually revealed as the altered jaw of an orangu-tan placed with the skull of a human, it was socleverly done that it influenced scientific understand-ing about the early evolution of humans for somedecades. Because the identity of the hoaxer is still notknown for certain, the reason for its perpetration is amystery. Several factors conspired to keep the hoaxfrom being discovered sooner. One was the absencefor many decades of other fossil human remains.Another was the inaccessibility of the fossil. A.S.Woodward of the British Museum kept it lockedaway from investigators. Indeed, an eminent paleon-tologist was thrown out of the museum bodily whenhe was discovered attempting to opcn the specimencase in Woodward's absence! As time went on,however, and more fossils were found, a pattern ofhominid evolution in which Piltdown man wasincreasingly anomalous was elucidated. Thesefindings contributed to widespread skepticism, heldsince its discovery, that Piltdown man was authentic.Eventually, after Woodward's retirement, and withthe development of new analytic tools and investiga-tion of the specimen, the fraud was uncovered. Again,the self-correcting process of science and the impor-tance of consistency of scientific results were para-mount in solving the problem.

How can teachers infuse the ethics of scientificpractice into their curricula? They can do so bystressing laboratory-oriented, open-ended activitiesdesigned to allow students to explore and discovernew ideas for themselves. Such activities are momeffective than self-contained lessons in internalizingideas for students. But even if laboratory activities arenot a practicable approach to every scientific concept,the teacher may well describe the path taken byScientists in exploring these problems, including well-chosen examples of wrong turns and overlookedevidence. Students should learn that science correctsitself in many ways. They should also understand thatearly scientists whose work has now been supersededwere not stupid, quaint, or primitive. Often falsestarts are necessary in order to eliminate the incorrectapproaches. Simply formulating the problem is oftenan enormous step in the right direction.

Sedtion E Social Issues in Solace

OUR present world is so dependent on the discover-ies of science and technology that progress is almostuniversally identified with progress in science andtechnologyoften to the disregard for progress inother human areas such as global politics, economics,and human justice. Because science is such a largepart of today's world, it is more important than everthat each student understand its workings and itsmaterial basis. The presentation of some topics inscience, however, sometimes disturbs individualswho hold religious or philosophical beliefs that theyfeel conflict with certain findings of science.

Teachers art given the job of teaching their subjectsto students, of representing the knowledge in a givenarea at an appropriate pedagogical level, and ofhelping their students make informed decisions aboutissues they may encounter in their future years. Howcan teachers meet the challenge of explaining sociallysensitive issues in science to their students? Someguidelines are given as follows:

Education's goal is understanding, not belief.

Education does not compel belief; the goal is toencourage understanding. Students do not have toaccept everything that is taught in school. But they doneed to understand the major strands of scientificthought because this thought is the backbone of ourintellectual heritage and the basis for the constructionof future knowledge.

A major task of education is to explain the method-ology and evidence that bears on accepted conclu-sions. To teach about communism in a history class,for example, is not to advocate communism andshould not be construed as an attempt to undermine astudent's democratic beliefs. But the students who donot learn in a history class the fundamentals of aphilosophical-political-social system that governshundreds of millions of people are missing somethingimportant about today's global politics as well as vitalinformation that will help them make intelligent deci-sions in the voting booth as adults.

In the same way there are scientific issues thatarouse social controversy. Science teachers areexpected to present and interpret these issues for theirstudents, but the issues must bc dealt with as scien-

3Chapter IThe Nature of Science 19

tific istues and discussed in the light of acceptedscientific evidence.-In carrying out this obligation, theteacher does not exceed.the boundaries of scientificinquiry or the role of a science teacher. The teachermust also make every effort to delineate and separatenonscientific material in reaching a scientific conclu-sion.

The educator's role Is to promote scientificunderstanding.

Educators must present accepted scientific under-standing in a conscientious way and should besupported inthis goal by their communities. Anyeducator who communicates science to students isbound to encounter sensitivities to certain issues.Some of these issues are ethical, some involveclarification of scientific methods and philosophy,and some-are not strictly within the realm of science.While recognizing the right of individuals.to hold andpractice their-own beliefs, teachers muSt not bepressured by anyone to distort or suppress science orto go beyond what they are,professionally obligatedand charged to teach. Administrators especiallyshould be sensitive to the pressure&faced by teachersin communicating the philosophy, substance, techno-logical implications, and ethical issues of science.

Slo one can be an expert on all scientific issues.Every teacher must feel free to say and know when tosay, "I don't know; that's outside my range of exper-tise," and to suggest other resources to the studentwho wants to pursue the question further.

Furthermore, every teacher must feel ;lee to sayand know when to say, "Sorry, but that's not aquestion for science," and explain why. Such ques-tions should be treated with respect and referred tofamily or clergy for further discussion.

At times some students may insist-that certainconclusions of science cannot be true because ofcertain religious or philosophical beliefs that theyhold. This is a difficult problem for these students andtheir families, and such difficulties should be ac-knowledged and respected. It is appropriate for ateacher to express in this regard, "I understand thatyou may have personal reservations about acceptingthis scientific evidence, but it is scientific knowledgeabout which there is no reasonable doubt amongscientists in this field, and it is my responsibility toteach it because it is part of our common intellectualheritage."

20 Part IWhat Is Scierice?

Sometimes it is difficult to separate the sciencecurriculum from social and ethical concerns thatpertain to students or are a matter of vital publicdebate. In these cases, teachers are ethically bound toteach the scientific facts and the scientific perspec-tives on the issue. It is perfectly acceptable to ac-knowledge that nonscientific concerns (such as legalrights, aesthetics, and economics) bear on an issuethat is not purely scientific but has scientific content.But the educator must distinguish carefully betweenthe scientific and nonscientific components of theissue and not present the latter as though they werethe former.

Socially sensitive Issues have a place In thescience classroom.

The following examples are meant to exploreseveral issues that are commonly associated withsocial sensitivity. We do not provide solutions to theproblems but only suggest perspectives that educatorsmay use to present them to students.

Conservation. Controversies over conservationissues art wt two-sided struggles between lovers ofnature atl,; the voices of industry and progress, nor dosuch controversies have simple solutions. But noworkable solution of this issue or any other issue withscientific content can conflict with the relevantscientific evidence 2-kl principles. Students should betaught that they must evaluate public policy andchoose their stances on issues, with an appreciation ofthe empirical constraints on the problem that sciencecan provide. For example, one cannot achieve anintellectually defensible stance on the use of naturalresources without a knowledge as to which naturalresources cannot be replaced and the rates at whichrenewable ones can be renewed. Beyond theseconsiderations are those of present human needs, theneed to preserve natural beauty for posterity, and theneed to adjust how humans now use natural resourcesto preserve nonrenewable ones for the future. Allthese considerations require scientific understanding.

Students should also understand that technologyhas often brought, along with its advances, someundesirable secondary effects such as pollution, acidrain, mutagenic agents, and biotic poisons. Suchundesirable effects can often be reduced by furthertechnological advances, at a cost that must be evalu-ated by the standards of public policy. Scientific and

32

Evolution is the central organizing theory of biology and has fundamental importance in othr sciencesas well. It is anf accepted scientific ex, -nation and therefore no more controversial in scientific circlesthan the theories of gravitation and electron flow.

technological knowledge is essential for intelligentjudgment on these issues. Cost-benefit considerationsare not merely scientific questions. Whether the issueis power generation or agricultural crop management,the educator should seize the opportunity to explorethe relationship between science and other subjectsand to help students develop the habit of rational,orderly thought in an area of popular misinformation,emotion, and instant solutions.

Conservation should not be taught simply as amatter of classic Malthusian population growthaccording to which natural resources are stripped by

. unchecked population control. Rather, there is now aneo-Malthusian component: Some populations usemom of the available resources than others. Forinstance, an American may use 50 times more energythan the average resident of India; as 6 percent of thewodd's population, the United States uses 40 percentof the world's resources. One additional American,therefore, can have a disproportionate effect on theworld's supply of resources. Students should beeducated about these perspectives in order to helpthem make informed judgments about their habits andpriorities and to help them to set policies for the nextgeneration.

Animal experimentation. This is a very difficult,emotionally charged issue. People are very sensitiveto uses of animals that are abusive or that can beportrayed in some lights as abusive. There are manylegitimate feelings that certain expeziments may beunnecessary to carry out or to repeat, and that thegood that cbmes from such work does not sufficientlycounterbalance the discomfort to the experimentalsubjects. Distress at such conditions may becomedismay or disgust with the scientific community forallowing such practices to continue.

Students need to leam how important it is toscientists, too, that unnecessary experimentation beavoided. Cost-benefit analyses must be considered incarrying out research. Concerning scientific andmedical issues, one thing is clear: The use of lab

animals can save lives, and not just human lives. Ifanimal experimentation were forbidden, we could nottest certain vaccines and lifesaving medicines. Wecould not develop new surgical techniques, nor fightepidemics of disease. And we would have to useother humans as test subjects at all stages of research.(Apart from the obvious ethical considerations, it isworth noting that we would have to wait an averageof 25 years for the first results of experiments ongenetic effects, as opposed to a few weeks for mice ora few months for rabbits.) We could not as effectivelytrain new physicians, surgeons, and veterinarians.

It is sometimes difficult to conceive of how ourlives would be different if animal experimentationwere forbidden. One has only to look at the changesin disease and death rates of infectious childhoodillnesses in our own century to realize how much wetake for granted the advances that have been built onresponsible experimentation with animal subjects.This observation does not mean, of course, that everyanimal experiment saves lives nor that laboratoryanimals are always kept in the best possible condi-tions. Public awareness of this issue should contributeboth to the maintenance of strict humane standards inlaboratories and to the public appreciation of whatsuch experimentation means to public health andmedicine. These goals should be important to allscience educators in presenting this complex andemotional issue to students.

Evolution. Evolution is the central organizingtheory of biology and has fundamental importance inother sciences as well. It is an accepted scientificexplanation and therefore no more controversial inscientific circles than the theories of gravitation andelectron flow. When scientists say that gravity is afact, this is based on many observations of theattractions that objects have for each other. Whatcauses that attraction and how these forces workforms a body of investigation that comprises thetheory of gravitation. In the same way anyone canobserve the workings of electricity by connecting a

Chapter 1The Nature of Science 21

battery to wires and a light bulb. It is a fact that thebulb lights because of electrical energy, even thoughthe electron flow cannot be observed directly. Thetheory of electron flow is how we explain that factand how electrons behave. Though we cannot seeelecttonsand there are probably ideas that we haveabout electrons that will be modified with furtherinvestigationwe are reasonably confident in sayingthat the motion of the electrons explains the lightingof the bulb. Saying that we understand how gravityand electricity work does not mean that we under-stand everything about gravitation or electron flow.Recently, for example, physicists were intrigued byreports that a previously unobserved force may act onordinary bodies in addition to the familiar force ofgravity. Current theory classifies all the forces ofnature into four fundamental types, of which the forceof gravity is one. If further investigation and testingsubstantiate the new reports, the theory of fundamen-tal forceswilthave to be modified to include a theoryof the new fifth force.

And so it iS with evolution. Just as scientistsobserve the fact that.apples fall and devised thetheory of gravitation to explain the fall, scientistsobserve the fact that animals and plants change overtime. They constructed the theory of evolution toexplain how these changes occurred. Scienti6ts basethe theory of evolution on observances of the se-quences of appearance, change, diversification, anddisappearance of forms through the fossil record.Scientists breed wild and cultured plants and animalsand note how inherited characteristics arc modifiedand passed on to offspring. They observe howcharacteristics arc also modified by genetic muta-tions, which contribute natural variations on whichnatural selection acts. Scientists also observe thedetailed correspondence of genetic and biochemicalsequences among closely related organisms that havebeen inferred from evidence of fossils and anatomy.Asmas predicted, there is a higher degree o' corre-spondence in the genetic and biochemical composi-tion.of closer relatives than of more distant relatives.Scientists also.compare the gradual differentiation ofembryonic stages from nearly identical beginnings.To establish relationships, they identify uniquecharacteristics of development, such as going throughthe metamorphosis of a butterfly or the veliger stageof a larval mollusk.

These observations constitute some of the evidemethat evolution has occurred, evolution is the most

Some students may be concerned about evolutionand its bearing on their religious be/left. Teach-ers--and textbooksshould make it very clearthat from a scientific perspective, evolution, likeother scientific topics, does not bear on anindividual's religious beliefs. Science is nottheistic, nor is it atheistic; it does not presupposereligious explanations.

consistent and accountable explanation of theseobservations. The theory of evolution, like othertheories, is more than the sum of the facts from whichit is derived. It is the best explanation for the facts,and it has predictive value. How evolution hasworkedits patterns, processes, mechanisms, andhistorycomposes the theory of evolution, which isconstantly being ziodified as new evidence emerges.Like the idea of a fifth force in physics, new mecha-nisms of evolutionary theory, such as punctuat, dequilibria, species selection, and periodicity of massextinction, are currcnt subjects of debate which, ifthey turn out to be well supported by all the availableevidence, will modify current evolutionary theory.Regardless of the existence of a fifth force, applesstill fall. And, regardless of whether the changes inplants and animals are gradual or sporadic, theevidence remains that plants and animals haveevolved over time. Thus, the theory of evolution isthe accepted seentific explanation of hem thesechanges occurred.

It is very important for students to understand theobserved facts and evidence that contribute to andform the basis for potential modification of theoverarching theories by which science operates andadvances...It is equally important for students tounderstand theories, because theories give meaning tothe facts and guide further gathering of facts andevidence. Without theory, facts have little meaning,and without facts, theories arc empty structures.

Occasionally, allegedly scientific evidence thatappears to falsify or contravene the theories ofevolution, geologic dating, thc fossil record, or otherrelated knowledge may be brought to the attention ofthe teacher. Criticisms of scientific evidence andtheory on scientific grounds are part of science,teachers should treat the scientific challenges to the

Chapter tThe Nature of Science 23

understanding of evolution in the same manner thatthey treat challenges to other well-established scien-tific theories. If teachers have the background andresources to investigate the claims, they should do sothoroughly and scientifically. If they do not have thebackground and resources to do so, they shouldindicate that they are not prepared to deal with theparticular claim and that they have confidence thatevery effort has been made to make their curriculumas scientifically accurate as possible.

Teachers should be aware that the theory of evolu-tion has been tested and refined for over a hundredyears and that the majority of criticisms that find theirway into popularly circulated publications have notbeen validated scientifically; usually, the criticismshave been evaluated and rejected by the scientificcommunity. Teachers should consider the validity ofsuch criticisms carefully before accepting them ordeciding whether they are worth consideration. Theparticular case of "creation science" (or "scientificcreationism") has been thoroughly studied by theleading scientific societies and rejected as not quali-fying as a scientific explanation.

Some students may be concerned about evolutionand its bearing on their religious beliefs. Teachersand textbooksshould make it very clear that from ascientific perspective, evolution, like other scientifictopics, does not bear on an individual's religiousbeliefs. Science is not theistic, nor is it atheistic; itdoes not presuppose religious explanations. Scienceis concerned with the mechanics, processes, patterns,and history of nature; it is neutral with respect todivinity, the supemattral, or ultimate causes. In fact,many of the scientists who have made importantcontributions to evolutionary biology, genetics, andgeology have been deeply religious persons frommany different faiths who did not find a conflictbetween their religious beliefs and their scientificunderstandings. Some people however, reject thetheory of evolution purely on the basis of religiousfaith. Consistent with the State Board of Education'spolicy, concepts in the science curriculum should notbe suppressed or voided on the grounds that they maybe contrary to an individual's beliefs; personal beliefsshould be respected and not demeaned. Thc way inwhich scientific understanding is related to religion isa matter for each individual to resolve; thus, the StateBoard's policy is that there should be a clear separa-tion between science and religion.

24 Part IWhat Is Science?

Human reproduction. To make responsible deci-sions about their own lives. ..-,tudents must haveknow:edge of and respect for their own bodies. Theymust understand not only the heart, liver, and lungsbui also the reproductive organs. Dangers facing ourcitizens and others throughout the world because ofsexually transmitted diseases, birth defects, and thecondition of young women who experience preg-nancy and motherhood long before they am readypersist as everyday images in our technologicallyadvanced world. With scientific and technologicaladvances comes a responsibility to educate studentsablut these dangers.

All students should understand the reproductivesystem, the causes of birth defects and advances inovercoming them, the ecological problems posed byoverpopulation, and the means by which humansregulate their reproductive rate. Particularly in thepast decade, which has seen the rise and rapid spreadof the acquired immunodeficiency syndrome (AIDS)virus and the herpes viruses through a substantial partof the American and global population, education onthese issues is mom important than ever. We cannothope to stem the flood of sexually transmitted dis-eases through crir society without fundamentaleducation about their etiologies and prevention,

Overpopulation is a biological issue with distincthuman ramifications. It is weli known that an ecosys-tem can support only a limited number of organisms.As populations gmw, they strain natural ecosystemsby overusing limited resources and by degrading theenvironment. This strain bas an ach2rse effect on thequality of life and frequently opens the door for othermaladies such as contaminated resources and disease.Students must appreciate, therefore, that environ-mental planning and research must include an analy-sis of how different population levels will affect theenvironment. Such populations include thc plants andanimals that humans use for food, shelter, clothing,and other purposes; and they also include humansthemselves. Technology may not find answers fastenough to countcr the impact of expanding humanpopulations; therefore, people will have to makedifficult but well-informed decisions about planningfamilies and planning their use of environmentalresources to the best advantage.

On the issue of human reproduction itself, manystudies have shown that students have received aconsiderable amount of misinformation about sexual-

36

. . .

Technology may not find answers fast enough to counter the impact of expanding human populations;therefore, people will have to make difficult but well-informed decisions about planning families andplanningtheir use of environmental resources to the best advantage.

ity from their peers, and as a population they are notsufficiently educated about this topic in their homes.Public education must include reliable, scientificallybased, candid information on the anatomy and physi-ology of the human reproductive system, menstrua-tion, pregnancy, birth, and birth control methods,including abstinence. Public education should includea discussion of the causes and transmission of sexu-ally transmitted diseases. These topics should betreated professionally and openly. Students should beencouraged to ask questions. (See the State )oardpolicy statement in the front of this document con-cerning excusing students from the discussion ofcertain subjects.) If a teacher feels uncomfortablewith the subject, students should be referred to otherpersonnel in the school system or to outside agencies.

These and other scientific or scientifically relatedissues may raise controversy in the science class-room. But controversy should not be a stranger in theclassroom. The task of the science teacher is to guidestudents in the development of their abilities toapproach controver§ial subjects coolly and rationally,

with clear and critical understanding of what isunderstood in science, what is uncertain and to whatdegree, what is scientific and what is not, and how thescientific and technological factors bear on thecontroversy. The teacher is ethically and profession-ally bound to confine science instruction to the facts,hypotheses, and theories of science.

School boards, administrators, and parents mustsupport the teaching of rigorous science, a rationalapplication of science to broader issues in whichscience plays a part, and a careful study of the ethicalissues raised by scientific and technological activitiesthemselves. Teachers can stress that science as asystem of knowledge is based on empirical evidencerather than on belief. While every student ought tofeel comfortable in class, a teacher must not makeaccommodation at the expense of sound science orsound pedagogy. Science instruction should respectthe private beliefs of students; on the other hand, theteaching of scienee cannot be suppressed merelybecause individuals disagree with it on religious orphilosophical grounds.

4

Chapter IThe Nature of Science 25

alwiwirim

,

Chapter 2

The Major Themesof Science

THE themes of science are ideas that integrate theconcepts of different scientific disciplines in waysthat are useful to the presentation and teaching ofscientific content. As opposed to theories, whichunify and make sense of facts and hypotheses relatedto a particular natural phenomenon, themes arcpedagogical tools that cut across disciplines. Theincorporation of themes into science curricula is amajor goal of this framework. They am meant tointegrate concepts and facts, to provide a contextthrough which to present content matter, and toencourage better writing in science instructionalmaterials.

The major themes of science arc explained in thischapter. In Part II, the content portion of this frame-work, each paragraph ends with a bracketed referenceto themes that may suggest ways the material can bepresented. We stress that many thematic organizationsare possible and present here some criteria and possi-bilities for developing themes in science curricula.

Section A Introduction

THIS Science Framework differs from, previousframeworks and addenda in its emphasis on themes ofscience. This section discusses (1) why dimes areessential; (2) what some of the major themes inscience are; and (3) how instructional materials andcurricula can incorporate themes in their presenta-tions of science.

As Project 2061 of the American Association forthe Advancement of Science (AAAS) has noted in itsbook, Science for All Americans, themes should be a

26 PartIVhat Is Science?

major emphasis of science curricula in order toreinforce the importance of understanding ideasrather than the memorization of seemingly isolatedfacts. Ideas connect facts, just as the framework of ahousc connects its building blocks. This vital frame-work is missing from much of what is taught asscience today, and it must be restored. Along with theemphasis on the concepts and practices presented inChapter 1, incorporation of major themes in thescience curriculum is the principal focus of thisframework.

What are themes? They could also be called bigideas, overarching concepts, unifying constructs, orunderlying assumptions. They are distinct from factsand concepts. A fact is a statement based on con-firmed observation and inference, such as the numberof electrons in an atom of iron, the date of the discov-ery of helium, or the descent of birds from dinosaurs.A concept often involves several facts; for example,the concept of continental drift, the need for repeat-able observations in constructing science, or howmagnets work. Themes are larger ideas; they link thetheoretical structures of the various scientific disci-plines and show how they arc logically parallel andcohesive. Scientific literacy lies not only in knowingfacts and concepts but also in understanding theconnections that make such information manageableand useful.

What am the major themes of science? Science canbe organized in many ways; those presented hereshould be regarded as only one way to integrate theoverarching concepts of science into a curriculumthat spans scientific disciplines. Thc suggestedarrangement of themes is designed to encompass andconnect a great deal of the basic data and evidence of

38

science. No doubt there are alternative arrangementsthat would work equally well. The important point isthat at least some thematic structure will improve therecitation of disunited scientific-facts and examplesthat has come to pass for science in many currentcurricula and instructional materials.

Six themes, explained in the following pages, arcdeveloped in this framework. They are:

1. Energy2. Evolution3. Patterns of Change4. Scale and Structure5. Stability6. Systems and Interactions

The presentation of science could be organizedalong other thematic lines; possibilities includeactions, reactions, interactions, matter, diversity andunity, hierarchy, energy and matter, and many others.While the particular configuration and nutber ofthemes is not crucial, the organization of contentalong thematic lines is.

Educators and developers of instructional materialsare encouraged te weave these or alternative thematicstrands into science curricula. The main criterion of agood theme is its ability to integrate facts and con-cepts into overarching constructs; thus, diversity andunity would make a geod theme; conservation,applied to biology or physics, might also. Dinosaursor apples, no matter how diversely or inventivelyused, are not themes in the sense described here.

Themes are also not the same as theories, whichwere discussed at length in the preceding chapter.Theories are organized around content in particulardisciplines of science, such as the theories of gravita-tion in physics, evolution in biology, or continentaldrift in geology. Themes, such as energy or patternsof change, cut across sp:cific content matter. Byshowing the interrelationships of different facts andideas, themes serve primarily as pedagogical tools forthe presentation of science.

With themes as a major emphasis, science curriculaalign with similar advances in other fields of educa-tion. These major themesevolution, energy, pat-terns of change, and so forthoccur again and againin the sciences, whether one studies ecology, platetectonics, meteorology, or organic chemistry. This isnot surprising; unifying constructs are a part of anyphilosophically united discipline. Themes also appearin the arts, for example. In the study of painting,

4"...1t .

Scienee can be organized in.many ways; thosepresented here should be regarded as only oneway to integrate the overarching concepts ofscience into a curriculum that spans scientificdisciplines. The suggested arrangement of themesis designed to encompass and connect a greatdeal of the basic data and evidence of science. Nodoubt there are alternative arrangements thatwould work equally well.

"Science is constructed of facts, as a house is ofstones. But a collection of facts is no more ascience than a heap of stones is a house."

Henri Poincari (180-1934), Science and Hypothesis

music, or drama, there are essential elements ofaesthetics, such as balance and symmetry, direction,form and proportion, and tension and release, thatpermeate human expression and give meaning andpurpose to our understanding of how art affects us. Atheme in science might be compared to a theme in asymphony or a novel. In a symphony, a theme is ampeated musical idea that gives structure and unity tothe music. In a novel, a theme such as success, warand peace, love, or duty provides a conceptual basisfor the unfolding of the plot. In science a theme ismom like the theme of a novel, whereas the contentor subject matter of science might be similar to theplot of a novel. A theme represents a recurring ideathat provides a context for explaining facts andevents.

Section B 'Why Themes Are'EsSential

THEMES are necessary in the teaching of sciencebecause they are necessary in the doing of science. Ascholar does not merely collect facts and categorizethem. Facts are useful only when tied to the largertheoretical questions of the natural worldhow itworks and how its parts fit together. Charles Darwinunderstood this truth perfectly well and expressed iteloquently in a letter to Fawcett:

Chapter 2The Major Themes of Science 27

About 20 years ago there was much talk that geolo-gists ought only to observe and not theorize.... And Iwell remember someone saying at the time that at thisrate a man may as well go out to a gravel pit andcount the pebbles and describe the colours.... Howodd that anyone should not see that all observationmust be for or against some view, if it is to be of anyservice.

Darwin's message is that discrete pebbles ofpsticulate knowledge build nothing. They must buildan overarching structum. There must be somc the-matic connection and theoretical integration in orderfor science to be a philosophical discipline and notmerely a collecting and dissecting activity. A the-matic basis to a science curriculum reflects whatscicntists really do and what science really is.

Recent critics of science education have beendismayed by the lack of progress in students' under-standing of the-major concepts and issues in science.They cite the historical (and current) fragmentation ofthe major disciplines of science and complain thatidvia seem to be the stock-in-trade of science lessons.Paul Hurd, Professor Emeritus at Stanford University,has oliserved that science is often taught "as a foreignlanguage" in which isolated terms and apparentlymeaningless facts arc arrayed for students' readingand regurgitation. Instead, themes should connect therealms of science; they should be stressed as studentslearn science; and they should also provide a frame-work to guidc teachers in developing instructionaltools.

Science and technology arc expanding so rapidlythat a thematic approach for students to use in learn-ing science is more than just helpful. It is essential.Each branch of science has accumulated an enormousamount of detailed information. If the basic conceptsof one field can be transferred by connection oranalogy to another field, students will understand thatthere is a purpose and a logic to the system. If curric-ula and instructors are successful in developingthemes for students to usc in connecting and integrat-ing science facts, then this intellectual habit will carryover and cnrich other fields and disciplines. In thisway an integrative, thematic approach to learning willhelp students not only to develop a meaningfulframework for understanding science but also toapproach problems in other disciplines as well as intheir daily lives as citizens, consumers, and workers.

28 Part IWhat Is Science?

AS noted before, this selection of themes is not theonly possible configuration nor even the optimalnumber. These themes am emphatically not intendedto be the titles of textbook chapters, units, or instmc-tional programs. Thcy are suggested as means oflinking facts and idcas within and among scientificdisciplines. They are not intended to be buzzwords.Indeed, the purpose of including thematic strands inscience curricula would be dcfcated if the focus ofscience cducation now shifted to constant iteration ofthese isolated terms. Rather, themes should beintegrated in their appropriate philosophical andempirical forms into existing curricula, to makc thecurricula more unified and more logically developedfor students. In other words, it does not matterwhether or not publishers and teachers usc these cxactthemes in teaching science as long as they communi-cate explicitly the interconnections of facts throughmajor idcas of science.

Energy

Encrgy is a central conccpt of the physical sciencesthat pervades biological and geological sciencesbecause it underlies any system of interactions.Energy can be taught as a bond linking variousscientific disciplines. Defined in physical terms,energy is the capacity to do work or the ability tomakc things move; in chemical terms, it provides thebasis for reactions between compounds; and inbiological terms it provides living systems with theability to maintain their systems, to grow, and toreproduce.

In thc physical sciences, energy can be explored invarious manifestations (heat, light, sound, electricity,and so forth), in conversions from one Lan toanother. Energy is perhaps the most important themeto the physical scicnccs because all physical phenom-ena and interactions involve energy. Whether onediscusscs the energy of hcat, light, sound, magnetism,or electricity; the conversions of energy from kinctic

4 0

to potential or from electrical to heat or sound; oreven the products formed by the combination ef anacid and base, energy is involved.

In the earth sciences the flow of the earth's energycomes from two sources. First, them are forces withinthe earth, fueled by nuclear mactions within themantle and core, that translate through the crust andare responsible for the processes that drive mountainbuilding, continental drift, volcanic eruptions, andearthquakes. Second, there are the forces on thesurface of the earth, such as wind, precipitation,physical and chemical reactions, and the activities ofliving organisms (mostly driven by the sun's energy),that alter the face of the earth and are responsible formany geological processes.

In the biological sciences the flow of energythrough individuals drives metabolism, growth, anddevelopment. The flow of energy through ecosystemsdetermines how organisms interact through thetrophic levels of communities. Because all liferequires energy, biochemistry is really the study ofhow energy facilitates biochemical reactions thatallow the body to synthesize biochemical moleculesthe basis of growth.

The theme of energy is important to considerationsof ethical behavior and the relationships of scienceand technology to society. Sources of energy on earthinclude solar, wind, and water power, geotheimalenergy; nuclear energy; and fossil fuels. Somesources of energy are virtually inexhaustible, such assolar, wind, water, and nuclear. Renewable sources,such as water power, can be recycled and replaced,while nonrenewable sources, such as fossil fuels,cannot be replaced. Students should appreciate thesedistinctions, the limitations of some sources ofenergy, and the need to conserve them or avoid theiruse.

Evolution

Evolution in a general sense can be described aschange through time, and virtually all natural entitiesand systems change through time. But evolution isnot just the history of natural things; it is also thestudy of patterns and processes that shape thesehistories. These patterns and processes may beastrophysical, geological, biological, or biochemical,

and all contribute to the evolution of the universe aswe know it.

Evolution is mom than simple change because it ischange with a direction: that direction is time.Through time, life has evolved from simple formsinto the present array of organisms on earth. Throughtime, the earth has also evolved from its originalformation: oceans have formed; mountains have risenand have been leveled; continents and oceans havebeen formed, sundered, and re-formed; and thehistories of past oceans and terranes (sections of landbuffeted by tectonic plate action) have left theirrecords in the geologic column. Evolution is notconfined to the earth and its systems but extends tothe entire universe. The progression of time has seengalaxies flung across space, interactions amongcelestial bodies influencru by their relative positionsand gravitational attractions, solar systems flourishand die, and the universe expand at a changing rate. Itis literally true that "even the stars have histories,"and these histories are known in considerable detail.

Evolution embodies history and therefore is a partof every discipline in which history has a role.Current evidence indicates that the universe is at least16 billion years old and that the present solar systemcondensed in more or less its present form about 5billion years ago. The earth is about 4.6 billion yearsold, the oldest known rocks are nearly 4 billion yearsold, the first oceans are known from about 3.8 billionyears ago, and the first forms of life from about 3.5billion years ago. In order to teach life science, earthscience, or astronomy, evolution should be a funda-mental, central concept of the curriculum.

Evolution, which Darwin described as "descentwith modification," is the central organizing principlein life science. Theodosius Dobzhansky said thatnothing in biology makes sense without it. Evolutionexplains both the inherited similarities and thediversification inherent in all forms of life. Whileproviding a comparative basis for Lludies of anatomy,structure, adaptation, biochemistry, and ecology,evolution is the basis for classifying living things andthe operating principle on which biomedical researchis founded.

History illuminates the study of all events andpatterns in nature because these events leave theirmarks on their products. Light spectra emanatingfrom distant stars can tell astronomers how old thcstar system is and where it stands in its life cycle. The

Chapter 2The Major Themes of Science 29

sediments of natural geological features, such as theGrand Canyon, are traces of the past that can be readlike a history book, telling what kinds of environ-ments existed through time in a particularplace, andhow that place has changed. Fossils, ofcourse, are thesignature of life's history and evolution. Living thingsalso show the marks of history, by retaining charac-teristics, however modified, that have been inheritedfrom their ancestors. (An example is the bones of themammalian middle ear, inherited and modified fromthe ancestors of the first mammals, in which theywere bones of the lower jaw.) Using evidence ofinherited characteristics, scientists classify livingthings into natural evolutionary groups.

Within evolution there are some recurringsubthemes that can be woven into instructionalcurricula. One such subtheme is direction, and, asnoted earlier in the treatment ofevolution, timeprovides the direction to evolution. In most naturalsystems, what happens next depends to a large extenton what has happened before. In ecosystems, succes-sion of a biome is more likely to have a predictabledirection based on previous successional stages of thebiome than it is to be random, because one succes-sional community sets the stage for the next. Theevolution of life on earth has been facilitated by theevaution of the atmosphere, which the organisms onearth have changed substcruially through time. Thishas been an interactive procesf; (see a related discus-sion under the theme of systems and interactions).

A related subtheme is that of constraints because, asjust no"):1, what happens next is frequently con-strained by what has happened before. Other kinds ofconstraints are physicochemical; they place limits onthe future potential of systems. (If bones and shellswere made of silicates instead of calcium phosphateand cacium carbonate, how would the architecture oflife differ?) Some constraints are historical in thesense of descent: Organisms, as they evolve, have towork with the genetic tools they have inherited tomodify their stmctures into new adaptations. (Verte-brates, for example, are built on a four-limbedpattem; in the course of vertebrate evolution, wingsfor Hying have had to be fashioned from existinglimb systems and have not sprung full-blown as newstructures from the vertebral columns.) So there arestrong constraints on evolution. There are constraintson physical phenomena, too. The sun affects andconstrains planetary conditions of climate, geophysi-cal processes, and rates of rotation and revolution.

30 Part IWhat Is Science?

A third subtheme is that of chance. The randomnessof Brownian movement, genetic mutations, theHeisenberg uncertainty principle, and the toss ofcoins are familiar concepts in science curricula.Chance has played an important role in the develop-ment of molecules, structures, and societies because itpresents natural variation in what is possible. Ofcourse, each case is determined by specific factorsand is anything but random. However, we use theterm chance to describe what may happen in anygiven case, given the possibilities. For example, thechance impact of a giant asteroid with the earthbillions of years ago appears to have thrown intospace a chunk of earth that eventually became themoon.,The chance colonization of a new continent bya small group of mammals triggered the adaptiveradiation of horses in the New World; such chanceevents through the history of the Tertiary period, backand forth between America and Europe, fostered theevolution of horses. Random mutations are typicalchance events; yet such mutations need the rightcombination of a genetic and physiological environ-ment, to say nothing of the adaptive and physicalenvironment of an organism, to be successful in theireffects.

Chance factors important in the history of lifeinclude the unpredictable effects of genetic recombi-nation, the restructuring of the genome, and themigration of new individuals in and out of a popula-tion and of populations into new areas. On a largerscale the introduction of predators or competitors,long-term and short-term changes in climate, andenvironmental catastrophes are all chance factors thatshape the history of the earth and its life.

Patterns of Change

Change through time, of course, is one pattern ofchange, but there arc other kinds, Rates and patternsof change are essential features of the natural world.Analyses of changes help us to describe and under-stand what is happening in a natural system and, tosome extent, control changes (particularly in techno-logical applications). Understanding different kindsof changes helps us to predict what will happen next.Knowing about different patterns of change helps usto identify patterns of nature as we encounter them

42

C

and to look for underlyingmechanisms and connec-tions..Pattems of change can be usefully divided intothree types: (1) trendS;.(2) cycles; and (3) irregularchanges. Some systems or processes show more thanone kind of pattern of change.

Changes that occur in steady trends are not neces-sarily all steady in the same sense, but they doprogress in one direction and have fairly simplemathematical descriptions. Examples include thevelocity of falling objects in acceleration, the decayof radioactive material, and the colonization ofoffshore islands by continental plants and animals.

Cyclical changes can be defined as an interval oftime during which a sequence or recurring sequencesof events or phenomena are completed; they arecharacterized by the range in variation from a maxi-mum to minimum, by qualitative distinctions thatappear and reappear, and so forth. Cyclical changesare often found in systems containing feedbackmehanisms or where a system depends on theperiodicity of another system (such as the life cyclesof annual plants and animals, which are dependent onthe earth's annual revolution). Cyclical changes arecommon to living systems: They include life cycles,seasonal cycles, biochemical cycles of nutrients,water, gases, and so forth; and the flow of energy andmatter through food webs and food chains. In earthscience cyclical changes include the various planetarycycles and their effects on seasons, tides, andweather, the rock cycle; the cycles of natural com-pounds such as water, minerals, and so forth; and thegreat geophysical tectonic cycles of mountain build-ing, plate movement, and subduction, coupled withcycles of deposition, lithification, and erosion. In thephysical sciences, cyclical phenomena include soundwaves and ocean waves, feedback in electronicsystems, and the action/reaction systems of chemis-try, particularly cell chemistry.

Irregular changes arc those that manifest the naturalunpredictability of systems. These were discussed ina itlated way under the theme of evolution. Randomchanges may occur in reaction to small changes instable conditions; some, for example, may appearcyclical but actually are never repeated in exactly thesame way. These include the motions and periodici-ties of planetary bodies, the predator-prey cycles ofecosystems, population cycles and the dynamicequilibrium of populations, and plant successioncycles. Some random pattems of change may be

4

unpredictable in details but in a larger sense are verypredictable, and these include the examples justmentioned. The percentage of heads in a long seriesof coin tosses is expected to approximate 50 percent,but in a short series the fluctuation from this figuremay be great. The toss of a single coin is consideredsuch a randomly govemed event that we use it, forinstance, as an arbiter of fairness to assign the kickoffat the start of football games.

Scale and Structure

The kinds of structures that can be described in thenatural world are many. The diversity of life, ofgeological forms and microstructures, of chemicaland physical structures, configurations, combinations,and interactions appears to be almost endless. And itcan be endlessly described in instructional programs,often to the exclusion of other important themes inscience. The point is to show how different kinds ofstructures are related, how they explain and illumi-nate each other, and how structure at different hierar-chical levels (a phenomenon of scaling) shows uniqueproperties at each level.

The structure of the natural world requires languageto explain it, but there are many ways to describenatural phenomena. Customarily, we recognize aphenomenon and give it a name that describes thephenomenon in the terms that make the most sense tous. Sometimes in science curricula, remembering thenames and their definitions seems to become an endin itself. This is partly because scientific terminologyis complex. A name, however, should not becomemore important than the phenomenon being describedor than its empirical or logical relationships withother phenomena. Pure description, as Darwin'squotation in the preceding section points out, is not ofmuch use until it is employed in the service of anidea.

The structure of matterwhether molecules,mountain ranges, or ecosystemscan generally beapproached in several ways. One way is reductionist,a continuing search for the minutest levels of opera-tion of natural phenomena. Research in the geneticcode, the microstructure of cells, the lattice of acrystal, and the properties of neutrinos are all in-

Chapter 2The Major Themes of Science 31

tended to explore the finest-scale workings of thenatural universe. The complementary way to studythe same natural phenomena is synthetic, in which allthe levels of phenomena in a system are examined tosee what roles they play in the overall behavior of thesystem. In a description of the structure ofanysystem, both approaches are useful. One can reducethe study of an ecosystem to observations on individ-ual organisms, their interactions with other organ-isms, and their own internal metabolic workings.Conversely, a vast body of knowledge can be synthe-sized about an ecosystem, including its interactions ofpredation, competition, and coevolution and itsdiversity and richness of species; these patterns andprocesses can be-compared to those of other ecosys-tems.

There are component levels to the structures ofmost natural systemswhether one considers thehierarchy from atoms to molecules to compounds inchemistry, or the hierarchy from organdies to cells totissues to organs to individuals to populations,species, and so on in biological organisms. What isusually striking about the structure of any naturalsystem is that cach level of its hierarchy has what arecalled emergent properties; that is, the phenomena atone level of the hierarchy cannot always be predictedfrom knowledge of another level. Somc properties, ofcourse, are readily predictable from other levelssuch as the properties of diamond from knowledge ofthe tetrahedral arrangement of carbon atoms. Othersare less readily determined; for example, one couldscarcely predict the behavior of a deer simply byknowing the structure of its liver. The behavior of thedeer is an emergent property of the level of itsstructure that interacts with its environment andcannot be easily reduced to lower levels of its struc-ture.

The theme of scale and structure is intimately tiedwith that of systems and interactions because mostsystems are studied at some scale. As noted above,one could study a deer in several ways: as a part of anecosystem; as a natural system of its own withcirculatory, respiratory, and other functions; or as ahost for many living systems of bacteria, parasites,and othcr organisms. The importance of any struc-tural level in a hierarchy depends on mescale beingstudied.

The interplay of structure and function is anotherimportant component of scale and structure because It

32 Part IWhat Is Science?

shows how parts function and how thcir actions workto support the whole system. The function of thedeer's legs in running, for example, is an importantpart of its survival, and its locomotory adaptationscan be contrasted with those of a crobadile or anelephant. The deer's digestive system, with itsadaptations to digest plant material efficiently, alsocontributes to its overall survival. In a steel building,the function of cach beam and the walls connectingthem extends the microstructure and strength im-parted by the arrangements of the atoms in the steel.

Stability

Stability refers to constancy; that is, the ways inwhich systems do not change and why. The ultimatefate of many systems is to settle into a balancedsteady state or a state of equilibrium. In such states qllforces are balanced. It is important to distinguishbetween the state of equilibrium and the stcady state.The former is typified by a person sitting on a step ofa stopped escalator, the latter by a person walkingdown a moving escalator just as fast as the escalatormoves upward. Equilibrium is rare in living systemsbecause living systems are inherently dynamic. (Whatphysicists call steady state is what chemists andbiologists call dynamic equilibrium.)

There am several kinds of equilibrium. A systemcan be in static equilibrium, as when a rock rests atthe foot of a cliff, or in dynamic equilibrium, wherethe surface appearance is steady but much action isoccurring at underlying levels. An example is a dishof water and carbon dioxide in equilibrium. Equalnumbers of water and carbon dioxide molecules amalways escaping into the atmosphere and returning tothe solution, yet observable concentrations andpressures remain in a steady state. Other examples arethe cellular and metabolic homeostasis of an individ-ual organism and species and populational densitiesin an ecosystem.

Stability is related to the idea that nature is predict-able. Given a set of initial experimental conditions,results arc expected to be replicable. Indeed, failure toobtain reproducibility begins an immediate search foruncontrolled variables. Science is based on observa-tions and set in a testable framework of ideas. Scicn-

44

-

tific theories and laws usually remain fairly stablebecause they are based on consistent evidence.

There is only an apparent contradiction between thetheme of stability and those of evolution and patternsof change. The different themes may be applied todifferent situations or to different parts of the samenatural situation. For example, the apparent stabilityin the composition of a lush tropical forest may maskconstant change in its plant and animal populations.Students will learn to recognize these concepts,differentiate between them, and appreciate when it isappropriate to describe natural systems in these terms.

Systems and Interactions

Natural'systems may include solar systems, ecosys-tems, individual organisms, and chemical and physi-cal systems. By defining the boundaries of a system,a study of the system and its parts and interactions is

possible.There are many kinds of interactions in systems.

The components of an ecosystem (individual species)may interact through predation, competition, com-mensalism, mutualism, parasitism, or any number ofothcr patterns. At any time, a single component of asystem can be interacting in various ways. A deer inan ecosystem can be a herbivore, an item of prey for acarnivore, and a living system itself with manysubsystems of life functions (circulation, respiration,digestion, and so forth). To study systems, we gener-ally focus on one or a few aspects of interactions at atime to avoid an overload of information. These inter-actionsare commonly described in simplified termsas models. Models almost never simulate all the fac-tors that are interacting, nor all the ways in which thefactors interact, but they do provide a way of describ-ing natural phenomena that are organized in systems.

Some aspects of systems can be studied in thelanguage of technology: input and output. Air andfuel go into an engine, and mechanical energy,exhaust, and heat come out. Carbon dioxide, solarenergy, and water react in a chloroplast to producesugars, oxygen, energy, and heat in the photosyn-thetic system. The fruit, seeds, and oxygen that arcthe products of flowering plants are input for animalsin the same ecosystem.

Feedback is an important feature of interactions inmany systems. We are all familiar with the squealfrom a loudspeaker as a microphone is placed tooclose to it, but some forms of feedback arc not soimmediate. If a deer population increases in an areaone year it may overgraze its habitat. As a result thestarvation rate may increase the next year, and thepopulation may be reduced to its original carryingcapacity. In turn, the abundance or condition 3f otherorganisms that depend on the deer for part of theirbiotic interactions as well as the entire system and itsinteractions are affected. (Obviously, there is a lessonhere for human intervention and interaction withother living things.)

Section D Incorporating Themes

THE role that themes play in science programs willultimdtely depend on the knowledge base of class-room teachers and the techniques they employ.Incorporating themes into the science curriculum ismost likely to happen when there is close and contin-ual dialogue between teachers, science specialists,university faculty, and curriculum developers.Connecting the important science concepts withscience themes will improve students' ability to makemore meaningful the relationships between scienceconcepts and other related disciplines.

This section develops a number of ways that themescan be used to enhance the science curriculum.

Themes should be used to ir.tegrateconcepts and facts at all :evels of thecurriculum.

Science is too often presented as an endless anddetailed description of natural phenomena, a paradeof seemingly unconnected experiments and activitiesThemes can integrate these separate pieces of infor-mation into broad and logically cohesive structures inwhich relationships among pieces of information arcshown to illuminate the phenomena that arc beingdescribed.

Chapter 2The Major Themes of Science 33

L

For example, when describing natural phenomena,instructional materials frequently present a series ofboldfaced tenns that are then defined, often usingother terms that also require definition. Scienceinstruction thus becomes little more than an exercisein the memorization of terms. Through the use ofthemes, such as those of scale and structure andsysteMs and interactions, students can see how theparts fit together logically and how the informationthey arc learning is used to describe other kinds ofphenomena. A flower's parts can be named, de-scribed, and detailed, but this information is moreuseful and more vivid to a student if these parts aredescribed in terms of how they facilitate reproductionor how their great diversity evolved from a basicfloral plan or how they compare with reproductivesystems in other kinds of plants and animals.

The integration of themes into science curriculadoes not mean that the usual curricular divisions ofphysical, earth, and life sciences need be discarded; infact, they should not be. Within the individual disci-plines, themes need to be instituted and developedthroughout a year's study and from one year toanother. In a general science curriculum, there is evenmore opportunity to show how individuzl disciplinesare connected by thcmatic strands. Rather than beingreorganized around themes, science curricula shouldbc permeated by themes.

Consider an example of the theme ofenergy. In thephysical sciences, energy can bc explained in thecontext of basic chemical reactions and physical

-phenomena. Energy is required for or is a product ofmost chemical reactions. The physical forms ofenergykinetic and potentialare basic concepts ofphysics. In the earth sciences, energy drives geo-physical processes of mountain building and conti-nental drift, erosion and deposition of sediments,weather, and the expansion of the universe. In the lifesciences, energy is the basis of growth and develop-ment of all living things: Each must gain energy insome way. Metabolism is based on deriving energyfrom biochemical processes. If a general scienceteacher discusses all of these topics in the course of ayear, the theme of energy will surface again andagain, and students will see it as a major, overarchingidea of science. This is what might be called ahorizontal use of the theme ofenergy to cut acrossdisciplinary lines.

34 Pan IWhat Is Science?

Now consider a more vertical concept: how themescan be develoPed through grade levels, continuingwith the theme of energy. An elementary teacher canexplain to students that energy is needed to makethings move or work. Experimenting with differentkinds of levers, the students can learn that some tasksrequire more energy than others. A simple pinwheelcan bc used to illustrate that there am many differentforms of energy. You can make the pinwheel moveby blowing on it, or you can hold it in the wind, oryou can place it in front of a jet of steam from akettle, or you can attach it to a small electric motor.In the upper elementary grades, such an activity canalso be used to demonstrate the conversion of energy,a very important concept. In the higher grades theforms of energy can bc classified as light, heat,electrical, nuclear, and so on. The flow of energy inliving organisms and through ecosystems can bestudied, modeled, and measured. Complex social andethical issues involving scientific information aboutsources of energy for humans can be discussed andevaluated in light of this information.

It is possible that educators and providers ofeducational materials may wish to use themes crea-tively in the organization ofone or more disciplinesand' ai various grade levels. Energy is frequentlyfound in curricula in these contexts, especially inphysical or general science programs. This device isencouraged as a way to show the interconnectednessof scientific knowledge. But it is not mandatory oreven recommended to reorganize the entire curricu-lum to do so, as long as thematic strands permeatecurricula to provide depth of meaning and integrationof information.

Of course, not all themes are for all teaeners. Thetheme of stability, for example, may be difficult tobring to kindergartners in any context. The theme ofevolution may bc equally inappropriate for a chemis-try teacher trying to convey molecular structure andchemical reactions. This should not be of concern.The same material can be presented in the context ofenergy or scale and structure. In teaching the primarygrades, teachers can best build the foundations forscience education by (I) instilling in students the joyof science through enjoyable, expanding activitiesand experiences; and (2) beginning to teach theprocesses of science, showing how they form thebasis of all scientific activity.

4 6

Themes should be used to integrate themain subfields of scientific disciplines.

By using themes to integrate the principal subfieldsof scientific disciplines, teachers can help students tosee the logical and material interrelationships of allsciences. For example, the_subfields of life sciencesuch as genetics, evolution, and paleontology must beclearly connected. Genetics provides the understand-ing for the raw material of evolutionary change asseen in the fossil record. These connections are theprincipal ideas by which the facts of the subfields areexplained.

The theme of evolution, in particular, as well asthose of patterns of change and scale and structure,are unifying strands in the biological science curricu-lum. In a similar way the understanding of platetectonics must be shown to proceed from lines ofevidence coming from many different fields ofscience, including reversals of the earth's magneticfield, the geophysical data of matching mountainranges, the technological monitoring of crustal "hotspots," the development of sonar, and the paleonto-logical evidence of ancient distributiOns of plants andanimals. Instructional materials must explain andemphasize these thematic connections in order to beacceptable.

Themes in science should direct the designof classroom activities.

Themes can be used to connect classroom activitiesand to provide them with a logical sequence andscope of instmction. For example, in a study of howenergy flows through biological systems, students caninitially monitor the flow of nut.rients through a feweasily kept organisms, such as houseplants, parame-cia, flour beetles, or hamsters. Later, they can applythis knowledge to a consideration of the energy flowthrough ecosystems via food chains and food webs.Using the theme of energy to connect these twoactivities fosters a spiraling effect of the conceptrather than the treatment of the two activities as

isolated. Activities should be used to explain termsand concepts in the service of themes because activelearning better promotes the internalization of ideasand processes.

The emphasis on themes in sciencerequires a recoitsideration of how muchdetailed material should be Included Inscience curricula.

Explaining the connections created by the use ofthemes in a curriculum takes time and space. To someextent omission of various traditional terms andconcepts that are not well integrated in currentinstructional materials will be required. In evaluatingwhat should be included, teachers and curriculumplanners should give weight to those terms and con-cepts that support and develop the basic ideas of afield and the overarching themes that connect theseideas.

Current science textbooks are plagued by "thementioning problem." This is what happens when aninstructional program tries to include too many termsand concepts. They end up bcing mentioned insteadof being explained. There is no optimal number ofterms that should be covered and defined in a curricu-lum at a given grade level. If a term serves no furtheruse in a chapter or unit than to define itself, its utilitymust be questioned. More than likely, this tenn iscovered but not mally explained or integrated in anyuseful way.

Some traditions of science education, includingtime-honored ones, may be found faulty if examinedwith the above considerations. For example, studentstraditionally learn in earth science classes that thereare three kinds of rocks: igneous, metamorphic, andsedimentary. This taxonomy is a false one. Igneousrocks are extruded from within the earth, but they canbe laid down just like sedimentary layers, which formthrough the action of wind, water, and ice. Bothigneous and sedimentary rocks are subject to meta-morphism by the pressure of overlying rocks throughlong spans of time. These kinds of rocks are notmutually exclusive. Furthermore, their explication asdiffemnt kinds obscures the processes of sedimenta-tion, metamorphism, and extrusion from within the

Chapter 2The Major Themes of Science 35

earth's mantle that are only three of many importantgeological mechanisms. These processes of geologycould better be explained through the themes ofsystems and interactions, patterns of change, evolu-tion, and energy.

The emphasis on themes in science curriculaprovides a focus around which the terms and conceptsgiven in an instructional program may be evaluated.One danger, however, is to take too literally thelimited number of themes that are suggested in thisframavork. Other formulations are possible: Diver-sity, matter, hierarchy, motion, and conservation areexantles of other themes around which curriculamight be organized, and there are certainly manymore..0ther sets of themes am also possible; Project2061, for example, uses systems, models, constancy,pattems of change, evolution, and scale. The point isfor educators to ask of curricula and instructionalprograms, Why is this material being included here?What larger purpose does it serve in explaining thisdiscipline or concept Of science? Themes providesome guidelines for this kind of evaluation.

Using themes In curricula can improve thequality of prose.

When logical and structural relationships are empha-sized in instructional materials, the writing is oftenimproved. To explain relationships and themes ade-quately, writers will probably have to abandon typicalreadability formulas. (This idea is considered atgreater length in Chapter 8, "Instructional MaterialsCriteria.")

Assessment should be thematically based.

The use of themes not only encourages betterlogical connections in science textbooks but alsoencourages such connections in review and assess-ment materials and in activities. The strict repetitionof facts learned in chapters and units can be replacedby activities that encourage students to discover andconstruct connections between the important ideas of

36 Part IWhat Is Science?

science in a thematic context. How do these facts andconcepts, for example, form cyclical patterns, showthe hierarchical scale in the system, demonstrate therole of eVolution in producing this pattern, underscorethe importance of energy flGw? This is more interest-ing than the typical chapter review heading "WhatHave We Learned?"

Themes can be used to lay out basicprinciples of science that will operate inmany subfields and other disciplines ofscience.

For example, the understanding of scale andstructure is applicable whether one studies geologicalstructures, biological structures, chemical structures,or what physicists call the structure ofmatter. Thestudent who expects to find systems in which giveninteractions will be encountered and in which emer-gent properties of each level in the structural hierar-chy will be explained and related is a student who isreally being trained to understand science. Studentscan learn to expect that history leaves its mark onmany details of structure, whether one studies lifescience or earth science.

Learning how to construct and apply conceptualmodels, one of the tools of advanced science, dependson the ability to see patterns, interactions, scale instructure, and the flow of energy in a variety of ways.These are all manifestations of the basic themeselucidated here. Furthermore, the understanding ofthemes such as evolution and patterns of change canhelp a student to anticipate concepts not only inscience but also in historysocial science,Englishlanguage arts, and other disciplines.

The use of conceptual themes will not by itselfsolve all the problems of science education, andeducators should not be tempted to view themes as anew panacea. However, the incorporation of themesin thoughtful and judicious ways should improve theintegration of facts and ideas, the interrelationships oftheories and of disciplines, and the quality of instruc-tional materials. It is clear that science education willnot begin to reflect more closely on what science isall about until the overarching themes and ideas ofscience become the most important feature of scienceeducation at all instructional levels.

4 8

37

I

38 Part llThe Content of Science

1.1 -

Overview

THE content of a science program is its heart. To takethe thematic appmach described in this framework,educators must make connections among scientificdisciplines that have traditionally been taught assepäratesubjects. This can be accomplished in a greatmany ways. What follows should be interpreted as anillustration of one way that a conceptual apprbachmight be organized within the traditional contentareas of science. The themes thaLannotate the contentdetailed hem are only one set tint encompasses theimportant ideas of science; other sets are not only ac-ceptable but also encouraged. Because this organiza-tional scheme is somewhat different from previousones, a few words of explanation are necessary.

Most sections begin with a paragraph about theunifying theories in the discipline. These paragraphsare meant to guide teachers in making the connec-tions among the ideas within the discipline. There is adifference between theories, which are conceptualand empirical entities within the disciplines, andthemes, which are pedagogical tools that cut acrossdisciplines. The theoretical summary is followed by aset of questions that are central to the content area.The descriptions of content appropriate to variousgrade levels are then developed in the form of narra-tive responses to these questions. The purposes of thistechnique are to eliminate the emphasis on facwids---the isolated facts and definitions that have longdominated science instructionand to provide asense of discourse for instructional purposes. Thechoice and sequence of the questions are not defini-tive nor exclusive; another set of questions couldportray the content equally well.

The questiors are content-oriented, not theme-oriented. The narrative msponses, however, arewritten from the perspective of one or more of the

major.themes of science, which are identified at theconclusion of the paragraph. They could often, just asappropriately, be written from other perspectives andaddmss different themes. To illustrate this point, con-sider the first set of questions in Chapter 3, Section G,Energy: Light, which are: "How does light enable usto see? What are the sources of light? What is light?"A narrative written for the kindergarten through gradethree response to those questions from the perspectiveof the themes of energy, scale and structure, andsystems and interactions might be expressed asfollows:

When we see something, our eyes and brains areresponding to the light that comes from objects weare looking at. Light itself is not something that wesee or touch. Light comes from objects and enters oureyes, the organ of the body that is sensitive to light. Apicture of what we are looking at is formed in oureyes and brain. Light is not like other things; it is notordinary matter. The eye can see both very dim andvery bright light, but there are limits. Because the sunis so bright a source of light, too much light entersour eyes if we look at it directly, and serious damageto our eyes occurs. Mc't objects do not emit theirown light but reflect light from other sources. We cansee them by means of this reflected light. The sun isour primary source of light. Other sources includeelectric lights of all sorts and objects that arc burning.We can classify the light we see according to itsbrightness and its color.

In contrast, a narrative focusing on the themes ofpatterns of change and systems and interactionsmight read as follows:

Light is given off by a variety of familiar sources,most importantly the sun. We seldom should look

directly at or into a light source because our eyes, theorgans that receive light, are very sensitive. We canobserve and discuss patterns in the intensity of lightthat allow us to see best because the human eye issensitive to only a certain range of lightif the lightis dimmer or brighter than the light in this range, themore difficulty we have with our vision. We alsn cannote patterns in the amount of light that objectsreflect, because different objects reflect differentamounts of light. It is this reflected lightthat allowsus to see.

To take a second example, in Chapter 5, Section C,Ecosystems, the first question is: What arc ecosys-tems, and how do organisms interact in ecosystems?Part of the response for grades three through six is thcfollowing paragraph, written from the perspective ofsystems and interactions:

All organisms have roles in their environments. Theyeat some species and serve as food for others. Someorganisms, like trees, shelter other species. Others,like fungi, decompose them. Some organisms fillmore than one role.

An alternative passage, from the view of scale andstructure:

All organisms have roles in their environments. Boththe role they play and the ecosystem itself depend onthe scale at which we investigate them. Under a rock,for example, we might find organisms and microor-ganisms that cat other species and their own kind,serve as food for other species, or decompose deadorganic material. We would not expect to find a largerange of diversity in kind or number of organisms. Ifwe expand our scale of observation to include theentire forest in which the rock is located, we will finda range of organisms much wider in terms of num-bers, types, and sizes, but they would all fill the sameroles of producer, consumer, and decomposer.

Here is an example, from Chapter 4, Section C,Oceanography, of how the saltiness of the oceanmight be explained to junior high school studentsfrom the standpoint of scale and structure andpatterns of change:

Salts in the ocean have come largely from the earth'sinterior, mainly by volcanic activity. These salts(containing mainly chlorine, sodium, magnesium,sulfur, calcium, and potassium) contribute to the

shells of marine animals and are recycled into thewaters and ocean sediments when these animals die.

The same concept can be written from the stand-point of evolution:

Originally, salts in the oceans came from dissolvedminerals that were extruded from inside the earth.New material, brought up at spreading zones, hasincreased the dissolved mineral content in the oceans'waters even as these salts have been lost throughdeposition and subduction of oceanic crust. Freshwa-ter runoff from continental surfaces has also contrib-uted to the oceans' salt content through time. Al-though the oceans have always been salty, it isdiffficult to determine precisely how the dissolvedsalt content has fluctuated through time.

These illustrations arc given to demonstrate thatdifferent themes can be used to frame the samecontent. This framework insists that science prose beenjoyable to read, and this is a goal that we have alsotricd to achieve in its writing. Whcn the prosc flowsmore naturally, the connections among themes areclear, a mere checklist of isolated facts is moredifficult to create or defend. Finally, it should benoted that vocabulary, though present in the narra-tives, is not a dominant force. Indeed, vocabularyshould be used in an appropriate context anti notintroduced for its own sake.

The intended audience of these narrative descrip-tions is not students, but educators and tcxtbookpublishers. Essential vocabulary has been includedfor these readers, but it is not necessarily appropriatefor the students of the grade spans indicated. Forexample, in life sciences, emphasis is given to thecomparative structures of plants and animals, and theword stomate is used. Kindergartners can and shouldunderstand that plants have structures that performspecific functions, and their teacher may well usc thcword stomate in context, but thc objective of the les-son should not be thc students' ability to spell ordefine the word stomatc. Appropriate vocabularyshould be used at all levels, vocabulary should notdominate the curriculum or bc an end in itself.

At the high school level, the use of mathematics hassometimes assumed a role similar to vocabulary at theelementary levelas a barrier and an end in itself. Inthe text of Part II, we sometimes have used a formulaas shorthand for a concept or relationship. Students

5 .1.

Overview 39

need not memorize the formula for the accelerationdue-to gravity with time, or to know how to calculatepH. It iS important for everyone to understand accel-eration ns it relates to riding a bicycle or driving a carandAo understand pH as it relates to chemical proper-

Aids or to acid rain. Proficiency in mathematics shouldnot be a prerequisite to learning science. Manystudents will be motivated to learn mom mathematicswhen they see it applied in the context of a scientificproblem. The content that is delineated here is for allstudents, not only those who plan to attend collegebut also those who need to acquire scientific literacyfor their lives as informed citizens.

40 Pad IIThe Content of Science

In certain cases, content that has caused confusionor misconceptions in the past is presented at a greaterlevel of detail than is warranted for most readers.These comments, primarily intended for authors andeditors, are often presented as sidebars.

The presentation by grade spans is intended to becumulative. Each grade span after kindergartenthrough grade three presupposes not only the materialin the prior levels but also its review and elaborationat higher levels. The effort in this presentation, and inthe curricula that we hope it inspires, is to deepenconcepts when they arc revisited, rather than to repeatideas at the same level of understanding.

r 0t ) 4..,

rChapter 3

Physical Sciences

. . .

IN the study of matter and its interactions underfamiliar conditions, the central organizing principle isthat the amount of matter stays constant. It is neithercreated nor destroyed; only its form is changed. Ingeneral, the number of atoms, the basic buildingblocks of matter, remains constant. Mass is anexcellent measure of the amount of matter, so weexpress the constancy of matter as the principle ofconservation of mass. Strictly speaking, mass andenergy are interrelated in such a way that the trueprinciple is one of mass-energy conservation. Theconversion of mass to energy is observable only whenvery large energy changes occur, as in nuclear trans-formations. The focus in kindergarten through gradetwelve is on the study of matter under familiarconditions, when energy changes arc not large.

A-1 What Is matter, and what are itsproperties?

A-2 What are the basic units of matter, andwhere did matter come from?

A-3 What principles govern the Interactionsof matter? How does chemical structuredetermine the physical properties ofmatter?

. '

What is matter, and what are its properties?

Kindergarten Through Grade Three

Matter is the name we give to all the stuff in ourphysical world. From stars to dust, from elephants tofleas, everything is made of the same basic buildingblocks. Although the scale of our universe rangesfrom the very large to the very small, all of it ismatter. [Scale and Structure, Stability]

All matter has properties that can be observed,defined, and recorded. Matter occupies space, it hassubstance, and we can measure its weight. Dependingon the particular form of matter of which they arcmade, some solid objects float in water while otherssink. Many forms of matter are identifiable by theircolor, texture, or shape; by their hardness or flexibil-ity; by their taste and odor; by the sound or light thatthey emit and that we can perceive. [Scale andStructure, Systems and Interactions]

All things that we can sense directly are constructedof progressively smaller things. We use tools likemicmscopcs, telescopes, or thermometers to perceivethings for which our senses arc poorly adapted orwhich exist beyond the range of our scnscs. Tomeasure and talk about our observations of matterwith others, we use standardized tools like rulers,scales, and clocks. The more we know about theproperties of matter, the better able we are to describe

Chapter 3Physical Sciences 41

Careful observation is needed to distinguishsupeificially similar objects, such as an orangefrom an orange-shaped candle, or a glass of hotwater from a glass of cold water.

Young students need practice in using theirsenses to observe and to gain confidence in theirown. observational skills. They need to observeand report and judge for theirown benefit, not tomeet an adult standard of what is right or wrong.

its stmcture, and the better we can apply our intellectsto constructing an understanding of the world. [Scaleand Structure]

Most things we see are mixtures of several puresubstances. We make a mixturc when we dissolvesugar in water. The taste of sugar is found throughoutthe mixture, which looks like water. The water andsugar can bc separated again by evaporating the waterto leave the sugar. [Systems and Interactions)

The matter around us exists in three forms or states:solid, liquid, and gas. Water, for example, is ice as asolid, water as a liquid, and steam as a gas. The stateof water can be changed by heating or cooling it.Each of the states of matter has distinguishing charac-teristics. [Energy, Patterns of Change, Scale andStructure]

A-1 What is matter, and what are its properties?

Grades Three Through Six

The basic building blocks of ordinarymatter arevery small particles called atoms. Atoms arc muchtoo small to be seen with ordinary microscopes, but

=a, 11.

they can be seen with recently invented devices calledatomic force microscopes. There arc about 100different kinds of atoms. The smallest particle of apure substance that rctains the properties of thesubstance is usually a molecule. A molecule is agroup of atoms tightly bound together. Because therearc so many ways to put atoms together, there are analmost unlimited number of different kinds of mole-cules and different kinds of pure substances. Sub-stances that are made of only one kind of atom arecalled elements. [Scale and Structure]

The properties of matter depend very much on thescale at which we look. For example, sand flowsthrough your hands almost like a liquid. But an antcarries a single grain of sand very much as you mightcarry a rock. Very often, however, the properties ofmatter at larger scales depend on its properties atsmaller scales. Solid objects and liquids arc made ofparticles that stick together; gases are made ofparticles that do not stick together. This accounts formany of the differences in properties between gaseson the one hand and liquids and solids on the other.For example, gases are compressible or springyseewhat happcns if you.strike the handle of a pluggedbicycle pumpbecause the particles in gases do nottouch. Liquids and solids are not very compressible,because their molecules do touch [Scale and Struc-ture)

To get a better understanding ofmatter at a basiclevel, it is useful to study the properties of puresubstances. Some properties, such as the amount ofspace an object occupies, simply depend on howmuch matter is present and do not help us understandthe substance itself. Other properties, such as color olhardness, do not generally depend on how muchsubstance is present. Studying such properties cangive us clues about how the substance is organized ata more basic level. (Patterns of Change, Scale andStructure)

This very fundamental principlethat the amount of matter (mass) remains constantcan sometimes bedifficult to demonstrate successfully in practice by deiermining the mass before and after an interaction.This is particularly true if the interaction causes a gas to be produced, due either to a change of state or

zhemical change. However, it is important to include gases to help students extend their understand-ing of this principle.

42 Part IIThe Content of Science

--------54

Because many properties of matter depend on the fact that atom-size building blocks exist, but not on thedistinction of whether these are atoms or molecules, it is convenient to simply use the generic term partide whenever the distinction is not important.

The properties of most things around us, becausethey are mixtures, are very different from the proper-ties of the substances that constitute the mixture. Thestrength of a fiberglass fishing rod, for example, ismany times greater than the strength of either theplastic or the glass that, together, make up the solidmixture that we call fiberglass. Mixtures and theirproperties are very important to people who designand build things.

The amount of matter in an object is referred to asits mass. Mass is measured indirectly with a balance,which compares one mass with another according tothe effect of gravity. If the effect is equal, then themasses are the same. [Scale and Structure, Systemsand Interactions]

When matter interacts with other matter underordinary circumstances, it changes in various ways,but it does not disappear nor is it created. The amountof matter (mass) remains constant. [Stability]

A-1 What is matter, and what are its properties"

Grades Six Through Nine

It is useful to make a distinction between thoseproperties of matter that can be measured withoutchanging the substance into another substancephysical propertiesand those properties that areobserved when the substance changes to anothersubstance, !mown as chemical properties. Examplesof physical properties include the boiling and freezingtemperature of a substance and its color [Stabilk,Scale and Structure]

Mixtures of elements or compounds can be sepa-rated using physical processes such as flotation,filtration, distillation, chromatography, and magneticseparation. All of these processes depend on differ-ences in the physical properties of the substances.[Systems and Interactions]

Density is a property of substances thct describesthe amount of the substance that is packed into thcvolume which it occupies. Some substances are

denser than others; the densest solids arc about ahundred times denser than the least &Ilse ones undernormal conditions. A substance sinks in a liquid if itis denser than the liquid; it floats in the liquid if it isless dense than the liquid. Oil floats on water becauseit is less dense than water. [Scale and Structure,Patterns of Change]

The density of a substance depends on both themass of the atoms of which it is made and the way inwhich they are arranged or packed together. Thedensity of nearly all solids and liquids lies in therange between 0.2 glare and 20 glen?. The density ofgases, however, depends greatly on their temperatureand pmssure. At atmospheric pressure, the density ofmost gases is roughly 1/1000 that of the correspond-ing liquids and solids. That is why it is not so easy torecognize the fact that gases do possess mass and cmnbe weighed. Scicntists did not understand this pointclearly until the eighteenth century. [Scale andStructure, Systems and Interactions]

The individual particles that make up matter are inconstant, random motion. In a solid, neighboringatoms are bound together strongly and vibrate backand forth. In a liquid, the particles are not so stronglyheld together. In addition to vibrating, they can slidepast one another. However, they are still boundtogether and cannot easily move apart from one an-other. In a gas, the particles are independent of eachother. They can move as far from one another as thecontainer space allows. These differences are re-flected in the density of matter. The fact that a gasconsists of particles in rapid motion can easily beobserved by studying the way in which a perfume canbe detected rapidly at a distance. [Energy, Patterns ofChange]

A-1 What is matter, and what are its properties"

Grades Nine Through Twelve

How the things of the universe look depends verymuch on the scale at which one is looking. When we

Chapter 3Physical Sciences 43

use the tools of science to help us perceive theproperties of matter at the atomic or subatomic levels,we learn new things because we see things in a newway. Chemistry is the branch of science concernedwith the behavior of matter at the molecular andatomic levels. Over the past two centuries, chemistshave developed an elaborate theory that explains andpredicts the chemical behavior of matter very suc-cessfully and in great detail. Atomic physics isconcerned with the behavior of individual atoms.Nuclear physics studies the structure of the nucleus,and elementary-particle physics (sometimes calledhigh-energy physics) is concerned with the verysmallest building blocks of which nuclear particlesand all other matter are made. [Scale and Structure,Patterns of Change]

Atoms consist of electrons, which occupy most ofthe space in the atom, and very tiny nuclei consistingof protons and neutrons. Protons and neutrons haveapproximately the same mass, which is about 2,000times greater than the mass of an electmn. (Thoughthe nucleus contains almost all the mass of an atom, itoccupies a smaller proportion of the volume of theatom than the sun occupies of the solar system.)

POIMI

The periodic table was originally developed inthe latter half of the nineteenth century as a wayto rationalize a seemingly limitless body ofinformation about the chemical properties oftheelements. Precise description of the propertiesand behavior of atoms requires a model moreelaborate than the simple planetary picturefurnished by the Bohr model. The precise de-scription is not pictorial, but mathematical. Thisdescription, pioneered during the period1925-1935, was the first major triumph of thethen new field of quantum mechanics on w..ichmodern chemistry and physics are firmly based.Students should be helped to understand howperiodic relationships can be used systematicallyto predict chemical-behavior at least roughly,and so be led away from dependence on memori-zation. [Systems and Interactions, Stability,Patterns of Change]

44 Part IIThe Content of Science

Chemistry is concerned primarily with the arrange-ments of the electrons in the atom, since the spatialarrangement and energy of the outermost electronsdetermines the chemical properties of the atom.While it is difficult to observe the shapes of atomsdirectly, we can readily measure the energies of theelectrons within them.

Models of atomic structure help us think about howchemical reactions take place. The simplest model,the Bohr atom, depicts the atom as a miniature solarsystem with the electrons orbiting the central nucleus.The Bohr model can explain some (though not all)features of the behavior of atoms. For instance, atomsin which the outermost one or two electrons areweakly bound to the atom easily lose these electrons.Consequently, such atoms exhibit metallic behavior.In solution the atoms can release electrons to formpositive ions; in solid metals the atoms release someof their electrons to the solid as a whole, and the solidcan conduct electricity because the electrons movefreely through the solid. [Scale and Structure, Pat-terns of Change]

The way in which the properties of elementsdepend on the number of electrons contained in theiratoms is exhibited clearly in the periodic table of theelements. [Scale and Structure]

Mass is a property of matter that directly affccts thesize of the gravitational attraction to other matter andthe response of mattei to unbalanced forces. Underordinary circumstances, mass is an expression of theamount of matter, determined, for example, bycounting all of the atoms in the sample ofmatter. Inthese circumstances, conservation ofmass impliesconservation of matter, and vice versa. [Stability,Scale and Structure]

What are the basic units of matter, and where didmatter come from?

Kindergarten Through Grade Three

What we consider to be the building blocks ofmatter depends on how closely we look at matter. Thebuilding blocks of a house might be considered to bewood, brick, stone, and so forth. The building blocksof wood art different kinds of cells that are observ-able with a microscope. There are some things,

r) 6

however, that continue to appear the same as we lookcloser and closer, even with a microscope. Examplesof these kinds of things are water, iron, plastic, andglass. The basic unit of a pure substance is smallerthan a piece or amount that we can see or touch. [Pat-terns of Change, Stability, Scale and Structure]

A2 What are the basic units of matter, and where didmatter come from?

Grades Three Through Six

A pure substance, such as salt, is composed of verysmall particles which are all the same and which allhave the properties of that substance, salt. Theseparticles can get so small that we can no longer touchor see them, even with a microscope; they are stillsalt. However, if we dissolve the salt in water, webmak the particles into even smallza- units that itolonger have the properties of salt. These basic units,of which salt as well as all ordinary matter is com-posed, are called atoms. When the salt dissolves, theatoms are separated and rearranged. All ordinarymatter is made up of different combinations of atoms.[Patterns of Change, Scale and Structure]

Atoms arc much too small to be seen, even with anordinary microscope. (A penny contains more thanten thousand million billion billion atoms.) Atomscan be detected, both directly 4nd indirectly, in manydifferent ways. The properties of the things we seedepend both on the particular atoms of which they arcmade and on the way in which the atoms arc ar-ranged. When ice melts into water, the arrangementof the atoms is changed. A very important specialcase of such change is chemical change. In manysubstances, atoms are strongly held together in tightclusters called molecules. In chemical reactions, thereis rearrangement of the atoms within molecules. Theburning of a match involves chemical reactions. Inthe burning process, the atoms of the match and theatoms of the surrounding air change their arrange-ment, regrouping into molecules different from thoseoriginally present. But the atoms themselves areunchanged. Atoms last much longer than the thingsmade of them. All of the atoms of which you aremade were once part of something else. Most atomshemselves were constructed from simpler atomsbillions of years ago inside a star. [Scale and Struc-ture, Stability, Patterns of Change ]

A-2 What are the basic units of matter, and where didmatter come from?

Geades'Six Through Nine

Substances containing only one kind of atom arcpure elements. Ninety-one different elements occurnaturally, and about 14 more can be made artificiallyin the laboratory. A universally accepted chemicalsymbol is used for each element. Atoms of someelements'can link-together very weakly (as in solidneon at very low temperatures); others link strongly(as in the diamond form of carbon). In som ele-ments, strongly bound molecular units arc formed.For example, two nitrogen atoms form.a tightlybound molecule which is given the symbol N2, andoxygen atoms form 02 molecules. [Systems andInteractions, Stability, Patterns of Change]

Atoms of different elements can react to formstable, homogeneous compounds. Energy is oftenreleased in such reactions, but in others, energy mustbe added. Compounds have properties quite differentfrom those of the elements of which they are com-posed. [Systems and Interactions, Patterns of Change]

Atoms are made up of three kinds of particles,called electrons, protons, and neutrons. While anatom is itself thy, the protons and neutrons arcconfined in a much tinier nucleus, and the electronssurround the nucleus in a "cloud." The electron cloudis 100,000 times bigger acnoss than the nucleus. Eachelectron has a fixed amount of negative electriccharge. Each proton has an equal amount of positivecharge. Neutrons have no electric charge. The num-ber of electrons and protons in an atom arc equal, sothe atom itself is electrically neutral. The propertiesof an atom arc determined by the number:: of elec-trons, protons, and neutrons it contains. LScale andStructure, Stability]

The properties of a molecule arc determined by thenumber and types of atoms it contains and how theyarc arranged. The oxygen molecules we breatheconsist of two oxygen atoms each; each of the carbondioxide molecules we exhale has one carbon atomsituated between a pair of oxygen atoms. In the quartzcrystals that arc the major component of ordinarysand, there are two oxygen atoms for every siliconatom. The silicon and oxygen atoms form a regulararray, with each silicon atom surrounded by fouroxygen atoms; each oxygen atom is connected to twosilicon atoms. [Scale and Structure]

Chapter 3Physical Sciences 45

Sticking, linking, and bonding are all words used toindicate the existence of attractive forces betweenatoms or molecules. Thcse forces are deduced fromthe observed properties of substances. Strong forcesbetween atoms result in the formation of stronglybound groups called molecules. The origin of theseattractive forces is the attraction between the posi-tively charged nuclei and the negatively chargedelectmn clouds. [Energy, Systems and Interactions,Stability]

A-2 What are the basic units of matter, and where didmatter come from?

Grades Nine Through Twelve

Thc known properties of matter at the atomic andsubatomic levels make it possible to rcconstruct thehistory of the universe. The encrgy of stars is derivedfrom a process called nuclear fusion in which lightnuclei (nuclei comprising small numbers of protonsand neutrons) combinc to form heavy nuclei (nucleicomprising larger numbers of protons and neutrons).In this way, chemical elements mom complex thanhydrogen and helium (the two simplest) are formcd.In all stars, fusion produces some of thc elements.But processes called supernova events, which takeplace only in the violent explosion of large stars(much biggcr than our sun), are required for theformation of others of the elements. The explosionspews these newly formed elements into spacc, whcrethey later help to form other new stars. Two succes-sive supernova processes are required to form all ofthe naturally occurring elements. We thus know thatour solar system centers on a sun that is at least athird-gcncration star, formcd about 4.6 billion ycarsago. Thc material constituting our earth, as well asthe rest of the solar systcm, has comc in part fromsupernovae which exploded and dicd at an earliertimc in thc approximately 20-billion-year history ofthe universe. [Evolution, Patterns of Change, Energy]

Thc chemical properties of an element are deter-mined almost entirely by the number of electrons itsatoms contain, which is equal to the number ofprotons in the nucleus. Most chemical elements havetwo or more isotopes. The isotopes of an clementdiffer only in the number of neutrons in thc nucleus.For example, an.atom of the most common isotope ofcarbon, carbon 12, contains six ele..;trons, six protons,and six neutrons. Thc isotope cai.bon 14 contains six

46 Part ll--The Content of Science

electmns, six protons, and eight neutrons. The nucleiof carbon 12 are stable; undcr ordinary conditionsthey remain unchanged indefinitely. Like manyisotopes, carbon 14 has an unstable nucleus thatdccays radioactively. Measurement of thc ratio ofcarbon 14 atoms to carbon 12 atoms present in asample of once-living matter is the basis of a power-ful tool for measuring the ages of such samples. Fordetermining the ages of rocks, mcteoritcs, and manyother types of samples, other radioactive isotopes areused. Radioactive isotopes are valuable tools forstudying chemical and biological processes. [Evolu-tion, Patterns of Changc, Stability]

What principles govern the interactions of matter?How does chemical structure determine the physicalproperties of matter?

Kindergarten Through Grade Three

Substanccs behave differently whcn thcy interact.For example, solutions are formed when somesubstances are added to water, but others do notdissolve. This principle can be used to separate amixture of sugar and sand. The amount of substanccdissolved affects the properties of the solution, suchas color or taste. [Systems and Interactions, Stability]

A 3 What principles govern the interactions of matter?How does chemical structure determine thephysical properties of matter?

Grades Three Through Six

We observe objccts behaving in many differentways, depending on their structure and their sur-roundings. Lying organisms, for example, grow andchange their shapes. Crystals also grow, but in amuch simpler way. Some things float in water whileothcrs do not, somc things dissolve in water whileothcrs do not. Many substances can undergo changcsthat do not involve alteration of thcir material compo-sition. Watcr, for example, can freeze, melt, orevaporate, but it remains water in all thrce states. Thecomponc.ts af mixtures of solid substances, such assalt and sand, can be separated from one anothcr. Socan mixtures of liquid substances, such as alcohol and

A) C.)

Many students at the grade three-through-six level wiltprepare their own foods and use householdequipment and chemicals.They should learn to examine and respect these. All substances should betreated as potentially hazardous, especially when inappropriately used or handled. Substances can becategorized as hazardous in relation to their properties, such as flammability, corrosive nature (acid,base), or toxicity.

Students should understand the importance of radioisotopes in biochemistry, medicine, and industo.They should be aware that there are man., ..atural sources of radioactivity to which the biosphere hasbeen exposed since earliest times and that nuclear reactors are known to have existed in nature.

water. Substances can be distinguished by the ways inwhich they interact with one another. Oily sub-stances, for example, tend to mix with other oilysubstances but not with water. Other familiar sub-stances, such as vinegar, antifreeze, and householdammonia, mix readily with water. Some substanceshave special properties that allow them to interactwith both groups. Soap is such a substance. Whenadded to oil and water, soap allows the two to mix.

A-3 What pnrriples govern the interactions of matter?How does chemical structure determine thephysical properties of matter?

Grades Six Through Nine

The basic building blocks of large-scale matter,atoms and molecules, can combine in many ways.The field of science that deals with these combinations is called chemistry. Chemistry is devoted tounderstanding the properties and interactions ofgroups of atoms and how these affect the propertiesof substances. We use chemical theory to understandhow compounds can be formed, naturally or artifi-cially. Many interactions and changes are possible,from simple phase changes induced by heating orcooling to synthetic fabrication of new materials (e.g.,polymers). Many common substances mix withwater; some also react with it and ueate what arccalled acids or bases. An acid substance can beneutralized by adding a proper amount of a basicsubstance. [Systems and Interactions, Scale andStructure]

Chemical reactions either absorb or give off energy,often in the form of heat energy but also in other

forms such as light energy or electrical energy.[Systems and Interactions, Scale and Structure]

Chemists continually create new atomic arrange-ments to fill human needs. For example, compoundsarc being synthesized to replace the commerciallyimportant Freons that do damage to the ozone layerof the upper atmosphere. It is important to know asmuch as possible about substances because, dmongother reasons, many forms arc dangerous if not usedknowledgeably. They may be dangerous in them-selves, they may combine to form dangerous sub-stances, or their Wneficial applications may haveundesirable long-term effects. It requires goodjudgment, based on an understanding of chemical andbiochemical principles, to make wise decisions aboutsubstances that, though useful, may be hazardous ifnot properly controlled. [Systems and Interactions]

=1

The interactions of matter can be detected inmany substances, including most hou.seholdchemicals, by using colored indkaturs. The ideathat a given quantity of a substance will reactwith a fixed quantity of a second substanceshould be introduced early in the study of science. Students can titrate clear ammonia 11 ithwhite vinegar using red cabbage indicator, orthey can compare antacid tablets quantitatively.Such experiments should be used to reinforce thedistinction between absolute quantities andconcentrations.

Chapter 3Physical Sciences 47

-1

A-3 What principles govern the interactions of matter?How does chemical structure determine thephysical prOperties of matter?

Grades Nine Through Twelve

The number and arrangement of electricallycharged particles within atoms or molecules governthe predictable arrangements and rearrangements ofthe atoms in new substances. In these chemicalreactions, matter is neither created nor destroyed butmemly rearranged; mass is conserved and the atomsthemselves remain unchanged. The electrical forcesof attraction and repulsion between the particles de-termine how the atoms am bonded, or connected, toone another and how the connections will change.[Systems and Interactions, Patterns of Change]

The study of chemical reactions has lcd, over a longhistory starting with iron, bronze, and glass manufac-ture, to the crcation of a vast complex of industriesthat produce materials essential to modem life.Among these materials are plastics, fuels, metals, andmedicines. An understanding of chemistry is essentialto understanding agricultum, health, geology, ;:nd theuse of natural resources. Chemical mactions of dimctsignificance to society are also involved in themanufacture of fertilizers, in the burning of fuels, incooking, photography, medicine, and pollutioncontrol, among many other fields. [Systems andInteractions, Energy]

In many circumstances, atoms and molecules arepresent in the form of ionsatoms or molecules thathave lost one or more of their outermost electrons orgained one or mom extra electrons. Because they cancarry electrical charge from one place to another asthey move, ions arc of central importance in manysolutions (such as thc liquid in automobile batteries),in living systems (ionic balance is essential to properfunction and metabolism), and in many crystals (suchas table salt). [Systems and Interactions, Scale andStructure, Energy]

The complex interactions among the atomic ormolecu:ar units of a substance determine the large-scale behavior of the substance. If the forces betweenatoms or molecules are very weak, the substance islikely to be a gas at normal temperatures. If strongerattractions exist, the substance may be a liquid. Stillstronger forces lead to the formation of solids ofvarious typcs. In metals, the atoms am organized witha minimum of space between them, and some diet:-

48 Part llThe Content of Science

trons can move relatively freely throughout the solid.This property underlies the familiar properties ofmetals: electrical conduction, malleability, luster, andthe ability to take a high polish.

Intermediate between metals, which conduct elec-tricity well, and nonmetals, which conduct electricityvery poorly because all the electrons are tightlybound to the atoms, is the class of materials calledsemiconductors. In semiconductors, the numbcr ofelectrons that are free to move can be controlledpmcisely over a wide range by means of tiny amountsof deliberately added impurities. By exploiting thisproperty, it becomes possible to fabricate manydi ffemnt kinds of electrical switches and amplifiersand to build a wide range of devices that includeminiatum radios, computers, and information trans-mission systems. [Systems and Interactions]

Modern chemical and physical techniques haveadvanced to the point that materials with certainproperties can be "custom built" in very smallamounts. Such materials include liquid crystals usedin watches and other custom-built materials uscd insuperconducting magnets, radiation detection devices,and chips for advanced miniature computer networks.As more is understood about the relationships be-tween structum and properties and about ways tocontrol chemical reactions (see Section B), it will bepossible to manufacture larger quantities of suchmaterials and create new applications and ncwindustries. [Scale and Structure]

Many substances, both natural and artificial, arctoxic to human life, as arc radioactive products. Foreach such substance, it is important to establish safetolerance levels and to devise procedures to ensurethat these levels are not exceeded. Waste disposal andfood pmservation and production problems haveimportant social, political, economic, and scientificaspects. Satisfactory solutions of these problemsmquirc a substantial public understanding of all ofthese aspects. [Systems and Interactions)

Se6tion B Reaptions and Interact!6nS

IN the study of the changes in the properties ofsubstances as they interact, chemists observe thechanges in internal organization and in energycontent as a function of timc, temperature, concentra-

60

tion of substances, type of solvent, and so forth. Thescience of chemistry aims to understand the detailedprinciples governing how such changes take place sothat new substances arc governed by a principle ofminimization of the energy, provided that a suitablepathway for change is available. A molecular colli-sion model is successful in explaining most featuresof substances undergoing change. Molecules react toform different molecules when they collide withsufficient kinetic energy and in the appropriateorientation. In kindergarten through grade twelve, thefocus is on establishing an understanding of the mainfeatures of chemical change and the roles of energyand time. Students should gain considerable experi-ence in observation of substances and change and inmaking inferences about what is happening on themicroscopic level after constructing physical andmental models of the structure of matter at themolecular level.

B-1 What happens when substanceschange?

B-2 What controls how substances change?

What happens when substances change?

Kindergarten Through Grade Three

Two substances can interact to form new sub-stances with different observable properties. Suchchanges can occur instantly, such as when vinegar orlemon juice is added to milk, or take much time, aswhen an iron nail rusts in water. In some reactions, asolid plus a liquid will produce a gas, as whenvinegar is added to baking soda. In other cases, asolid may be formed from a gas, such as when carbondioxide is blown through a limewater solution. Inevery case, careful observatkn is needed to see thatnew substances arc formed. [Systems and Interac-tions, Patterns of Change]

Chfunical change can be helped by adding heat andcan be useful, as when a cookie is baked from rawingredients. Chemical reactions arc useful in otherways, as when soap is made to foam better in waterwhich has been treated with washing soda to precipi-tate salts as carbonates. [Energy)

B-1 What happens when substances change?

Grades Three Through Six

The amount of matter present before and afterreactions remains the same when measured as masswith a balance.

Compounds result when true chemical reaction hasoccurred. It is sometimes difficult to distinguishbetween the formation of a new compound from theinteraction of substances and the formation of a mix-ture. The latter can generally bc separated by physicalmethods such as filtration, chromatography, ordistillation; the former defy reseparation by simplemeans into the original components. Even in theformation of mixtures, energy changes, observed astemperature changes, may occur. [Scale and Struc-ture, Energy]

Compounds have well-defined compositionsinvolving new molecular combinations of wholenumbers of atoms with new linkages. In mixtures, nolinkages are broken or formed, but existing units areintermingled. Thus, in the formation of water mole-cules, linkages in hydrogen and oxygen moleculesmust be broken so that new arrangements in H20 canbc made, whereas to mix NH3molecules with 1120molecules, no linkages need bc broken. Compoundsalso have well-defined geometric arrangements ofatoms. Some arc in a straight line, others arc triangu-lar, or pyramidal. Simple rules govern the greatmajority of possible atomic arrangements. It isimportant to establish that drawings of molecules on

The reaction of vinegar with baking soda can bepetformed in a two-liter plastic bottle to demonstrate that the amount of matter remains the sameafter reaction. Other methods may be subject tobuoyancy corrections.

Students at the grade three-through-six levelbenefit from continual practice in careful obser-vation and in making inferences from suchexperiments as the lighting and subsequentburning of a candle. Hot packs and cold paGks,familiar t& sports enthusiasts, are ideal subjectsfor observation and inference.

Chapter 3Physical Sciences 49

Students should be introduced to the concepz ofthe use of models in science by such exercises asconstructing molecules from toothpicks andcandies or bolts with nuts and washers followingcertain valency rules for allowed combinations.The HONC rule (H=1, 0=2, N=3, C=4) can beused to construct correct models of large nunz-bers of real molecules. Change of one moleculeto another can be accomplished only by pullingapart the appropriate stick or cornection. Classconstructed molecules can be intermingledwithout breakage to sinzulate a mimure.

paper or the chalkboard are a poor representation ofthe real shapcs of three-dimensional atoms andmolecules. [Scale and Structure, Patterns of Changcj

Many substances that seem quite different react insimilar ways. For example, acids present in manyhousehold chemicals or foodstuffs will change thecolor of plant extracts in a similar way. Those whichare bases will have an opposite effect. [Patterns ofChange]

Heat energy assists many chemical rcactions; on theother hand, reactions can also result in continuousproduction of heat. [Energy]

B-1 What happens when substances change?

Grades Six Through Nine

In chemical reactions, atoms arc neither created nordestroyed. By using familiar symbols for atoms, thescience student can convert this conservation prin-ciple to a useful bookkeeping method for atoms. Suchchemical equations arc useful in keeping track of thequantities of substances involved by using mass as ameasure of quantity. Just as in a bank, where weigh-ing is used to count large numbers of coins of definedmass, atoms have defined masses, and so total massesmust balance, even though the organization of unitsmay change. Amounts of chemicals needed forcomplete reaction, product yields, and leftoverunmacted quantities can thus be predicted and/ormeasured.

50 Part IIThe Content of Sdence

In some reactions, the changes in linkages result ina reorganization of electrons within substances, sothat electrons can be transferred between substances.Such reactions can be used to form useful devicescalled batteries and to create coatings of metalsthrough electroplating.

Certain reactions can be classified as displace-ments, in which one atom or group in a substance isexchanged with that from another substance. Thisconcept explains why precipitates form whcn twosolutions arc mixed.

Even in the complex chemical systems found inliving organisms, chemical reactions follow the samebasic principles, conservation, accountability, reac-tion type. For example, the process of photosynthesisin plants requires the presence of all the ingredients(light, carbon dioxide, water, chlorophyll) in theproper amounts in ordcr that a certain amount ofproduct starch and oxygen can be produced. Thehuman body needs a balanced diet to carry out theproper chemical reactions needed for healthful living.[Scale and Structure, Patterns of Change, Systemsand Interactions]

B-1 What happens when substances change?

Grades Nine Through Twelve

Whcn atoms arc rearranged in a chemical reaction,there is a very small change in mass, but it is far toosmall to be significant. The total electric charge of thesystem of atoms also rcmains constant as they recom-bine under the influence of the electric forces thatunderlie all chemical interactions. The total energy ofthe system also remains constant in a reaction, butenergy is converted from the electrical form involved

In explaining nuclear processes, nuclear theoryplays a role at the subatomic level that is analo-gous to the role played by atomic theory on theatomic level. Neutrons and protons in nucleioccupy energy states analogous to the energystates of electrons in atoms. Comervation ofmass-energy is important as meAsurable mass-energy interconversion occurs. Other morecomplex conservation rules also exist.

6 2

Many textbooks also have photographs of the burning of the Hindenberg airship to demonstrate thedanger of large amounts of energy released unintentionally.

in atomic bonding to other forms, or vice versa.[Energy]

Conservation (constancy) of mass, electric charge,and energy are extremely important theoreticalconsiderations in the study of chemical reactions andmake it possible to account for everything occurringin reactions. Balanced quantitative equations such as:

2H2 + 02 r_t 2F120 + 3.92 x 10-19joules of energyper molecule of H20 produced

describe the arrangements and numbers of atoms inboth the reactants and the products in the reaction ofhydrogen gas and oxygen gas to form water. The plussign before the quantity of joules of energy indicatesthat this is released to the surroundings when thisreaction takes place. This energy must have comefrom reorganization of the electrical forces as thehydrogen and oxygen atoms arc bonded in the watermolecule.

In practical situations, scientists usually work withmuch larger numbers than one molecule. A commonunit is the mole, which refers to 6.02 x HP mole-cules. The energy released when hydrogen andoxygen react to produce 1 mole of water is3.92 x 10 -19 joules/molecule x 6.02 x 1023molecules = 2.36 x 103joules. This is a largeamount of energy and indicates that if hydrogen isreadily available, reacting it (burning) with oxygenfrom the air can be a useful source of heat. [Scale andStlucture, Energy]

Charge balance can also be accounted for by use ofquantitative equations, such as:

HCO; + Ca2+> CaCO3+ H+,

which represents what happens when baking soda isadded to hard water containing calcium ions. Theequation predicts that the solution will become morcacid because more hydrogen atoms are added.

In many chemical reactions, energy must be addedfrom external sources to accomplish a desired reor-ganization of electrical forces. Such energy is com-monly added as heat or as electrical energy. This isespecially important in the manufacture of very

63

important simple chemicalsfrequently elementsfrom naturally occurring ores. Obvious examples arethe production of iron and aluminum carried out on avery large scale. The energy per mole needed to meltand reuse materials such as aluminum cans is muchless than that needed to free aluminum from its ores.Thus, recycling must gain in importance as energycosts increase.

The nuclei of atoms are unaffected by chemicalprocesses; however, they can be altered by nuclearprocesses. Since the amount of energy involved inforces within the nucleus is much larger than thatinvolved in chemical reactions, much more energymay be released per nuclear event. Such processesinvolve about a million times more energy than thetypical chemical reaction and can result in the trans-mutation of an atom of one element to an atom ofanother.

Understanding nuclear reactions enables us to con-struct electrical power plants that do not producecarbon dioxide or smog-producing substances. It alsoenables the construction of extremely destructiveweapons and the production of radioisotopes of great

The mole unit is historically based on the numberof hydrogen atoms in I gram of hydrogen atoms.Today it is more precisely the number of atoms inexactly 12 grams of atoms of an isotope of car-boncarbon 12. Students need help in realizingthat this awkward-sounding number is a usefulconcept in helping do bookkeeping of atoms andenables us to use convenient mass quantities as asubstituk: for actual counting. It is no more com-plicated than handling eggs in dozens and keep-ing track of the differing masses of small, large,or extra-large eggs by using a balance.

Chapter 3Physical Sciences 51

importance to medicine, industry, and research inbiology and chemistry. Radioisotopes also occur innature, and the study of these natural radioisotopeshas enabled scientists to determine the age of samplesof inorganic and organic matter. Such knowledge isimportant to history and archeology as well as togeochemistry. For example, with the use of samplesfrom the earth, the moon, and meteorites, scientistshave been able to develop dating techniques that arcused to build up a consistent set of ages for the earthand the various portions of the solar system.

What controls how substances change?

Kindergarten Through Grade Three

Change is affected by surroundings. On a hot day,an ice cube melts more rapidly, while it will survivefor a long time in a freezer. If a cup of water is sealedin a plastic bag, condensation on the plastic demon-strates that the liquid has changed to a gas and thenback to a liquid. If the cup is left in the open, changeto a gas occurs, but the evidence is different.

Change often must be initiated by providingenergy; for example, a match is needed to light a fire.[Pattems of Change, Energy]

B-2 What controls how substances change?

Grades Three Through Six

Measurements can be used to explore the effects ofchanging conditions on the way change occurs. Forexample, the time a seltzer tablet takes to dissolve canbe measured as a function of the temperature of thewater. Food preparation involves relationshipsbetween temperature and time.

The kinetic-molecular theory of matter explainshow chemical interactions can take time and dependon temperature. Molecules must meet and collidewith enough impact for successful change. [Energy,Patterns of Change]

B-2 What controls how substances change?

Grades Six Through Nine

The ease with which chemical substances gain orlose electrons in forming compounds or in forming

52 Part IIThe Content of Science

ions in water solution is related to the basic electricalstructure of the substance. For the chemical elements,this property is related to their position in the periodictable. Many other properties of elements and familiesof elements can be related to their location in thistable.

In forming linkages with each other, atoms are incontest for attraction of the electronc farthest awayfrom the nuclei. This contest is often unequal andresults in linkages in which the electrical charge isnot symmetrically distributed. Such linkages arecalled polar bonds. Molecules containing polar bondsare frequently unsymmetrical and are called polarmolecules. These molecules with unsymmetricalcharge shapes attract each other. Thus, substanceswith polar molecules tend to mix well with other sub-stances with polar molecules but not with substancesconsisting of nonpolar molecules, and vice versa.This prindple explains why wax dissolves in oil butnot in water, why gasoline and watcr do not mix, andwhy many other observed phenomena occur. [Scaleand Structure, Patterns of Change]

A certain energy is released or used by each mole-cule changed in a chemical reaction. Since a mole is afixed number of molecules and has a determinedmass for each substance, the reaction energy isproponional to the mass of the reacting substance.ApproA;mate reaction energy can be determined bymeasuring the temperature change and mass of thereacting substances in water solutions. However, heatenergy is easily lost, so insulated equipment andcareful control are needed. (See Section E, Energy:Heat.) [Energy, Stale and Structure]

Certain reactions arc aided by the presence ofsubstances called catalysts or enzymes. The amountof these substances present is not important, and they

Here is one way to demonstrate equilibriwn inachemical reaction system. Prepare a tube con-taining pure alcohol (ethanol), a few cobalt chlo-ride crystals to color it, and a few drops of water.This system is very sensitive to temperature,changing color from pink to blue and back againas the temperature is raised and lowered.

64

1

Chemical reaction% appear to be difficult to understand, but various demonstrations can be used toinitiate discussion. For instance, two oil drops on a thin film of water will not coalesce unless they actually touch and are pushed together, but if a small amount of detergent is added, they coalesce readily.This set of observations is analogous to what happens when two atoms combine chemically in theabsence or presence of a catalyst.

arc not changcd in the reaction. Thcy arc especiallyimportant to thc function of living systcms, whichmust carry out complicatcd chemical rcactions withina vcry small rangc of tcmperaturc. [Systcms andInteractions, Energy]

Closcd systcms oftcn reach an equilibrium situ-ation. For example, watcr in a clear, scalcd containercan bc sccn not to evaporate completely. However,thc amount of liquid varies with the temperature.[Stability]

B2 What controls how substances change?

Grades Nine Through Twelve

Thc collision modcl for chcmical rcactions explainsthc obscrvablc features. Thc more molcculcs that arcpresent, the grcatcr thc chance of intcraction. Themore rapidly molecules arc moving, thc greater is thcchance that thcy will collide with sufficient cncrgy toundergo the desired changes in structural organiza-tion. A catalyst assists this organizational stcp byhelping to hold thc molecules togcthcr in a moresuitable oricntation for successful rcaction. Thus, lesscncrgy is nccdcd, and thc rcaction can proceed at alower temperaturc. [Pattcrns of Changc, Energy,Systcms and Interactions]

Elements that are metals can bc compared in tcrmsof ability to transfer electrons by mcans of cellvoltage measurements or comparative displak.err 'qireaction observations. Metals that arc widcly dissimi-lar in this scrics can bc uscd in a battcry or electricalenergy source. Many similar reactions arc involvcd incorrosion of commonly uscd mctals. Protectionmethods can bc dcviscd once thc chemical reactionsoccurring are understood. Electron transfer reactionsare important in living systems in vital cell proLesses.[Systems and Interactions, Stability]

6 5

THE ccntral organizing principlc of classical mc-chanics is thc set of three laws callcd Newton's lawt.of motion. Thcsc laws can bc applicd to specificsituations; most notablc arc thosc in which thc forceis cithcr gravitational or cicctromagnctic. In light ofthc more general laws of relativistic mechanicspioneered by Einstcin and of thc laws of quantummcchanics, Ncwton's laws bccomc a special casc.However, for most cascs involving familiar scalcs ofsize and speed, classical mcchanics is complctclysatisfactory.

C-1 What Is motion? What are some basickinds of motion? How Is motiondescribed?

C-2 What Is force? What are thecharacteristics of forces? What Is therelationship of force to motion?

C-3 What are machines, and what do theydo? What principles govern their ac-tion?

1Le-4=What is motion? What are some basic. kinds ofmotion? How is motion described?

Kindergarten Through Grade Three

Thc location of stationary objects can be specifiedwith reference to othcr stationary objects. Distances

Chapter 3Physical Sciences 53

between objects can be measured. The motion ofmoving objects can be described and categorized(straight, circular, crooked, and so forth), and speedcan be described as fast, slow, thc same, and so forth.[Patterns of Change]

C-1 What is motion? What are some basic kinds ofmotion? How is motion described?

Grades Three Through Six

A moving object is one that changes position astimc passes. Speed is a measure of the distancetraveled (change in position) by the object during acertain time interval; it is, for example, the distanccmoved in one second or in one hour. The units ofspeed will be determined by the units used to measuredistancc and time. For example, a speedometerprovides a quick reading of the speed of a car in milesper hour. The motion of an object at a certain speedalso has a direction. Direction can be specified invarious ways: up/down, left/right, compass directions,and so forth. [Patterns of Change, Systems andInteractions]

C-1 What is motion? What are some basic kinds ofmotion? How is motion described?

Grades Six Through Nine

Speed (v) is expressed quantitatively by the relationv = d/t, in which d is thc distance moved during atime interval t. Thc units of speed depend on the unitschosen for distance and time. If the speed is notconstan over the distancc d, v should be interpretedas the average speed. Speed in a particular direction isgiven the name velocity. Thus, to specify the velocity

of an object, it is necessary to give the speed and thedirection in which the object is moving. Measure-ments of both position and speed depend on whichreference system is chosen. [Patterns of Change]

Various kinds of motion are characterized by thebehavior of an object's velocity. Three common andimportant kinds of motion are constant velocity(constant speed in a straight line), uniform circularmotion (speed is constant, direction continuouslychanges), and oscillatory motion (speed continuouslychanges and direction reverses periodically). [Patternsof Change]

C-1 What is motion? What are some basic kinds ofmotion? How is motion described?

Grades Nine Through Twelve

When the velocity of an object is changing, wc saythe object is accelerating. The concept of accelerationis difficult for students and therefore should bepresented with many real examples. Acceleration (a)is defined as the change in velocity (tv) divided bythe change in :ime (At); i.c., a E. tv/At. Accelerationis thc quantity that tells us the ratc at which thcvelocity is changing.

Likc velocity, acceleration has a direction. Manyimportant physical situations occur in which accelera-tion is constant or nearly so. The ability to representand analyze motion in one dimcnsion both quantita-tively and graphically when cithcr thc velocity or theacceleration is constant is important. A much deeperunderstanding of the concepts of displacement,velocity, and acceleration is obtained by the usc ofmultiple representations and repeated practice relat-ing them to thc motion of real objects. [Patterns ofChange]

Science concepts should be related to the everyday experience of students and introduced in languagewith which the students are familiar. Therefore, customary (common or everyday) units such as feet andinches would be used initially when discussing concepts such as position and speed. Metric units shouldbe introduced early and continually reinforced, but when new concepts are being learned, the units withwhich students are most familiar should be used. However, teachers should be aware that some studentswill be more familiar with metric units than others. This applies from kindergarten through gradetwelve.

54 Part 11The Content of SdenceGE;

4= iiM 1 II 10 1. imin m a .

The extension of the concept of speed to include direction is important, because the relation of force tomotion involves both speed and its direction. Velocity should be introduced when the relation of force tomotion is discussed.

Another important motion is uniform circularmotion, such as that of a ball on the end of a string,the rotation of a centrifuge, or the nearly circularmotion of the earth around the sun. For this type ofmotion, the speed is constant, but the direction of thevelocity is changing, so the object is accelerating. Theacceleration is toward the center of the circle. [Pat-terns of Change]

Wave motion is another common and importanttype of motion. A mechanical wave is a repetitivedisturbance that propagates (moves) through acontinuous medium. Ripples on the surface of waterand sound waves am typical mechanical waves.When a wave propagates through a medium, theindividual particles move back and forth. The distur-bance itself propagates through the medium bysetting new parts of the medium into oscillation.Although no particle actually moves very far, thewave moves and carries energy through the mediumfrom one location to another. (Sce. Section H, En-ergy: Sound.) [Systems and Interactions, Energy]

Waves fall into two general categories. The first istransverse waves, in which the particles of the me-dium uscillate perpendicular to the direction ofpropagation of the wave. The second is longitudinalwaves, in which the particles oscillate parallel to thedirection of propagation. Sound waves in air andliquids are longitudinal. Sound waves in solids can beboth longitudinal and transverse. Some more compli-cated waves, like surface water waves, are combina-tions of the two. [Systems and Interactions]

A wave is characterized by its wavelength (X), itsfrequency (f), and its propagation speed (v). The rela-tionship of these quantities is given by the expressionv = f X. Waves conform to the principle of superposi-tion: Any number of waves can pass through thesame part of the medium simultaneously, and theireffects arc cumulative. The phenomena of standingwaves and interference are results of the principle ofsuperposition. [Systems and Interactions]

What is force? What are the characteristics of forces?What is the relationship of force to motion?

Kindergarten Through Grade Three

Force is the name given to pushes and pulls.Objects (both inanimate and animate) exert forces onother objects. [Systems and Interactions]

Gravity is the name given to the pull of the earth onother objccts. The weight of an object can be meas-ured with a scale. [Systems and Interactions]

A particular object can be acted on by multipleforces. The effect of the forces on the object dependson whether the forces balance (cancel each other out).[Systems and Interactions]

If the several forces acting on an object (includinggravity) do not cancel out, they cause a change in themotion of the object. The change can be speeding up,slowing down, starting, stopping, or turning. [Sys-tems and Imeractions]

If an object is at rest, then the several forces actingon an object totally balance each other (cancel eachother out). [Systems and Interactions]

C-2 What is force? What are the characteristics offorces? What is the relationship of force to motion?

Grades Three Through Six

Forces are often measured with a spring scale. Thecustomary units of force arc pounds (lb.) and ounces

Light waves are not mechanical waves and do notrequire a medium for propagation. However, tlze)have many properties in common with mechanical waves and are described by the same mathe-matical language used to describe mechanicalwaves. (See Section G, Energy: Light.)

es 7Chapter 3Physical Sciences 55

(oz.). The SI metric unit of force is the newton (N). Aforce of orir; pound is equal to a force of 4.5 newtons.[Systems and Interactions]

The direction in which a force is exerted is impor-tant in determining its effect. The effect of two forcesacting in the same direction is the same as if therewere one force equal to the sum of the separate

A person riding in a jet airliner cruising at 450miles per hour 3,500 feet above the surface of theearth might describe the posi:ion and speed of aperson walking down the aisle this way, "She is25 feet from the rear exit movbig towards it at 2miles per hour." A person on the ground lookingup at the plane might say, "She is 2 miles southand 3,500 feet above me moving north at 448miles per hour." From this example, we see theimportance of specifying the reference system.Students need practice using both informal andformal reference and coordinate systems. Theproperty of velocity, that there is no inherentdifference between being at rest and moving atconstant velocity, is difficult for students tounderstand. Because of its importance in devel-oping an understanding of the relation of force tomotion, it should receive considerable attentionthroughout grades six through twelve.

Even students intending to major in science incollege have considerable difficulty in fullyunderstanding the difference between velocityand acceleradon, even in the simplest case ofone-dimensional motion. However, it is necessaryto introduce acceleration if Newton's second lawis to be introduced. When acceleration is intro-duced, it should first be approached conceptuallyand related to students' intuitive notions ofspeeding up and slowing down before defining itmathematically. Students familiar with dragacing will have no problems here.

56 Part 11The Content of Scianco

forces. If two forces have opposite directions, theeffect is the same as a single force ir the direction ofthe larger and equal to the difference of the twoforces. If the two equal forces have opposite direc-tions, they balance each otha out and there is no netforce. If two forces act at an angle with respect toeach other, then the effect is the same as that of asingle force acting at an intermediate angle. Unlesstwo fore= point in exactly opposite directions, theycan never cancel each other out, regardless of theirmagnitude. [Systems and Interactions]

In ordinary situations, moving objects slow downand come to rest. Under these circumstances, mostobjects collide with or rub against other objects orsurfaces and experience "backward" forcesforcesthat act in the direction opposite to the direction ofmotion. These forces, which exist in several varieties,are broadly labeled frictional forces. Frictional forcesalways act to oppose motion. They can be used tocontroi motion, as is done with automobile brakes.Friction with air slows the space shuttle so that it canland at a conveniently low speed.

Objects do not have to touch in order to exert forceson each other. Gravity is an attractive force betweenany two masses and acts even when the objects attfar apart. Objects fall to earth and the moon orbits theearth because of this force. Forces between magnetsand forces between electrically charged objccts alsoact over a distance without the objects being incontact. [Systems and Interactions]

If one object exerts a force on another object, thesecond object exerts an equal force in the oppositedirection on the first. For example, in order to start towalk or run, a girl must push with her foot against thefloor in the direction opposite to that in which sheintends to move. The floor pushes back against herfoot. This unbalanced force (floor pushing on girl) isthe direct cause of the change in her forward motion.[Systems and Interactions]

The intuitive notion that there exists somethinginside or associated with an object that keeps it inmotion corresponds to the scientific concept calledmomentum. Consider expressions such as "If anobject has a lot of momentum, it is hard to stop it orto change its direction", or "A large truck has a lotmore momentum than a small car going the samespeed"; or "The faster you go the more momentumyou have." These statements make sense to manystudents before they have formally studied momen-

Newton' s.third law focuses on an important property of forces. As with Newton's first and second laws,the concept behind Newton' s third law should be taught first, and then it can be given a name. It is notimportant chat students remember a memorize_ definition of Newton' s third law using words that do notmake any sense to them. What is important is that they have a conceptual undeistanding uf its content.

The fundamental pi operties of force are not intuitive for most students. Consequently, they need to bereintroduced and reinforced at all levelskindergarten through grade twelve. P ?cause it is difficult tochange misconceptions that have been held for several years, appropriate and useful conceptions offorces should be established as early as possible. At the kindergarten through grade three level, studentsshould be given many opportunities to ident1:15' forces and explore the difference between instances whenthey balance and when they do not. These should be experiences in which they directly feel and sensethe forces. [Systems and Interactions]

tum. Momentum depends botn vu how much matterthere is (its mass) and on the velocity of the mass.Momentum has the same direction as the velocity ofthe object. Like velocity, the actual value of momen-tum depends on the reference frame in which thevelocity is measured. [Patterns of Change]

Net forces cause the momentum of an object tochange. Conversely, if the net force actil1 6 ctl anobject is zero, its momentum will remain constant.For example, air friction exerts a force opposite to thedirection of motion on an object thrown horizontally.This force ca...ses the forward momentum to decrease(the object slows down). At the same time, gravityexerts a force in the downwi.-d direction, whichcauscs the object to start moving downward (if it wasinitially moving horizontally). [Systems atitt Intcrak..

tions]

C-2 What is force? What are the characteristics offorces? What is the relationship of force to motion?

Grades Six Through Nine

If a net force acts on an object, its momentum willchange, and the longer the net force acts, the more themomentum will change. When the net force acting onan object is zero, the object's momentum will notchange. It means that an ooject in motion willcontinue to move in a straight linc at constant speed,or if it is not moving, it will not start to move if thereis no net force acting on it. [Patterns of Change,Systems and Interactions]

Particular attention needs to bc devoted to thecommon experience of objects on earth alwayscoming to a stop once the cause of the motion hasbeen removed (a box sliding on the floor, a carcoasting to a stop, and so forth). In all these cases, theobject's forward momentum is changed (reduced) bythe unbalanced force of friction, the greater toefrictional force, the less time it takes for the object tostop. Conversely, if an object's forydard momentumremains constant in the presence of friction, theremust bc another force acting on the object to balarkethe frictional force. [Systems and Interactions]

Near the surface of the earth, the force of graNityexerted by the earth on an object does not changeappreciably with changes in elevation of the objea.When an object falls toward the earth, the speed it ha:,

when it hits the ground increases as the height fromwhich it is dropped increases. This is not due to thefact that the force is greater when it is higher (acommonly held misconception), but is readily explained by the concepts of forces and acceleration.The constant force of gravity produces a constantacceleration. The higher the point from which theobject falls, the longer it accelerates, producinghigher velocity and momentum. [Systems and Interactions]

Mass and force of gravity have exact meanings inscience, but the term weight, as used popularly, canhave several meanings. Usually, the term is related togravity and refers to a force whose magnitude isproportional to mass. When the term is used in

Chapter 3Physical Sciences 57

Only very simple and straigWorward examples similar to those mentioned should be studied at thislevel.Their purpose is to provide a lot of evcryday applications in which the concepts of force and mo-mentwn can be distinguished and clarified. [Systems and Interactions]

science, it must be distinguished from mass andshould be defined carefully.

The magnitude of weight can be thought of as thatquantity measured by a bathroom scale. Normally,you are not moving when you weigh yourself, so theupward force of the scale on you exactly balances theforce of gravity. In this case your weight equals theforce of gravity. However, if you weigh yourself inan elevator, you will find that your weight changes asthe elevator starts up or comes to a stop. The force ofgravity does not change, but additional forces whichcause the change in speed also cause the change inweight. An astronaut in free-fall, floating around thecabin of a spacecraft in low earth orbit, would registerzero weight on the scale and so could be said to be"weightless," even though the forcc of gravity is onlyslightly reduced. The focus in science should be onthe relationship between force and mass, not on themeaning of the term weight. [Systems and Interac-tions]

The implications of Newton's second law are far-ranging and affect practically everything we doin our daily lives. In those instances for which the

forces are easily identified (exerted by animateobjects, for example), it is easier for students todetermine whether an unbalanced force exists.For example, in a tug-of-war the players exertforces on the rope. If they balance, the rope doesnot move. Another class of examples that is fairlystraigWorward involves objects subjected only tothe force of gravity (for example, a ball in flightafter it has left the thrower's hand). If air frictionis negligible, there is only one force acting on theobject; it can not be balanced, and the object'smomentum will change in response lo the unbalanced force.

58 Part llThe Content of Science

C-2 What is force? What are the characteristics offorces? What is the relationship of force to motion?

Grades Nine Through Twelve

The force of gravity acting on an object near thesurface of the earth in newtons is numerically equalto the product of the object's mass in kilograms andthe "acceleration of gravity" (g = 9.8 mIs2, Fs= mg.)[Systems and Interactions]

The force of gravity acts between all pairs ofo ,jects, not just between the earth and other objects.The size of the force increases with the mass of eachobject. However, unless at least one of the objects isvery massive (like the earth), the force of attractionbetween the objects is usually negligible compared toother forces. The force of gravity decreases as thedistance between the objects increases. It is neces-sary, however, to go very far from a planet or the sunbefore its gravity is reduced substantially. The forceof the earth's gravity at an elevation typical of mostearth satellites is reduced by only 5 to 10 percentfrom that at the surface of the earth. [Systems andInteractions]

At a fundamental level there are four basic forces:the attractive force of gravitation that acts between allmatter, the electric force that acts between chargedmatter and can be either attractive or repulsive, andtwo kinds of nuclear forces that act to hold atomicnuclei together. The first two act over large distances,while the two nuclear forces decrease to zero justoutside the nucleus. The forces we experience in oureveryday lives are the result of either gravitation orelectric force. Forces of friction and other contactforces are due to the electric force acting at the atomicand molecular level. [Systems and Interactions]

The particles of fluids (gases or liquids) exertforces on cach other and on surfaces with which theyare in contact. Pressure is the amount of force actingon one unit of arca. Particles are free to move in afluid. In equilibrium the particles will be distributedso that pressure at any point is the same in all direc-tions. [Systems and Interactions]

7 i)

mol'w

There is some ambiguity attached to the concepts of weight al weightlessness because they can bedefined in slightly different ways. Any of these definitions is acceptable, provided it is used consistently.Textbook authors should take care to do so. For a clear, complete discussion of this point, together witha set of recommendations, see Robert A. Nelson, SI: The International System of Units, (Second edition).Stony Brook, N.Y .: American Association of Physics Teachers, 1982, pp. 47-57.

Pressure in a fluid increases with the depth of thefluid. This can be understood in terms of the pressurerequired to support the fluid above that location.[Systems and Interactions]

Fluids exert forces on objects immersed in them,just as they exert forces on other parts of the fluid.Whether an object sinks or floats depends on whetherits weight is greater than or less than the weight of avolume of fluid equal to the volume of the object.This can be understood by considering the forcesacting on an equal volume of fluid. Since this volumeof fluid does not move, the net forcc must be zero.Further, since the force of gravity acts down, theremust be an equal force acting in the up direction.When the volume of fluid is replaced with the actualobject, the same force acts on the actual object. Thatis, the upward force exerted by a fluid on a sub-merged object (buoyant force) is equal to the weightof an equal volume of fluid (volume of fluid dis-placed). This is Archimedes's principle. [Systems andInteractions]

Newton's second law relates acceleration to forccand mass and can bc stated: Acceleration is directlyproportional to the net force, is inversely proportionalto the mass of the object, and is in the direction of thenet force. In symbols, a = FN. [Systems and Interac-tions]

When a drag racer accelerates along a straighttrack, the acceleration is parallel to the direction ofmotion and to the velocity. When the racer brakes toa stop, the acceleration is opposite to the direction ofmotion and the velocity. In this case, accelerationaffects the speed but not the direction of motion.When a train goes around a circular curve at constantspeed, the acceleration is directed inward along theradius of the circle, perpendicular to the direction ofmotion and the velocity. Now, the acceleration affectsthe direction of motion, but not the speed. In oscilla-tory motion, the acceleration is always directed

opposite to the displacement from the equilibriumpoint. [Systems and Interactions]

A net force (F) acting for a time (At) causes achange in the momentum of an object: (A(tnv) F At =A (Inv). The direction of the change is in the directionof the net force. If the force is not constant during thetime interval, then average force can be uscd in theformula. If there is no net force, there will be nochange in momentum. This fact is stated as theprinciple of conservation of momentum and appliesto group:, of objects as well as to single objects. Asingle object without external forces or a group ofobjects that interact with each other but have noeffect on other objects constitutes a system. Theprinciple can be stated. If there is no external netforce acting on a system, then the momentum of thesystem remains constant, regardless of the interac-tions among the parts of the system. [Systems andInteractions]

"Isaac Newton formulated his First Law ofMotion in the eighteenth century. It stated that'every body continues in its state of rest, or ofuniform motion in a right line, unless it is com-pelled to change that state by forces impressedupon it.'

"(Joseph) Needham' s researches have now es-tablished that this law was stated in China in thefourth or third century BC. We read in the MoChing: 'The cessation of motion is due to theopposing force . .. If there is no opposingforce . . . the motion will never stop. This is astrue as that an ox is not a horse."

Robert Temple, The Genius of China

I I Chapter 3Physical Sciences 59

Students in kindergarten through grade three can explore how various simple machines change theeffect of the applied force. [Systems and Interactions]

What are machines, and what do they do? Whatprinciples govern their action?

Kindergarten Through Grade Three

Machines are made of parts that move, such as alever. Simple machines, such as soft drink bottleopeners, contain only one part. More complicatedmachines, such as a can opener, contain several partsconnected togcthcr in various ways. The purpos:: ofall machines is the same: to change the effect of anapplied force. The change might be the direction ofthe force, the magnitude of the force, or both. Forexample, a crowbar can be used to increase themagnitude of force applied by the user. [Systems andInteractions]

C-3 What are machines, and what do they do? Whatprinciples govern their action?

Grades Three Through Six

There are several kinds of simple machines. Amongthem are levers, inclined planes, wedges, and screws.If a certain force is applied to a machine through acertain distance, a machine's output can be either alarger force acting over a smaller distance or asmaller force acting over a greater distance. A

Students should reexamine the operation ofvarious machines using the concepts of "work"and energy.They. should identify the system thatloses energy and the system that gains energyand verify that the work output ofa machine is nogreater than the work put in. (Energy, Systemsand Interactions]

60 Part 11The Content of Science '72

machine can either increase thc magnitude of anapplied force or it can increase the distance throughwhich the force acts. It cannot do both at the sametime. All machines can be analyzed and understoodon this basis. [Systems and Interactions, Energy]

C-3 What are machines, and what do they do? Whatprinciples govern their action?

Grades Six Through Nine

The product of the force and the distance throughwhich it acts (force x distance) is given the namework. [Energy, Systems and Interactions]

The basic principle governing all machines issimply stated in terms of the concept of work: Thework output of a machine can be no greater than thework put into it. In any real machine, the work outputis less than the work input because there is frictionbetween the moving parts. iEnergy, Systems andInteractions]

C-3 What are machines, and what do they do? Whatprinciples govern their action?

Grades Nine Through Twelve

Work (W) is equal to the product of force (F) anddistance (x) moved in the direction of the force. If thedirection of the applied force is the same as thedirection of motion, W = Fx. If F is not constant, thcnthe average value of F must be used. The unit of workis thc newton-meter (Nm), called the joule (J).[Energy, Systems and Interactions]

The rate at which work is done is called power: P =Wit. The unit of power is the joule per second (Rs),and is given the name watt (W). An obsolete (but stillfrequently used) unit of power is the horsepower (lip),equal to 745.7 W. (Energy, Systems and Interactions)

The efficiency of a machine is the ratio of theoutput of the machine to the input. Careful design canimprove the efficiency of a machine (for example, byminimizing friction).

The definition of work in the preceding section can be confusing to students because in everyday lan-

guage we use the word "work" to mean more than is implied by this restrictive definition. For example,if you hold a heavy book in your outstretched stationary hand, you do not do any work on thebook in thescientific sense. It is certainly true, however, that your arm gets tired. You are likely to say, "This sure ishard work!" Students can appreciate the usefulness of the restrictive scientific definition, however, when

it is used in the context of energy transfers by mechanical means. In this example, no energy was trans-ferred mechanically from the person to the book, so no work was done on the book. [Energy, Systems

and Interactions]

"

THE idca that separate systems can separately gain orlose energy, but that thc total energy of all interactingsystems remains constant, is known as conservationof energy. It is onc of the great conservation prin-ciples around which science is organized. Mass is oneform of energy that must be taken into account incases involving atoms and thcir components. In suchcases, a unified principle of conservation of mass-energy replaces the separate principles of conserva-tion of mass and conservation of energy.

D-1 What is energy? What are itscharacteristics?

D-2 What do we do with energy? Whatchanges occur as we use it?

What is energy? What are its characteristics?

Kindergarten Through Grade Three

Forms of energy can be classified in several ways,depending on our purposes. Energy is manifcstcdwhen we drop a ball, strike a match, make waves in abathtub, clap our hands or rub them briskly together,or turn on a flashlight. Each form of energy has itsown characteristics. For example, a given materialwill transmit some forms of enc:gy and absorb or

reflect othcrs. A sheet of thick paper transmits soundbut not light. A stretched sheet of plastic wrap tram.-mits iight but not watcr waves. Heat is a form ofenergy oftcn produced by conversion from othcrforms, as can easily be dcmonstratcd by the warmingof a dark object exposcd to sunlight. The capacity ofwaves to carry energy can be dcmonstratcd byobserving how water waves (for example, in wavetanks) sct floating objccts into motion. Energy isrequired whcn work is donc on a system or whenmatter changes its form. [Energy, Systcms and Inter-actions, Patterns of Change]

D-1 What is energy? What are its characteristics?

Grades Three Through Six

Energy passes through ecosystcms in food chainsmainly in the form of the chemical energy supplied toeach organism by the nourishmcnt it consumcs. Allorganisms convert some of this energy into hcat.Animals also convert somc of it into mechanicalenergy. Green rlants convert light energy into cherni

al energy by means of the phuLuLhemkalcalled photosynthcsis. (See Chapter 5, Section A.Living Things.) [Systems and Interactions, Energy]

D-1 What is energy? What are its characteristics?

Grades Six Through Nine

When systems interact, energy is oftcn transferredfrom onc system to another. When energy conversiontakes place, thc total energy is conserved Sometimesconversion processes invoNe conversion of part ofthc energy to undesired forms, typically to heat

Chapter 3Physical Sciences 61

a

energy. In teims of systems, we say that part of theenergy is transferred to a third system, the environ-ment, in the form of heat energy. [Systems and Inter-actions, Energy]

Under nuclear conditions, when the energy of asubstance is changed, its mass does not change.Under certain conditions, such as when nuclear fusionor fission occurs, mass and energy are interconverted,and measurable mass changes occur.

The unit of energy is the joule, named after theEnglish physicist James Prescott Joule in recognitionof his key contributions to our understanding oftheprinciple of energy conservation. When energy istransported from one place to another (e.g., by anelectric transmission line), we measure the rate atwhich it is transported. When a device transformsenergy from one form to another (as an electric motordoes), we measure the rate at which it does so. Therate at which energy is transmitted or transformed iscalled power. The basic unit of power is the watt (W),named after the Scottish engineer James Watt, whomade crucial improvements to the steam engine andthereby contributed to the industrial revolution.[Energy, Patterns of Change]

Conversion of energy from one form to anotherusually has some effect on the surroundings. This isespecially true of conversion of heat energy intomechanical energy, which is accomplished by heatengines. Heat engines (such as gasoline engines andsteam turbines) inevitably produce a certain amountof waste heat. Sometimes the waste heat is useful, aswhen steam from power plants is used for heatingbuildings. Sometimes it is an environmental pollutant,as when river water used for cooling is warmed somuch that it affects the ecological balance of theriver. [Energy, Systems and Interactions]

Because there ere two fundamental ways in which asystem can change, there are two basic types ofenergy. A system can change when the distance be-tween the parts of a system change or the parts arcrearranged. Energy associated with these kinds ofchanges is traditionally called potential energy. Thesecond way the parts of a system can change is bygoing faster or slower. The energy that things havebecause they arc in motion is called kinetic energy.Other forms of energy are really manifestations ofthese two basic types. For example, chemical energyis the electrical potential energy of a system of atomsand molecules capable of being rearranged. Heat

62 Part ft---The Content of Science

energy is the total kinetic and potential energy of therandom motions of the particles ofa substance.[Energy]

The use of electrical energy is pervasive in ourtechnological society. Electrical energy caa beobtained by the conversion of gravitational potentialenergy (hydroelectric plants do this), chemical energy(fossil fuel plants do this), or potential energy ofatomic nuclei (nuclear plants do this). Other con-version processes furnish small amounts of electricalenergy as well. [Energy, Systems and Interactions]

Electromagnetic waves transfer energy from theirsource to where they are absorbed at the speed oflight. Electromagnetic energy has many forms, someof which are familiar. Among these familiar formsare light, infrared radiation, radio waves, and X rays.The forms differ because their wavelengths varywidely. For example, X rays will penetrate objectsthat are opaque to light; we can feel infrared radiationas heat energy is absorbed by our skin. Nevertheless,all of these forms of energy transfer share manyproperties in common. [Energy, Systems and Interac-tions]

D-1 What is energy? What are its characteristics?

Grades Nine Through Twelve

Chemical energy is the electrical potential energyassociated with the configuration of electrons inmolecules. Each molecule has a specific spaualconfiguration and therefore a specific electronicpotential energy. In chemical reactions, the configura-tions change and, therefore, the electrical potentialenergy changes as well. In exothermic reactions,energy is released to the environment as the electricpotential energy of the molecules decreases. Anexample of such a reaction is the main reaction in theburning of coal:

C 02> CO2+ 6.54 x 1049 joules per moleculeof CO2 produced.

(See Section B, Reactions and Interactions.) Therelease is usually in the form of heat energy, butsometimes in the form of electrical or electromag-netic energy. In endothermic reactions, energy mustbe supplied from outside to make the reaction pro-ceed. In such reactions, the electric potential energyof the molecules increases. An example of an endo-

thermic reaction is the production of mercury fromthe ore cinnabar:

2Hg0 + 1.51 x 1019jou1es per molecule ofHg0> 2Hg + 02.Photosynthetic reactions are endothermic; the

energy input comes from light. The reactions are wellunderstood but complex. Roughly speaking, however,the overall reaction is:

water + carbon dioxide + light energy> sugar.(See Chapter 5, Section A, Living Things.) [Energy,Systems and Interactions]

What do we do with energy? What changes occuras we use it?

Kindergarten Through Grade Three

Energy is used to do mechanical work. Most of thisenergy is provided by using fuel to produce heatenergy and then using the heat energy to run a heatengine. The heat engine does either the desiredmechanical work directly (as when a gasoline enginedrives an automobile) or indirectly through conver-sion to electrical energy, which then drives an electricmotor that does the work (as in a trolley car or avacuum cleaner). (See Section C, Force and Motion.)Heat engines ineviiably produce waste heat. (SeeSection E, Energy: Heat.) [Energy, Systems andInteractions]

The ultimate source of most of the energy we use isthe sun. We call the sun a renewable resource becauseits energy is available forever for practical purposes.Coal and petroleum have, ultimately, solar origins:They are the remains of green plants that lived anddied millions of years ago. But we use coal and oil farfaster than they are produced. We therefore call themnonrenewable resources. (See Chapter 4, Section B,Geology and Natural Resources.) [Energy, Systemsand Interactions, Patterns of Change]

D-2 What do we do with energy? What changes occuras wo use it?

Grades Three Through SixThe transfer of energy is necessary for change to

occur in matter. Energy transfers areessential to allliving organisms. [Energy, Systems and Interactions]

Humans use energy in many ways, including formsnot available to other living things. Electric energy isused for heating, lighting, mechanical motion, andinformation transpott and processing. Nuclear energyand the energy of fuels are used for a vast variety ofpurposes. [Energy]

D-2 What do we do with energy? What changes occuras we use it?

Grades Six Through Nine

All energy conversion processes have undesirableside effects. We try to minimize these effects bothdirectly, by careful design, and indirectly, by balanc-ing various resources in building an energy network.For example, hydroelectricity is a renewable resourcebecause rain and snow fall in the mountains everyyear. However, reservoirs flood valuable propertythat has other possible uses, and dams occasionallybreak disastrously. Coal is nonrenewable, dangerousto mine, and contains potential pollutants which aredifficult to remove; in addition, burning coal pro-duces carbon dioxide, which may have undesirable

In dealing with energy and power quantitativelyor semiquantitatively, give preference to SImetric units: the joule, the watt, and their mul-tiples. Students who have familiarity with U.S.customary units (e.g., the foot-pound, Btu, andhorsepower) should be encouraged to learn howto convert to SI metric. Other units of energysometimes used are the kilowatt-hour and thektlocalorie.The use of these units is discouragedby international convention and is slowly dyingout,

It is unfortunate that the tcrm "potential energy"is used to descibe a type of energy because of po-sition. Kinetic energy has just as much ability tobe converted into another form as does potentialenergy. Many persons have developed miscon-ceptions regarding energy because of the use ofthis term. This needs to be clarified with students.

t"nr.t.)

Chapter 3Physical Sciences 63

climatic effects. Nuclear power does not exhaustdesirable resources and does not produce carbondioxide, but the waste products are difficult andexpensive to store reliably. Energy conservation isvery useful, but there are limits beyond which energyuse cannot be reduced. The search for the optimumbalance is one having many scientific, technical,political, economic, and social aspects. [Energy,Patterns of Change]

Technological applications of energy conversionare numerous. Heating, cooling, and cooking devicesuse energy, either in the form of the chemical energyof fuel or in the form of electrical energy. Undesir-able heat transfer is minimized by means of insulatingmaterials. Electricity is useful for energy transmissionand communication because of the convenience andspeed of transmission. Information can be processedin very elaborate ways by means of tiny, ofteninexpensive, devices using electronic techniques.[Energy, Systems and Interactions]

D-2 What do we do with energy? What changes occuras we use it?

Grades Nine Through Twelve

Electromagnetic energy is used in many ways.Infrared photography and detection, microwaveovens, and X-ray technologies are but a few ex-amples. Information is processed rapidly in the formof electric pulses, as is done in computers. Mostinformation is transmitted electromagnetically, eitherby cable, by light pipe, or by radio transmission.Much of the electric energy consumed by people isgenerated using heat engines of various types. Themost common of these is the steam plant, whichtransforms the energy stored in fossil fuels or inuranium into the disordered energy of heat and,thence, by means of a steam turbine, into orderedmechanical energy. The mechanical energy is thenused to drive an electric generator. Electric energy isdifficult to store at present and must usually betransformed into some other form of energy forstorage. However, the advent of a new generation ofsuperconductors may make it possible to store theenergy directly and efficiently in the form of themagnetic field of a surrconducting coil. [Energy,Systems and Interactions]

64 Part IIThe Content of Science

SectiopE Enerby: Heat

HEAT and temperature are words commonly used inour everyday language. The concepts of heat, tem-perature, and other thermal properties of matter areintimately related to the concepts of force and mo-tion. The concepts of force and motion are useful todescribe the interaction of a few objects. The con-cepts of heat and temperature are useful for describ-ing the large-scale effects of the interactions of thevast numbers of atoms or molecules of which asubstance is composed. Because there are such largenumbers of particles interacting, new principles arisethat are based simply on statistical concepts that sup-plement the principle of energy conservation.

E-1 What Is heat energy? Where does itcome from, and what are Its properties?

E-2 How do we use heat energy?

What is heat energy? Where does it come from, andwhat are its properties?

Kindergarten Through Grade Three

The form of energy called heat energy can beproduced in many ways. Heat energy is produced inan object when it is exposed to the sun, to other lightsources, or to fire. It can also be produced by rubbingi.wo objects together. Heat flows from a hotter regionor object to a cooler one. We say that the region fromwhich the heat flows has a higher temperature thanthe region to which it flows. If an object is not too hotor too cold, we can tell its approximate temperatureby feeling it. (See Section D. Energy: Sources andTransformations.) [Energy, Systems and Interaction]

E-1 What is heat energy? Where does it come from,and what are its properties?

Grades Three Through Six

Heat and temperature are not he same thing but arerelated to one anoth. Temperature can be measuredwith a thermometer. Most materials expand with

Organelles in the cells of green plants have the ability to convert light energy into chemical energy,

which can be stored, transported, and used by the plant in a variety of ways. The ability of animals to

see is based on the conversion of light energy into electrical energy in sensitive cells in their eyes. The

ability of animals to hear is based on the conversion of sound energy into electrical energy by sensitive

cells in their ears. Electric eels, sharks, manyfishes, and duck-billed platypuses are among the animals

that have organs sensitive to electrical energy, which they use to detect their prey. (See Chapter 5,

Section A, Living Things.) (Energy, Evolution, Systems and interactions)

increasing temperature and contract with decreasingtemperature. That is how familiar thermometerswork. Heat cannot be measumd directly. However, anincrease of the temperature of an object can meanthat heat is flowing into it; a decrease of the tempera-ture can mean that heat is flowing out of it. Heataffects matter in many ways. Chemical reactionsrequire an input or output of heat energy in predict-able amounts, as do phase changesmelting orfreezing, boiling or conden.sation. [Energy, Patternsof Change]

E-1 What is heat energy? Where does it come from,and what are its properties?

Grades Six Through Nine

Heat and temperature arc not the same thing but arerelated to one another. Heat affects matter in manyways. A thermometer is a device for predicting whichway heat energy will flow from any object to anyother one; that is, which of the two objects has thehigher temperature. [Energy]

The molecules of any substance are in constantdisordered, random motion. Heat energy is the totalkinetic and potential energy of the disordered motionof the molecules of the substance. The temperature ofa substance is a measure of the average randommotional energy of the molecules (or other particles)composing the substance. Temperature is usually notmeasured directly, by measuring this average kineticenergy, but indirectly, by using a device whosemacroscopic properties are affected by temperatureA mercury-in-glass thermometer is such a device in

which the volume of a fixed quantity of mercuryvaries with temperature. [Systems and Interactions,Energy]

Phase changes always involve the flow of heat intoor out of an object. But*this heat flow does not resultin a temperatum change. (For example, the tempera-ture of a kettle of pum water always remains at theboiling temperature of water, 100°C, no matter howhard it boils.) For this reason, the amount of heatenergy required to produce a phase change in acertain mass of substance is called its latent (hidden)hcat. [Energy, Patterns of Change]

In order to change the phase of a substanceforexample, to boil a liquidits molecules must berearranged. This requires a change in the potentialenergy of the bonds holding the particles together,rather than a change in the random disordered mo-tional energy of the molecules. For this reason, theheat added does not result in a temperature change.[Patterns of Change, Energy]

Heat energy can be transferred from one place toanother by processes called conduction, convection,and radiation. Heat energy flows quickly by conduc-tion through substances called heat conductors and

slowly through substances called heat insulators.Insulators are important in reducing the cost of homeheating and cooling, as wel as making homes morecomfortable. In convection, heat is transferred bywarm matter (for example, air) moving into a coolerregion. Good insulation prevents large-scale motionof air. Wool is a good insulator because it traps air intiny cells so that convection cannot take place. Inradiation, a body at high temperature emits electro-magnetic radiation which is absorbed by a coolerbody. Highly reflecting surfaces are effective atreducing heat transfer by radiation. That is why aThermos bottle is silvered and thermal or solarcurtains arc aluminized. [Energy, Systems andInteractions]

f'7 1.1i I

Chapter 3Physical Sciences 65

E-1 What is heat energy? Where does it come from,and what are its properties?

Grades Nine Through Twelve

As heat energy is removed from a sample, itstemperature decreases. In principle, a point is reachedat which no further energy can be removed becauseall of the molecules have the minimum possibleenergy. This is the lowest temperature possible and iscalled absolute zero. On the absolute or Kelvintemperature scale, absolute zero is assigned thetemperature value T = 0 K. The size of the kelvin (thedegree of the absolute scale) is defined by fixing thetemperature of the so-called triple point of water at273.16 K, exactly. Absolute temperatures, expressedin kelvin, must be used in the ideal gas law, and useof the absolute temperature scale makes many otherphysical and chemical calculations simple. TheCelsius scale is often convenient for everyday use.The zero of the Celsius scale (0°C) is set by thedefinition 0°C = 273.15 K. The Celsius degree is ofthe same "size" as the kelvin. [Energy]

Because heat is a form of energy, it can be pro-duced only by conversion from other forms of energyand can never be created from nothing. This state-ment is one form of the first law of thermodynamics.[Energy]

Disordered heat energy can be converted to orderedmacroscopic motion (mechanical energy) by a heatengine. The statement that the mechanical energy isconverted from heat energy and not created fromnothing is one form of the first law of thermodynam-ics. However, the conversion can never be complete.A heat engine always takes heat energy in from asource at a relatively high temperature and ejects asmaller amount of heat energy to something at alower temperature. The amount of ejected heat cannever be zero. Thus, some of the heat energy taken inby the engine at high temperature must always beejected to the environment at a lower temperature andis lost to the engine. This is the meaning of thesecond law of thermodynamics. The second lawlimits the maximum possible efficiency (work outputdivided by heat energy input) of any heat engine to avalue less than 100 percent. [Energy, Systems andInteractions]

Because some heat energy is always rejected to theenvironment when a heat engine operates, the tem-perature of the environment is raised. Sometimes this

66 Part liThe Content of Science

so-called waste heat can be used (e.g., for steamheating), but usually it is not desired and is calledthermal pollution. (For example, the summer tem-perature of the Connecticut River, whose waters areused to cool many electric generating plants, oftenexceeds 100°F, to the detriment of the fish and otheraquatic life.) Measures must be taken to minimizethese undesirable effects; sometimes this involvesconsiderable cost. [Energy, Systems and Interactions]

Entropy is a measure of the disorder of the energycontained in a system. If a system is isolated, itsentropy can only remain the same or increase. (This isan alternative statement of the second law of thermo-dynamics.) But if two systems interact, the entropy ofone system can be reduced at the expense of theother, provided the total entropy of both systemsincreases or remains the same. Living organismsconstantly decrease their own entropy at the expenseof the entropy of their surroundings. So do heatengines, crystals (as they grow out of solution), andother systems as well. [Energy, Systems and Interac-tions, Patterns of Change]

How do we use heat energy?

Kindergarten Through Grade Three

Heat is essential to pll living organisms. Weproduce heat energy ourselves by metabolizing food.We also produce heat energy by burning fuel to warmour houses. By adding heat to our environment, we

Many effects operate to convert ordered, large-scale motion to disordered, small-scale motion.Friction is one of these effects. When an objectrubs against another, the molecules on thesurface are disturbed and set in motion. Theythen set their neighbors in motion. The orderedmotion of the entire object is converted intodisordered motion of its molecules. The spread-ing of the motion through the body is the flow ofheat energy. [Energy]

P7()10

can raise its temperature to a comfortable level. Weuse cooling devices to remove heat from our environ-ment and thus to lower the temperature to a comfort-able level. We use heat energy also to drive heatengines (such as automobile engines) and thus to domechanical work. [Energy, Systems and Interactions]

E-2 How do we use heat energy?

Grades Three Through Six

Heat flows by itself only from an object at a highertemperature to another object at a lower temperature.Thermometers can be used to predict which way heatwill flow when two substances are placed in contact.As heat flows, the warmer body cools and thc coolerone warms until the two achieve the same tempera-ture. This final temperature lies somewhere betweenthe initial temperatures of the two bodies. [Energy,Systems and Interactions]

E-2 How do we use heat energy?

Grades Six Through Nine

It is possible to make heat energy flow from acooler object to a warmer one, but only at the cost ofother energy. Any device that does this is called arefrigerator. Household refrigerators, air conditioners,ice-making machines, and the space-heating devicescalled heat pumps are examples of refrigerators.[Energy, Systems and Interactions]

E-2 How do we use heat energy?

Grades Nine Through Twelve

Heat engines include steam engines, steam turbines,gas turbines (such as jet engines), and internalcombustion engines. A heat engine designed tooperate in reverse uses mechanical energy to take inheat energy at a low temperature and reject it at ahigher temperature. Such a device is called a refrig-erator or a heat pump. [Energy, Systems and Interac-tions]

The efficiency of a heat engine depends on manyfactors, some of which can be optimized by carefulengineering. But there is an upper limit set on theefficiency of a heat engine by the second law ofthermodynamics. If the engine takes in heat attemperature Tin and rejects waste heat at temperatureT., its efficiency can never exceed the Camot

7 r.

As an example of entropy, consider ten pennieson a tray, all heads up. The tray is shaken; thepennies will probably settle with some heads upand some tads up. The ordered, low-entropy state(ten heads) has been transformed into a disor-dered, high-entropy state (some heads, sometails). Further shaking is very unlikely to producethe reverse process. But you can always producethe ten-heads state by turning over all the pennieswith tails up. Doing this requires energy. (En-ergy, Patterns of Change)

efficiency, e = (Tin-- TJTin. It follows from thisrelationship that an efficient heat engine should takeheat in at the highest practicable temperature andexhaust heat at the lowest practicable temperature inorder to have the highest efficiency. [Energy, Sys-tems and Interactions]

.Section F Energy: Electricity andMagnetism

AT a fundamental level, electricity and magnetismarc manifestations of the same basic phenomenoncalled electromagnetism. In our everyday lives wesometimes experience them separately and at othertimcs as the combined phenomenon. For example,static electricity can be understood simply as anelectrical phenomenon. Similarly, at a certain level ofunderstanding, it is useful to consider the attractionand repulsion of permanent magnets as simply amagnetic phenomenon. However, radio and TVsignals and electric motors can be understood only aselectromagnetic phenomena. The complete theory ofelectnomagnetism, called quantum electrodynamics(which includes the effects of quantum mechanics), isat present our most precise and best tested physicaltheory.

F-1 What are electricity and magnetism?What are they like, and what are theirbasic properties? How do they interact?

Chapter 3Physical Sciences 67

F-2 How do we use electncity andmagnetism?

What are electricity and magnetism? What are theylike, and what are their basic properties? How dothey interact?

Kindergarten Through Grade Three

When you walk across a rug on a dry day, you mayget a shock whcn you touch a doorknob. Clothescoming out of a dryer stick together. When it isstormy, you sometimes see lightning. These phenom-ena are seen because matter can be electricallycharged by friction. The large sparks that am light-ning bolts and me tiny sparks you feel when youtouch the doorknob result from the flow of electri-cally charged matter from one place to another.Electric forces can act over a distance without theobjects having to touch. This is seen whcn a balloonwhich has been electrically charged by frictionato.,Icts hair on a person's arm or head withoutactually touching it. [Systems and Interactions]

Electric charge can be made to flow through wiresconnected to batteries or electric generators. Themoving electric charge can be used to light lamps, runmotors, and power radios and cassette players. Weusc this kind of electricity continually in our everydaylives. [Systems and Interactions, Energy]

Electricity used to power battery-driven toys,radios, and flashlights is safe and will not producedangerous elecuic shocks. The electricity from wallsockets used to run household appliances is verydangerous if it is used improperly. Students should bewarned never to experiment with household electriccircuits and should be taught about the dangers offrayed wiring, of touching the metal prongs ofelectric plugs, and of inserting any kind of object intoelectric outlets. [Systems and Interactions)

Magnets attract and repel onc another and attractcommon materials made from iron or steel. Magnetscan attract steel paper clips at a distance, and thiseffect can be transmitted through a series of severalclips in contact with one another. Magnets do notattract common materials other than iron and steel.[Systems and Interactions]

68 Part IIThe Content of Science

F-1 What are electricity and magnetism? What arethey Ike, and what are their basic properties?How do they interact?

Grades Three Through Six

Electric charge comes in two kinds, arbitrarilynamed positive (+) and negative (-). Particles havinglike charges exert repulsive forces on onc another.Panictz.i; having opposite charges exert attractiveforces on one another. (See Section A, Matter.) Thiseffect can be seen using charged plastic balls sus-pendtd from threads. [Systems and Interactions,Scale and Structure, Patterns of Change]

Electricity is most familiarly encountered in theform of electric current. When electric charge flows,it is called a current. Some materials carry electriccharge from place to place better than others; thesearc called conductors. Metals and salt solutions areconductors. The flow of charge requires a completecircuit of conducting material through which chargecan pass easily. A battery, a generator, or other deviceis needed to pump the charge through the circuit.Materials that do not carry electric charge well arccalled insulators. Clean glass and most plastics arcinsulators. [Systems and Interactions, Patterns ofChange, Energy]

The magnetic force is readily observed in perma-nent magnets. Magnets affect only certain matenils,notably steel and other materials made from iron,cobalt, and nickel. Magnets can be used to separateobjects made of such magnetic materials from other,nonmagnetic materials. Objects made of magneticmaterials can be magnetizedmade into magnetsby placing them near strong permanent magnets.[Systems and Interactions]

Magnetism and electricity are related, but they arenot the same thing. Electrical attraction and repulsionarise from electric charges, but there are no suchthings as magnetic charges. Magnetism arises fromelectric currentthat is, moving electric charge.Whenever there is an electric current, any magneticmaterial in the neighborhood will experience a force.The material becomes magnetized and remains so aslong as the electric current persists. Electromagnetsare a direct application of this principle. The earth is 41huge magnet, and this property of the earth arisesfrom the large electric currents that exist in theearth's metallic core. [Systems and Interactions, Scaleand Structure, Energy]

8 0

Most students have difficulty understanding the concept of complete circuit. It is helpful to distinguish

carefully between charge and energy. Energy is transferred from a battery to a light bulb by the circu-

lating charge. The complete circuit is necessary to provide a path for the charge to get back to the

battery.When the battery has run down, it has not run out of charge; rather, it has run out of the ability

to change chemically anyfurther. Since it cannot change further, it can no longer transfer energy by

pushing the charge around the circuit. (Patterns of Change, Systems and Interactions, Energy)

F-1 What are electricity and magnetism? What arethey like, and what are their basic properties?How do they interact?

Grades Six Through Nine

Just as an electric current can produce magneticforces, magnets can in turn cause electric currents. Anelectric current can be produced in a conducting loop

(a circuit) by moving it in thc vicinity of a magnet.The mechanical energy of motion is thus convertedinto electrical energy. This is how most electricgenerators work; by turning a coiled conductor in thespace between the poles of a magnet, a generator

converts mechanical energy into electrical energy.[Energy, Systems and Interactions]

In addition to the attractive and repulsive forcesexerted by charged objects on one another, an electri-

cally charged object can attract an uncharged object.

This attraction is due to the induced polarization ofthe charges. In the uncharged object, the + and -

charges are present in equal numbcrs, and the systemhas zero net charge. Suppose the charged object

possesses more positive than negative charges, so it

has a net positive charge. Due to the forces exerted by

this net positive charge, the charges on the uncharged

object separate, the negative charges moving as close

as possible to thc charged object and the positivecharges moving as far away as possible. The netresult is an attractive force, because the unlikecharges are closer together than the like charges. A

plastic comb run through your hair will attract littlebits of uncharged paper, which will then stick to the

comb. After a while, they are sometimes repelled.This happens when enough of the charge on the comb

has leaked onto a bit of paper to result in a netrepulsive force. [Systems and Interactions]

Electrical resistance is dr opposition offered by

matter to the flow of electric charge. Most conductors

offer some resistance to the flow of electric chargeAs a result, some electrical energy is converted toheat energy. Current will not continue to exist in a

circuit with resistance without something to drive it,such as a generator or a battcry. Thc driving influenceis expressed quantitatively as a voltage, and the unit

is called the volt (V). Most common battery-powereddevices are low voltage, 1-1/2 to 12 volts. This isnormally not a high enough voltage to cause percep-tible electric shocks. Common household lights andappliances, however, normally operate at 110 to 120

V. This is sufficient voltage to causc dangerous orfatal shocks. [Energy, Systems and Interactions]

Superconducting materials are an important excep-tion to the rule that even good conductors offer someresistance to the flow of charge. At sufficiently low

temperature, a superconductor loses all of its resis-

tance to current. [Systems and Interactions, Scale and

Structure, Energy]All matter is made up of elementary particles.

Among these elementary particles, electrons and

protons contain an equal amount of negative andpositive electric charge, respectively (See Section AMatter.) In most metals, electric currents arc theresult of the flow of electrons, while the positivecharges remain in place. (This is not true in allconductors.) In insulators, few electric charges arefree to move. [Scale and Structure]

Commercial electric energy is almost alwaystransmitted in the form of alternating current (AC) InAC systems, the current switches direction (oscil-lates) many times a second. In the U.S , the frequency

is 60 Hz; in many other countries it is SO Hz. Al-though the electrons flow back and forth rather than

moving in one direction like the water in a river, theelectrons nevertheless transfer energy to the variousdevices plugged into the circuit. [Systems and Inter-

actions]

E iChapter 3Physical Sciences 69

The operation of the magnetic compass dependson the fact that the earth is a huge electromagnet.The compass, consisting of a small magnetsuspended on a low-friction axis, is free to swingin a horizontal plane. The end of the compassneedle that points north is called the north pole(short for north-seeking pole) of the magnet. Theend that points south is called the south pole(short for south-seeking pole). As unlike magneticpoles attract one another, the north magneticpole of the earthlocated near the geographicNorth Poleis actually a magnetic south pole.(Systems and Interactions]

The voltage (the driving pressure) of commercialelectric systems is also carefully controlled. In theUnited States, the standard voltage is 110 V to 120 V;in many other countries 220 V is standard. [Energy,Systems and Interactions]

F-1 What are electricity and magnetism? What arethey like, and what are their basic properties?How do they interact?

Grades Nine Through Twelve

Electric charge never disappears or suddenlyappears in ordinary chemical or physical processes,because the electrons and protons that carry thecharge cannot disappear or suddenly appear. This isexpressed by saying electric charge is conserved.(Stability]

Electric and magnetic fields are theoretical con-cepts that emphasize the effect of electric and mag-netic forces on charged particles. They do not de-scribe the original charges and currents that producethe forces. These am very useful conccpts, because itis much easier in most cases to understand the effectsby knowing the fields rather than by knowing theconfiguration of charges and currents that produce thefields. For example, specifying that the magnetic fieldin the gap of a permanent magnet is a particularstrength cmibles an electrical engineer to readilycalculate the effect the magnet will have on anelectron that passes through its gap. Specifying thefield, however, tells thc engineer little about the

70 Part llThe Content of Science

magnetic details of the material of which the magnetis made. (Systems and Interactions]

Radio waves, microwaves, infrared radiation,visible light, ultraviolet radiation, X rays, and gammarays all transmit energy from one location to another.In order to understand how this energy is transmitted,it is useful to develop a model that considers all ofthese as waves. They arc given the name electromag-netic waves. These waves are fundamentally differentfrom sound waves or other waves that occur inmatter, aside from having a much higher spea (Thespeed of light in vacuum (c) is 300 million meters persecond (mls), compared with about 300 rills for soundin air. There is nothing material that vibrates as thewave passes, as the air particles do with sound wav;s,for example. Instead, a mathematical description canbe given that involves the periodic variation ofelectric and magnetic fields. The electromagneticwaves mentioned in this paragraph all have the samespeed but diffcr in frequency and wavelength. Radiowaves have the longest wavelength and lowestfrequency, while gamma rays have the shortestwavelength and highest fmquency. The frequenciesof standard AM and FM radio signals range fromabout one million to 100 million Hz (cycles persecond). [Energy, Systems and Interactions]

The work required to drive electric charge througha conductor against electrical resistance can bemeasured in terms of electric potential difference (V),often called voltage. The current driven through agiven conductor that is part of a circuit depends onthe potential difference between the ends of theconductor. For metals and some other kinds ofconductors, the relation between potential differenceand current (0, is given by Ohm's law,

V = iRIn this relation, the proportionality constant R iscalled the electrical resistance. V is measured in volts,i in amperes, and R in ohms.

Some electrical energy is converted to heat whencharges flow through a part of a circuit with resis-tance. The rate at which electrical energy in a circuitis transferred from the source to other parts of thecircuit is power P. Power is measured in watts (W).Electrical appliances arc often marked with a voltagerating, a current rating, and a power rating. Forexample, light bulbs arc specified by their voltagerating and power rating. (Energy, Systems andInteractions)

2

The concept of field is difficult to understand and requires significant mathematical sophistication -o

appreciate fully. It is introduced because the terms "electric field" and "magnetic field" are part of oureveryday language. It is possible for stu&nts at this level to understand that they describe the effect of

charges and currents and that larger fields produce larger effects. [Systems and Interactions]

When a potential difference V exists between twopoints in a circuit, the electrical power P that isconverted into other kinds of energy when a current ipasses through the circuit is given ty Joule's (pro-nounced Jowell's) law,

P = ViIf the conductor between the two points in the circuitconforms to Ohm's law, Joule's law can be written ineither of the following two forms:

P = i2R or P = V 2/R[Ene:gy, Systems and Interactions]

Power companies scl: energy to thcir customers. Atthe customer's location, this electrical energy isconverted to other kinds of energy. The usual unit ofelectric energy is the kilowatt-hour (kW h). One 1000W light bulb buming for one hour will transform 1kW h of electrical energy to heat and light. In manyplaces in the United States, the charge for a kilowatt-hour is ten cents at the present time. [Energy, Sys-tems and Interactions]

Electrons can be extracted from conductors andmade to move at high speeds through vacuumthrough the use of sufficiently high voltages. Usingthis basic technique, X rays, television images, andfluorescent lighting can be produced. rystems andInteractions, Energy]

How do we use electricity and magnetism?

Kindergarten Through Grade Three

Electricity is used to make motors run, light lamps,operate telephones and television sets, heat homes,and do many other things. [Patterns of Change,Systems and Interactions]

Magnetism can be used to separate materialscontaining iron from those that do not. Permanentmagnets arc frequently used to hold notes and mcs-

sages to vertical metal surfaces (refrigerator doors,for example). [Systems and Interactions]

F-2 How do we use electricity and magnetism?

Grades Three-Through Six

Current electricity is used to transport energy.Electrical energy, carried from one place to anotherby conductors, is the most versatile form of energyavailable. Most conductors offer some resistance toelectric current, causing some of the electric energyto be converted to heat in the conductor. This conver-sion is often undesirable, as in electric transmissionlines. But it can be desirable as well, as in the opera-tion of electric heaters and incandescent light bulbs(See Section D, Energy: Sources and Transforma-tions.) [Energy, Scale and Structure, Systems andInteractions]

F-2 How do we use electricity and magnetism?

Grades Six Through Nine

Electromagnets arc important components inelectric motors and generators. But they arc also usedby themaelves to attract, separate, and carry magneticmaterials, such as iron. In ore processing, electromag-nets are scmetimes used to separate magnetic par-ticles from nonmagnetic particles in crushed or,[Systems and Interactions]

Cassette tape recorders and VCRs store magneticpatterns on a plastic tape coated with a material thatcan be magnetized. These patterns are electronicallyconverted to electric currents that pmduce the pictureon the video tube and drive the speakers. The speak-ers convert the electric energy to sound energy.[Energy, Systems and Interactions]

F-2 How do we use electricity and magnetism?

Grades Nine Through Twelve

Superconductors are beginning to make importantcontributions to technology. The absence of resis-

Chapter 3Physical Sciences 71

"My chief trouble was that the idea was soelementary, so simple in logic that it seemeddifficult to believe no one else had thought ofputting it into practice."

Guglielmo Marconi (1874-1937)

tance makes possible more efficient electric genera-tors. Very powerful electromagnets are made out ofsuperconductors and are used in many branches ofscience, technology, and medicine. Superconductingmagnets may make possible high-speed, almostfrictionless, magnetically levitated trains that rideabove their tracks. The recently developed high-temperature superconductors will likely expand theuse of superconductors into new areas over thc nextseveral years. [Systems and Interactions]

The very strong magnetic fields produced bysuperconducting magnets offcr possiblities of im-proved transportation systems and better medicaldiagnostic methods, but they also pose unknown iisksto the human body. Scientists and medical profession-als must be continually alert to the possibility of dam-age to thc human body. [Systems and Interactions]

Electrostatic copying machines make use of theattractive electric force. A large drum is coated with athin film of a photoconductor, a material which is aninsulator in thc dark but a conductor in the light. Thcdrum is electrically charged. Then a camera lensprojects an image of a document onto thc drum.Where the image is dark, thc charge is not disturbed.Where the image is 3ht. the charge flows 'hroughthc photoconducting film and leaks away. Thus thedruir holds an electrostatic image of thc originaldocument. A fine, black, waxy powder sticks to thecharged (dark) regions only, thus forming an image inpowder. The powder is subsequently "ironed" onto asheet of paper. [Systems and Interactions]

The use of miniaturized electronics is pervasive inour modem technological world. Tcns of millions ofelectronic parts can be put on on microchip smallerthan the nail of your little finger at a cost of only afew dollars. This has made possible very sophisti-cated desktop computers for both home and industry.These am more powerful than even the largestcomputcrs of only a few decades ago. [Patterns ofChange, Evolution, Scale and Structure]

72 Part llThe Content of Science

Section G Ener6y: Iight

Lot-cr enables us to scc; sight is considered by manyto be the most important of our senses. Youngerstudents in particular have difficulty understandingthe properties of light simply because it is so closelyconnected with vision. Even after the distinctionbetween light and vision has been made, it is not casyto understand what light really is. We can certainlyunderstand and describe many properties of light at afairly elementary level. But to get at what light reallyis requires the usc of a highly mathematical theory.For physicists and othcr scientists who study and uselight, this theory, called quantum electrodynamics,provides onc of thc most precise and cxact under-standings of all physical phenomena.

G-1 How does light enable us to see? Whatare the sources of liaht? What is light?

G-2 What are the properties of light?

G-3 How do we use light?

How does light enable us to see? What are thesources of light? What is light?

Kindergarten Through Grade Three

When we see something, our eyes and brains arcresponding to the light that comes from the objectswe arc looking at. Light itself is not something thatwc see o touch. Light comcs from objects and entersour eyes; thc eye is thc organ of thc body that issensitive to light. A picture of what we are looking atis formed in our eyes and brain. Light is not like otherthings; it is not ordinary matter. The eye can see inboth very dim and .ry bright light, but there arelimits. Because th ,.. sun is so bright a source of light,too much light enters our cycs if we look at it di-rectly, and s4sious damage to our eyes occurs. Mostobjects do not L.mit their own light, but reflect lightfrom othcr sources. We can see them by means of thisreflected light. The sun is our primary sourcc of light.Other sources include electric light:, of all sons andobjects that arc buming. Wc can classify thc light wc

F,4

see according to its brightness and its color. [Energy,Scale and Structure, Systems and Interactions]

G-1 How does light enable us to see? What are thesources of light? What is light?

Grades Three Through Six

Light radiates outward in all directions from the sunand from other hot objects. Some things can emitlight without being hot (glow-in-the-dark paint andfireflies, for example). Light travels at great speed. Ifnot interrupted, light travels in straight lines. [Sys-tems and Interactions]

Light is a way that energy is transferred from thesource that emits the light to the object or substancethat absorbs it. [Systems and Interactions]

All surfaces reflect some of the light that strikesthem. We are able to see objects that reflect light aswelt as objects that emit their own light. When lightreaches the eye, the cornea and lens of the eye focusthe light on the retina where it is absorbed. The retinacontains nerve cells that respond to light and transmitelectrical impulses to the brain via the optic nervc.The brain further interprets these signals to produethe visual images of objects we see. [Systems andInteractions]

G-1 How does light enable us to see? What are thesources of light? What is light?

Grades Six Through Nine

Light, infrareu radiation, and ultraviolet radiationare forms of electromagtetic radiation. (See SectionF, Energy: Elecnicity and Magnetism.) Visible lightis distinguished from other forms by its particularrange of wavelengths, to which our eyes arc sensitive.Many insects and some birds (such as hummingbirds)can see using a wider range of wavelengths, includinga part of thc ultraviolet region of the electromagneticspectrum. [Energy, Scale and Structure, Systems andInteractions]

G-1 How does light enable us to see? What are thesources of light? What is light?

Grades Nine Through Twelve

Different models for light arc useful in helping usunderstand it. To best understand how light is emitted

-

and absorbed, we use the model that considers lightas particles, called photons. The energy of individualphotons increases as the wavelength of light de-creases. Light's behavior is best understood in tr-msof waves when we study the propagation of light.[Scale and Structure, Systems and Interactions]

What are the properties of light?

Kindergarten Through Grade Three

We observe and classify light in terms of itsintensity (brightness) and color. Wc cannot scc whenthe light is too faint; when light is too bright, it can beharmful to our eyes. We give names to differentcolors. Light passes more readily through somematerials than through others. [Systems and Inter.u.tions]

Shadows result when an object blocks the lightcommg from a bright source. The object that casts theshadow is located lrtween the light source and thesurface that is lit by the light on which the shadow isseen. If the object moves Closer to the light source,the shadow gets bigger because the object blocksmore of the light. [Systems and Interactions]

The direction of light going out from an object ischanged when it hits a mirror. Our eyes cannot tell ifthe direction of the light has been changed. That iswhy our eyes and brain form a picture which seems totell us that the object is on thc other sidc of themirror. [Systems and Interactions]

6-2 What are the properties of light?

Grades Three Through Six

Lenses bend light that passes through them. Whene look at an object through a lens, our eyes do not

know that the lens has bent the light. Depending onexactly how far the lens is from the object and oureyes, the object seems larger or smaller than it reallyis. [Systems and Interactions]

Most substances (even mirrors) absorb some of thelight that strikes them. The absorbed light is con-vened into heat energy. Substances like clear glassthat absorb very little light arc said to be 'imnsparent[Energy, Systems and Interactions]

8 5

Chapter 3Physical Sciences 73

The cornea (front part of the eye) is mainly re-sponsible for focusing the light that enters the eye.The lens (located behind the cornea) provides the

fine adjustment that lets us focus on objects closeup as well as far away. A prevalent misconceptionis that tht lens is primarily responsible for focus-ing the light that enters our eyes.

Most surfaces reflect some of the light that strikesthem, some more than others. Objects like clearplastic and glass (contact lenses, for example) aresometimes hard to see because they reflect so littlelight. [Systems and Interactions]

G-2 What are the properties of light?

Grades Six Through Nine

The speed of light is very much greater than thespeeds of other familiar things. It takes lightonly abouteight minutes to reach the earth from the sun, whichis approximately 150 million kilometers away. Alight-year is the distance that light travels in one year,almost 10 trillion kilometers. [Scale and Structure]

G-2 What are the properties of light?

Grades Nine Through Twelve

The speed of light can be measured in severaldifferent ways. Formerly, it was determined experi-mentally in terms of a standard meter and standardsecond. Today, the speed of light (c) can be measurt dso precisely that the unit of length, the meter, isdermedln terms of c, as is the unit of time, thesecond. [Scale and Stmcture]

The speed of light in vacuum is exactly the samefor all observers. This statement is one of the funda-mental principles of the theory of relativity. [Scaleand Structure] The speed of light is related to its fre-quency (I) and its wavelength (A); the relation isf= O.. (See Section C, Force and Motion.) Forvisible light, the range of wavelengths runs from 400urn (nanometers) to 700 nm. [Scale and Structure]

Like all waves, light waves conform to the principleof superposition. When waves superposepassthrough the same spacein such a way that their

74 Part 11--The Content of Science.

crests correspond and their troughs correspond, theresult is a larger wave; this is called constructiveinterference. When the waves superpose so that thecrest on one corresponds to the trough of the other,and vice versa, the result is a smaller wave or no waveat all. This is called destructive interference. Interfer-ence can be demonstrated by letting light from thesame source pass through two narrow, parallel slitsand then fall on a screen. [Systems and Interactions]

How do we use light?

Kindergarten Through Grade Three

We can see only if there is light present. Devices toreflect light can be used to see ourselves or aroundcorners. If the light is coming from all directions, asin fog, it is difficult to see objects. [Systems andInteractions]

G-3 How do we use light?

Grades Three Through Six

What we see as white light consists of light ofmany colors mixed together. Sometimes white light isseen to separate into colors, as in the rainbow, or inlight patterns reflected by a soap bubble, or in lightpassing through a prism. The light is separated intoseparate colors because light of different colors isbent differently when it passes from air into water orglass, or vice versa. [Systems and Interactions, Scaleand Structure]

When a surface appears colored, it is because itreflects more light of some colors thanof othercolors. The light that is not reflected is absotbed.Thus a red flower is red becauge it is a good absorberof blue and green light, reflecting only red light to oureyes. If we try to observe a red flower in pure bluelight, it appears black because the blue light isabsorbed. If we go into a store to buy a red shirt, wemust be careful not to look at it in colored light.Outside the store, in the sunlight, the shirt may appearto be a very different color. When red, yellow, andblue paint are mixed together, the mixture appearsdark brown or black. This is because each of thecolored paints absorbs-some of the white light fallingon it. With the proper mixture, all colors are absorbed

6

equally, and little or no reflected light is seen. [En-ergy, Scale and Structure, Systems and Interactions]

Many technologies and devices use or manipulatelight. Among them are cameras, camcorders, com-puter monitors, VCRs and videodisk players, tele-scopes, micmscopes, and the light-pipe endoscopesused by surgeons for such procedures as arthroscopicsurgery. [Systems and Interactions]

G-3 How do we use light?

Grades Six Through Nine

Energy is transferred from the source of light to thesubstance that absorbs the light. This energy can thenbe converted to other forms. It can provide the energyfor certain chemical reactions; it can be convertedinto heat energy; or, by means of photovoltaic de-vices, it can be converted directly into electric energy.[Energy. Systems and Interactions]

Some light is absorbed by fluorescent substances,the energy stored temporarily and ther, emitted,usually as a different color. If blue light shines on aglow-in-the-dark toy, it glows brightly yellow orgreen for a few minutes after the light is turned off. Ifred light is used, there is no afterglow because redlight does not have enough energy to activate thefluorescent substance. Manufacturers of washingmachine detergents add fluorescent materials to makeclothing look "whiter than white." When the washedclothing is put in sunlight, some of the ultravioletlight in the sunlight is absorbed by the substance inthe clothir:g and then reemitted as blue or violet light,making the clothing look whiter. A similar effect isoften used in amusement park fun houses to producestartling images. [Energy, Scale and Structure,Systems and Interactions]

6-3 How do we use light?

Grades Nine Through Twelve

A beam of light can carry a great amount of infor-mation. For this reason, many telephone transmissioncables are being replaced by fiber-optic lines. [Sys-tems and Interactions, Scale.and Structure]

When light of a sufficiently short wavelength (highenough energy) falls on a metal surface, the surfacecan emit electrons. This emission is called the pho-toelectric effect. The photoelectric effect has manyuseful applications. Equally important, a study of theeffect leads to a better understanding of the interac-

tion between light and matter. (Energy, Scale andStructure, Systems and Interaction]

Lascrs arc devices that produce light of preciselyone wavelength. The beam of light that emerges fromthe laser does not diverge, as do light bcams fromother sources. When the laser beam strikes a surface,this concentrated energy is absorbed into a very smallarea.The amount of heat energy transferred in thisway, even from low-power lasers, can easily damageunprotected eyes. From high-power lasers, the heatcan be sufficient to cut through thick layers of steel.In medicine, lasers have become invaluable for de-positing precise amounts of heat energy to cut awayunwanted substances. A serious social issue that mustbe debated and discussed is the use of very highpower.lasers in satellite-based military weaponsystems. [Energy, Systems and Interactions]

Section H Enerty: Sound

THE science of sound, called acoustics, is interdisci-plinary. It involves the physical aspects of the crea-tion and transmission of energy in the form of soundwaves to the eardrum as well as the interpretation bythe auditory nerve and brain of the electrical nerveimpulses generated in the middle ear by the vibratingeardrum. Physical acoustics, the process up to theeardrum, is considered in this section. The remainderof the process is in the domain of physiological andpsychological acoustics.

H-1 Where does sound come from? Whatare its sources? How can sound bedescribed?

H-2 How does sound enable us to hear?How do we produce sounds?

H-3 How do we use sound?

Where does sound come from? What are itssources? How can sound be described?

Kindergarten Through Grade Three

Sound comes from many sources. Sound can beproduced by making an object vibrate (movr back

r-1 Chapter 3Physical Sciences 75

and forth). All sounds can ultimately be traced to avibration of some matetial object, whether it be thestrings of a guitar or violin, the membrane of a drum,the reed in a clarinet, the speaker cone of a loud-speaker, the vocal cords in our throats, or two spoonsbeing hit together. The vibration is transmitted toanything the vibrating object touches, including theair that surrounds it. [Systems and Interactions]

The range of loudness of sound is very wide; it runsfrom the threshold of hearing to very loud sounds thatcan cause pain and ear damage. It is important toavoid excessively loud sounds. [Scale and Structure]

H-1 Where does sound come from? What are itssources? How can sound be described?

Grades Three Through Six

We are most familiar with sound that travels fromits source to our ears through air, but sound can travelthrough other substances as well. Whales communi-cate over great distances by means of sound thattravels through seawater. [Systems and Interactions]

Sound can be reflected or absorbed by walls andother surfaces. Echoes are the reflection of sound wehear from large surfaces. Because some surfacesabsorb sound well, they are used to soften or reducethe loudness of sounds generated in a room. Carpetsand acoustical tile are used to reduce the noise levelin a classroom, for example. [Energy, Systems andInteractions]

Higher or lower tones of sound are produced,depending on how fast the sound source vibrates; thedifference between high and low is known as pitch.The faster the vibration, the higher the pitch. [Energy,Scale and-Structure, Systems and Interactions]

H-1 Where does sound come from? What are itssources? How can sound be described?

Grades Six Through Nine

Sound is a mechanical wave in matter. Like allwaves, sound transfers energy when it travels througha mediut . from one place to another. The energyexists in the form. of rapid back-and-forth motion ofthe particles composing the medium. [Energy,Systems and Interactions]

The sensation of musical pitch is determined by thefrequency of the sound that produces the sensation. Asound of a particular frequency traveling through air

76 Part IIThe Content of Science

has a particular wavelength. (See Section C, Forceand Motion.) The pitch can be changed by changingthe frequency of the vibrating source. The pitch of astringed instrument, for example, can be changed byincreasing or reducing the length of the string or bychanging its tension. The pitch of a wind instrumentcan be changed by changing the effective length ofthe vibrating column of air inside the instrument. Amusical sound of a given frequency, traveling throughair, has a particular wavelength. The intensity ofsound vibrations is perceived as loudness and can bevaried by changing the amplitude of the vibratingsource. [Energy, systems and Interactions, Scale andStructure]

Earthquake waves are sound waves that travelthrough the earth. (See Chapter 4, Section B, Geologyand Natural Resources.) Their frequency is too low tohear. However, they transfer great amounts of vibra-tional energy and can shake objects, such as build-ings, hard enough to do a great deal ofdamage. So-called sonic booms, produced by airplanes movingfaster than the speed of sound, sometimes also carryenough sound energy to do damage. [Energy, Scaleand Structure, Systems and Interactions]

H-1 Where does sound come from? What are itssources? How can sound be described?

Grades Nine Through Twelve

Sound waves consist of rapid vibrations of mole-cules in solids, liquids, and gases. For example, thevibrating surface of a bell starts a sound wave in thesurrounding air by pushing against the adjacent airmolecules back and forth. One back-and-forthvibration composes one cycle of the sound. Thedisturbed molecules in turn push against neighboringmolecules and disturb them, and so forth. The dis-turbed molecules do not move very far. What travelsaway from the bell at the speed of sound is thecollision process itself. [Energy, Systems and Interac-tions]

The speed of sound through air is about 340 metresper second, the exact value depending on the tem-perature and humidity. (This is roughly one and a halftimes as fast as the speed of a commercial jet plane.)Sound travels faster through liquids and solids thanthrough gases. Sound cannot travel through a vacuumbecause there is nothing in a vacuum that can vibrate.[Scale and Structure]

68

The frequency of a sound is perceived by an observer to be the same as the frequency of the suurce cm!)if the observer and the source are at rest with respect to the intervening medium. If either the source orthe observer is moving with respect to the medium, the source frequency and the observed frequent) Lanbe different.This is called the Doppler effect. Relative motion that brings the source and the obsenercloser together increases the perceived frequency, relative motion that separates the source and the observer decreases the perceived frequency. (See Chapter 4, Section A, Astronomy.) [ Energy, Scale andStructure, Patterns of Change]

The propagation of a sound ware depends on thespringiness of the medium through which it propa-gates. If you hit a steel bar with a hammer, you distortthe bar, and it springs back to its undisturbed shape.But in doing so, the disturbed material distortsneighboring material. Solids are springy, both incompression (back-and-forth squeezing) and in shear(side-to-side twisting). [Systems and Interactions]

Waves, including sound waves, intcract stronglywith structures whose size is roughly comparable totheir wavelength. Some objccts have resonant fre-quencies at which they tcnd to vibrate. These frequen-cies can be measured. [Energy, Scale and Structure]

. .

How does sound enabie us to hear? How do weproduce sounds?

Kindergarten Through Grade Three

The car is the organ of the body that receivessound. In humans, the car is sensitive to a wide rangeof sounds, both soft and loud in intensity and highand low in pitch. Loud sounds can cause damage tothe ear and should be avoided. Some sounds are toohigh-pitched for humans to hear, but some animals,including dogs and dcer, demonstrate ability to hearthem. [Systems and Interactions]

H-2 How does sound enable us to hear? How do weproduce sounds?

Grades Three Through Six

Whcn sound reaches our cars, the vibrating air ncxtto the cardrum sets the eardrum to vibration. Thevibrating eanirum stimulates nerve cells, whichtransmit electrical impulses through the auditory

nerve to thc brain, producing thc scnsation of sound.Thc energy carried by normal sound waves is small,and the car can hear such sounds because it is verysensitive. Likc most othcr mammals, humans canproduce sound by passing air across thc vocal cords,causing thcm to vibrate. Thc sound thus produced canbe modified by shaping thc mouth, lips, and tongue toproduce speech. Speech is thc primary mode of com-munication among humans. Many other animals cornmunicate with thc sounds thcy make, though theinformation they communicatc is much morc re-stricted than that of human speech. [Scale and StruLture, Systems and Interactions]

H 2 How does sound enato:e us to hear' How do weproduce sounds?

Grades Six Through Nine

It. is important to distinguish clearly between thephysical vibration that is onc of the factors compos-ing sound waves and the physiological sensation ofsound. Sound waves stimulate thc sensory process,but that proccss is electromechanical and inr oh escomplex interpretation on the part of the brain. EN Ln

though both processes arc called sound, confusingthcm can result in unanswerable questions, forexample, "If a tree falls in the forest ant: there is noonc thcrc to hcar it, is thcrc any sound?" [Scale andStructure, Systcms and Interactions]

How do we use sound?

Kindergarten Through

Sound arises from a greatRecbgnizing thc sourcc and

Grade Three

variety of sources.understanding thc

Chapter 3Physical Sciences 77

meaning of sounds from our environment is veryimportant in our interaction with the environment.We use sounds to communicate with one another byspeaking, singing, and listening. [Evolution, Systemsand Interaction]

H3 How do we use sound?

Grades Three Through Six

Two .;ars are better than one for locating a soundsome. Stereo sound systems represent a technologi-cal application of this fact. Some animals are muchbetter adapted than humans for sound source location.In the predator-prey relationship, for example, manypredators can orient their external cars to focus on thesounds they hear to locate their prey. In a similarfashion, many prey animals can focus their hearing tolocate and thus avoid predators. [ Evolution, Systemsand Interactions]

Sound frequencies beyond the range of humanperception are used by some animals adapted to doso. Bats and dolpnins, for example, make sounds withfrequencies higher than those that humans can hearand use the echoes for navigation and hunting.[Evolution, Systems and Interactions]

H3 How do we use sound?

Grades Six Through Nine

Musical tones are sounds having a fundamentalfrequency component, together with a set of higherfrequency components called harmonics. Tuningforks are designed to produce predominantly thefundamental frequency, but musical instruments arecarefully designed to produce a typical harmonicspectrum. The production of music represents ahighly developed technological application having along histery. [Scale and Structure]

In persons who have impaired hearing, the car losessensitivity to a range of sound. In older persons, theloss is usually at the high-frequency end of the rangeof human hearing. Nearly all elderly persons have

78 Part liThe Content of Science

some degree of hearing loss. In persons whose earshave been damaged by exposure to loud sounds, likerock musicians and persons who work in loud envi-ronments without proper car protection, the loss istypically in the midrange of frequency. Hearing aidsare camfully tailored so that they selectively amplifysound at the frequencies where the hearing loss hasoccurred. Present-day hearing aids are an imperfectsubstitute for normal hearing, but they arc extremelyhelpful to many persons. Hearing-aid technology iscurrently improving rapidly. [Patterns of Change,Systems and Interactions]

H-3 How do we use sound?

Grades Nine Through Twelve

In sonar, a pulse of sound is used to determine thedistance to the object that reflected it. This requires aknowledge of the speed of sound and the elapsed timefrom transmission of the pulse to detection of theecho. Sonars are used to find fish and measure waterdepth. Sophisticated sonars can apply the Dopplereffect, using the frequency of the reflected sound todetermine the speed of the object producing the echo.Bats use sonar (also called echolocation) to avoidobstacles and to catch their prey as they fly in thedark. The frequency used by bats is well beyond theupper limit of human cars. Other animals use similarbut less well-developed sonar techniques. [Evolution,Systems and Interactions]

Very high frequency sound (ultrasound) has avariety of applications in medicine and industry.Medical ultrasonic imaging is used for a variety ofnoninvasive examination and diagnostic techniques,notably in obstetrics and cancer diagnosis. Thetechnique depends on differential reflection orabsorption of sound by various body structures. Theshort wavelength of high-frequency sound makcspossible high resolution of detail in the image ob-tained. High-energy, focused sound pulses are used inlithotripsy to break up kidney stones, making surgeryunnecessary in many cases. [Systems and Interac-tions, Energy]

0

Chapter 4

Earth Sciences

BEFORE Galileo's invention of the telescope in1609, stargazers relied on their unaided sight. Thelenses used by Galileo enabled him to see roughly tentimes more stars than could be seen earlier with theunaided eye. Today, scientists use such modem-dayinstruments as reflector telescopes, radio telescopes,and spectroscopes to expand their "vision" of theuniverse far beyond the imaginationg of early as-tronomers. These and other tools of astronomy haveled scientists closer to understanding the evolution ofour universe.

A-1 What kinds of objects does the universecontain, and how do these objectsrelate to one another?

A-2 How has the universe evolved?

A-3 How do we learn about the contents andstructure of the universe?

What kinds of objects does the universe contain, andhow do these objects relate to one another?

Kindergarten Through Grade Three

When the sun is up, it is daytime; daylight comesfrom the sun. When the sun is down, it is nighttime,and the stars can be seen. The sun provides heat aswell as light; it is usually warmer during the day thanat night. The moon may be visible in the daytime orthe nighttime. [Patterns of Change]

91.

Every day, the sun rises in the east, moves higheruntil about noon, and then moves lower until it sets inthe west. In autumn the daylight period grows gradu-ally shorter, becoming shortest about the time ofwinter vacation. Then it grows longer, becominglongest about the time that summer vacation starts.

The sun does not always rise and set in exactly thesame places. In summer the sun rises to the north ofeast and sets to the north of west. At noon it is high inthe sky. In winter the sun rises to the south of east andsets to the south of west, and does not rise very high inthe sky at noon. Days are longer in summer than inwinter because the sun travels a longer path above thehorizon. This variation is the main cause of theclimatic changes of the seasons. [Patterns of Change]

The moon also rises and sets. The moon appears tochange shape over the course of a month. First, itwaxes (increases) from a crescent to a full disk, thenwanes back to a crescent before waxing again. If weobserve and record the shape of the moon every twoor three days for about a month, we can see the entirecycle of the moon. [Patterns of Change]

The carth we live on is a gigantic sphere, or globe,made mostly of rock. It only appears to be flat becausewe sec just a tiny part of it. People live all around theglobe. There is no top and no bottom; people do notfall off the earth because they are held to it by a forcecalled gravity. Wherever we are on the surface of theearth, down is toward the center of the earth.

The apparent daily motions of the sun, the moon,the planets, and the stars are due to the rotation of theearth about its axis. If we observe the sun and th.moon every two or three days, we can see that themoon grows fuller (waxes) as it moves farther awayfrom the sun in the sky and becomes thinner (wanes)as it returns toward the sun. The phases of the moondepend on the angle between the sun and the moon, as

Chapter 4Earth Sciences 79

Although children are often taught that the earth is a sphere, many students have not mastered thisconcept by the time they reach the grades three-through-six level. Activities and discussions that allowstudents to compare their concepts of the world are very important in helping them to grasp the conceptof the spherical earth.

we see them from the earth. When the moon is full, italways rises about the same time the sun sets. Thereason is that W C on earth must be between the sunand the moon in order to see the entire illuminatedface of the moon. When the moon is new, it rises andsets at about the same time as the sun. This is becausewe see the sun and the moon in approximately thesame direction, and most of the lighted side of themoon is facing away from us. [Patterns of Change]

Eclipses occur when the earth, sun, and moon comeinto alignment so that the earth's shadow falls on themoon (lunar eclipse) or the moon's shadow falls on

Because a year is a very long time in the life of achild, many students find it difficult to graspsome of the motions, such as the motion of theplanets relative to the stellar background. A visitto a planetariwn will give vivid pictures of boththe gross structure of the universe and of thedirectly observable cOnsequences of rotation inthe solar system.

The sun, moon, and stars are fascinating tochildren in the primary grades. They are natu-rally curious about the moon' s changing appear-ance and the sun' s progress across the sky.Although most young children cannot grasp thesephenomena, they can observe the sky in a system-atic way and observe patterns. Helping studentsdiscover these patterns of change through theirown observations encourages their curiosityabout the world as they acquire basic knowledgeabout astronomy.

80 Part IfThe Content of Science

the earth (solar eclipse). Eclipses do not occur everymonth because usually the sun, earth, and moon arenot exactly in line.

The universe is rich and varied. Among other thingsit contains rocky spheres like earth; globes largelymade of liquid and gas like Jupiter; bigger and hotterglobes of gas like the sun; huge numbers of otherstars much like the sunsome smaller and longer-lived, some bigger and shorter-lived; and groups ofstars. The universe also contains clouds of gas anddust. There is much other material in the universe aswell; but we have not yet observed it, and we knowvery little about it. Most objects we see are separatedfrom one another by vast, seemingly empty space.[Scale and Structure, Systems and Interactions]

A-1 What kinds of objects does the universe contain,and how do these objects relate to one another?

Grades Three Through Six

When we look at the stars at night, wesee themmoving westward in the sky. Some stars rise in thecast and set in the west. But some stars never set atall; they revolve in counterclockwise circles aroundthe pole star, never passing below the horizon. Welearn to identify stars by their positions with respectto their neighbors; these patterns are called constella-tions. [Patterns of Change]

Some of the brightest objects in the nighttime sky(aside from the moon) do not stay in the same placerelative to the neighboring stars. Instead, they moveslowly against the stellar background. These objectsare called planets. [Patterns of Change]

Although some planets are considerably brighterthan most stars, planets are easily mistaken for starswhen they are observed only once. By observing thesame planet every few nights for several weeks, wecan see that it wanders among the constellations. Likethe moon, the planets shine by reflected sunlight. Allplanets, including earth, orbit about the sun. It is very

The relative sizes of objects are not easy for students to grasp. It is important to make clear whichobjects (or systems of objects) are parts of which others. A visit to a planetarium or use of the smallplanetariums that many school districts own can be of great help in clarification as well as in conveyinga sense of excitement. (Scale and Structure]

Traditionally, the teaching of astronomy in the primary grades has been largely restricted to studies ofthe solar system. This a good start; but with the rapid increase in knowledge about the rest of the uni-verse, it is important to introduce broader concepts, even at the grades three-through-six level. Oursolar system is an example of systems all through the universe, but there are many other astronomicalobjects and phenomena in the universe. Students in the later primary grades can come to appreciate thatthe universe is a dynamic place at all scales of size and acquire some basic ideas about such centralmatters as stellar evolution, the history of the universe, and the place of the earth and of humankind in amuch larger environment. This approach avoids the artificial division of the study of astroaomy into"the solar system" and "everything else."

likely that other stars also have systems of planets,but these have not yet been ouserved directly. [Pat-terns of Change]

Our solar system is only a tiny part of the universe,but it is the part we know the best because it is thepart closest to us. Besides the planets, other objectsorbit the sun. These include asteroids, which aresmall rocky or metallic objects ranging in size from akilometer or less to almost a thousand kilometers,meteoroids, which are chunks of matter ranging insize from tiny specks to many tons; and comets,which contain large amounts of ice and other materi-als that vaporize 1. .o long tails when the cometscome near the sun. [Systems and Interactions]

Meteoroids that enter the earth's atmosphere getvery hot and glow as they fall; that is why they arecalled shooting stars. Only a very few of the largestmeteoroids actually reach the earth's surfacc, theserocky or metallic objects from spacc are calledmeteorites. [Scale and Structure, Patterns of Change]

A-1 What kinds of objects does tilt, .niverse contain,and how do these objects relate to one another?

Grades Six Through Nine

As far as we can tell, every object in the universerotates. These rotations are most directly visible inthe apparcnt motions of the sun, the moon, the

planets, and the stars through the sky. The mostmarked apparent motthnthe diumai (daily) mo-tionis a direct consequence of the rotation of theearth about its own axis. [Stability, Patterns ofChange]

The seasonal variations in the path of the sunth.ough the sky are a consequence of the revolutionof the earth around the sun. The axis of the earth isinclined at an angle of 23-112 degrees with respect tuthe poles of the solar system, and the orientation ofthe axis remains constant as the earth revolves aroundthe sun. Consequently, if we start at a given place onearth, we see the daily path of the sun vary throughthe seasons. The variation is greater at high latitudesand smaller at low latitudes. [Patterns of Change]

Astronomers have already discovered many kindsof fascinating objects. Astronomical objects come inmany different sizes, and some are parts of others.Globes of rock and of gas orbit around the sun (andvery likely around other stars) and around oneanother under the action of gravity. We call someorbiting objects planets and others moons or satel-lites; these terms tell how objects move, rather thanwhat they are made of. Our sun is a medium-sizedstar among many, many stars. Stars are often found ingroups called clusters (containing a dozen to a millionstars). Galaxies contain a billion to a trillion stars, 4Swell as huge gas-and-dust clouds. Our own galaxy,

Chapter 4Earth Sciences 81

Understanding the seasons requires students to shift their point of view back and forth from that ofanobserver standing on the earth and moving with it to that of an observer in space watching the earthmove about the sun. Many students have difficulty with this viewpoint. A model that students can ma-nipulate is extremely helpfulIt is important to correct the common misconception that the summer iswarmer than the winter because the earth is closer to the sun in summer. This happens to be correct forthe southern-hemisphere summer, but the northern-hemisphere summer occurs when the earth is rela-tively far from the sun. Variations in the sunearth distance have only a minor effect on climate.

theyilky Way, is a member of a cluster of a fewdozen galaxies called the Local Group. Among othercomponents of the universe are gas-and-dust cloudsand unseen matter. At every step in scaleclusters,groups of clusters, galaxies, and groups of galaxiesthere exists a variety of structures. A collection ofobjects at a given scale of size is called a system (e.g.,solar system). Study of the structure of a system canyield information about the history of the system.[Systems and Interactions, Scale and Structure]

Among the objects composing the universe, as-tronomers know the most about our own solar systembecause all its parts are relatively close to us andtherefore relatively easy to observe in detail. Planetsand other components of the solar system are so closeto us that we have already sent space probes to manyof them. Objects in the solar system are often classi-fied according to the way they move; planets orbitdirectly around the sun, whereas satellites orbitaround planets. The earth is a planet; the moon is asatellite of the earth. Asteroids, comets, and meteor-oids all orbit around the sun, much as planets do. Butthey are much smaller than planets and may haveorbits that cross planetary orbits.

The solar system is bound together by gravitation,the force of attraction that every body in the universeexerts on every other body. (See Chapter 3, SectionC, Force and Motion.) Larger astronomical systemsstars, clusters of stars, galaxies, and clusters ofgalaxiesare also bound by gravitation. Many starsare members of pairs called binary systems and orbitaround a common center under the influence ofgravity. Because the strength of the gravitationalforce can be calculated, it is possible to predict theorbits of planets and of their satellites with exquisiteaccuracy. [Stability]

82 Part IIThe Content of Science

Objects in the solar system may also be classifiedand studied in tenns of what they are made of andhow they were fonned. This tells more about theirroles in the solar system than their motion alone does.[Scale and Structure, Evolution]

It takes a substantial amount of scientific thinkingand observation, which often takes time, beforescientists understand new discoveries thoroughly. Inall probability most of the types of objects that theuniverse contains have not yet been discovered. Newobjects and new categories of objects are constantlybeing discovered. The past few decades have beenparticularly fruitful for such discoveries, and theycontinue at a pace that appears to be increasing.[Patterns of Change]

A-1 What kinds of objects does the universe contain,and how do these objects relate to one another?

Grades Nine Through Twelve

At every step in the scale of size, astronomicalobjects rotate about their own axes and revolve inorbits. Everything in the universe is made of the same

Astronomy is progressing at an extraordinaryrate. Consequently, sources more than five or tenyears old are likely to lack important information.

The stellar groupings we call constellations arenot necessarily groups of stars that are relativelyclose to each other. They only appear that way

from an earthly viewpoint.

94

kinds of matterfundamental particles, chemicalelements, and compoundsknown on earth, and allobey the same laws of nature that apply on earth. (SeeChapter 3.) [Stability, Energy, Systems and Interac-tions]

From our vantage point on earth, we try to learnmore and more about how the universe works, yetthere am still many important processes about whichwe know little or nothing. But we have built a theo-retical structure that provides a good working under-standing of the behavior of vast numbers of objectsand the relationships among them, and we have cometo understand many of the principles that underlie theworkings of the universe. [Evolution]

Star clusters, nebulae, galaxies, and clusters ofgalaxies are bound by gravity, the same force thatholds our solar system together. Because the strengthof the gravitational force can be calculated, it ispossible to pmdict how the stars in a galaxy willmove with respect to each other. Such calculationshave shown that there is much more matter than wecan observe. Thus, 90 percent of the matter in theuniverse is of an unknown natum. The task of detect-ing the as yet unseen matter by means other thangravity, and thus learning more about it, is majorproblem of modem astronomy. [Systems and Interac-tions, Stability]

The most pervasive force on the astronomical scaleis gravitation. Symmetry and regularity, so oftenfound in astronomical objects, usually arise from theaction of gravity and other forces, notably the electro-magnetic force. (See Chapter 3, Section C, Force andMotion; and Section F, Energy: Electricity andMagnetism.) [Scale and Structure, Stability]

Meteoroids (and occasionally asteroids and comets)can come close to planets much larger than they are,so that the gravitational force exerted on them by theplanets deflects them greatly. As a msult, thesesmaller bodies often have orbits that am less stablethan the orbits of planets. When a meteomid comesclose to the earth, it can be captured by the earth'sgravity and fall to the earth as a meteor, visible in thesky. Most meteors am quite small (typically the Si7Xof sand grains) and are vaporized under the action ofatmospheric friction long before they reach theearth's surface. Only the very largest meteors machthe surface, and their remains are called meteorites.[Stability, Systems and Interactions]

Astronomers not only discover new objects but also

95

High school astronomy has traditionally beentaught as an elective or as part of other sciencecourses, but this practice is changing. Newastronomy curricula for secondary students arebecoming available. Many of these curriculapresent astronomy in the context of the history ofscience, the understanding of planetary geology,and the development of mathematics and physics.

When a body is not too far from a much moremassive body, it orbits around the more massivebody, which is called its primary. The less mas-sive body is called the secondary. Planets orbitthe sun in this way, and satellites (moons) andrings orbit the planets. The motions are governedby the gravitat5nal force. Newton showed that,because the gravitational force conforms to aninversesquare behavior, the orbtt of everysecondary around its primary conforms toKepler' s laws:

I . The orbit is an ellipse, with the primary atone focus.

2. The line joining the primary and the secondary sweeps out equal areas in equal times.

3. When several secondaries orbit the sameprimary, the squares of their orbit periods(T) are proportional to the cubes of theiraverage distances (a) from the primary.

a 13 = T12

a 23 T 12

In this equotion the subscripts 1 and 2 refer toany two secondaries about the same primary.With a little extension, Kepler' s laws also de-scribe the motion of stars in their local clusters,of clusters in their galaxies, and of galaxies withrespect to one another.

Chapter 4Earth Sciences 83

=Moe

Studies show that a great majority of students atthe high school level retain misconceptionsabout phenomena that are often taught at theelementary and middle school levels. For ex-ample, asking students to explain why we haveseasons often evokes unusual ideas about theway the earth orbits the sun and how-light isabsorbed by the earth and other bodies.Thus;before the teacher begins a unit on stars or anyother topic in astronomy, he or she should askquestions to find out what students think aboutthe elementary concepts that underlie the unit.

create new themies and models. For example, it haslong been known that comets eventually "die" as theirices evaporate in the warmth of the sun. Where does anew supply of comas come from? Jan Oort proposedthat they come from a hugc- swarm of ice and dust,called the Oort cloud, beyond the outermost planetsof the solar system. This theory is now widelyaccepted, even though no one has directly obsetvedthe Oort cloud. This is because Oort's theory iscurrently the best explanation for why we see cometstoday.

Beyond the solar system are stars of many types.The appearance of a starthe amount and color ofthe light it emitsdepends mainly on two factors: itsmass and its age. Among the important types of starsare main-sequence stars with their many subtypes, redand blue giants, white dwarfs, neutron stars (amongthem pulsars), and stellar black holes. Closely relatedare the proto-stellar and post-stellar nebulae. Manystars arc most readily seen by the visible light theyemit; others emit mainly radio waves or X rays.Groupings of stars also have typical appearances.Among the types are open clusters, globular clusters,galaxies of many types including quasars, and galaxyclusters. Each system has a typical history. [Energy,Evolution, Stability, Systems and Interactions,Patterns of Change]

Because the nearest objects are the easiest toobserve, we know the most about them. More distantobjects may turn out to be more important in gaininga deeper understanding of the structure and history ofthe universe, but we cannot as yet obsetve many of

84 Part llThe Content of Science

them well enough to evaluate their importance. Theunseen-mass problem exemplifies how much we stillhave to learn.

How has the universe evolved?

Kindergarten Through Grade Three

When we look at the sky, we can see many types ofobjects. All of them are far away, but some of themarc much farther away than others. The object thatlooks very much the Imightest is the sun, which is thestar closest to earth. The sun gives us so much lightthat we cannot see anything else in th3 sky dming thedaytime, except sometimes the moon. The sun is inthe center of a systein that includes the earth andeight other planets, satellites (moons and tings),asteroids, comets, and so forth.

There arc many stars other than the sun. They arevery far away, but we can see many of them when welook up at the clear night sky. Many of these starsmay have planets as the sun does, but they arc so hardto see at such great distance that we have not yet seenany such planets. When the sky is clear and dark, wecan trace arrangements of stars (constellations andasterisms). [Scale and Structure, Systems and Interac-tions]

A-2 How has the universe evolved?

Grades Three Through Six

The setting point of the sun can be recorded eachday to find long-term patterns or change. Thesepatterns can help us to devise a calendar to mark theseasons.

We can make models to explain why the sun,moon, and stars seem to Ilse in the cast and set in thewest; why the moon goes through phases, and whywe have seasons.

Telescopes may be thought of as funnels thatcollect and concentrate light. Because the amount oflight that a telescope can collect depends mainly onhow big its main lens or mirror is, astronomers keeptrying to build bigger and bigger telescopes.

We have sent space probes to the earth's moon,several comets, and all but one of the planets. Won-derful photographs, videotapes, laser disks, and

96

planetarium programs are available that describethese space probes and richly illustrate what we havelearned about them.

A-2 How has the universe evolved?

Grades Six Through Nine

We learn about how the universe evolved bystudying astronomical bodies. With telescopes andother devices, astronomers measure where objectst.re, how they move, what they are made of, and howthey change. This helps us to reconstruct the earlyhistory of the universe. [Scale and Structure, Patternsof Change]

The universe is very old. Estimates based on theinformation currently available yield an age some-where between 18 and 21 billion years, though thatestimate may yet be revised to a greater age. There isstrong evidence that the universe "began" with acolossal explosion called the "big bang." (See Chap-ter 3, Section A, Matter.)

In the first million years or so, matter and energyevolved from forms now unfamiliar into forms weknow today. Prominent were the simplest gases,hydrogen and helium. The earliest stars condensedfrom this mixture. In condensing to form a star, thematter heats up until the nuclear fusion process canstart. Hydrogen nuclei fuse to foam helium nuclei,and energy is released in the process.

When a star having roughly the mass of the sub. orless has fused most of its hydrogena process thattakes billions of yearsit expands greatly andbecomes a red giant. It then quickly fuses nearly allof the remaining hydrogen over a much shorter periodand ends up as a white dwarf. While it is not certain,it appears that white dwarfs eventually cool down andbecome brr wn dwarfs; if this process occurs, it takesa long time. But stars more massive than the sun(roughly, more than two and a half times moremassive) die by exploding violently, producing thespectacular displays called supernovas. A supernovaspews much of its matter into the surrounding space,where it mixes with interstellar hydrogen and helium.Later generations of stars start with this enrichedmixture of hydrogen,telium, and more complexelements. Orr!' own solar system condensed in thisway about 4.6 billion years ago. Most of the hydro-gen and helium ended up in the sun and in the gas-giant planets (Jupiter, Saturn, Uranus, and Neptune).

9 7

The earth and similar objects nearer the sunMercury, Venus, Mars, and the mooncondensed attemperatures too high for hydrogen and other lightgases to condense. The matter accreting onto theearth transferred its energy of motion into heatenergy. This accretionary heat was the initial heat of

Most students are familiar with three states ofmatter: solid, liquid, and gas. Plasmas are afourth state of matter in which the atoms arebroken up into positively and negatively chargedparticles. A common example of a plasma is theglowing matter inside a neon light.Plasmas of awide range of densities exist in the universefrom thin interstellar clouds to the interiors ofstars.The Crab Nebula is a dramatic example ofa plasma. Electromagnetic forces are very impor-tant in governing the behavior of plasmas.

The distances to a few hundred of the neareststars can be measured by the parallax method.When we observe a nearby star twice at sixmonths apart, we see it from viewpoints that areabout 300 million km apart, because the earthmoves around the sun. As ct result, we see a slightshift in the position of the nearby star relative tostars much farther away. By measuring the shift,we can calculate the distance to the nearby star.Measurement of greater distances depends on avariety of other methods, which can be. cross-checked.

One method, devised about 1910 by HenriettaLeavitt, uses the so-called Cepheid variables. Theabsolute brightness of a Cepheid variable deter-mines its period, which can be readily observed.By measuring its apparent brightness, we candetermine its distance and thus the distance of itsneighbors. Still greater distances can be mea-sured by other methods, notably by means of thered shift.

Chapter 4Earth Sciences 85

A visit to a planetarium is very usefid in givingstudents a feeling fw- the scale, number, and

. variety of astronomical objects and distances.

the earth. During this period the matter differentiatedinto core, mantle, crust, aunosphere, and hydrosphereaccording to density. Dense material sank, and lessdense material rose, forming layers. Thecores ofearthlike planets are formed largely of metals, themantles are formed largely of matter less dense thanthe metals, and the crusts are formed largely of lessdense rocks. We live on the crust in the thin zonewhere the crust and its waters meet the bottom of theatmosphere, and our deepest wells have not yet dugall the way to the mantle. [Evolution, Scale andStrucnare]

Is there life elsewhere in the universe? At presentany discussion must be highly speculative. Neitherliving organisms nor the traces of extinct livingorganisms have been found to date on any of theplanets and moons we have visited with space probes.However, one can argue plausibly that life is possibleelsewhere. Although no planets have been defmitelydetected around other stars, there are vast numbers ofsunlike stars in the universe. Among the many planetsthey may have, there may be many having conditionsmuch like those on earth. On at least some of those,some kind of life may have evolved; the laws ofnature are the same everywhere in the universe. Atpresent, however, we know very little. If life existsoutside our solar system, we could probably notdetect it in the foreseeable future unless it includedintelligent beings who transmitted electromagneticsignals. There has been much discussion aboutwhether we could detect such signals. Searches forthem by NASA have been ursuccessful to date, butmore extensive efforts can be expected in.the future.In any case we cannot at present expect to have dircctcontact with any intelligent beings that may existbecause of the vast distances involved.

A-2 How has the universe evolved?

Grades Nine Through Twelve

The universe contains an immense quantity of thesimplest element, hydrogen, and a lesser but still

86 Part IIThe Content of Science

immense quantityof the next simplest element,helium. Because the universe is so large, the atoms ofthese elements are mostly spread out as extremelythin gases. However, there are places where the gasesare thick enoughthough still very thinto appearto us as clouds. When such clouds condense under theinfluence of gravitation, fusion begins and stars form.Stars contain very concentrated matter, and most starsare very hotmuch hotter than familiar flames. Starscome in a wide range of masses, from 1 percent or 2percent of the sun's mass (that is, a hundred timesbigger than Jupiter) to 40 or more times the sun'smass. [Evolution, Energy]

In the interiors of the stars, hydrogen fuses intohelium, and large amounts of energy are released.More massive stars fuse helium into many still morecomplex elements, releasing more energy. Theseprocesses are called nuclear fusion processes. Theenergy works its way to the surface of the star whereit radiates outward into space. This is how stars shine.In massive stars, fusion takes place much faster thanin less massive stars. Even though the massive starsbegin with more fuel, they run out of fuel much fasterthan the less massive ones. [Energy, Evolution,Stability]

The evolution of the galaxies is an important areaof study. When we look at the most distant parts ofthe universe that we can see with instruments, we seea part of the universe that looks rather different fromthe part nearer to us. The reason is that the light fromdistant parts of the universe has taken so long to reachus-10 billion years or morethat we see a sampleof what the universe was like a long time ago when itwas much younger than it is today. That is, looking atdistant objects is like looking back in time. A strikingfeature of the young universe is the very energeticgalaxies called quasars. Although the relationshipbetween quasars and the less distant galaxies that wesee by the light they have emitted relatively recentlyis not fully understood, the study ofquasars has con-tributed much to our understanding of the evolutionof the universe and is expected to contribute muchmore as we learn more about them. [Evolution, Scaleand Structure, Patterns of Change]

It has been known since the 1920s that the universeis expanding at a measurable rate. The major evi-dence supporting this understanding is the so-calledred shift. When we use spectrographs to look atdistant galaxies, we find that their spectra are shifted

CI 0../ (...)

toward longer wavelengths. The more distant thegalaxy, the greater the shift. This observation can beunderstood by an analogy. Imagine a balloon withsmall spots painted all over its surface. If the balloonis inflated, the spots will separate. The farther apartany two spots are, the faster they will separate. Wecan pmject the expansion backward, with propercorrections for gravitational and other effects. Whenwe do so, we find that the universe must have beenvery small about 20 billion years ago.

Will the universe continue to expand indefinitely,or will it reach a maximum size and begin to col-lapse? The answer depends on the total mass of theuniverse, which we do not yet know precisely enoughto make an answer. We do know, however, that theuniverse will continue to expand for a very long time,at least much longer than the time since the beginningof the universe.

The evidence supporting the big bang picture arisesfrom a variety of sources, but the most compelling isthe so-called 3 K background radiation. All models ofthe very early universe agree that during the firstthree minutes or so, light and other forms of electro-magnetic radiation could not travel very far withoutcolliding with matter that absorbed it. After aboutthree minutes, the universe had expanded and cooledto the point where it became transpamnt, and much ofthe light emitted by matter at that time has continuedto propagate without further collision with matter. Forthis reason the spectrum of the radiation preserves arecord of the temperature of the universe at the outsetof transparency. Because the universe continues toexpand, the radiation has been Doppler shifted (seeChapter 3, Section G, Energy: Sound) to the lowtemperature of about 3 K, which it displays today.

The rate of expansion, which has been known sinceabout 1930, makes possible a reconstruction of thesituation that existed at the onset of transparency.Many properties of the background radiation cannotbe explained by any plausible model other than the

41=1,1111011SMENINIMMI177KISI

big bang picture. Many versions of the big bangmodel have been proposed to explain the very earliestepochsback to 10-43seconds after the big bang.Explanations of the very earliest epochs of theuniverse art also explanations of the structure ofmatter a! its most fundamental level. However, muchwork remains to be done. Many aspects are highlyuncertain. And as with all science, the focus of thesemodels is on the mechanics, not on any notion offinal cause. [Evolution, Energy, Scale and Structure,Systems and Interactions]

How do we learn about the contents and structure ofthe universe?

Kindergarten Through Grade Three

Most astronomical objects are so far away that wecannot visit them; all we can do is observe them fmmafar. We can tell that the sun is far away, for example,by noting that it is sometimes hidden from view byclouds, so it must be farther away than the clouds.

A-3 How do we learn about the contents and structureof the universe?

Grades Three Through Six

Astronomers use telescopes to gather light fromdistant objects. Some telescopes are large spyglasses;others look quite different. Some telescopes measurekinds of light not detected by our eyes, such as radiowaves or X rays. Such telescopes look very differentfrom the more familiar ones that are designed to workwith visible light. For example, radio telescopes looklike large television dish antennas. They collect radiowaves from stars and other astronomical objects(these are naturally generated electromagmtic waves

The daily movement of the sun can be observed and recorded by marking the shadow of a wooden postset in the groundfrom time to time during the day. Each day that we can see the moon, we can record itsshape by drawing a picture of it. Both of these activities are astronomical observations from which moresophisticated conclusions can be drawn as the student grows older.

Chapter 4Earth Sciences 87

99

Many astronomical observations are accessible to stwients at this level through the use of simple equip-ment. For example, the setting of the sun can be observed every clear day, the time being noted with aclock or watch and a protractor being used to -estimate the angle between the setting point and someconvenient fixed object, such as a building. Long-term patterns can be discerned and models con-structed to explain the observations.Many photographs, videotapes, laser disks, and planetarium pro-grams are available to extend and enrich the observations and inferences the students have made bythemselves.

analogous to light, and not artificial radio signals).Analysis of these radio waves is analogous to analysisof visible light collected by optical telescopes, andthe information gathered complements the informa-tion gathered by optical astronomy.

Astronomers put their observing instruments wherethey can see best. Most telescopes are far frominterfering city lights, on top of tall mountains, wherethe air is clear and stable. Many instruments are putin spacecraft and launched into space, entirely abovethe air, to get the clearest possible view.

The first step in studying an astronomical object isto establish its location in the sky so that it can belocated again. When that task is done, it is possible tostudy how the object moves, allowing us to find outabout its distance and its relation to other objects.Most astronomers work at learning as much aspossible about the objects they are studyingtheirsize, mass, shape, composition, temperature, andother conditions. This information can then be used todetermine how the objects must have evolved tobecome as we see them now. [Evolution, Scale andStructure]

A-3 How do we learn about the contents and structureof the universe?

Grades Six Through Nine

Because astronomical objects are so far away, ittakes fine technology to extract as much informationas possible from the tiny amount of light that reachesus from them. Much ingenuity goes into designingequipment for catching, magnifying, and analyzingthe light. With the advent of spacecraft, it has becomepossible to detect light waves coming from the ob-jects that do not penetrate our atmosphere and couldnot previously be observed. [Scale and Structure]

88 Part IIThe Content of Science

Galileo first used a telescope to look at the sky in1609. There have been great improvements in tele-scopes since Galileo's earliest instruments. Throughthe nineteenth century, telescopes were improvedthrough the use of larger and batter lenses. In thetwentieth century the most powerful telescopes arebased on large mirrors rather than lenses. Because itis not practical to make good mirrors much largerthan those currently in use, the telescopes of the1990s use many relatively small mirrors, which areelectronically controlled to act together as one verylarge mirror.

Astronomers rarely search the sky at random. Theyalmost always try to obtain specific types of informa-tion and carefully design their obser:ina iristrumentswith that specific information in mind. That is -,vhyastronomers use so many different kinds of instru-ments. [Systems and Interactions]

Visible light is only one kind of electromagneticradiation. Other kinds, which have different wave-lengths, cannot be detected by our eyes. (See Chapter3, Section G, Energy: Light.) Astronomers usedevices to collect and analyze radiation of thesewavelengths, too, because information can be ob-tained that is not present in visible light. From thelongest to the shortest wavelength, the electromag-netic wavelengths useful to astronomers are calledradio waves, microwaves, infrared radiation, visiblelight, ultraviolet radiation, X rays, and gamma rays.Some of these forms of radiation penetrate theatmosphere poorly or not at all, and the observinginstruments must be launched into space. [Energy]

When an object is first discovered, very littleusually is known about it beyond its position in thesky and its brightness. A spectroscope attached to atelescope can be used to break the light (or otherradiation) into its component wavelength and analyze

1 0

it. The resulting informa!ion can be used to determinethe size of the object, its temperature, chemicalcomposition, pressure, linear and rotational speeds,amount of mapetization, and several other character-istics. When many related objects have been studied,it is often possible to compare their similarities anddiffemnces. Such comparisons can reveal how theobjects evolve and how they Mate to other categoriesof objects. [Stability, Scale and Structure, Systemsand Interactions, Energy]

A-3 How do we learn about the contents and structureof the universe?

Grades Nine Through Twelve

Astronomers am rarely able to manipulate theobjects they study, as is possible in other experimen-tal sciences. However, they can sometimes simulatethe conditions on those objects in the laboratory, orthey can use their observations to make predictionsabout further observations on the same objects ordifferent ones. The process of planned observation,theory building, prediction on the basis of theory, andfurther observation characterizes the scientificpractice of astronomy. In particular, astronomersdraw heavily on the theoretical structures and obser-vations of physics to carry on their work. Astrono-mers and physicists who carry out this type of workare called astrophysicists. [Systems and Interactions]

Spacecraft can carry instruments designed to makemeasurements and observations not possible withinthe atmosphere. Studying a few space missiors canteach much about devices and methods, accomplish-ments and limitations. Some missions on whichspacecraft have carried astronomical instrumentationhave been Apollo, Viking, Voyager 2, Giotto,Venera, and various space shuttles.

A wide variety of observational data, obtained frommany objects at many different times and places, canbe used to build theoretical models of the structure ofthe universe or some part of it. It is possible to inferhow the universe (or parts of it) has evolved over timespans that are vastly longer than the time over whichhuman observation has taken place. Computer model-ing has made possible much more detailed studiesthan were previously possible. [Systems and Interac-tions]

Astronomy is an interdisciplinary field. High-energy particle physics, chemiStry, geology, biology,

Capable of predicting solar and lunar eclipseswith remarkable accuracy, Mayan astronomers,like many around the globe, attained a high levelof astronomical knowledge. They could calculatethe average period of Venus' s synodic revolutionas well as determine the length of the year, thelength of seasons, and the length of a lunar month.Remnants of what appears to be a Mayan obser-vatory can still be seen in the stone ruins of Cara-col, in Chichen Itza on the Yucatan peninsula.

*--Att.0.**4.0 eachnig #0**101',.4-g:otii*Oni

intuaktfAtheneurfabataliowcd:t11.0***."'ervatnsmadc :0:60Xt**.#44-401):900,0**00.. óoftopApoinicd

.pastronqxñy and 4,*0:0.:*,_obiosiooliat aut.= ne-14.00;;*0becan a 4vo1orcqtt1 '44047'

::tre't'tn-4"44111ill'Off4ihtitotico-lis$0--;:4400hIctoio:

101: Chapter 4--Earth Sciences 89

electronics, optics, mathematics, computer science,space science, and a wide range of other technicalfields are applied to questions that astronomers askabout the composition, structure, and evolution ofouruniverse.

Astronomer is a general term .tat applies to scien-tists who focus their efforts on learning about theuniverse and objects in it. More specific terms thatapply to scientists in fields within or related toastronomy include astrophysicists, radio astronomers,cosmologists, planetologists, and exobiologists.

PLATE tectonics is the unifying theory of geologytoday. But only 40 years ago, this theory had nottaken shape. Sonie elements of it then proposed, suchas continental drift, were strongly disputed becauseno known mechanism could move the continents.Since about 1960, new evidence about tectonics hasaccumulated that has explained continental drift, aswell as the origins of mountain belts, earthquakes,volcanic activity, and deep oceanic trenches.

The earth's early evolution, perhaps even before thecrustal plates fonned, set the stage for the earth'sunique ability to support life. In that formative period,outgassing from the cooling earth released most ofthe water and gases that became the oceans and theatmosphere; later plate movements and their resultingvolcanic activity undoubtedly added more of each.The free oxygen in the atmosphere, upon which muchlife depends, was produced by photosynthesizinggreen plants in the early seas.

There are still many questions about how life firstevolved, about how mountain belts in continentalinteriors can be explained by plate tectonics, and whysome volcanoes occur well within the crustal plates,to mention just a few.

Two other very important building blocks ofastudent's geological education are the concept ofdeep time (the ancient age of the earth) and theprinciple of uniformitarianism. Small children, ofcourse, cannot grasp the vastness of time, and evenolder children may feel disoriented by the vast abyssof time through whidh the earth and its life havepassed. But deep time really is the backdrop against

93 Part llThe Content of Science

which geological and biological evolution haveoccurred. Uniformitarianism simply means that thelaws of nature have always been in operation as theyare now. It is a primary working assumption ofsdence as we approach questions of time and thepast; it is an affirmation of method and of empiricalreality that is necessary in order to draw any scientificconclusions at all.

B-1 How has plate tectonics shaped theevolution of the earth?

B-2 How are rocks and minerals formed,how are they distinguished, and howare they classified?

B-3 What is the history of the earth, andhow have geomorphic processesshapqd the earth's present features?

B-4 What are the responsibilities of humanstoward natural resources?

How has plate tectonics shaped the evolution of theearth?

Kindergarten Through Grade Three

The earth's surface has not always had itspresentform; it has changed over time. We can see thatmoving water, wind, and ice change the features ofthe earth, while beneath the surface more changes areconstantly occurring. Stress in the earth's crust,caused by the movement of the earth, is releasedthrough earthquakes and volcanoes. [Energy; Systemsand Interactions; Evolution]

B-1 How has plate tectonics shaped the evolution ofthe earth?

Grades Three Through Six

The earth is broadly differentiated into a crust,mantle, and core. Each is different in its composition,structure, and temperature. One result of thesedifferences is that the crust, which makes up thecontinents and ocean bottoms, floats on the moltenmantle and moves slowly on it. Because we have notyet drilled into the mantle and core, we learn about

11)2

People often think that continental plates are on the land and that oceanic plates are beneath the water.This is not strictly so. A great deal of formerly oceanic rock has been elevated onto the continentalsurfaces and gives us our best knowledge of ancient deep-sea deposits. Some plates straddle continentaland marine areas; for example, the North American plate extends from the western edge of NorthAmerica east to the submarine Mid-Atlantic ridge in the middle of the Atlantic Ocean.

the interior of the earth by recording and chartingenergy waves from earthquakes and other evidence.

As the earth moves through space, pressure buildsup inside the earth and is released. Earthquakes occuralong fault lines, which reflect the pattems of energyreleased from beneath the earth's surface. Earth-quakes often occur along a line that can be drawn ona map; this line helps us to recognize the edges ofcrustal plates and places where the crust is beingstretched.

Both the continents and ocean bottoms are dividedinto plates. Where different plates lie next to eachother, the plates may be slipping past each other indifferent directions, or one may be moving below orabove the other, or the two may be moving apart asnew material comes up from beneath the surface.[Energy, Systems and Interactions]

B-1 How has plate tectonics shaped the evolution ofthe earth?

Grades Six Through Nine

Plate tectonics is a name for crustal processes thatare driven by heat within the earth, where forces arecontinually shifting and releasing energy. Overgeologic time, tectonic forces have been responsiblefor all the major features of the earth's crust, frommountains and valleys to ocean floors and trenches.Tectonic processes such as plate movements andmountain building are the chief source of construc-tion and elevation of geologic features. These pro-cesses counter the constant destructive effects oferosion and weathering, which wear down surfacefeatures over time. [Energy, Patterns of Change,Evolution]

There are several lines of evidence by which weunderstand plate tectonics. First, there is structuralevidence: physical features that show us that pro-cesses tcok place (e.g., mountain ranges, volcanoes,

faults, uplifted plateaus, and so forth). Second, thereis geophysical evidence: measurements and recordsof stress, strain, and forces that cause movementswithin the earth (e.g., earthquakes and earthquakewaves, records of magnetic reversals in rocks withiron-bearing minerals). Third, there is paleontologicalevidence that indicates that the floras and faunas ofnow widely separated, climatically different conti-nents were once identical or nearly so; records ofmarine fossils from ancient ocean basins now sepa-rated by thy land provide us with similar conclusionsabout plate movements through time (continentaldrift, openings and closings of ocean basins, and soforth). [Energy, Evolution, Patterns of Change]

B-1 How has plate tectonics shaped the evolution ofthe earth?

Grades Nine Through Twelve

Plate tectonics is a unifying theory that explains awealth of evidence for large-scale geological changethrough time. The principal mechanisms of tectonics

Geologic and geomorphic processes and struc-tures should be distinguished. Geological proc-esses include the large-scale movements of platetectonics that contribute to the development ofmountains, valleys, and so forth. Geomorphicprocesses such as erosion and deposition sculptthese larger features into today' s surface featuresthat, for example, make the Rocky Mountains (arelatively young range) different in shape anddetail today from the older Appalachians, eventhough they were formed by the same geologicprocesses.

1)3Chapter 4Earth Sciences 91

The history of the development of the theory of continental drift is a classic example of how scienceworks. Since the 1500s explorers had noticed the match of the continental edges of South America andAfrica and had wondered about whether they had once fit together.

Alfred Wegener, the German meteorologist, is well known for proposing in the early 1900s three lines ofevidence that supported drifting continents: (1) the similarity of fossil records; (2) the continuity ofmountain ranges; and (3) the identical surface features from ancient glaciations, all on what are nowwidely separated continents. But although Wegener' s ideas were well accepted among scientists on thesouthern continents, geophysicists rejected the idea because there was no known mechanism to move thecontinents, plowing solid through solid.

Following World War II, with the wartime development of echo sounding, the sea floor was charted andits topography detailed. In the 1960s magnetic stripes, records of magnetic reversals, were discoveredin association with oceanic sea floor ridges. These stripes make symmetrical patterns on either side ofthe ridges; the stripes away from the ridges were found to be older. It thus became apparent that a newsea floor was being thrust up along the ridges and that the ocean floors were spreading away from thesegreat sutures.This discovery, perhaps more than anything else, was the evidence needed to support thereality of continental drift. With other concurrent discoveries, it led to the development of what we nowknow as plate tectonic theory.

92 Part 11The Content of Science

104

(thermoconvection) come from within the earth,whose interior is constantly changing and shifting asconvection currents within the interior move and heatis transferred from inside the earth to the crust. Thisbuilds up and releases energy. "onvection motion inthe upper mantle of the earth appears to drive themovement of crustal plates en the surface, andtogether they create mountain belts, earthquakezones, and volcanic belts. As a result, the surface ofthe earth is in constant change, both from causes thatlie within the earth and from the effects of solarenergy that drive the wind and ocean-current patterns.The direction that these winds and ocean currentsfollow is, in turn, governed by Coriolis force. [En-ergy, Patterns of Change, Systems and Interactions]

Surface features and processes that are manifesta-tions of tectonics include earthquakes, volcanoes,mountain building and plate collision, and seafloorspreading. [Patterns of Change, Evolution]

Continental and oceanic plates am distinguished bytheir densities (continental material is less dense) andtheir ages (older rocks are usually confined to conti-nental plates because the older oceanic rocks, whichare denser than continental rocks, have all beensubducted). For this mason, as far as we know, nooceanic plates are older than about 200 million years(Jurassic period):.[Evolution, Patterns of Change]

In addition to spreading centers (divergent plateboundaries; e.g., mid-oceanic ridges) and subductionzones (convergent plate boundaries; e.g., thePeruChile trench or the Himalayas), there are otherkinds of plate boundaries. Some former plate bounda-ries are seismically inactivu at present, yet at one timewere very active. In other boundaries, notably trans-form boundaries such as the San Andreas Fault,plates slide past each other with no significant loss ofland mass from either plate to the lower crust. Some-times, however, these boundaries are characterized byoccaSional large earthquakes. [Patterns of Change,Energy]

The past positions of the continents can be recon-structed by analyzing the magnetic orientation ofiron-bearing minerals in their rocks. When theserocks were laid down, their iron minerals assumedpositions marking the magnetic declination at thetime (that is, they pointed toward the magnetic polesof the earth, as fossil compasses). A magnetic needlewill point straight down over a magnetic pole andoccupy a horizontal position at the magnetic equator,

105

in between these points it will show varying degmesof inclination. As a rosult the vertical component ofthis inclination (magnetic dip) can be used to deter-mine the latitude (but not the longitude) at the timethe magnetic minerals were fomied or deposited.Such minerals also indicate that the earth's magneticfield has reversed many times through geologichistory. (The reasons for this are not entirely clear,but processes within the earth am the most likelycauses.) Data from these investigations have beenused to reconstruct the ancient positions of thecontinents. [Evolution, Patterns of Change, Systemsand Interactions]

How are rocks and minerals formed, how are theydistinguished, and how are they classified?

Kindergarten Through Grade Three

Rocks are made of minerals. Minerals are madefrom pure elements in the eanh that combine to forma great array of substances. Minerals are identified bykey characteristics, including hardness, color, andother features. [Scale and Structure]

Most rocks are combinations of several differentminerals, and they are formed in many differentenvironments. Some am formed under heat andpressure inside the earth. Some are laid down in wetand cool environments by water, wind, and ice. Somerocks am melted within the earth and cooled into rockagain. [Scale and Structure, Patterns of Change]

B-2 How are rocks and minerals formed, how are theydistinguished, and how are they classified?

Grades Three Through Six

Minerals vary in their hardness, crystal form, andcolor because they have different chemical makeups

Crystals have no power to heal, enhance energy,or reduce your electric bill; neither does waterwitching have any demonstrable scientific value;nor can animals predict earthquakes, thoughsome are more sensitive to the precursor wavesof earthquakes than humans are.

Chapter 4Earth Sciences 93

:..

Students should not be taught that there are three kinds of rocks. Instead, they should be taught theprocesses that explain the origin of rocks and the changes that rocks frequently experience after beinglaid down. Igneous and sedimentary rocks have different sources and enVironments of formation, butboth of these are subject to metamorphism; metamorphism is a process that resultsfrom increased tem-perature and pressure within the earth.

and because they form under different conditionswithin the earth. The internal crystal structure of amineral is unique, even though the shape and color ofa mineral can vary, deiniding on the conditionsunder which it was formed. [Scale and Structure,Patterns of Change]

Rocks are classified by how they are formed withinthe rock cycle fluid, which is the cycle of deposition,formation, and erosion of rocks. Rocks that were oncefluid within the earth (igneous) can be brought to thesurface and cooled (volcanic) or hardened within theearth (plutonic). Rocks that are forined on the earth'ssurface are laid down by wster, wind, and ice intosediments. Both igneous and sedimentary rocks canbe buried and affected by high temperatures, pres-sure, and hot fluids within the earth so that theirphysical structure and their chemical arrangement arechanged (metamorphism). [Scale and Structure,Energy, Patterns of Change]

B-2 How are rocks and minerals formed, how are theydistinguished, and how are they classified?

Grades Six Through Nine

Minerals are further classified by criteria of luster,crystal structure, cleavage, and their reaction tocertain chemicals. Minerals have ramy uses, fromjewelry to precision instruments, and are the sourceof all our metals. Rocks are used in paving, building,farming, and other industries. [Scale and Structure]

In addiiion to being classified by how they wereformed, rocks are classified by their mineral contents.Igneous rocks and sedimentary rocks generally havedifferent mineral contents. Igneous rocks are furtherclassified by their cooling historieswhether theycooled within the earth or on its surface, hovi quickly,and so on. Sedimentary rocks are largely made up ofparticles of other rocks. They are also composed oforganic remains and chemical precipitates. Sedimen-

94 Part 9The Content of Science

tary rocks are further classified by these components.[Scale and Structure, Energy]

Sediments become rocks mostly by compressionand cementation of their particles. Some rocks, suchas mudstones, aiv more consolidated by pressure thancemented; other rocks, such as sandstones, arecemented. The cement comes mostly from silicates,sulfates, carbonates, or iron oxid.3s that are dissolvedin water and fill spaces between the particles of thesediments. Pressure squeezes out most of the water.[Scale and Structure, Patterns of Change]

B-2 How are rocks and minerals formed, how are theydistinguished, and how are they classified?

Grades Nine Through Twelve

Because igneous rocks cool and solidify at differentrates, they are classified in part according to theconditions under which they were formed. This givesevidence of their sources and of the processes beneaththe earth's surface that extrude them. Sedimentaryrocks are further classified by the sizes of theirparticles. When rocks have undergone metamor-phism, whether they are igneous or sedimentary inorigin, they are studied and classified according totheir metamorphic structure, w.hich relates to theconditions and degree of alteration. Thus, importantinformation about metamorphic rocks includes theirmineral content and texture. [Energy, Scale andStructure]

/Ms

The properties that separate different forms ofminerals should be taught as manifestations ofcher.ical composition and energy bonds and theconditions under which such minerals were

formed in the earth.

Gravity causes all sedimentary rocks to be laiddown as nearly horizontal beds (except in structuressuch as talus slopes), conforming to the surface onwhich they rest. Through tectonic processes andmetamorphism, these layers may become com-pressed, warped, folded, fractured, or overturned.Their original depositional structures can be obscuredbecause the structure of the rock has been physicallyand chemically transformed. Erosion may removesome layers completely in some areas. [Energy, Scaleand Structure, Patterns of Change]

Almost all fossils are found in sedimentary rocks.Sedimentary rocks also provide evidenccof pastenvironments through analysis of their fossil, mineral,and organic content; their depositional structures(such as ripple marks); and their larger features (suchas cross-bedding). [Systems and Interactions, Evolu-tion]

Minerals have physical and chemical properties bywhich they am analyzed and classified. Bonds ofchemical energy give mineral crystals their physicalstructure, which can be altered by the cnergy of heatand pressure. The chemical and physical structure ofeach mineral is diagnostic; when these are altered, adifferent mineral is frequently formed. [Scale andStructure, Energy]

What is the history of the earth, and how havegeomorphic processes shaped the earth's presentfeatures?

Kindergarten Through Grade Three

The earth is very old. Through time, many changeshave occurred in its features. Mountains have beenelevated, worn, and washed away. Rivers have arisen,changed their course, and disappeared. Lakes andponds and continental arms of the seas have expandedand dried up. The earth's surface is constantlychanging. Through time, many different kinds ofplants and animals have lived on the face of the earth,and most of these are now extinct. [Evolution,Patterns of Change]

Geologists say, "The present is the key to the past."This means that we can observe the earth and its lifetoday to give us clues about how it was in the past. Itdoes not mean that things have always been as theyare today. Many things about the earth and its life

have changed through time. (See C,hapter 5, SectionB, Cells, Genetics, and Evolution.) [Evolution]

Mountains, valleys, plains, deserts, rivers, lakes,and oceans are all features of the surface of the earth.They are formed by the construction and uplift ofland by forces within the earth and by the processesof wind, water, and ice that wear down surfacefeatures over time. [Scale and Structure, Patterns ofChange, Evolution, Systems and Interactions]

B-3 What is the history of the earth, and how havegeomorphic processes shaped the earth's presentfeatures?

Grades Three Through Six

In an undisturbed sequence of rock strata, the oldestrocks are on the bottom, and the upper ones aresuccessively younger. Similar rock strata in differentareas can be compared and matchcd to demonstratethat they were laid down at the same time. Both thecomposition of rocks and their fossils can be used tomatch strata. [Evolution, Scale and Structure]

Through time many landforms have risen andsubsided, as the processes of uplift and erosion havecontinued to work. Different featums of the earthhave different ages: the high, craggy Himalayas areyounger than the low, rounded Adirondacks; parts ofthe Pacific Ocean seafloor are older than the AtlanticOcean seafloor. Many groups of living things ha' eevolved and become extinct. This sequence of changein living things, a result of the process of evolution,can be seen in the fossil record. Because differentliving things evolved at specific times in the past andthen became extinct, the presence of their fossils inrocks can tell us the age in which the rocks weredeposited. (See Chapter 5, Section B, Cells, Genetics,and Evolution.) [Evolution, Patterns of Change]

1 0 7

8-3 What is the history of the earth, and how havegeomorphic processes shaped the earth's presentfeatures?

Grades Six Through Nine

Uniformitarianism is the assumption that thechemical and physical laws of nature as we knowthem now have always been in operation. Throughthis assumption scientists are able to study patternsand rates of changes in the earth through geologictime and tc, see how they have differed. Uniformitari-

Chapter 4Earlh Sciences 95

The formation of the earth and its atmosphere isdiscussed in Section A, Astronomy.

nism does not imply that rates and processes havealways been the same as they are today. [Patterns ofChange, Stability]

The age of rocks can be measurtd by absolutemeans (radioactive decay of isotopes of variouselernents; each calibration is independent and usefulfor different ranges of time) and by relative means(comparisons of rock sequences, fossil assemblages,and so on). These methods provide the means to placegeologic events in a time sequence called the geo-logic time scale. [Evolution, Scale and Structure]

The history of the earth is marked by changes in sealevel and the uplift and subsidence of landforrns, theformation and breakup of continents, and the open-ings and closings of ocean basins. The piticipaldriving force of these changes is slow convection inthe earth's upper mantle. With these changes havecome changes in the flora and fauna that reflectdifferent environments in an area over time. [Systemsand Interactions, Patterns of Change, Evolution]

Soils are formed from the weathc ring of rocks andthe decomposition oforganisms. Soils can be charac-terized according to their chemical composition andphysical structure. Different kinds of soils are pecu-liar to different areas and owe their compositions tothe rocks that are in an area, the climate, and theorganisms in the area. The extent to which societiescan farm and develop agricultural resources dependson the properties of their local soils. [Scale andStructure, Evolution, Systems and Interactions]

Soils are part otthe rock cycle because they areformed from the breakdown of rock (and organicmaterial) and later may become lith,lied themselves.Soils in a region reflect their local geology anddetermine in part what kinds of plants can grow in aregion. [Patterns of Change]

Geographic features of the earth's surface aremanifestations of its geology. The topography of a

region; the content and mineral resources of its rocksand soils; its economic resources, transportationr.Tates, water sources, and potential for agriculture,fishing, and support ofdomesticated animals allultimately depend on geology. (See History-SocialScience Framework.) [Scale and Structure, Systemsand Interactions]

B-3 What is the history of the earth, and how havegeomorphic processes shaped the earth's presentfeatures?

Grades Nine Through Twelve

Uniformitarianism is the basic operating principleof historical geology. It affirms that the laws of theuniverse have always been in operation as they arenow, although natural rates and processes (such aserosional rates, which were surely altered by theevolution of land plants) may have differed in thepast. [Evolution, Patterns of Change, Stability]

The age of rocks and formations can be comparedby relative means (the comparison of rock sequencesarid fossil assemblages, called stratigraphy) or byabsolute means (radioactive decay, which can becalculated independently of the strata in which theelements are found and which depend only on chem-istry and physics). Isotopes of different elements areuseful for calibrating different ranges of time. Carbondating is useful only to about 50,000 to 70,000 yearsin the past, even with enhanced techniques. Bycontrast, rubidium-strontium dating is useful up toalmost 50 billion years in the past, although at a scaleso vast that it can be calibrated only to the nearestseveral billion years. For events in the more recentpast, carbon, potassium-argon, or uranium-leadisotopes are more useful. [Scale and Structure,Evolution, Stability]

The ancient environments of the earth can bestudied through sedimentologic analysis and throughpaleoecology. Through time, the movements of platesand changes in the configurations of bodies of waterhave had tremendous effects cin the evolution of lifeon earth, the geography of plants and animals, and the

Uniformitarianism should not be called "the law of uniformity" or "the law of uniform change."It implies neither uniformity nor uniform change, and it is not a law but a principle.

96 Part IIThe Content of Science1 I)

vMOO....,..The age of the earth and the growth of tlze geologic time scale are good examples of how scientificunderstanding evolves and is refined through time. It is instructive to show how Lord Kelvin's originalcalculations of the maximum possible age of the earth were too low because he assumed that the earth

had cooled uniformly from an originally molten state. He did not know thatradioactivity inside the earth

provided an important source of energy that invalidmed his calculations. When nuclear energy wasunderstood, Kelvin' s arguments were no longer va;td. Isotopic radiometric dating, based on the uni-formitarian principles of physics and chemistry, provides a set of independent time scales for the geo-

logic record.This is the source of absolute dates, which are complemented by the relative dates pro-

vided by fossils and stratigraphy.

vast changes in climates of marine and continentalareas. (See Chapter 5, Section B, Cells, Genetics, andEvolution.) [Evolution, Stability]

All of the biological processes of carth's lifedepend on the rock cycle, the water cycle, and thenutrient cycle of soils. Together, these cycles deter-mine the character and resources of earth's dynamicenvironment. [Patterns of Change, Evolution]

What are the responsibilities of humans towardnatural resources?

Kindergarten Through Grade Three

All resources used by humans, including fuels,metals, and building materials, ultimately come fromthe earth. Many of these resources are not in endlesssupply. They have taken many thousands and mil-lions of years to develop and accumulate. They mustbe used with care, conserved, and recycled. [Energy,Systems and Interactions]

B-4 What are the responsibilities of humans towardnatural resources?

Grades Three Through Six

Humans use air, fresh water, soil, minerals, fossilfuels, and other sources of energy that come from theearth. Some of these materials are nonrenewable; theycannot be replaced or can be replaced only at suchslow rates and under such rare conditions (e.g., fossilfuels) that they am for all practical purposes not

renewable at all. Therefore, their use must be seen asephemeral, and they must be conserved judiciously.[Energy, Systems and Interactions]

B-4 What are the responsibilities of humans towardnatural resources?

Grades Six Through Nine

Energy is often required to convert matter from aless useful into a more useful form for human needs;e.g., ore into metal, seawater into fresh water, and theretrieval and refinement of fossil fuels. (See Chapter3, Section D, Energy: Sources and Transfmmations.)Conservation and management of resources areethical and practical concerns involving pubac policyand individual responsibility. [Energy, Systems andInteractions]

Geological phenomena such as earthquakes andlandslides affect how people must plan their citiesand their uses of resources. Buildings, dams, andbridges must be constructed to resist earthquakes andshould not be situated on unstable soil or near activefault zones. This is also true for areas subject tolandslides. Public landfills must be planned responsi-bly to allow maximal use of the land once it isreclaimed. Toxic wastes buried in landfills adverselyaffect the groundwater supply and thus affect publicwater and public health. Improperly graded andsettled landfills arc unsuitable for building. Aque-ducts that run across fault zones should be designedto accommodate movement because earthquakes maybreak them and cause great waste of water. [Systemsand Interactions, Patterns of Change]

1 ;)Chapter 4Earth Sciences 97

4"17,140

8-4 What are the responsibilities cl humans towardnatural resources?

Grades Nine Through Twelve

Nonrenewable resources can be conserved throughcareful use, recycling, and-applicatioa ofenergy. Ifthe energy appliedin recycling and conserving comesfrom another nonrenewable source, then the effect isto trade one nonrenewable resource for another. If theenergyis taken from a renewable source or inexhaust-ible file fa practical purposes, such as the wind, sun,waterixt. ;er, or from nuclear energy, then a net gainin resources is generally made. [Energy, Systems andInteractions]

In addition to the potential slangers of earthquakesand landslides, soil types must be considered whenplanning houses and other buildings. Sedimentarystructures such as talus slopes and the "toes" of hillsare not suitable for buildings and should not beremoved. The angle of repose of beds is important toconsider. [Patterns of Change]

Environmental reclamation involves the need torestore mining sites, clean up oil spills, and dispose oftoxic wastes properly. These responsibilities alwaysaccompany the exploitation of natural resources.[Energy, Systems and Interactions]

The water cycle provides not only water in the formof precipitation (rain and snow); it is also the sourceof the eanh's groundwater resources. Much of theUnited States depends on gmundwater as its watersource.for humans and agricuhure. There isa finiteamount of fresh water on earth,.and many groundwa-ter sources are renewed at a slower rate than they areused, because their ultimate source is precipitation.The permeability and porosity-of rocks under thesurface determines groundwater movement andresources. The composition of these rocks also affectsthe mineral composition-ancithe quality of the waterfor human use. [Energy, Systems and Interactions]

,Sectian C Oceanography

IN the earth sciences, the disciplines of geology,oceanography, and meteomlogy are interconnected,and one should not be studied in isolation from theothers. The water cycle should be taught as a vitalpart of oceanography, as well as of geology and

98 Part 11The Content of Science

meteorology. The water cycle integrates the earth, air,and water components of the earth's surface environ-ments. Ocean water evaporates, condenses, andprecipitates over land and water. Movement of waterthrough rivers, lakes, and oceans recycles nutrients,nourishes living things, and sculpts the earth's surfacefeatures. Water is the single most important determi-nant of how life persists on earth. We have water onearth because of tectonic processes that released andcombined hydrogen and oxygen within the earth toform the original oceans and atmosphere. Gravityholds the atmosphere on earth, which in turn allowsthe water cycle to occur. This in turn controls theclimate and weather on the earth's surface. Therefore,meteorology is best presented as an extension ofoceanography and geology.

It is important for students to understand that solarenergy and forces within the earth and the earth'srotation are the basis for the circulation of oceanwaters and the water cycle. Much of eanh's secon-dary atmdsphere has come from outgassing, releasedby tectonic processes. Astronomers are interested inother planets that show signs of tectonic processes.The planets may have once had molten interiors andthus couldhave. held atmospheres and oceans capableof supporting life.

Other vital areas in oceanography are the structuresand environments of the ocean bottoms and theirhistories through time, the habitats and life that theoceans have sustained through time, and the composi-tion of the oceans' waters. There are many divisionsof oceanography, including biological, chemical, andphysical, but the study of oceans is interwoven withthe theory of tectonics and its ramifications for thestructure and evolution of the oceans.

C-1 What is the water cycle? How does thewater cycle affect the climate, weather,and life of the earth? How does wateraffect surface features of the land andthe ocean floor?

C-2 What are the oceans? What are theenvironments and topography of theocean bottoms? How do the oceanssupport life, and how have the oceansand their marine life changed throughtime?

1 10

C-3 How do waters circulate in the ocean,and how does this circulation affectweather and 'climate?

C-4 How.do humans Interact with theoceans? What may be some long4termeffects of humaninteractions with theoceanic, environment-0

What is the water cycle? How does the water cycleaffect the-climate, weather,.and life of the earth? Howdoes water-affect surface features of the land and theocean floor?

Kindergarten Through Grade Three

Rain, snow, hail,,and.sleet all come from clouds,which are made of water. This water cOmes mainlyfrom the oceans and rises into the air as water vaporwhen the sun evaporates water on the ocearf s sur-face. (Often, water can evaporate from the surfacesimply when the air is cooler or warmer than thewater, as when fog rises from a ,;ler, or when warmand cold air masses meet.) Most falls directlyback into ihe ocean. Much of the water that falls tothe earth's surface runs into rivers and streams thatreturn it to the oceans, where the cycle starts again.The-fresh water provided by the water cycle isnecessary to all terrestrial life on "earth. [Systems andInteractions, Patterns of Change]

C-1 What is the water cycle? How does the watercycle affect the climate, weather, and life of theearth? How does water affect surface features ofthe land and the ocean floor?

Grades Three Through Six

Precipitation comes from water vapor that con-denses in clouds when weather conditions are appro-priate. It provides the continental land areas with theirsource of fresh water, which plants and animals needto live. Water may be collected in natural waterwaysand reservoirs or tapped by wells from below groundsurface; but it all comes from precipitation. Thiswater may sink below ground, and it may also draininto streams and rivers That carry it to the sea. [Sys-tems and Interactions, Patterns of Change]

C-1 WhSt is the water cycle? How does the watercycle affect the climate, weather, and life of thearth?-flow -Coeswateraffect surface features ofthe lind.and-theCCean floor?

Gradei.Six Thrdugh Nine

Evaporation of water frem-the surfaces of theoceans is the principal source of the clouds that formprecipitation. Because the earth constantly rotates,these clouds circulate over the land surfaces ihpattenis that are affected by thetopography Of Idealregions..The oceans also affect ciimatebecause theyretain heat energy better than the air or the landsurfaces do. bifferences in the water, air, and landtemperatures cause the condensation of water vaporthat creates precipitation for the water cycle. Precipi-tation gradually erodes rocky surface features of theland, washes away soil, and redistributes it in rivers,lakes, and oceans, thereby creating new geologicalfeatures by erOsion arid depoSition. (See Section-13,Geology arid Natural Resources.) [Systems andInteractions, Patterns of Change]

Water evaporating from the ocears leaves mostsalts and particulate matter behind, and the evapo-rated water condehses into clouds. Precipitation fromthese clouds falls over land and water surfaces. Muchof the rain and snow that falls on continental surfacescollects in rivers and is returned to the oceans en-riched with nutrients. [Systems and Interactions]

C-1 What is the water cycle? How does the watercycle affect the climate, weather, and life of theearth? How does water affect surface features ofthe land and the ocean floor?

Grades Nine Through Twelve

The water cycle sustains the earth's land life, whichis in constant need of new supplies of fresh water.This cycle can continue became the earth's gravita-tional field holds the atmosphere on the planet. As theearth constantly rotates and the sun warms a portionof the earth's surface, differential conditions oftemperature and moisture are created and changed inthe atmosphere, causing ocean currents, winds, andevaporation, condensation, and precipitation of water.

Water vapor reacts chemically with gases andparticles dissolved in the atmosphere, and these areprecipitated along with water. (Acid rain is a harmfulby-produa of such chemical reactions.) As precipita-tion falls, its physical and chemical action on the

iii Chapter 4Earth Sciences 99

earth's surface features causes rock to erode anddissolve and soil to wash away. These effects areusually. gradual, but cataStrophic rates and events canalso occur during episodes of especially high precipi-tation. (See Section B, Geology andNatural Re-sources.) groded material it tOnsported to other landand water Surfaces, and also to the oceans, where itenriches themineral and nutrient content of nearshorewaters. It can also form deltas,,undersea fans, andother submarine geomorphic features.

The water cycle describes the flow of water throughevaporation, condensationintbclouds, and precipita-tion over.water and land, returning most water to theoceans: Additional water comes from melting of polarIce caps.:Enough water is stored in the ice caps to

produce large variations in ocean volume and sealevel through time; this has happened repeatedly inthe past. [Patterns of Change]

What are the oceans? What are the environmentsand topography of the ocean bottoms? How do theoceans support life, and how have the oceans andtheir marine life changed through time?

Kindergarten Through Grade Three

The oceans are vast bodies of salt water that coveralmost three-fourths of the earth's surface. Their

112100 Part 11.The Content of Science

deepest parts aredeeper than the highest mountains.[Scale and Structure]

The oceans are salty, unlike freshwater lakes andstreams. Many forms of life live in the oceans, mostlynear the shores...(See Chapter 5; Section A, Living'Things, and,SectiorrC, Ecosystems.) [Scale andStructure; Systems and Interactions]

Through time, many different kinds of life havelived in the oceans. Most of these forms are nowextinct. [Evolution]

C-2 What are the oceans? What are the environmentsand topography of the ocean bottoms? How dothe oceans support life,-and h.-Jw have the oceansand their marine tife changed through time?

Grades Three Thrcugh Six

Oceans cover three-fourths of the earth's surface,butcOmpared with the mass and volume of the wholeearth, they are really only-thin-films on_parts of theouter surface. The four largest oceans (Atlantic,Pacific, Indian, and Arctic) are connected, thougheach has its own features of water circulation, cli-mate, and marine life. The ocean bottoms are punctu-'ated by mountain ranges, active and extinct volca-noes, and deep trenches. [Scale and Stmcture]

The oceans are salty because of the salts that are-dissolved in ocean waters. Some dissolved compo-nents (such as nitrogen, silicon, calcium, and phos-phoms) and other minerals are used by marine life asnutrients and to build their skeletons. Marine organ-isms take in oxygen and carbon dioxide that aredissolved in sea water..(See Chapter 5, Section A,Living Things, and,Section C, Ecosystems.) Water iscycled through the earth's environments. Because theoceans contain most of the water on earth, there aremany forms of life that depend on the oceans. Theoceans have a profound effect on local Aveatherpatterns and general climatic conditions. (See SectionD, Meteorology.) [Systems and Interactions]

The oceans provide many different habitats formarine life, ranging from shallow shores and tidepools to abyssal depths. Characteristics of thesephysical environments, such as light, temperature,and proximity to upwelling areas, are primary deter-minants of the living communities that they support.(See Chapter 5, Section C, Ecosystems.) [Scale andStructure]

Over geologic time, the continents have movedwith respect to each other and to the poles. (See

Section 13, Geology and Natural Resources.) Forsome time until about 200 million years ago, a giantsupercontinent (Pangea) was composed of nearly allof the present continents and was surrounded by oneworld ocean. Today, the world oceans arc connected,but continental drift has separated the supercontinentPangea into several continents. As the continentshave drifted, new oceans have formed, and newspecies of marine life have evolved and filled them.Marine life has evolved through time as the oceanshave changed. (See Section B, Geology and NaIuralResources', and Chapter 5, Section B, Cells, Genet-ics, and Evolution.) [Evolution]

C-2 What are the oceans? What are the environmentsand topography of the ocean bottoms? How dothe oceans support life, and how have the oceansand their marine life changed through time?

Grades Six Through Nine

The surfaces of continents and the bottoms ofoccaris conipose-great pieces of the earth's outer crustcalled plates. Ocean waters dever the oceanic crustcind parts of the continental margins. Along thecontinental margins am shallow waters rich withnutrients. Where ocean plates meet continental plates,trenches form on active margins where subduction isoccurring. Mountain ranges (e.g., the Andes) canarise from this interaction. The ocean bottoms arestreaked by, mountain ranges, trenches, and faultzones where plates meet. Like continents, the oceanicplates have been continually moving through time.Active and extinct volcanoes mark undersea "hotspots" where molten material from the earth's interiorescapes to the surface. (See Section B, Geology andNatural Resources.) [Scale and Structure, Systemsand Interactions]

Oceans are large masses of salt water that retainheat much longer than air or smaller bodies of freshwater do. They tend to moisten air that passes overthem and moderate the air temperature. This air inturn moderates the temperature of continental mar-gins. (See Chapter 3, Section A, Matter.) [Scale andStructure, Systems and Interactions]

Chemical components in the oceans have comelargely from the earth's crust and upper mantle,mainly by volcanic activity. Some of these compo-nents (containing mainly chlorine, sodium, magne-sium, sulfur, calcium, and potassium) contribute tothe shells of marine organisms and are recycled into

113 Chapter 4Earth Sciences 101

The oceans have alwaysbeen salty, because salts and other minerals and compounds were part of thecrust of the earth when the primordial ocean was formed. As water goes through the water cycle, thesecompounds are left in the sea-and not carried in the evaporation of ocean water. Therefore, the ques-tion iS.not "Why are the oceans salty?" but rather "Why aren' t snow, rain, rivers, and streams salty?"The answer is that-evaporation leaves the salts behind.

the 'waters and ocean sediments when these organ-isms die. [Scale and Structure, Patterns of Change]

Within the oceans are many kinds of environmentsthat support ecosystems of marine organisms. Theseecosystems crirbo classified according to the depth ofthe enviromnent (tidal, subtidal, abyssal, and so

-forth): Like terrestrial ecosystems, they have theirown fOod chains and webs. The primary producers ofthe Wean are microscopic plants in the plankton;these form the base of food chains of planktonicherblVores and carnivores, as well aS larger inverii-brates and vertebrates. The flow of nutrients andenergy in the-ocean is concentrated around continen-

ial-margins andnear the surface of the ocean. Someorganisms also 'hie at the deep ocean bottom, wheremostofthem gain energy from the constant rain offecal matter and-dedaying plankton from the surface.Much of the ocean is nutrient poor and sparse of life.(See Chapter 5, Section A, Living Things, andSection C, Ecosystems.) [Scale and Structure, Sys-tems and Interactions, Energy, Patterns of Change]

The ocean floor, like the continents, is made up ofcrustal plates, but the oceanic crust is slightly denserthan continental crust. Through time, these plateshave been moved as new material has been pushed upfrom the upper mantle. As the surface plates havemoved;.some ocean-basins-(e:g., the Atlantic) havebeen opened. The shapes and positions of the conti-nents and oceans have changed remarkably throughtime. (See Section B, Geology and Natural Re-sources.) [Evolution, Patterns of Change]

The sea level and the volume of ocean water haverisen and fallen frequently through geologic time, andtectonic processes and glaciations have controlledthese Patterns. These changes have had great effectson marine life and on land climates. Many differentkinds of marine animals that used to be very numer-ous and diverse, such as the ammonites and trilobites,are now extinct. Their ecological roles have been

102 Part IIThe Content of Science

taken up by other kinds of animals. [Evolution,Systems and Interactions

C-2 What are the oceans? What are the environmentsand topography of the ocean bottoms? How dothe oceans support life, and how have the oceansand their marine life changed through time?

Grades Nine Through Twelve

Sea levels have fluctuated through time. (SeeSection B, Geology and NaturalResources.) Becausecurrent sea levels are relatively high, the continentalmargins are covered with ocean water. Beneath thewaters are various kinds of geomorphic features.Where rivers empty into oceans and seas, submarinefans may form that are similar to or extensions ofdeltaic fans. These environments are generally richwith nutrients. In the deep sea, submarine canyons,abyssal plains, and oceanic islands are among thefeatures composing the topography of the ocean floor.[Scale and Structure]

Ocean waters are rich in minerals and salts. Thesesubstances have always been present in the oceans,and new material is constantly but slowly added-byextrusion of additional material from the earth's_-interior-at-rifting-zone-S." alidirom runoff of materialfrom the earth's land surfaces. [Systems and Interac-tions, Patterns of Change]

Various chemical elements are cycled through theskeletons of marine animals and plants, and these inturn produce biological nutrients that are cycledthrough marine ecosystems. Additional minerals andnutrients reach the oceans through runoff from landas water returns to the oceans through rivers. [Scaleand Structure, Systems and Interactions, Energy,Patterns of Change]

Ocean environments are of two general types:coastal and open water. Environments in coastalwaters are generally characterizcd by their depth and

114

, _AummomP111111111111

distance-from the shore (tidal, subtidal, littoral, ,and soforth). Depending on local topography, wave energy,arittmitrient richness, ecosystems may host reefcommunitiesrburrowing comMunities, and a varietyof ePifatinal.inyertebrates. Open-water ecosystemsare gerierallyliniiteiliby their organisms' need forlight: phytoplankton,need light to manufactureenergy; ancrother OrganismSfeed on-them andcontintiethe,foOd:chains-and webs of the open ocean.BeloW4hout 290 ineiers, productivity declinescOnsiderablY.. The-ocean floor supports communities.that are-ftieled.by the detritus that rains constantlyfrom *ye...Other abyssal communities-live neardeep-sdayents and are supported by geothermal-rather thair solar. energy. [Systems and.Interactions,

BAIPNA.At-the-end:of the Paleozoic era, all the continents

Were-Merged into the supercontinent Pangaea. Nearthe end:ofthe Triassic periOd, about 200 million yearsAgo; the.AdantieOccanpegan to ferm by the riftingof conthlental plates;.this rifting.is still occurring, andthe Mid7Atlantic ridge remains an active source ofseafloor, extension. The Tethys Sea, separating themerthern and southern centinents, began to develop-shortly thereafter. The Red Sea is an exaMple Of ayoung ocean in an early stage of extension. ThePacific, Indian, and Arctic oceans are similarly scoredwith the reconk of ancient movements and faults. Itis difficult to reconstruct the histories of the oceansbefore 200 million years ago because the oceanbottom from earlier times has been subducted. (SeeSection B, Geology and Natural Resources.) [Evolu-tion]

Marine communities, like their individual organ-isms, have evolved through time. (For example,clams have replaced brachiopods as the main epifau-

11111

During the Mesozoic era, shallow seas coveredmuch of Europe and North America. Ichthyo-saurs, plesiosaurs, and mosasaurs were amongthe top predators, but these now-extinct formshave been replaced in their ecological adaptivezones by large fishes, porpoises and dolphins,sharks, and whales. Many such examples illumi-nate the history of marine life.

nal filter feeders; corals have replaced sponges andmdistid clams, as the.pkincipal reef builders.) Verie-brates evolved in the oceans, probably in the Cam-briari period;in the Devenian period, they firstinvaded* land. Some fishes, such as sharks, havechanged little since.the-Paleozoic era. Others, like theray-finned Mlles, have diversified remarkably. Manyinvertebrate groupsrincluding clams, snails, corals,arid arthropods; have-also dive:sified in many ways.The invertebrate marine life of the past is the bestrepresented sector of the -fossil record. (See Chapter5, Section B,tells, Genetics, and EvOlution.) [Evolu-tion]

How do waters circulate in the ocean, and how doesthis circulation affect weather and climate?

Kindergarten Through Grade Three

Water in the oceans moves because the motion ispowered by the sun's energy; the earth rotates andreceives solar energy that drives the winds. Wavesart one kind of movement we can see in the oceans.Water in the oceans is always moving; and as its coldand wami layers move, their temperatures affect thetemperature and moisture of the air that passes overthe oceans and onto the land. As the atmospheremoves, different air masses collide or mix. This inturn causes patterns of climate and weather on land.The temperature difference also causes wind. (SeeSection D, Meteorology.) [Systems and Interactions,Patterns of Change]

C-3 How do waters circulate in the ocean, and howdoes this circulation affect weather and climate?

Grades Three Through Six

Cold water, like cold air, sinks because it is denserthan when it is warm. As it sinks, warmer water risesto the surface. Water also circulates because the earthrotates, and the force of this rotation causes move-ment of surface waters. The earth receives more solarenergy in tropical areas and less at the poles; thiswarming differential caves ocean water circulation.Tides are caused by the gravitational pull of the moonand sun on the earth.

I I 5Chapter 4Earth Sciences 103

1

The oxygen isotope ratio in marine shells can beused to -constructa record of the variation ofoceanic temperatures through time.

As ocean water circulates, its temperature affectsthe temperature of the air-above it. This createspatternS of climate and weather when this air movesover land. Movement of the atmosphere causesdifferent-air Masses to collide or mix. This, in turn,causes weather on land. Plgces near the ocean oftenhave more moderate climates than places slightlyinland..But such areas are often prone to hurricanesand other Oceanic storms. (See Section D, Meteorol-ogy.) [Systems and Interactions, Patterns of Change]

C-3 How do waters circulate in the ocean, and howdoes this circulation affect weather and climate?

Grades Six Through Nine

Waters circulate piimarily because of winds andsolar heating. The_direction that-these currents followis caused by the earth's rotation. Solar heat alsocauses cycles of water convection. As-the earthrotates, its ocean waters circulate past the continentsin patterns that determine global climatic conditionsbecause air that passes over oceans often is warmer orcooler than air that passes over continental surfaces.(For example, the Atlantic Gulf Stream gives Londona milder climate than Buffalo, New York, eventhough London is farther north. In the same way, SanFrancisco's waters are usually colder than those*outside New York City because the California currentmoves from north to south, whereas the eastern GulfStream nms from south to north.) (See Section D,Meteorology.)

Ocean tides are caused mainly by the gravitationalpull of the moon on the earth. The gravitationalattraction of the sun also affects tides; this varies withgnvitational attraction over the span of a year and isespecially strong when the sun, moon, and earth arealigned in one plane. The sun-earth and earth-moonrevolutions am not synchronized, but each is regularin its timing; consequently, especially high and lowtides can be predicted by calculating the times at

104 Part II--The Content of Science

which the sun and moon together will exert thestrongest and weakest effects on the earth. [Systemsand Interactions, Patterns of Change]

C-3 How do waters circulate in the ocean, and howdoes this circulation affect weather and climate?

Grades Nirge Through Twelve

Waves are phenomena of water movement gener-ally caused by wind; they may also be produced byearthquakes, undersea landslides, volcanoes, or othergeological activity. Tides are predictable, periodicfluctuations of ocean waters caused-by the gravita-tional attraction of the sun and the moon on the earth.The surface circulation of the oceans is priMarilycaused by Coriolis processes, whereas deep oceancirculation is caused mainly by the difference indensity between wanner and colder waters. Becausethe earth rotates, surface currents flow in closed loops(gyms) that move clockwise in the Northern Hemi-spham and counterclockwise in the Southern Hemi-sphere. [Systems and Interactions, Energy, Patterns ofChange]

The oceans moderate climates on land. The reasonsfor this effect include (1) the high heat capacity ofwater, which can warm or cool air that then passesover land; (2) the mixing of surface waters by wavesand currents; and (3) the evaporation of water fromthe ocean's surface. Long-term weather patterns canbe caused by oceanic disturbances, such as the Pacificoscillation and the associated El Nino phenomena.[Systems and Interactions, Energy, Patterns ofChange]

How do humans interact with the oceans? What maybe some long-term effects of human interaction withthe oceanic environment?

Kindergarten Through Grade Three

People use the oceans for fishing and collectingfood, swimming and boating, transportating peopleand products, drilling for petroleum, and collectingminerals. They also dump waste materials into theoceans.

I61

C-4 How do humans interact with the oceans? Whatmay be some long-term offects of human

interaction with the oceanic environment?

drades Three Through Six

Water iS essentiato all forms of life. Humans usethe Oceans for food, energy, minerals, and medicine,.and dispbsal of waste.

C-4 Hew do'humans interact with the oceans? Whatmay be some long-term effects of humaninteraction with the oceanic environment?

Grades Six Through Nine

The oceans are frequently used as a dumpingground for waste materials. Disposal of toxic wasteshave caused environmental problems and, unlesscarefully regulated, can threaten the future of muchmarine life. Pollutants carried into oceans and lakesaffect living things and need to be controlled byindividual behavior and public policy.

The ocean basins are also a source of fossil fuels(petroleum), which can be retrieved from depositsbeneath the continental shelveS. The benefits of thesefuels may be offset by the cost of retrieving them andby the hazards to coastlines, shipping, and marine lifeposed by oil spills and other accidents. Like otherfossil fuels, submarine resources are nonrenewable.

C-4 How do humans interact with the oceans? Whatmay be some long-term effects of humaninteraction with the oceanic environment?

Grades Nine Through Twelve

If humans am to continue using the oceans asrepositories of waste material, they must have athorough understanding of ocean currents, conditions,marine ecology, and marine geology. Marine msourcemanagement includes an understanding not only ofscience but also of sociology, economics, ethics, andgovernment

As in freshwater ecosystems, marine eutrophicationoccurs when the natural nutrients that contain nitratesand phbsphates become concentrated, encouragingalgal blooms. (In current usage, eutrophication refersto the inadvertent nourishing of algae in lakes to thedetriment of other living things.) Some algal bloomsare toxic to marine animals. Eutrophication is often

117

Energy consumption in America is on the rise,according to the U. S. Department of Energy(DOE), In order to keep domestic petroleumproduction at its current levels, we will need 32billion barrels of new oil reserves by 1995.Throughout the 1980s, California legislatorsfought off numerous attempts to open offshoreleases for oil exploration along envirohmentallysensitive areas. The DOE estimates that as muchas 60 percent of the crude oil still to be discov-ered in America will come from public lands, and56 percent of that amount is likely to be fromoffshore drilling. Because oil reserves have bothdomestic and strategic value, future voters will befaced with the important task of weighing the en-vironmental consequences of their energy deci-sions. These informed decisions will requirevoters to have a deep knowledge of all forms ofenergy supplies and to examine thoroughly theenvironmental impacts associated with thedevelopment and use of each energy source.

caused by sewage outfalls and runoff from fertilizedlawns and fields that deposit high concentrations ofnutrients into waterways.

Occasionally, heavy metals (e.g., mercury) accumu-late to abnormally high levels in the tissues of shell-fish living in coastal waters polluted by industrialwaste. These minerals become concentrated in thehigher levels of food chains and have at times poi-soned humans who have consumed contaminated fishand shellfish.

Fishing for marine invertebrates, fishes, andmammals in international waters requires interna-tional cooperation and agreement. Cultural differ-ences in the use and harvesting of these resources hasbeen a frequent source of misunderstanding anddispute. International agreements should be guided bya thorough understanding of marine ecology andecosystems and by realistic biological predictions ofhow such populations should be managed, used, and

Chapter 4Earth Sciences 105

prevented from becoming extinct. (See theDepartment's History-Social Science Framework.)[Systems and Interactions, Patterns of Change]

:METEORCLOGY is the study of our atmosphere andWeather. AlthOugh meteoroloists have long collecteddata on the earth's surface to predict weather patterns,the advent of weather satellitet vastly increased theirability to monitor the earth's atmosphere and alert thepublic not only of impending dangers (e.g., hurri-eants)but also of long-term atmospheric perturba-tions such as ozone depletions and increases in car-bon dioxide. Further systems analysis of the-complexintéractiorisbetween earth's masses of air, water, andland may yield insight into the kinds of efforts thatmust be undertaken to mitigate disturbing globaltrends (e.g., atmospheric warming and pollution).

0-1 What are the physical bases of theearth's clIniate and weather?

D-2 What are the major phenomena ofclimate and weather? What are thelarge- and smzil-scale causes ofclimate and weather?

D-3 How are we affected by weather? Howdo we predict it? How can we alter it?

What are the physical bases of the eart'sclimate and weather?

Kindergarten Through Grade Three

We live on the surface of the earth,surrounded by ablanket of air called the atmosphere, which we need

to live. We breathe the air of the atmosphere; wedepend on the atmosphere for rain. Rain falls fromclouds, which consist of tiny particles of water or ice.Clouds are made to move by the wind. Sometimes wecan see a cloud grow bigger or smaller. [Patterns ofChange]

The earth is warmed by heat from the sun. It isusually wanner in the daytime than at night. It isusually warmer in summer than in winter. The earthis not so close to the sun that we boil, nor so far fromthe sun that we freeze. [Patterns of Change]

Most of the earth is covered by the water of theoceans. The sun heats the water, which is continu-ously evaporated into the atmosphere to form clouds.Clouds may move a long distance before producingprecipitation. Water falling on the ground may soakinto the ground or flow immediately into streams andrivers. Eventually, the water finds its way back to theocean. [Systems and Interactions],

D-i What are the physical bases of the earth's climateand weather?

Grades Three Through Six

The sun heats the waternear the surface of theoceans. The water holds the heat a long time, releas-ing it very slowly. Colder air moving over the wateris warmed by the water. Warm air is less dense thancold air and cold air moves in, pushing the warm airupward. As the air rises, it cools and descends again.This cycle is the "engine" that drives the winds.Warm winds passing over cold regions tend to warmthem. In many places, the wind blows from the samedirection much of the time (prevailing winds).[Patterns of Change, Systems and Interactions]

Warming of the atmosphere results, among otherthings, in formation of regions of nonhomogeneouspressure. The variation of atmospheric pressure canbe measured with a barometer. Meteorologistsdepend on a network of thousands of stations atwhich the the atmospheric pressure is measured atregular intervals. The results arc displayed on weather

AN/Mk 1110.,

The discovery and careful charting of jet stream winds is an a ;hievement of the past halfcentury.Airplanes make much use of jet stream winds, riding them downstream and avoiding them upstream.Taking advantage of jct stream winds can be worth a considerable detour.

106 Part llThe Content of Science 118

maps. Air tends:to move from high- to low-pressureregions. [System's and Interactions]

Because the earth is round, sunlight falls on parts ofitmear.dreequator.more intensely than on parts nearthe poles. Generally-speaking, the equatorial regionsare warmer than the polar regions. [Stability]

The earth's axis is inclined with respect to the planeof its orbit. As a result, the region of most intensesunlight moves northward and Southward over theyear. At the same time, the length of the day varies.Taken together; these effects determine the seasons.When it issurrimer in the Northern Hemisphere, it iswinter in'the Southern Hemisphere. (See Section A,Asubrionly).[Patterns of Change]

Climate is die daily and seasonal weather that apartieular region experiences over a period of time.Climate isdescribed as the average conditions and theextrenies-that have been experienced by the region.-[Scale and Structure]

The.earth's atmosphere consists of a mixture ofgases. About four-fifths is nitrogen, and most of therest is oxygen,-which has an essential role in.lifeproceSses. The-atmosphere also contains Small butsignificant amotints of other gases. Carbon dioxideand water yapor are.the most important, both forclimate and for life. Nearly all of the atmosphere lieswithin about 50 kilometers of the earth's surface.[Scale andStructure, Stability]

Water constantly evaporates-from the earth'ssurface, the bulk of it from the oceans. The water istransported as vapor-by the winds, often over longdistances. The vapor forms clouds that releaseprecipitation as rain, snow, and other forms. Most ofthe precipitation falls back into the ocean, but somefalls on land: Some of the water falling on land soaksin to form groundwater. Depending on geologicalfonnations, groundwater may stay where it is for longperiods, or it may percolate quickly over considerabledistances, or it may reappear at lower points on thesurface as springs that feed streams and lakes. Muchgroundwater is returned to the atmosphere as vaporthrough the process of transpiration in plants. Thisprocess is especially important in rain forests andaffects weather and climate. Runoff water goesdirectly to streams, which coalesce into larger streamsand rivem. Most rivers flow into the oceans; someflow into deserts and are completely evaporated.[Patterns of Change]

When water evaporates, it changes from the liquidto the gaseous state, and we cannot see it. When air

Change in temperature is both an importantweather effect and an important cause of weatherchanges. Systematic temperature measurement isvital to understanding weather. Galileo was thefirst person to measure temperature quantita-tively, about 1592, but the first reliable ther-mometers were made early in the eighteenthcentury by Gabriel Daniel Fahrenheit. Ile took00 to be the lowest temperature he could achievewith an ice-salt mixture and 1000 to be his wife' sbody temperature. Because there are 100 degreesbetween these two fixed points, Fahrenheit' sscale is a centigrade (100-degree) scale. Fahren-heit soon found that his fixed points were notreadily reproducible and shifted to the freezingand boiling points of water. In order to keep thenew scale compatible with his old one, he as-signed the value 32° to the freezing point and212° to the boiling point. The modern Celsiusscale is also a centigrade scale, but the chosenfixed points are more reproducible.

containing water vapor cools, the vapor condensesback into the liquid state. (See Chapter 3, Section A,Matter.) This liquid water forms tiny droplets or icecrystals that make the air opaque. When this occurson the ground, we call the effect fog. When it occursabove us in the air, we see the result as clouds.[Patterns of Change, Systems and Interactions]

D-1 What are the physical bases of the earth's climateand weather?

Grades Six Through Nine

The overall temperature of the earth is determinedlargely by two factors: its distance from the sun andthe properties of the atmosphere. If it were too closeto or too far from the sun, the earth would be too hotor too cold to support life, regardless of other condi-tions. But within these broad limits, the propert;es ofthe atmosphere are very important in determininghow much of the heat of the sun is retained by theearth and how much is reflected. [Stability]

119 Chapter 4Earth Sciences 107

Success in agriculture depends heavily on closeundgrstanding and exploitation of microclitnates.Farmers,have known for millenia, for example,that frost will damage crops in a hollow whencrops grown on the hillside above escape frost,or that fruit will mature on trees on hills facingsouth while it does not ripen on neighboring,northward-facing hillsides. The California grape-growing industry has benefited greatly from newand.more detailed understanding ofmicrocli-mates all over the state.

Most students are aware of the dramatic climaticdifferences between the California coast, theCentral Valley, the mountains, and the high andlow deserts. California students may not beaware that these wide variations over relativelysmall distances are atypical and result largelyfrom the prevailing westerlies blowingfrom theocean over a series of mountain barriers. Studyof weather maps will reveal that Midwesternclimate, for example, varies signcantly onlyover much larger distances.

The hottest part of the summer usually comes afterthe day when the sunlight is most intense and the dayis longest. TIfis is because it takes time to warm theearth and the sea. Similarly, the coldest part of thewinter usual; comes after the day when thc sunlightis least intense and the day is shortest. Because wateris heated so slowly, the delay is longest on parts ofthe land near the ocean; these parts have a coastalclimate. In the middle of the continents, far from theocean, the delay is shorter, and the extremes oftemperature are greaten these parts have a continentalclimate. The range of coastal climates depends verymuch on the direction of the prevailing winds .and thepresence of mountains. [Scale and Structure]

The atmosphere is divided roughly into severallayers. The lowest layer, the troposphere, is theregion where most weather phenomena take place.The stratosphere (above the troposphere) is less

108 Part IIThe Content of Science

turbulent but has some effect on weather. [Scale andStructure]

Most clouds,form in the troposphere. Cloudsconsist of tiny water droplets, or ice crystals, or acombination of both. Water vapor condenses aroundtiny particles in the air into these forms. Such par-ticles can be made of dust, or sca salt, or othersubstances. [Patterns of Change, Scale and Structure]

Differences in temperature between regions lead todifferences in barometric pressure. These pressuredifferences cause air to flow from high- to low-pressure areas. We call this flow wind. The greaterthe pressure difference, the stronger mc wind. How-ever, air masses do not flow in straight lines fromhigh to low pressure. Because the earth rotates, forceis exerted on the moving air in a direction perpen-dicular to its motion (Coriolis force). As a result,moving air masses follow a curved path. In theNorthern Hemisphere, air masses circulate clockwisearound high-pressure areas and counterclockwisearound low-pressure areas. The opposite is the case inthe Southern Hemisphere. These circulating airmasses interact with one another in a complicatedway that can be seen on a weather map. Weatherthe short-term variation of temperature, humidity,winds, and barometric pressure, among other things,in any given placeis a result of the details of theseinteractions. [Systems and Interactions]

Winds can be influenced by many things. Near thesurface, trees and buildings cause winds to break upinto a complex of irregular, twisting eddies. Theseeddies can cause the wind speed and direction tofluctuate rapidly. [Patterns of Change, Systems andInteractions]

Land breezes and sea breezes occur because theland warms up faster than the sea in the daytime andcools faster at night. In the daytime, for example, airrises over the warmer land, and cooler air rushes infrom the sea. Valley winds and mountain winds arccaused by a similar temperature difference. Down-slope winds flow down mountains, warming due tocompression as they sink. [Energy, Systems andInteractions]

On a larger scale, winds constitute the generalcirculation of the atmosphere. Prevailing winds arethe westerlies of the temperate zones, the trade windsof the tropics, and the polar easterlies. Between thewesterlies and the adjacent trade winds lies a regionof variable and frequently weak winds called the

1 2 0

horse latitudes. Between the Northern and Southernhemisphere trade winds arc the doldrums, whemsailing ships have often spent weeks in stifling heatwaiting for wind. Prevailing winds arise from thelarge-scale warming of air near the equator andcooling near the poles. [Scale and Stmcture, Systemsand Interactions]

Cold'air is generally associated with high pressure;and warm air, with low pressure. The equatorial"low" and the polar "high" are Tairly stable and donot move much; they influence the earth's weather ina fairly predictable way. The same is true of otherimportant highs and lows. [Stability, Systems andInteractions]

When large air masses migrate, the leading edgescan produce very strong winds. At an altitude ofabout 9 km, jet streams can form, and jet streamwinds can travel over 100 knots and occasionallyover 250 knots. [Patterns of Change]

DescriPtion of climate depends on the size of thearea whose climate is to be described (global climate,mesoclimate, microclimate). (Scale and Structure)

Global climate is governed by the intensity andvariation of sunshine with latitude, by the distributionof land and water, by ocean currents, by prevailingwinds, by areas of high and low atmospheric pres-sure, by mountain barriers, and by altitude. [Stability,Energy, Systems and Interactions]

The earth's atmosphere has not always been thesame as it is today. The earth was formed mom thanfour billion years ago from interstellar matter consist-ing largely of hydrogen and helium. During theformation of the earth, most of these light gasesescaped, leaving the earth with little atmosphere.Gases trapped in the intcrior at the earth's formationor produced by chemical reactions within the earthwere probably expelled at the surface. This process,called outgassing, resulted in a second atmospheofrom which today's atmospitem evolved. It is prob-able that the composition of these gases was similarto that emerging from volcanoes today: water vapor,85 percent; carbon dioxide, 10 percent; the rest,Mostly nitrogen with a variety of other more complergases such as ammonia and methane.

Much of the carbon dioxide in the second atmos-phere dissolved in rainwater and was transported tothe oceans. Through various chemical (and laterbiological) processes, this carbon was locked up insedimentary rocks such as limestone, which is a form

In 1785 Henry Cavendish carried out a measure-ment of the nitrogen and oxygen content of theatmosphere and found that he could nct accountfor about 1 percent of the total. A centuty was toelapse before the major constituent of this resi-due, argon, was discovered. Cavendish' s re-searches spanned a wide range; among otherthings, he was the first to isolate hydrogen andthe first to measure the universal gravitationalconstant in the laboratory.

of calcium carbonate. With much of the originalwater and carbon dioxide removed, nitrogen becamethe main constituent of the atmosphem.

Ultraviolet light from the sun, acting on watervapor, produced oxygen and hydrogen by a processcalled photodissociation. Most of the hydrogenescaped to space, leaving the oxygen behind. How-ever, the preponderance of the evidence indicates thatthe bulk of the oxygen in the modem atmospherearose from photosynthesis by primitive green algaeand similar photosynthesizing organisms. Photosyn-thesis consumes carbon dioxide and releases oxygen;the presence of photosynthesizing plants thuschanged the composition of the atmosphere in adramatic way. The present-day atmosphere consistsof about 78 percent nitrogen, 21 percent oxygen, andabout 1 percent of argon, carbon dioxide, other tracegases, and water vapor. [Evolution, Systems andInteractions, Patterns of Change]

D-1 What are the physical bases of tho earlh's climateand weather?

Grades Nine Through Twelve

Most of the light energy from the sun arrives at theearth in a range of wavelengths to which the clearatmosphere is fairly transparent. However, clouds areeftbctive in reflecting a large am..ant of energy backinto space, The overall temperature of the earth isinfluenced greatly by this proportion. Snow canreflect as much as 95 percent of the solar radiationthat strikes it; clouds, on the average, about 65 per-

121 Chapter 4Earth Sciences 109

Analysis of global warming trends is extremelyimportant, but it may be necessary to take signifi-cant action before the final results of scientificstudy are in. The risk lies in the possibility that itmay be too late to avoid serious consequences ifaction is delayed and it turns out that the currentprojections are confirmed. This is an excellente.xample of a problem having scientific contentthat must be decided on the basis of a variety ofsocial, economic, and political as well as scien-tific considerations.

cent; forests, from 3 percent to 10 percent. Theoverall average for the earth is about 30 percent. Theearth's heat balance is crucial; because the amount ofradiation from the sun is closely constant, any reduc-tion in energy radiated back to space increases theaverage temperature of the earth Over a year theaverage temperature varies by only about 0.1°C. Anyeffect that substantially exceeds this variation canresult in major climatic changes over the earth.[Energy, Systems and Interactions]

SunEght that reaches the surface is absorbed by theland and the water. When the land and water arewarmed, they reradiate energy upward at infraredwavelengths, longer on the average than the wave-lengths of incident light. The atmosphere is somewhatopaque to the reradiated energy and retains much ofthis radiation. The more that is retained, the warmerthe earth is, on the average. The opacity of the atmos-phere is affected by the presence of water vapor,carbon dioxide, ozone, methane, and ot.',er gasespresent in smaller amounts. The process of heatretention is called the greenhouse effect because theglass of a greenhouse acts in very much the same wayas the atmosphere in keeping the interior warm.[Energy, Systems and Interactions]

Considerable energy is required to evaporate water.Conversely, energy is released when water vaporcondensfs; thus, transfer of water from the sea via theair to semeplace where precipitation occurs involvesconsiderable transfer of energy as well as water. Thisenergy transfer is very important in weatherpro-cesses. The chinook phenomenon is a dramatic

110 Part ItThe Content of Science

example of release of energy stored in water vapor.Rising over the upwind slope of a mountain range,the air expands as the pressure decreases. Its tempera-ture does not decrease because heat is supped to theair as condensation of water vapor occurs, usuallywith precipitation. Descending the downwind side ofthe mountain range, the air compresses and warms,ending with a temperature considerably higher thanits temperature when it began to ascend the upwindslope. [Energy, Systems and Interactions]

Water vapor also affects the movement of air.Because the molecular weight of water is less thanthat of dry air, humid air tends to rise when sur-rounded by dry air at the same temperature. [Systemsand Interactions]

Climate has been observed and recorded at leastsince the time of the ancient Greeks, who recordedthe number of days of sunshine per year more than2,000 years ago. Humans create their own climatemodifications by building cities. Urban heat islandshave been known and studied formore than a cen-tury. There is evidence that air pollution can influ-ence the precipitation pattern over an area. [Systemsand Interactions, Stability]

Even the global climate may be changing as a resultof human activities. The observed increase in averagetemperatures over the past decades may be due toincreased quantities of greenhouse gases in theatmosphere. However, confirmation and quantitativeanalyses ait very difficult because other importanteffects not under human control are present. Amongthese effects the most notable is the sequence of iceages dating back at least as far as the Pleistocene, orabout a million years, whose traces have been care-fully analyzed. Nevertheless, there is a need for morestudy to evaluate the threat of current human activi-ties. [Systems and Interactions, Patterns of Change]

What are the major phenomena of climate andweather? What are the large- and small-scale causesof climate and weather?

Kindergarten Through Grade Three

The surface of the earth has cold and hot places.The land and water masses near the North and Southpoles are cold almost all the time because they

11r)a. 4 Zs

receive little sunlight. The air is warmed or cooled bythe land or water it is near. There are places on theearth that arc too hot and dry for people to livewithoitt water, or too cold for people to live therewithout shelter. Different places areyann and wet,warm and dry, cold and wet, and cold and dry. [Scaleand Structure]

Weather changes all the time. We see clear skies,clouds, rain, and snow; hot and cold days and nights;and calm and windy days and nights. Short-termweather changes are superimposed on more generalseasonal thanges. In California, it rains more in thewinter than in the summer, but this is not true every-where. [Systernsond Interaction, Stability, Patterns ofChange]

0-2 What are the major phenomena of climate andweather? What are the large- and smah-scalecauses of climate and weather?

Grades Three Through Six

When air is waimed and rises, it is replaced byneighboring air that rushes in. The resulting horizon-tal flow is called wind. There are winds that affectlarge parts of the earth (like the westerlies), and therearc winds that affect only small regions (like seabreezes). The mtation of the earth and friction betweenthe air and the surface affect the way in which the airflows. [Patterns of Change, Systems and Interactions]

When a mass of warm air moves into a cooler area,the leading edge is called a warm front. When a massof cold air moves into a waimer area, the leadingedge is called a cold front. [Scale and Structure]

Clouds are classified according to a standardscheme. To begin with, there are high, middle, andlow clouds; these terms refer to altitude above thesurface. The quantitative distinction among these

terms depends to some extent on the latitude. Inmiddle and low latitudes, high clouds generally formabove 6000 metres. Because the air is always yerycold and dry at this altitude, high clouds are almostalways thin and almost always made of ice crystals.Middle clouds have their bases between about 2000and 7000 metres; they usually consist of water dmp-lets, sorhetimes with some ice. Low clouds have theirbases below 2000 metres. They are almost alwayscomposed of water dmplets, except in cold weather,when they may contain ice and snow. [Scale andStructure]

Clouds are divided according to form into threemain classes: cirrus, cumulus, and stratus. Furtherdistinctions are made by means of such prefixes asalto- (high) and nimbo- (rainbearing). Types ofclouds have suung associations with types ofweath2r. [Scale and Structure]

0-2 What are the major phenomena of climate andweather? What are the large- and small-scalecauses of climate and weather?

Grades Six Through Nine

In summer, the warm water of tropical seas warmsthe air strongly, transferring much energy to the air.The result is a weather pattern involving very strongwinds and much rain (a tropical storm, a hurricane, ora typhoon). On a smaller scale, there are thunder-storms, caused when wann air is pushed up forcefullyby neighboring cold air. The stmng turbulence andrapid cooling result in heavy rain. The strong frictionproduces electric charge and results in lightning.Lightning is dangerous, and there are safety rules tofollow when lightning is near. Thunder is producedwhen a lightning flash quickly heats a small amountof air to a very high temperature. The air expands

Students should be encouraged to study the weather map in the daily newspaper on a regular basis andto view videotapes of a good television weather-map sequence, with frames frozen as necessary. Bystudying a series of maps on a daily basis, students can stt. the shon-term changes in weather; bycomparing different geographic areas, they can understand climatic differences; by comparing maps inefferent seasons, they can learn about the effect of seasonal changes on weather. However, weather is athree-dimensional phenomenon that cannot be completely represented on a weather map.

123 Chapter 4Earth Sciences 111

suddenly. After the flash the hot air quickly cools andcontracts. The two rapid movements are the source ofloud sound called thunder. You can tell how far awaya lightning flash is by counting the seconds betweenthe flashInd the thunder. Each three seconds corre-spond roughly to one kilometer. [Energy, Systemsand Interactions]

Some regions of the earth, called source legions,are consistent producers of large masses of warm orcold, dry or humid air. Major source regions at highlatitudes are arctic ice and the snow-covered plains inwinter. At low latitudes there are subtmpical oceansand hot desert regions. Air masses originating inthese source regions migrate and interact in middlealtitudes. The boundary between two air masses ofdifferent barometric pressure is called a front. Be-cause the pressure difference is due to temperaturedifference, the temperature usually varies considera-bly across a front. The humidity often varies as well.[Scale and Structure, Stability, Systems and Interac-tions]

Even though fronts appear as lines on weathermaps, they are boundaries that extend vertically aswell as horizontally. They are of four types:

1. A stationary from, which moves very little.2. A coldfront, which brings a considerable temper-

ature change over a short horizontal distance andis accompanied by changes in relative and abso-lute humidity, shifts in wind direction, pressurechanges, and clouds, often with precipitation.

3. A warm front, in which the wanner, less denseair rises over the cold air, producing clouds andprecipitation well in advance of the surfaceboundary of the front. The vertical slope of awarm front is much gentler than that of a coldfront. Precipitation is usually cold or moderateand covets a wide area.

4. An occludedfront, which results when a coldfront overtakes a warm front. The oncomingcold air mass may push the warm air upward,producing drastic temperature changes and oftenviolent weather, or the oncoming air mass maynot be much colder than the warm air and mayride over the warm air. This results in extendedunsettled weather. [Scale and Structure, Systemsand Interactions]

Hurricanes are storms with winds exceeding 64knots that form over the tropical waters of the world.

112 Part IIThe Content of Science

The temperature in a hurricane is usually above 26°C.Hurricanes are seasonal, occurring mainly in summerthrough autumn and usually from between 5° and 20°latitude. At higher latitudes not enough energy isavailable; at lower latitudes, the Coriolis force is notgreat enough to confer the characteristic powerfulspin on the storm. Friction between air and sea is animportant factor in the organization of hurricanes.[Energy, Panerns of Change]

Ocean currents arise from warming of seawater bythe sun and from frictional drag of the surface waterby the prevailing winds. Ocean currents are muchslower than winds but cany much more heat. Thetemperate climate of northern Europe, for example, isdue to the warming effect of tropical water carriedacross the Atlantic Ocean from the Gulf of Mexico bythe Gulf Stream. The California coast is cooled by thesouthward-flowing cold water of the Japan current.[Energy, Scale and Structure, Stability]

Long-term variations in ocean currents haveimportant economic effects. In the case of the south-ern oscillation or El Niflo, the prevailing cold currentoff the coast of South America is deflected. Theresulting warming of the water has disastrous effectson the important fishing industry, and the warming ofthe air suppresses rainfall, with equally disastrouseffects on agriculture. It is becoming evident that theEl Niflo phenomenon is only one part of a muchlarger pattern involving the entire Pacific Ocean. Asimilar phenomenon of smaller magnitude is onlynow coming to light in the smaller Atlantic Ocean.[Scale and Structure]

0-2 What are the major phenomena of climate andweather? What are the large- and small-scalecauses of climate and weather?

Grades Nine Through Twelve

Energy from the sun drives atmospheric circulation,whose pattern is very complex. In general, however,the winds in the upper atmosphere are westerlybecause of the rotation of the earth. However, theflow is not constant; it breaks up into eddies (cy-clones and anticyclones) that transfer heat andmomentum from equatorial to polar regions. [Energy,Patterns of Change]

Jet streams of various types arise from strong,large-scale tempera:we differences. The tropical

124

easterly jet stream arises from the summer heating ofland masses to temperatures that are higher than ths;neighboring oceanic temperatures toward the equator.Strong polar westerly jet streams, called the strato-spheric polar night jet streams, arise in winter fromthe normal temperature difference between lower andhigher latitudes. [Scale and Structure]

Jet streams have an important influence on themotion of fronts because air masses tend to bedeflected by jet streams, which themselves curveunder the action of the Coriolis force. Highs aredeflected generally southeastward; and lows, gener-ally northeastward. [Systems and Interactions]

When the jet stream bends, a wave deVelops in thefonn of a trough of relatively low pressure at lowerelevations and ridges of relatively high pressure athigher elevations. When an upper-level trough islocated to the west of an area of low pressure at thesurface, horizontal and vertical air movements resultin the fonnation of storms at the surface, driven bythe rising of warm and the descent of cool air. [Pat-terns of Change]

The amount of water vapor contained in air isdescribed in terms of the specific humidity and therelative humidity. The specific humidity is the ratioof the mass of water vapor contained in a quantity ofair to the total mass of the quantity of air. Relativehumidity is the quantity most frequently used inmeteorology and is often misunderstood. The maxi-mum amount of water vapor that can be contained ina given quantity of air depends very sensitively ontemperature. A small increase in temperature leads toa considerable increase in this maximum. Relativehumidity is the ratio of the amount of water vapor ina quantity of air to the maximum amount of watervapor that the air.can contain at the same temperature.As the temperature of a mass of air increases, itsrelative humidity rises rapidly. When the relativehumidity reaches 100 percent, further removal of heatleads to condensation of some water. For this reasonthe temperature at which a given sample of air attains100 percent relative humidity is called the dew pointif its value exceeds 0° C and the frost point if itsvalue is lower than 0° C. [Patterns of Change, Energy]

When warm unstable air rises in an unstableenvironment, a thunderstorm is born. The immediatesource of the instability may be uneven surfaceheating, or the effects of topography, or the lifting of

Relative humidity is measured with an instrumentcalled a hygrometer. Several varieties of hygrom-eters exist, including the convenient but not veryaccurate hair hygrometer, the wet-dry bulbthermonwer, and its variant, the sling psychrom-eter. (Systems and Interactions)

Clouds form when water condenses from air thatis cooled below its dew point. The condensationalmost always occurs on tiny airborne particlescalled condensation nuclei, whose sizes rangefrom about 0.2 micrometer to 1 micrometer.Although the air may look clean, it almost alwayscontains plenty of condensation nuclei; typicallythere are 100 to 1,000 per cubic centimeter. Evenwhen the air is dry, these particles often show upas dry haze. (Scale and Structure)

warm air along a frontal boundary. [Energy, Systemsand Interactions]

More severe thunderstorms form along fronts.There may be numerous storms in a line, and theymay produce high winds, large damaging hail, heavyrains that can cause flash flooding, and even toma-does. [Patterns of Change, Systems and Interactions]

Major ocean currunts do not follow the windsprecisely, though they are affected by the winds andby the Coriolis force that.affects the winds as well.Currents flow in semiclosed circular whirls calledgyms. [Stability, :kale and Structure]

In the North Atlantic, the prevailing winds blowclockwise and outward from the subtropical high,while the ocean currents flow in a more or lesscircular clockwise direction. As the water movesbeneath the wind, the Coriolis force deflects the waterto the right in the northern hemisphere. As a result,the surface water moves generally at right angles tothe wind. [Systems and Interactions]

As ocean currents transport warm water away fromits source, there is upwelling of cold water frombelow. The interaction of this cold water with the airhas profound effects on weather and climate. [En-ergy, Systems and Interactions]

3. 2 5 Chapter 4Earth Sciences 113

How are we affected by weather? How do we predictit? How can we alter it?

Kindergarten Through Grade Three

Weather forecasting is difficult Meteorologists arequite accurate in their predictions about two days intothe future. Over longer times, forecasting rapidlybecomes less reliable. [Patterns of Change]

Scientists have experimented with various ways ofchanging the weather, especially to make it rain.[SystemS and Interactions]

Severe weather can produce great damage bymeans of winds and floods. [Systems and Interac-tions]

0-3 How are we affected by weather? How do wepredict it? How can we alter it?

Grades Three Through Six

Forecasting weather is very important becausemuch of what people do is detennined by theweather. Forecasting beyond a few days is veryuncertain, but with sophisticated computer technol-ogy and better data-gathering networks, meteorolo-gists will probably be able to do a better job offorecasting for a longer time in the future. However,it is doubtful that meteorologists will ever be able topredict in advance the weather patterns for an entireseason. [Patterns of Change]

Severe weather can produce great damage. In someparts of the world, hurricanes are frequent Hurri-canes do damage mostly through their very strongwinds and by means of the surges of seawater theypush into coastal areas. Tornadoes, though very local,have even mom powerful winds than hurricanes andproduce severe, though localized, damage. Heavyrainstorms do damage largely through flash flooding.Lightning-caused fires sometimes do great damage,especially in forests. [Systems and Interactions]

Because particular types of clouds are stronglyassociated with types of weather, clouds are useful inshort-term weather forecasting. Puffy white cumulusclouds are associated with fair weather. Sometimes,cumulus clouds that are small in the morning growinto towering cumulus in the afternoon and produce

114 Part IIThe Content of Science

Becauk water condenses on airborne particles,scientists have tried to induce rain by seedingclouds with fine particles. One method involvesseeding cold clouds, which already contain waterdroplets at temperatures belowbut not too farbelow-0° C. The water is supercooled; that is, itdoes not freeze. Freezing can be induced byintroducing tiny crystals, such as silver nitratecrystals, which resemble ice crystals. As thisfreezing process progresses, crystals are formedthat are large enough to fall. To date, the resultsof seeding are uncertain, although some coun-tries have successfully sued others for "stealing"their rain through the seeding process. [Systemsand Interactions]

rain showers. Further growth into cumulonimbus mayresult in thundershowers. [Scale and Structure]

D-3 How are we affected by weather? How do wepredict it? How can we alter it?

Grades Six Through Nine

Clouds can indicate whether the local atmosphere isstable or unstable. When the atmosphere is stable, avolume of air that is raised or lowered tends to returnto its original position. When the atmosphere isunstable, a volume of air that is4-aised or loweredtends to continue in the same direction. Unstableatmospheres are associated with updrafts, downdrafts,turbulence, and precipitation. [Scale and Structure,Stability]

0-3 How are we affected by weather? How do wepredict it? How can we altor it?

Grades Nine Through Twelve

When a mass of air rises to regions of lowerpressure, it expands. If (as often happens) it does notexchange significant heat with neighboring air, itcools. Similarly, descending air warms. As long asrising air does not cool to its dew point (reach satura-

126

don), its temperature drops at about 10°C for everykilometer of rise. If the rising air cools to its dewpoint, water vapor condenses and clouds form.[Energy, Scale and Structure, Stability]

The droplets of water or ice crystals in clouds areso small that friction with air limits the speed of theirfall to negligible values. In order to fall as rain, thedroplets must grow to much larger sizes; the typical

raindrop is 0.5 mm in diameter and contains as muchwater as a million cloud droplets. Under properconditions, the droplets can coalesce as they collide,or they can collide with ice crystals and contribute tothe growth of the crystals. Once a raindrop of icecrystal is big enough to fall, it collides with smallerraindrops in its path and continues to grow. [Scaleand Structure, Systems and Interactions]

127 Chapter 4Earth Sciences 115

thapor 5

We Sciences

Secoon A Living Things

In previous frameworks the topic Living Things wasdivided into separate sections on plants, protists,animals, and human beings. Although it is feasible toseparate curricula into these component parts (andmany teaChers prefer instructional materials that doso), the present framework is designed to emphasizethe continuity and comparability of living systems,their components, needs, and histories. In this way

-the concepts of integrative themes are stressed.Whichever format is used, it is essential to show thatclassification of living things is based on evolution,because evolution explains both the similaritiesamong living things and the diverse paths taken bydifferent groups through geologic time.

A-1 What are the characteristics of livingthings?

A-2 How do the structures of living thingsperform their functions, interact witheach other, and contribute to themaintenance and growth of theorganism?

A-3 What are the relationships of livingorganisms, and how are living thingsclassified?

A-4, 'How do humans interact with otherliving things?

116 Part llThe Content of Science

What are the characteristics of living things?

Kindergarten Through Grade Three

Living things have characteristics by which theycan be described and distinguished from nonlivingthings (e.g., they take in nutrients, give off wastes,grow, reproduce, and respond to stimuli from theirenvironments). They are all made of smaller struc-tures that can be observed and studied (birds, forexample, have beaks, wings, feet, and feathers). Thestructures themselves am composed of smaller,observable features (bird wings, for example, havefeathers, skin, and bones). All living things needcertain resources to grow, such as food, water, andgases to breathe. If any of these things are lacking,the organism will die. [Energy, Systems and Interac-tions, Scale and Structumj

A-1 What are the characteristics of living things?

Grades Three Through Six

Living things are all composed of cells, or if theyare too small to have individual cells (i.e., are noncel-lular or one-celled), they still perform all the func-tions that specialized cells do in a larger body. Livingthings grow, metabolize food, reproduce, and interactwith their environments. All living things have basicrequimments of nutrition and growth, needing food,water, and gas exchange for respiration. Plants, aswell as some one-celled organisms that can photosyn-thesize, am able to make food out of air and water,

128

co otifolocular* Mien in.the -Amino Acid Sequences of Cyiochrome C,

Ies'from 14 Organitims.

,Rhoddspirlkith

106±th,q2,

*hilt 40 44 42 43, 41 41 -42 30. 41 40 38 30

$01000171000 40 0 30 25 27 gs gs 26 24 27 25 28 29

44 30- ,0 14 19 18 18 19 16 16 15 22 23

42 25 14 0 13 13 14 13 13 13 11 17 17

*On* 43 27- 19 13 0 10 12 :13 11 13 11 16 17

**NV* H 41 26. 18 13 10 0 8 11 9 11 9 13 14

,Chickenjurkey 41 26 18 14 11 8 0 12 5 11 9 12 13

Kangaroo 42 26 19 13 13 11 12 0 6 7 6 11 10

RàbbII 13924 16 13 11 4 8 6 0 6 4 8 9

.41 27 16 13 13 11 11 7 6 0 3 11 12

F$203000,000p, A 25 15 11 11 9 9 6 4 3 0 9 10

,AhatiuOldniciy. 38 28 22 17 45 13 12 11 8 11 9 0 1

tienvin 38 29 23 17 17 14 13 10 9 12 10 1 0

a-

J. 2Chapter 5Life Sciences 117

Young students should appreciate that they are growing individuals and know what their needs are forgrowth and health. They should be aware of the basic body systems that enable growth to occur. Energy,derivedfrom food, is necessary for all living things. Nutrition is based on good food habits. Humanshave a responsibility to conserve life and resources and not to overuse or threaten sources ofenergy.

using the energy from sunlight and nutrients from soilor water. All other organisms depend on obtainingfood from other sources of energy, usually by.feedingon other organisms or biochemical compounds.Living things depend on other living things in manyways. [Energy, Systems and Interactions, Scale andStructure]

A-1 What are the characteristics of living things?

Grades Six Through Nine

All living things have DNA and RNA, the geneticmaterial that determines the growth and developmentof each organism. Because all organisms have thisgenetic material, they must have evolved from asingle ancestor that also had DNA and RNA. (SeeSection B, Cells, Genetics, and Evolution.) Digestion,respiration, metabolism, water regulation, and repro-duction are functions common to all organisms; allbut the simplest organisms have specialized tissues,organs, and organ systems to perform these functions.

Living things use nonliving materials to build theirstructures and to enable them to perform certainnecessary functions of life (e.g., calcium and phos-phate in bones and teeth; carbon, nitrogen, and otherminerals in animals and plants; copper and iron in theblood). Cycles, such as those of carbon, nitrogen,oxygen, carbon dioxide, and other nutrients, areprocesses and patterns by which living things convertexternal materials to grow and maintain themselves.[Scale and Structure, Systems and Interactions,Energy, Patterns of Change]

A-1 What are the characteristics of living things?

Grades Nine Through Twelve

All living things have a homologous geneticmaterial, represented by RNA and DNA (in someviroses, only RNA or DNA is present). This feature

118 Part llThe Content of Science

demonstrates the unity of living things and theirevolution from a common source. The complexstructures, cycles, and processes that characterizeliving things require energy to grow and to maintainthem. [Energy, Evolution, Systems and Interact.:ons]

How do the structures of living things performtheir functions, interact with each other, andcontribute to the maintenance and growth of theorganism?

Kindergarten Through Grade Three

Living things have structures that do specific thingsto help the organism live and grow and meet theirneeds as they interact with their environments. [Scaleand Structure, Systems and Interactions]

Humans, like other animals, gain information aboutthe world around them through their senses. Theyneed fresh air, good food, rest, and exercise to stayhealthy.

A-2 How do the structures of living things performtheir functions, interact with each other, andcontribute to the maintenance and growth of theorganism?

Grades Three Through Six

Multicelled organisms have particular tissues (e.g.,bones, musclA, wood), organs (e.g., livers, lungs,hearts, stems, roots, leaves), and organ systems (e.g.,circulatory, respiratory, reproductive) that performspecific life functions (structural support, waterregulation, digestion, circulation of nutrients, and soforth). One-celled organisms perform all thesefunctions within their cell membranes, using special-ized organelles for each function. Organisms cantolerate some variations in the things they need in

/I

0

order to survive (light, temperature, water, nutrients),but they do best under certain conditions. [Scale andStructure, Systems and Interactions]

Variations in an organism's structum (e.g., flowercolor, bristle number in flies, sex) are passed to thenext generation through reproduction. Living thingshave structures that allow them to mproduce sexuallyor asexually, depending on their adaptations andevolutionary histories. Organisms progress throughlife cycles of birth, growth, reproduction, and death.(See Section B, Cells, Genetics, and Evolution.)These cycles include the growth and development ofthe young. There is variation in the rate of growth ofmost species (e.g., adolescence in mammals). [Pat-terns of Change]

Structums of organisms show their adaptations totheir environments and ways of life. (For example,tooth differences between herbivoms and carnivores;warm-blooded and cold-blooded adaptations; plantadaptations to pollination by insects, birds, andmammals.) Information about the environment iscollected by all organisms. This information helpsthem to adapt to local or temporary conditions, toobtain food, and to resist predation and death. Plantshave tissnes and organs that mact to light, water, and

other stimuli; animals have nervous systems thatprocess and store information from the environment.[Systems and Interactions]

A-2 How do the structures of living things performtheir functions, interact with each other, andcontribute to the maintenance and growth of theorganism?

Grades Six Through Nine

Organisms need energy to help them performfunctions necessary to life. They obtain energythrough various means, either from sunlight or bydigesting complex molecules and producing simplerones. [Energy, Systems and Interactions]

The digestive, osmoregulatory, circulatory, respira-tory, and mproductive systems have comparablefunctions in different groups of organisms, eventhough the oan systems that perform them are oftenquite different. Within large groups of organisms,such as animals or plants, tissues and organ systemsare homologous because they have been inheritedfrom a common ancestor. For example, the intestinesof vertebrates and most invertebrates are homolo-gous; however, these are not homologous to the

Science has recently entered the great age of molecular biology, which is marked by discoveries and useof recombinant DNA. Molecules of DNA, containing genetic information, can be moved in the labora-tory from one species to another. This opens seemingly endless possibilities for developing new types ofJiving organisms, for repairing genetic defects, and for discovering new improvements in agriculture,such as "engineered" food crop plants. The laboratory techniques for working with DNA are ultramod-ern, and new procedures are continually being discovered and introduced.

One of the biggest scientific studies ever started, certainly the biggest single undertaking ever proposedin biology, is the Hwnan Genome Project, which is designed to identify and characterize all the genes inhuman DNA. There are about three or four billion pairs of nucleotides (abbreviated as A, C, G, and T)in the DNA of a human cell. The project will attempt to map all the genes in each of the 23 humanchromosomes. The total number of human genes is probably between 50,000 and 100,000, and a genecontains about 1,000 pairs of nucleotides. Hereditary diseases usually result from mutations or otherchanges in genes. Several countries are starting work on this project, which will take at least 20 years tocomplete. Molecular biology will provide careers for many scientists in genetic engineering and bio-technology.

Chapter 5Life Sciences 119

The body systems of humans (support, respiration, circulation, and so forth) can be used as examples ofanimal systems necessary for the growth and maintenance of life.

organelles in unicellular organisms that perform theintestine's functfors, nor to analogous digestivestructures in plants. (See Section B, Cells, Ger tics,and Evolution.) [Systems and Interactions, Scale andStructure, Evolution]

There is a hierarchy to the structure of biologicalsystems. Cells are organized into tissues, tissues intoorgans, and organs into organ systems that performparticular functions in an individual. Individualsthemselves are organized into reproductive groups(such as populations and species) that are part oflarger-taxonomic units (species and higher categories)changing and evolving through time. Cells arecomposed of organelles that perform cellular func-tions, including reproduction. These functionalsystems are different at each hierarchical level (cells,tissues, organs, and so forth). Although separate, theycontribute to processes and patterns at other levels.[Scale and Structure, Systems and Interactions,Evolution]

Humans vary in their characteristics, most of whichare inherited from their parents. Individuals of thesame age can vary in growth, abilities, and develop-ment. During adolescence, growth is rapid and oftenuneven, and sexual maturation occurs at this time.[Note: Instruction in human reproduction and sexual-ity is subject to Education Code Section 51550.Special care should be taken that these conccpts,including reproductive anatomy, menstrual cycle,sexual intercourse, conception, pregnancy, and birth,are introduced at the appropriate level according tolocal district policy. See Appendix B. For relatedmaterial, consult the Health Instruction Framework.]

The genetic diversity of populations of organisms isgreatly increased by sexual reproduction, becausenew combinations of characters appear. Asexualreproduction does not allow such recombination. Thislimits potential variation and adaptation in asexualorganisms, but it also limits the spread of disadvanta-geous characters through a species. Some combina-tions of characters are better suited to some environ-ments than others.

120 Part iiThe Content of Science

A-2 How do the structures of living things performtheir functions, interact with each other, andcontribute to the maintenance and growth of theorganism?

Grades Nine Through Twelve

Metabolic energy is obtained in different ways bydifferent organisms. Energy is stored and released aschemical bonds and structures are formed or brokendown. (See Chapter 3, Section A, Matter, and SectionD, Energy: Sources and Transformations.) Plants andunicellular organisms, such as algae, can photosynthe-size and use this energy to convert carbon dioxide,water, and minerals into sugars and amino acids. Fungiobtain food and energy from plants, animals, or otherorganic 'truer. Viruses require host cells to obtainthe energy they need in order to grow and reproduce.Animals obtain proteins and other nutrients from theplant or animal material that they digest. [Energy,Scale and Structure, Systems and Interactions]

In similar ways the systems of circulation, respira-tion, support, osmoregulation, reproduction, and soforth can be directly compared among differentgroups of organisms. Some tissues and organ sys-tems, as well as biochemical molecules, are homolo-gous within large groups because they are inheritedfrom a common ancestor. Other functions are per-formed by completely different, nonhomologous (butanalogous) structures in different organisms. Thesestructures and functions are directly comparable atthe anatomical, histological, and biochemical levels.

All basic activities of organisms are biochemicaland are mediated by enzymes that regulate the rate atwhich chemical reactions occur. This regulatingsystem allows the organisms to maintain the steadystate of biochemical conditions known as homeosta-sis. The organism's health, well-being, and effective-ness in its environment depend on the ability tomaintain homeostasis. The basic biochemical pro-cesses of all organisms share fundamental similaritiesbecause the conditiods necessary for such biochemi-cal reactions to occur, and for enzymes to carry out

Organ and tissue systems are often presented in life science curricula as if they were systems peculiar tomammals (e.g., "The liver is an organ in a mammal that . . ." ). This approach is incorrect and mislead-ing. Such systems should be explained in terms of their general structures and functions in living things.As necessary, variations on these structures and functions can be explained for different groups. It isimportant to show where in the evolutionary sequence particular organs, tissues, and functions ap-peared, so students can grasp the concept of homology and the evidence by which scientists unite organ-isms into evolutionary groups.

their functions, are based on chemical and physicalprocesses that are universal. [Energy, Stability]

The human reproductive system, like the reproduc-tive systems of many other animals, is adapted for theconception and development of a relatively smallnumber of offspring (in contrast to insects or plants,for example). Some kinds of birds and mammals,including humans, have a longer developmental timeand are more dependent on parental care than otheranimals are. Unlike other animals, human beings arecapable of controlling their own reproductive ratesthrough the control of their behavior and the use of avariety of techniques to prevent conception. (See notein the section for the grades six-through-nine level.)

Because of its size and complexity, the structure ofthe animal nervous system makes a variety of re-sponses and behaviors possible. In general, as the sizeand complexity of the nervous system increase, sodoes the potential for learned behavior beyond simpleinnate responses. Human behavior, like that of mostmammals and birds, is both innate and learned.Humans can control their behavior in many ways.Behavior can be altered by biochemical means, suchas the use of drugs or alcohol. Good nutrition contrib-utes to the well-being of both the body and the mind.(See Health Instruction Framework.) [Scale andStructure, Systems and Interactions]

What are the relationships of living organisms, andhow are living things classified?

Kindergarten Through Grade Three

All living organisms are known to be related,because they have the characteristics of life (they

breathe, take in food, reproduce, and so forth). Lifehas been on the earth for a long time. Many plantsand animals, such as dinosaurs, trilobites, mammoths,giant tree ferns, and horsetail trees, lived long ago buthave become extinct. [Evolution]

A-3 What are the relationships of living organisms,and how are living things classified?

Grades Three Through Six

Groups of organisms are known to be relatedbecause they share essential features common to thembut not to other organisms. Examples are feathers,which all birds have but no other organisms have; fur,

Just as humans are mammals, they are alsoprimates, and they retain characteristics of otherprimates seen in the hands, eyes, brains, andgenetic and biochemical systems. Within theprimates, hwnans are classified with the otheranthropoid apes because they lack tails and havean unusual erect or sem:erect stance andsemibrachiating forelimbs. Anatomical, genetic,and biochemical data indicate that chimpanzeesand gorillas are the closest living apes to hu-mans . The first hominids (animals on the evolu-tionary line from the other apes to living humans)appeared over two million years ago; humanevolution since then has been marked by impor-tant changes, including upright posture, largerbrains, toolmaking, speech, art, and other cul-tural aspects.

Chapter 5Life Sciences 121

which is unique to mammals; and flowers, unique toflowering plants. Most groups of organisms have longhistories that are known from the fossil record. Theearly members of groups have some, but not all, ofthe characteristics shared by later forms. Many formshave become extinct, while other new forms haveevolved from preexisting ones.

Humans are mammals, with the basic characteris-tics bf mammals (hair, milk-giving, sets of teethreplaced only once, and so forth). Humans also havethe basic functions of mammals and other animals,including respiration, digestion, circulation, sensingthe environment, movement, and so forth. [Evolution,Scale and Structure, Systems and Interactions]

The major groups of living things are plants,animals, and a variety of one-celled forms. Livingthings are classified according to their commonancesuy. At each level of classification, distinctcharacters are used to identify the organisms withineach group. Living things are divided into threekingdoms'of multicellular organisms called fungi,plants, and animals, as well as a vast number of one-celled forms.

A-3 What are the relationships of living organisms,and how are living things classified?

Grades Six Through Nine

Groups of organisms are recognized because theyshare derived characteristics (evolutionary novelties)that appeared in their common ancestor and havebeen passed on. (For example, the first bird hadfeathers, and its offspring inherited them.) Many ofthese characteristics are adaptive, but the functions ofsome are not known. These characteristics serve asthe basis for diagnosing and classifying groups oforganisms. Within each of these groups are othe .groups that am distinguished by their own uniquecharacteristics. (For example, within mammals thereare hoofed animals, further divided into even-toedand odd-toed groups, and carnivores, which haveunique shearing teeth.) By identifying these uniquecharacteristics, we discover the evolutionary pattern,which is the basis for classification. [Systems andInteractions, Evolution]

Living things are conventionally divided into fivekingdoms, but only fungi, plants, and animals are

Usually, organisms are divided into five kingdoms (plants, animals, fungi, Protista, and Monera) in thetraditional Linnean system of classification. But Linnaeus' s system (which originally had only twokingdoms) was developed when far fewer organisms, both living and extinct, were known. Besides, histaxonomic ranks (order, family, and so forth) are too few to accommodate and reflect the descent oflife.(How can reptiles and their descendants, the birds, both be legitimately ranked as classes?) Accord-ingly, the five-kingdom arrangement needs revision. Plants, animals, and fungi are all legitimate group-ings, because each has unique characteristics. Monera and Protista do not; some of their members arecloser to the other three groups and share some characteristics with them, and so cannot be easilyclassified.

While it is still acceptable to call Protista, plants, animals, and fungi eukaryotes (comprising eubacteriaand archaebacteria) and the others prokaryotes (in reference to their cell types, with or without nuclei),or Monera (cells which lack a membrane-bound nucleus), these five groups should not be treated as ofequivalent rank. This situation arises because what we know goes beyond our ability to express it. Whatwe now know of the evolutionary relationships of organisms cannot easily fit into the relatively fewcategories of the Linnean system of classification. We can explain the unique characteristics that unitethe members of each group of eukaryotes and then show how the members of each evolved as well ashow each eukaryotic group is related to specific prokaryotes.

122 Pan llThe Content of Science

134

well-unified evolutionary groups. (The one-celledforms are often divided into Monera and Protista, butthe distinction, is arbitrary.) Within these kingdoms,there is a hierarchical arrangement of groups withingmups. Classification is founded on evolutionaryrelationships. The Linnean system of classificationwas established before evolution was understood, butin general it can be modified to accommodate newinformation and theory because it is a simple, work-able system. [Scale and Structure, Evolution]

Viruses arc:not placed in any kingdom of livingthings because they lack cells and either RNA orDNA and are uniquely tied to their hosts for growthand reproduction. It is likely that viruses evolvedfrom host cells and are most closely related to thegroups that host them.

The fossil histories of groups show that the simplestorganisms appeared first, then multicellular ones,which diversified into plants and animals. Withinplants, photosynthesizing green algae were the pre-cursors of multicellular plants, and the nonvascularmosses and liverwort.s appeared before the vascularplants; the most recen2 vascular plants to appear arethe angiosperms o flowering plants. This sequence ofappearance is supported independently by the patternsof shared derived characteristics from which phylo-genies of living and fossil organisms are constructed.(See Section B, Cells, Genetics, and Evolution.)

A-3 What are the relationships of living organisms,and how are living things classified?

Grades Nine Through Twelve

The purpose ot sudying organic diversity is todiscover the relationships of living and extinctorganisms by linking groups into evolutionary trees,based on shared derived characteristics. Life isconsidered to have had a single origin (to be a "natu-ral" evolutionary group) because all living thingshave the same genetic material (RNA or DNA). Thekingdoms of living things, plus viruses, are united inthese characteristics and within kingdoms arc brokendown into subgroups using successively less inclusivecharacteristics.

Discovering evolutionary relationships is less asearch for ancestors than for groups that arc mostclosely related to each other. We recognize theserelationships on the basis of shared derived character-istics, inherited from a common ancestor. Groups

Evolutionary relationships are best understood if.we use criteria of group membership, basing ourclassifications on shared characteristics. In thisway, we can diagram a pattern of characteristicsthat shows us the relationships of groups withingroups. (For example, the first birds evolvedfrom small carnivorous dinosaurs, so birds areproperly considered members of the dinosauria,regardless of how they are traditionally classi-fied. Similarly, humans evolved from otherapestailless primatesand are, in turn, apes,primates, mammals, anmiotes, vertebrates, andso forth.) Group memberships must be employedfully and consistently in evolutionary classifica-tion. Shared derived characteristics, diagrammedaccording to how widely they are distributedamong organisms, are the basis for understand-ing evolutionary relationships. (See the discus-sion of honwlogy under Section B, Cells, Genet-ics, and Evolution.) [Scale and Structure, Evolu-tion]

within groups are recognized by the characteristicsthat they share. (For example, al: mammals have fur,but not all mammals give birth to live young. Thosethat do, the marsupials and placentals, are moreclosely related to each other than either is to monotre-mes, which like other amniotcs retain the habit of egglaying. But monotremes, which have fur and givemilk, are closer to the other mammals than arc theother amniotes, such as birds and reptiles, which donot have fur and do not give milk.) [Scale and Struc-ture, Evolution]

Organisms are classified by shared derived charac-teristics, and their relationships are mapped by the useof cladograms (diagrams of derived characteristicsshared by successively inclusive groups of taxa; seeSection B, Cells, Genetics, and Evolution). Theevolutionary trees that result from cladograms can beused to test many kinds of hypotheses about evolu-tionary history, including how species relate, howevolutionary adaptations have been assembled, andhow species and adaptations have changed throughtime.

135Chapter SLife Sciences 123

A simple cladogram demonstrates how shared derived characteristics are mapped according to howthey are distributed among organisms. This shows us the relationships ofthese organisms. In this ex-ample, note that marsupial and placental mammals are united by the shared derived characteristic ofgiving live birth, which monotreme mammals and other vertebrates lack. All mammals are united byhaving fur and giving milk, as well as by the unique mammalian jaw joint.

Mammals are united with the birds and other reptiles by having an amniote egg; amphibiansare unitedwith amniotes (and separated fromfishes) by having four walking limbs; and so on. For any suchdiagram of evolutionary relationship, many more characteristics than the ones used in this simplecladogram are needed in order for it to be considered a robust hypothesis. Students can use these andadditional characteristics to identify the correct evolutionary placement of other organisms. (For ex-ample, lions would be placed at a branch from point A, because like elephants they have well-developedplacentas; lizards and snakes would branch off point B, because, like all other reptiles, they have colorvision (only primates have this among mammals] and they secrete uric acid; and so on.) It is important

for students to see the evidence and reasoning on which these methods are based in order to establishevolutionary relationships. They should not be told that organisms are classified based on some vague,undefined notion of similarity.

124 Part IIThe Content of Science I r.1 CN..k. tl r)

Evolutionary relationships are established byarranging shared derived characteristics on diagramsOf Oe distributions of these characteristics (clado-grams;see insert on page 121 and Figure 5). Sharedderived characteristics, such as feathers for bids orfur pt mammals, arc evolutionary novelties thatappear in an organism and are passed on to its descen-dants, inchiding descendant species. Shared derivedcharacteristics can be taken from many different kindsof inforM,,,Ion, including bones, leaves; reproductiveParts, soft tissues, genetic and molecular composi-tions, 0-4 behavioral traits. By mapping how differentcharactarisdcs are distributed among organisms, weCan pint the sequence in which these charactersappear4ind so establish the mlationships of theeigaPisms. (See Fig= 5.)

1.11111111111111111111111111111M

Mow do humans interact with other living things?

Kindergarten Through Grade Three

Humans use plants and animals for food and cloth-ing. They farm the soil, mine resources from the earth,and get energy by burning fuels, including wood,which is also used to make paper and to build. Peoplecan become sick from infection by some tiny organ-isms, but human systems can also fight such diseases.Other tiny organians produce foods, such as yogurtfrom cow's milk. Living things and essential msourcespeed to be respected. [Systems and Interactions]

A-4 How do humans interact with other living things?

Grades Three Through Six

Humans are part of the biosphere and are dependenton it. Humans rely on a great variety of living thingsfor many reasons. They need to exercise judgment,+my, and planning in their use of natural resources,including plants, animals, soil, and water, and in theirpractices of disposing of wastewater and materials.Human-caused extinctions continue at a rapid pace.Hundreds of species of plants and animals becomeextinct each year as humans destroy the natural habitatin tropical rain forests and other ecosystems to plantcrops and raise animals, harvest firewood, dam rivers,and drain estuaries. [Systems and Interactions]

A-4 How do humans interact with other living things?

Grades Six Through Nine

Humans first domesticated animals and plantsthousands of years ago. Humans have learned toselectively breed animals and plants to obtain desir-able characteristics (artificial selection), much asnatural selection has operated in evolutionary time.(See Section B, Cells, Genetics, and Evolution.) Bymanaging crops and animals and by judiciouslytilling and developing the earth, farmers have in-creased agricultural productivity and efficiency, par-ticularly with new breeding and genetic technologies.[Evolution, Systems and Interactions]

A-4 How do humans interact with other living things?

Grades Wine Through Twelve

Agricultural and biomedical advances have greatlyimproved the health of humans and the hardiness ofdomesticated plants and animals. The spread ofdisean caused by microorganisms has been drasti-cally reduced because of advances in microbiologyand epidemiology, coupled with improved publichealth laws and practices. These advances haveresulted in rapid human population growth, especiallyduring the last century. As a consequence, humansmust be increasingly conscious of the effects ofpopulation growth and take steps to plan safe,healthy, and spacious communities that nurture thebest physical and psychological conditions for theirinhabitants. They also need to consider the ethicalramifications of biomedical advances that can pro-long life beyond the natural capacity of a traumatizedbody. [Evolution, Systems and Lnteractions]

Human beings have complex social organizationsand behaviors that have allowed them to adapt to awide variety of environments. Unlike other organ-isms, humans have done this largely through culturalevolution, without changing important basic physicalcharacteristics. Through thought, reasoning, andtoolmaking, humans have manipulated their environ-ment to the point where they can change the geneticconstitution of species (e.g., through selective breed-ing and genetic engineering). They have learned touse the products of other organisms to build houses,gain food, and light disease, among other things.

Because of their evolutionary success, humans havedeveloped far-reaching interactions with most habi-

IRChapter 5life Sciences 125

Iian;(189frf9i5)

Ete.0,0404 4450tcyj.,.hoaktotinuolhotap.104 bi4cicsdientistSin?1001*,014411'000tOYA* ri4liatOletti.41*40On4L4Pdlailn---60the:wor ..A404#4044-***0.00.. blin4intOffeCt.korkWICOT,t.:X49wil1an cbcthistThewasthciirst,-,t4.4o:$0ybof*OirtOniaillitictlitee_OOnt*Oally4.40:

teOik.14.4?Ots!"400steRn,e;04**001-..-.1t,ixil#0.11,4-1.ncisJOilifiOlif11***10***6004,41040etio*kl.Oftiti*Oprii-0*,401***Ocecl0641,. . ,

oos4:14#0,woongiritgifookbretocto itinoil.f4t4thritis,NfkrcrO,

tats of the biosphere; these interactions are causinggreat changes in both the physical and biological en-vironments. (See Section C, Ecosystems.) The diver-sity of life is threatened by some human agricultural,industrial, political, and recreational practices.Humans have a responsibility and a vested interest inmaintaining natural ecosystems. [Evolution]

Section et Cells, Genetics, andEvolution'

THE unifying theory of biology is evolution; asTheodosius Dobzhansky said, nothing in biologymakes sense without it. It is accepted scientific fact,and has been since the mid-1800s, that organisms aredescended with modification from other organisms.The patterns, processes, and mechanisms of thi..descent make up the theory of evolution. Suchprocesses include (but are not limited to) geneticmutation and recombination of genetic material;populational processes of natural selection, geneticdrift, migration in and out of the population; andlarger-scale processes of speciation, extinction, andadaptive radiation.

'In this section, the term cells includes tlw mend areas of cellular andmolecular biology, as well as biochemical topics covered in high schoolbiology. Cells also includes general histological and structural features oftissue and organ systems, as well as cellular parts and components in coecelled and multicelled organisms. Genetics includes genetic structure anddevelopmental processes. Evolution includes population genetics,evolutionary biology, and paleontology.

126 Pan HThe Content of Science

Evolution is studied through many independentlines of evidence, including the fossil record; com-parative anatomy, development, and biochemistry;and genetic structure and change. Evolution explainswhy similar structures in different organisms aresimilar and is a highly predictive and (for past events)retrodictive theory. The classification of organismsindeed all of comparative biologyis based onevolution. Curricula must reflect this centrality ofevolution in the biulogical sciences.

The molecular theory of the gene. explains thestructure of genetic material and integrates a vastamount of evidence from biochemistry, genetics, anddevelopment. In the curriculum for kindergartenthrough grade twelve, the simpler elements andstrands of this theory should be stressed as central tomolecular biology and genetics because they give usthe chemical and physical bases of how the geneticmaterial changes. This theory is also the basis for ag-ricultural and other technological developments thatdepend on an understanding of molecular and cellularbiology, genetics, and evolution. [Scale and Structure,Evolution, Systems and Interactions]

B-1 What are cells? What are their compo-nent structures and their functions?How do they grow? What is the biochem-ical basis of life and of metabolism?

B-2 How are the characteristics of livingthings passed on through generations?How does heredity determine thedevelopment of individual organisms?

,-)

B-3 How has life changed and diversifiedthrough time? What processes andpatterns characterize the evolution oflife?

What are cells? What are their component structuresand their functions? How do they grow? What is thebiochemical basis of life and of metabolism?

Kindergarten Through Grade Three

All living things are made of smaller structures,such as tissues and organs. (See Section A, LiyingThings.) These structures perform the vital functionsof life and help the organism to interact with theenvironment and survive. [Scale and Structure,Systems and Interactions]

B-1 What are cells? What are their componentstructures and their functions? How do theygrow? What is the biochemical basis of life andof metabolism?

Grades Three Through Six

There are many different kinds of cells in animalsand plants, and different kinds of cells (e.g., muscle,blood, bone, skin, wood, and guard cells) performdifferent functions in the bodies of their wholeorganisms. The different functions of cells all contrib-ute to the well-being of the organism. [Scale andStructure, Systems and Interactions]

Living organinns have tissues and cells that can beexamined to reveal their component parts and func-tions. The component parts of most cells (e.g.,membranes, nucleus, and other small organelles) havedifferent functions, including the conversion and useof energy, protection, and reproduction. Someorganisms are one-celled or unicellular, and eventhese have component parts. Organisms that are verydifferent (e.g., sponges, humans, oak trees, ferns)nonetheless have parts that perform the same kinds offunctions for their organisms. [Scale and Structure,Systems and Interactions, Energy]

There is a hierarchy in the organization of livingsystems, from cells and their components to tissues,organs, organ systems, and whole organisms. At eachstep in the hierarchy, these component parts contrib-ute to the overall maintenance of the organism.

B-1 What are cells? What are their componentstructures and their functions? How do theygrow? What Is the biochemical basis of life andof motabollsm?

Grades Six Through Nine

An organism is an individual with parts that areorganized into a functional whole. The parts (cells,tissues, organs) cannot suivive apart from the whole;and at every level of organization, these parts havestmctures that perform specific life functions. Themajor kingdoms of living things are characterized bydifferences in how cells are organized and differencesin the structure of organs and tissues. [Evolution,Scale and Structure, Systems'and Interactions]

Living organisms combine atoms and moleculesinto particular structural and functional compounds.Through the conversion and use of energy, differentcell organelles perform the functions of life at thecellular level. [Energy, Scale and Structure]

The content and nutritional value of foods can beunderstood in terms of calories (or kilojoules) andnutrients. Food that is digested and absorbed maythen be oxidized by the cells to release energy neces-sary to maintain cellular functions and produce newcells. Some food sources carry levels of fats, choles-terol, or other substances that can be unhealthy inexcess quantities. [Energy, Scale and Structure]

In order for growth and maintenance of the body tooccur, cells must divide to form new cells. Old cellsare constantly dying off and being replaced by newones. Mitosis is one phase of the repeating cycle ofcell division that occurs constantly in the body. Thecell cycle is governed by environmental factors insideand outside the cell that signal the appropriate timefor division (in the case of cancer cells, this signal isnot observed). Normally, the newly produced cellsare identical to the parent cell or one-celled organism.[Patterns of Change, Stability, Energy]

B-1 What are cells? What are their componentstructures and their functions? How do theygrow? What is the biochemical basis of life andof metabolism?

Grades Nine Through Twelve

Cytoplasm and cell organdies have specific struc-tures and compositions, and they perform specificcellular functions, such as the production of enzymes,the metabolism of food, mitosis, and the removal of

1 3 9 Chapter 5tife Sciences 127

wastes. These functions are common to the cells of allliving things, even'though they are performed bydifferent structures/in different kinds of organisms.[Systems and Interactions, Scale and Structure]

Initially, most cells have the ability to become anykind of cell because they contain the same geneticinformation. Through the process of their growth anddevelopment, they differentiate and specialize instructure and function (e.g., to becOme blood or leafcells), but they retain the basic information that alsoallows them to reproduce themselves mitotically.[Systenis and Interactions, Scale and Structure]

The chemical and physical bases of metabolism,including photosynthesis and the Krebs cycle, arefundamental cellular processes. These cycles describethe releese and use ofenergy by the organism.Enzymes serve as catalysts to promote essentialchemicat reactions in cells. Cellular processes thatsustain end renew life can be understood by studyingthe interactions of molecules, atoms, and electrons.Large molecules (macromolecules: e.g., fats, polysac-charides, nucleic acids, and lipids) govern life func-tions by playing parts in the structure and regulationof the cell's metabolism. [Scale and Structure;Systems and Interactions, Energy]

Regulatory mechanisms in all organisms control theflow of energy and maintain homeostasis of bio-chemical reactions and metabolic rates. Although thenormal activities of life (e.g., feeding, locomotion)cause departures from equilibrium, regulatory sys-tems restore this balance and maintain the organismin working condition. (Disease often results fromfailures in these systems.) [Energy, Stability]

How are the characteristics of living things past.ed onthrough generations? How does heredity determinethe development of individual organisms?

Kindergarten Through Grade Three

Living things resemble their parents because allparents pass on their physical characteristics to theiroffspring. In organisms with two parents, the off-spring normally inherit characteristics of both.Usually, closer relationships mean more similarities:brothers and sisters tend to resemble each other more

128 Pea llThe Content of Science

closely than cousins or distant relatives do. [Scale andStructure, Systems and Interactions]

B-2 How are the characteristics of living things passedon through generations? How does hereditydetermine the development of individualorganisms?

Grades Three Through Six

Within a species there is usually considerablevariation in characteristics. In humans, hair color, eyecolor, and many other physical features are largelydetermined by heredity. The variation can be in theorganism 's appearance or in its genetic. makeup (orboth). Inheritance is coded by the genetic materialfound in the nuclei of cells. Some of this material,normally in equal amounts, comes from both parentsof multicelled organisms. Variation in this materialdetermines some of the variation in the characteristicsof individuals. Although many characteristics areinherited from parents, nutrition and other environ-mental factors during the growing period contributevitally to adult form and health. [Scale and Structure,Systems and Interactions]

Living organisnis progress through a life cycle thatis characteristic of their species.This cycle beginswith the combination of genetic material in the newcell and continues through all the phases of growthand development to the adult form through reproduc-tion and death. [Patterns of Change]

Students should understand that "mutants" and"mutations" are not terms laden with negativeconnotations. Mutations themselves are nothelpful, harmful, or neutral, but their effects are,in given situations. Mutations are the agents ofgenetic change in evolution, affecting nearly allstructural and developmental processes. Eachhuman carries dozens of mutations in the chro-mosomal material; thus, we could all be consid-ered "mutants" (a term that should probably beavoided because of its connotations). Manyembryonic deaths, on the other hand, arise fromlethal mutations.

140

Until the 1960s, most mutations were thought tobe harmful in their effects, and wild populationswere thought to have generally low levels ofgenetic variability. The discovery of neutralevolution in the 1960s changed this understand-ing. Molecular and genetic studies revealed thatthere was far more variation in organisms thanhad ever been suspected. Yet organisms seem tohave no trouble surviving in spite of all thisvariation. Therefore, most mutations could not bedeleterious in their effects but rather seem tohave no strong effects at all.

8-2 How are the characteristics of living things passedon through generations? How does hereditydetermine the development of individualorganisms?

Grades Six Through Nine

The genetic material DNA makes up the genes,which determine heredity. Genes are segments ofchromosomes in the nuclei of cells. The geneticsystem is organized so that variations and changescan occur in several major ways, including (1)mutations; (2) errors in copying genetic materialwhen cells divide; and (3) recombination of geneticmaterial. Not all genes are equally expressed; somehave mom influence on physical form and develop-ment than others. In some cases, one gene mayinfluence several characteristics; in other cases,several genes contribute to the same characteristic.Genetic factors contribute to individual variation, andsuch variations are the raw material of evolution.[Scale and Structure, Systems and Interactions,Evolution]

Mutations are changes in the DNA that may becaused by errors in replicating genetic material. Mostcauses of mutation (heat and cold, radiation, chemicalcompounds in the environment) are natural; a fewresult from active or accidental human interference,such as those from chemicals or X rays. Most muta-tions am neutral in their effects on the individualorganism, though many are harmful, and some arehelpful in their effects. The same mutation may have

harmful, neutral, or helpful effects in different geneticand external environments (e.g., mutations for dark orlight coat color in arctic mammals may be advanta-geous or not, depending on the season and the sur-roundings). [Evolution, Patterns of Change, Systemsand Interactions]

All living things follow the patterns of variouscycles (e.g., life cycle, respiration and energy release,reproductive cycle, Krebs cycle) and cyclical rhythms(e.g., daily, seasonal, annual). Other patterns ofchange may be directional (e.g., growth, develop-ment, and maturation). [Patterns of Change]

B-2 How are the characteristics of lMng things passedon through generations? How does hereditydetermine the development of individualorganisms?

Grades Nine Through Twelve

DNA, the genetic material, is universal to allorganisms (except some viruses which have onlyRNA or DNA). DNA is read and transcribed by RNApolymerase to produce a complementary strand ofRNA. DNA codes the production of proteins, whichare composed of 20 different amino acids, most ofwhich serve as catalysts for cellular functions ofgrowth and development. The sequence of theseamino acids is determined by the genetic code, readas codon triplets of the four RNA bases. Sixty-one ofthe 64 triplets code for the production of a specificamino acid, and the other three are stop signals.

There is great repetition in the genome, probablybecause this material has been duplicated and addi-tional material has been incorporated many timesthrough evolutionary history. There are active andinactive sections of DNA molecules, and not all partscode for characteristics. In fact, few sites appear tocode for specific features, and we know very little asyet about what function most DNA serves, althoughthe main purpose seems to be to code for specificproteins and to regulate growth.

If the sequences of DNA molecules are comparedin different organisms, the evolutionary relationshipsof the molecules can be determined; the degree towhich DNA sequences correspond in different organ-isms provides data about their evolutionary relation-ships. (See Figure 4, page 115.) DNA molecules canalso be artificially modified by the addition or dele-tion of genetic material to promote desirable charac-

i 4 Chapter 5Life Sciences 129

teristics (such as frost resistance in plants) or toeliminate undesirable ones (such as virulency in aninfective microorganism). [Scale and Structure,Systems and Interactions, Evolution]

The relationship between genotype and phenotypeis complex: normally, there is not a one-to-onecontspondence between genes and external charac-teristics of the organism. There is an explicit andinseparable relationship between genetics and evolu-tion. Darwin used the methods and benefits ofselective animal and plant breeding to convey theidea of natural selection by comparison to artificialielection. [Evolution, Systems and Interactions]

The genetic code instructs the production ofenzymes and other proteins in the cells. The relation-ship between the genetic code and the fully developedadult organism is not completely understood. Mostgenes do not appear to code for specific structures(e.g., fmgers) or functions (e.g., heating ability).Rather, most genes appear to regulate processes ofcell growth and enzyme production that function indevelopment. The need for insight into just howgenes contribute to development is one of the mostexciting frontiers in biology.

Developmental programs may be continuous, as invertebrates and many plants, or they may result in aseries of very differtnt looking, independent, free-living developmental stages. Examples include thecaterpillar-pupa-butterfly transition of lepidopteraninsects and the nauplius and veliger stages of manymarine invertebrates, as well as in the dual life cycleof sporophyte and gametophyte seen in vascularplants. [Patterns of Change, Systems and Interactions,Evolution]

How has life changed ;and diversified through time?What processes and patterns characterize theevolution of life?

Kindergarten Through Grade Three

Today, there are a great many kinds of livingthings, including plants, animals, fungi, and manyone-celled organisms. The fossil record indicates thatat one time there were only very simple, one-celledforms; but through time, the larger (many-celled)plants and animals evolved from these simple forms.

130 Part 11The Content of Science

As climates have changed through time, the variety oflife has changed accordingly and increased tremen-dously. Life has been on earth for a very long time.Fossils tell us about past life, most forms of which arenow extinct. [Evolution]

All living things have features that they inheritfrom their parents. All life forms are related to eachother because they share common features. Livingthings are grouped together on the basis of thesefeatures, which they have inheriteli from commonancestors. [Evolution]

In evolution, the selective value of traits dependson the environment. The peppered moth (Bistonbetularia) is a famous example of natural selec-tion under conditions of environmental change.Before the industrial revolution, both dark andlight moths were present in the population. Asindustrial pollution increased, light-colored treesdarkened, and the light-colored moths were moreconspicuous to the birds that fed on them. Hence,the proportion of light-colored moths in thepopulation decrzased. However, as industrialpollution declined, the tree trunks lightenedagain, and lighter-colored raoths were favored.

Students should understand that this is not anexample of evolutionary change from light-colored to dark-colored to light-colored moths,because both kinds were already in the popula-tion. This is an example of naturalselection, butin two senses. First, temporary conditions in theenvironment encouraged selection against dark-colored moths and then against light-coloredmoths. But second, and just as important, is theselection to maintain a balance of both black andwhite forms, which are adaptable to a variety ofenvironmental circumstances. This balanced se-lection increases the chances for survival of thespecies.This is in many ways the most interestingfeature of the evolution of thepeppered moth butone that is often misrepresented in textbooks.

142

B-3 How has life changed and diversified throughtime? What processes and patterns characterizethe evolution of life?

Grades' Three Through Six

Organisms resemble their parents because theyinherit features from them. New combinations andchanges in the genetic material cause variations inoffspring. Over geologic time, life has evolved anddifferentiated into the forms that live today. Only avery small proportion of all life forms that ale knownto have existed survive today. Many forms no longerliving are seen in the fossil record. The sequence ofthese forms in the fossil record helps us to see theorder in which life evolved.

The algae found in stromatolites (hardened mudlayers) ar- more complex than are many otherbacteria and microbes; therefore, the first lifemust have appeared somewhat earlier than 3 .5billion years ago. Many forms of life are knownfrom rocks older than 600 million years, but theyare mostly tiny and one-celled. During the Cam-brian period (ca. 500-570 million years ago),nearly all the present groups of multicelledanimals first appeared in the fossil record, butnot all at once.

143Chapter 5--Life Sciences 131

Evolution is an ongoing process. There are many direct examples ofquite recent natural selection (e.g.,rapid evolution of genetic resistance to antibiotics by pathogenic bacteria, to insecticides by insects, andto herbicides by weeds), evolution of new species (Hawaiian moths and fruit flies), and new adaptations(e.g., British titmice have learned to pry the lids off milk bottles so that they can drink the cream).

B-3 How has life changed and diversified throughtime? What processes and patterns characterizethe evolution of life?

Grades Six Through Nine

The earth is about 4.6 billion years old; the oldestrocks ate some 4 billion years old; and life on earth isfirst known from rocks 3.5 billion years old. Plants,animals, and fungi did not exist then. Instead, theselife forms were small, multichambered cells and tiny,thin filaments much like some one-celled organismsof today. They are often found arranged in thin bedsof hardened mud layers (stromatolites) similar to the

The evolution of life should be presented tostudents not as a disconnected series but as apattern of changing diversity united by evolution-ary relationships and distinguished by changes inthe environment and by adaptations to thosechanges. Nor is evolutionary history a sequenceof increasing complexity, because this does notadequately or accurately define evolution. Thehistory of life is not merely the evolution ofcomplex forms from simpler ones; for example,parasites are generally simpler than their non-parasitic relatives because theyfrequently losethe ability to perform certain vitalfunctions (suchas digestion and locomotion) that their hosts nowprovide for them. One-celled and other simple or-ganisms persist because they fit viable evolution-ary niches. Although multicellular organismsevolved from simple one-celled ones, it is mis-leading to portray evolutionary history as a drivetoward increasing complexity.

132 Part IIThe Content of Science

subtidal algal mats of today. (See Chapter 4, SectionB, Geology and Natural Resources.) [Evolution]

Scientific theories about the origin of life are basedon an understanding of what conditions were like onearth billions of years ago. The earliest rocks tell uswhat the earth, its waters, and its atmosphere werelike at that time, as far as can be known. Scientistscombine this information with what is known of thechemical and physical mquimments for life today,especially for the simplest forms oflife, to mcon-struct what the earliest life on earth may have beenlike and how life may have first evolved. Experimen-tal evidence is also used to understand how complexbiochemical molecules may have first been as-sembled. (See Chapter 4, Section B, Geology andNatural Resources.) [Evolution, Systems and Interac-tions]

Changes in the genetic material DNA am mspon-sible for new variations in individual organisms thatmay be passed on to their offspring. Changes occur inseveral ways, including recombination of geneticmaterial from pamnts and mutations. Natural selec-tion is an explanation of how these variations maycontribute to the survival of an individual to the ageof mproduction. Attaining reproductive age is impor-tant because that is when these characteristics can bepassed on. Natural selection has been extensivelydemonstrated in natural and laboratory populations ofmany kinds of organisms. Though an important factorin evolution, it is only one of many processes contrib-uting to evolutionary history. Others, such as adapta-tion, speciation, extinction, and chance events, arealso of primary importance.

Natural selection and adaptation are diffemntconcepts. Natural selection refers to the process bywhich organisms whose biological characteristicsbetter fit them to their environment are better mpre-sented genetically in future generations. With time,those that are mom poorly fitted would normallybecome less well mpresented. Adaptation is the

process by which organisms respond to the chal-lenges of their environments through natural selectionwith changes and variations in their form and behav-ior. [Evolution, Patterns of Change, Systems andInteractions]

Evolution, dermed as "descent with modification,"is the central organizing principle in life science. Itgives us a basis of comparison when we studyanatomy, structure, adaptation, and ecology. Homol-ogy provides the vehicle of comparison. Homologousfeatures am those that are inherited from the commonancestors of organisms (e.g., the forelimbs of fishes,birds, horses, and humans are homologous, becausethey have been inherited from a common ancestor,even though thT; are very different in ther structureand function). Tlius, homologies are defmed byancestry; the criteria used to recognize homologies ofstructure include the position of the structure (topol-ogy), its composition (histology), its developmentfrom the initial cell stages, and its biochemicalmakeup. Independent lines of evidence from anatomi-cal, molecular, and genetic material; development;and the fossil record enable us to establish homolo-gies, which we use to reconstruct the relationships oforganisms. Classification is based on evolutionaryrelationships, not on any arbitrary criteria or on vaguenotions of similarity. (See Section A, Living Things.)[Evolution, Patterns of Change, Systems and Interac-tions, Scale and Structure]

Although most changes in organisms occur in smallsteps over a long period of time, some major biologi-cal changes have taken place during relatively short

intervals and at certain points in the earth's history.These include the evolution, diversification, andextinction of much fossil life. [Evolution]

Extinction has been an inevitable biological processsince life began. Over 99 percent of all the organismsthat ever lived me now extinct. Extinction, therefore,is a natural process. But humans have also caused eircontributed to the extinction of many forms of lifeand continue to contribute to a rate that is muchhigher then at any previous time in human history.Extinction can stimulate further evolution by openingresource space. (See Section C, Ecosystems.)

B-3 How has life changed and diversified throughtime? What processes and patterns characterizethe evolution of life?

Grades Nine Thrc 3h Twelve

The earliest known organisms on earth are knownfrom coccoid and filamentous structures similar tothose of living cyanobacteria. They are associatedwith lithified algal mats known as stromatolites,preserved in rocks 3.5 billion years old in SouthAfrica and Australia. Because cyanobacteria aremetabolically more complex than other microbes(e.g., they photosynthesize), it is presumed that lifeoriginated on earth at a somewhat earlier time. (SeeChapter 4, Section B, Geology and Natural Re-sources.) [Evolution]

Conditions on earth when life first evolved areinferred from the geochemistry of the earliest rocks.Earth's earliest oceans and atmosphere were much

Homology should be kept distinct from similarity. Homology implies descent from a common ancestor.Cytochrome C molecules in humans and horses are homologous. They are also similar; their sequenresdiffer by only 1.1 percent. Consider two chains of ten nucleotides, with the sequences G-C-A-T-G-C-A-T-G-C andT-A-C-G-T-A-C-G-C-G. In each, there are two As, two Ts, three Gs, and three Cs, so the two

sequences are identical in composition. But there is no similarity between them because none of the sitesmatch when the two chains are laid end to end. By contrast, two other chains, C-A-T-G-C-A-T-G-C-Aand C-A-T-G-C-A-T-G-T-G, have identical nucleotides in their firs: eight positions, but different ones in

the last two. So they are 80 percent similar. If the two sequences had a common evolutionary origin,they would also be homologous in addition to being similar. If, however, they did not have a commonorigin, they would be similar but not homologous.

145 Chapter 5Life Sciences 133

Evolution is both a pattern and a process. It is also both a fact and a theory. It is a scientific fact thatorganisms have evolved through time. The mechanisms, patterns, and processes by which this evolutionhas occurred constitute the theory of evolution. Like gravitation and electricity, evolution explains alarge range of observations and hypotheses about the natural world. (See Chapter 1, "The Nature ofScience." ) As more detailed understanding increases, the theory of evolution itselfevolves.

different from what they are today. Available evi-dence does not clearly favor a single theory of howlife first evolved. Current theories explore severalpossible mechanism., but knowledge of these is veryincomplete. Experiments attempting to synthesizecomplex biochemical molecules have providedconsiderable insight into what conditions werenecessary for the earliest life to evolve. (See Chapter4, Section B, Geology and Natural Resources.)[Evolution]

Chemical evolution refers to the assembly of morecomplex organic molecules from simpler ones, given

Structural constraints, inherited by organismsfrom their ancestors, are surmounted in interest-ing ways as new adaptations evolve. One ex-ample is the "thumb" that the giant panda usesto strip bamboo leaves (this is not a thumb at all,but a modified wrist bone). Unknown adaptive ordevelopmental constraints prevented the modifi-cation of the true thumb, perhaps; but even moreinteresting, the panda's foot has grown a similar"thumb" from an ankle bone, even though ;he

foot is not used to strip bamboo leaves. Evidentlythe same genetic mechanism controls the devel-opment of the first digit on both the hand andfoot, even though natural selection is workingonly on the function of the panda' s thwnb. Thisshows the interaction of genetics with devdop-ment that contributes to the evolutionaryprocess.(This and other interesting evolutionary examplesare explained in The Panda's Thumb by StephenJay Gould.)

134 Pad 11--The Content of Science

appropriate materials, environmemal conditions, andinput energy. These complex molecules are part ofbiotic compounds. Chemical evolution differs fromorganic evolution, which is change in life forms byslf-replication (or as Darwin put it, "descent withmodification"). Chemical evolution entails no self-replication and no inheritance.

Evolution explains why biological patterns instructure, function, biochemistry, and genetics showthe same recurring themes of relationship. It alsoforms the basis for the establishment of homology,which is studied through the criteria of topology,histology, ontogeny, and so forth. Evolution unitesgenetics and molecular biology with earth history andthe physical sciences by showing the continuity ofchange and the records of these changes in the rocksand in the structural and biochemical compositions ofall organisms. [Evolution, Patterns of Change,Systems and Interactions, Scale and Structure]

The sequence established from cladograms (seeSection A, Living Things) can be compared with theindependent sequences ofappearance of organismsand their characteristics in the fossil record. It canalso be compared to the patterns of many biochemicalcompounds, including the genetic material, DNA andRNA. Evolutionar, relationships are thus understoodthrough a combination of independent lines ofevidence, including anatomical, genetic, and bio-chemical data, ontogeny, and the fossil record.Organisms are classified according to these evolu-lionary relationships. [Evolution, Patterns of Change,Systems and Interactions]

Genetic mutations and recombinations are two ofthe most important causes of the variations that formthe raw material for evolutionary change. Othersinclude errors in copying DNA, duplication andrearrangement of chromosomes, and addition anddeletion of genetic material. These variations areexpressed in the phenotype as evolutionary novelties,and they provide the material on which natural

146

selection can act. Natural selection can work onvariations in any characteristics at any time in anindividtfal's development. Through geologic time,adaptation to environmental factors has beer. 4 centraltheme in the evolution of life. Many fosFa lineagesshow the evolution of adaptations for feeding, loco-motion, reproduction, and coping with environmentalconditions. Because environmental conditions changeover geologic time, populations of organisms musthave sufficient variation and plasticity to meet thesechallenges or become extinct. Few evolutionarystrategies are guaranteed success, and these cannot bepredicted in advance. [Evolution]

Not all evolution is adaptive, and organisms cannotsimply invent the characteristics that would servethem well in particular circumstances. Evolution islimited by the possibilities for genetic and behavioralchange because organisms can use only the geneticand structural tools handed down by their ancestors.Even so, living things have great potential to bemodified by natural selection to meet environmentalneeds (e.g., the evolution of beak shapes in the smallgroup of Darwin's finches). [Evolution, Systems andInteractions, Scale and Stnicture]

The fossil record documents the appearance,diversification, and extinction of many life forms inrelation to environmental regimes and changesthrough earth history. (See Section C, Ecosystems,and Chapter 4, Section B, Geology and NaturalResources.) The sequence of life through time isknown from the geologic ranges of major groups ofliving things. Tectonic events, including mountainbuilding and continental drift, and climatic patternsthat result from these processes contribute to theseparation and diversification of species over time,such as the present geographic restriction of the Coastredwood.

Evolution, both a pattern and a process, has manycomponent patterns and processes, such as speciation,natural selection, adaptation, and so forth. Theprocesses of evolution are studied at the species,popuhtion, genetic, and molecular levels; all contrib-ute information that explains the diversity and unityof life. Rates of evolution vary, both among differentgroups of organisms and through geologic time.

Extinction is a natural part of life that has played animportant role in evolutionary history. Extinctionconsists of two modes: (1) a background of ordinaryextinctions of species; and (2) occasional events of

Understanding the history of life requires aknowledge of the geologic timetable (see Chap-ter 3, Section B, Geology and Natural Re-sources), including the ranges of some majorgroups of organisms and signifkant events in thehistory of life. These events include the emer-gence of important adaptations and groups oforganisms, as well as evolutionary radiationsand mass extinctions. The evolutionary and fossilhistories of a few representative groups shouldbe presented in life science curricula in detail, sothat students can have a concrete appreciationfor the data of the fossil record, the geologiccolumn, and the methodology of phylogeneticreconstruction.

mass extinction caused by some kind of biotic orphysical crisis. In earth history, mass extinctions haveoften been caused by regressions and transgressionsof oceans, continental drift, and other geologicprocesses; and perhaps by external agents such asextraterrestrial objects and processes. Explanations ofextinction must take into account both the extinct andthe survivors. (For example, any explanation ofdinosaur extinction at the end of the Cretaceousperiod must explain why other forms of life survived,see Chapter 4, Section B, Geology and NaturalResources.) Extinctions from the end of the Pleisto-cene Ice Age are still occurring, while others arecaused or hastened by the activities of humans.[Evolution, Patterns of Change]

The science of biology has made grcat progress inthe last ten years and has uncovered fundamental newconcepts. Molecular biology has become one ofbiology's major themes; molecular biologists areexploring new horizons not dreamed of a decade ago.At, ,ompanying these new insights is an expandingbia tchnology which is raising scientific and ethicalquestions in medicine, agriculture, and law while atthe same time forecasting far-reaching social andeconomic benefits for the state, the nation, and theworld.

These new scientific and ethical questions areforcing a reevaluation of public policy in scierm and

4 7Chapter 5Lite Sciences 135

tedraology, the health care industry, medical re-search, agriculture, and, most important, in publiceducation.-Unfortunately, high school classroomshave not similarly expanded their horizons in scienceand its ethical concerns and are falling further andfurther behind,the times.

As a consequence of the rapid development inmolecular biology and its technologies, the gulfbetween scientific advance and public understandingis widening. In a 1986 study for the National ScienceFoundation, Jon D. Miller found that 57 percent ofthe American people had little or no understanding ofDNA, the molecular biologists' lamp of knowledgeand target of technological manipulation,'

For a participating democracy to succeed andfh..aish, an informed public in which citizens makeknowledgeable decisions on technological issues isnecessary. Students and teachers must have both afinn understanding of the sciencs and an ethicalframework for applying these ideas in a technologicalsociety. Failure to emphasize boai science and ethicsin the biology curriculum means, in the final analysis,failure to fulfill teaching's most important function:to prepare citizens capable of informed decisionmaking in both the personal and public arenas.

F07 example, genetic engineering of bacterial DNAenabled medical researchers to mass-produce theenemical interferon, which is produced bk humancells as a natural defense to viral pathogens. Prior tothis biotechnological breakthrough, the interferonsupply was extremely limited and very costly, over$10,000 per milligram. Mass production decreasedcosts, allowing widespread distribution to many morecancer patients. Although interferon's overall effec-tiveness was less than hoped for, many thousands ofcancetpatients went into, remission after taking it.

Section C Ec9systems

EcoLootcAL theory is concerned with the study ofnatural systems. The balance of nature is in fact ashifting balance in which nothing is constant butchange. A human lifetime sees only glimpses of the

1.1on D. Miller. "Scientific literacy Among American Adults." Addressgiven at the Forum on Scientific literacy held by the American Assocta-eke for the Advancement of Science,Arlington, Virginia, October 6-7,1989.

136 Part IIThe Content of Science

vast scale of this change. There are many patterns:seasonal, reproductive, and populational cycles;migrations in and out of populations (which them-selves wink in and out of existence); and extinctions.

The study of ecosystems has a dual purpose: (1) toachieve a basic understanding of natural ecosystemsand how they work; and (2) to apply this understand-ing to making practical and ethical decisions aboutecosystems, often referred to as the science of conser-vation. Conservation of resources does not assumethat ecosystems do not change; the object is to ensurethat human intervention in ecosystems does notchange them so rapidly or radically that their speciesand ecological interactions are destroyed. Our chil-dren face a global crisis in conservation of naturalresources. We are only beginning to understand itsdepth and ramifications for the earth's food supply,atmosphere, water cycle, and biological diversity.Communicating this awareness to students involvesboth the fundamental aspects ofecological theory andthe applied theory of conservation biology in bothethical and practical aspects.

C-1 What are ecosystems, and how doorganisms interact In ecosystems?

C-2 How does energy flow within anecosystem?

C-3 How do ecosystems change?C-4 What are the responsibilities of humans

toward ecosystems?

What are ecosystems, and how do organismsinteract in ecosystems?

Kindergarten Through Grade Three

Living things need resources from their environ-ments in order to sustain life and help thcm grow.They need food, waterrand space to live and grow.Living things live in particular kinds of environments,because these are where they find the things and theconditions that they need to survive. Cycles, such asthe water cycle, are characteristics of environmentsthat support life. [Scale and Structure, Systems andInteractions, Patterns of Change]

t

Some living things, such as algae and plants,produce their own food. Most others, including allanimals, get food by eating or ingesting other livingthings. [Systems and Interactions, Energy]

Living things interact with other living things inmany ways, depending on each other for food,shelter, and mutually advantageous purposes such associal groupings. The same kinds of living thingsoften live together in groups. Usually, several differ-ent groups of interdependent living things live with ornear each other. [Systems and Interactions]

C-1 What are ecosystems, and how do organismsinteract in ecosystems?

Grades Three Through Six

All living things interact with each other and withthe physical environment. All organisms are part oftheir environments; they need things from theirenvironments that enable them to survive and grow.All organisms are influenced by environmentalforces, and each organism also influences its environ-ment to some extent. Interactions among organismsmay have helpful, harmful, or neutral effects on theorganisms involved. [Systems and Interactions]

All organisms have roles in their environments.They eat other species, often serve as food for otherspecies, and may shelter (trees) or decompose (fungi)other species. Some organisms fill more than onerole. [Systems and Interactions]

C-1 What are ecosystems, and how do organismsinteract in ecosystems?

Grades Six Through Nine

Populations are groups of the same kind of organ-ism (species) living together because they sharecommon environmental needs. A population is also anatural reproductive unit. [Systems and Interactions]

Species are groups of populations of the same kindof organism, reproductively isolated from otherspecies in their natural environments. (This definitionhas some exceptions, notably for many plant species,which hybridize freely in nature.) Each species has itsown niche, which is the sum of its interactions withother species and with its physical environment.[Systems and Interactions, Scale and Structure]

A community is a system of species that share anenvironment and interact with each other. Ecosystems

vary according to the physical characteristics of theirenvironments and also by the presence or absence ofparticular species. Each species has particular needsand interacts in particular ways with other species inthe environment. [Systems and Interactions]

Predation and competition are important regulator;of populations within ecosystems, and their effectshave been demonstrated in living ecosystems. How-ever, the ability to survive within the physical envi-ronment may be the most difficult task faced by mostorganisms and may be the prime factor underlyingboth adaptation and extinction. [Systems and Interac-tions, Energy]

The environment of a species consists of bothphysical and organic resources that can be exploitedand used by it and other species. There are manykinds of adaptive zones in biomes (e.g., carnivorousor herbivorous, flying or swimming, moth-pollinatedor wind-pollinated). Organisms have adaptations forcoping with their environments and surviving toreproduce. Some wiimal species live in social groups,which enhances their ability to survive. Many bio-logical processes, such as mating and food gathering,depend for their success on a certain population sizeor size range. [Evolution, Systems and Interactions]

The earth supports an incredible diversity ofhabitats that have different kinds of physical proper-ties and different associations of organisms. In eachhabitat the interaction of predation, competition, andso forth and the flow of energy through organisms inthe system can be studied and compared with those ofother ecosystems. [Energy, Scale and Structure,Systems and Interactions]

C-1 What are ecosystems, and how do organismsinteract in ecosystems?

Grades Nine Through Twelve

The physicochemical conditions (temperature, mois-ture, chemical cycles) of an environment limit thebiomes that can exist there. Among the biotic factorscontributing to the structure of biomes, interactionsrelating to the acquisition of food (predation, photo-synthesis, and so forth) and competition for availableresources are important. Many different organismsmay exploit resource zones (e.g., the coral reef envi-ronment) and may occupy the same adaptive zones(e.g., flight and insectivory in birds and bats), but theniche is a characteristic peculiar to individual species.

- --

Chapter 5Life Sciences 137

Ecosystems are frequently described by ecologistsas systems in which organisms compete for finite re-sources in the environment. In many cases, resourcesused by one species are not available for use by otherspecies (e.g., sunlight intercepted by upper canopytrees in a forest). In other cases, resources may appearto be incompletely exploited for reasons not con-nected with competition (e.g., despite the vast poten-tial for exploitation of grasslands by herbivorous mam-mals and insects, plant life flourishes and appears tobe undergrazed). A change in one part of an ecosys-tem may have far-reaching consequences for othe'parts of the ecosystem. [Systems and Interactions]

How does energy flow within an ecosystem?

Kindergarten Through Grade Three

Living things must gain cnergy from their environ-ment, either by converting it from sunlight (algae andplants) or by eating other organisms or organicmatter. Animals may eat plants, other animals, ordecomposing organic material in order to gainenergy.

-Cornbustio

ft Respiration

COOnatmosphere

41111Photosynthesis

Light

Diffusion

Plankton k

Diffusion

Decay

Carbonification

Foisil fuels(Oil, Gas, Coal)

138 Pad 11The Content of Science-

t

Decay crgartisms

C-2 How does energy flow within an ecosystem?

Gtades Three Through Six

Green plants are the foundation of the energy flowin most ecosystems because they produce their ownfond, 4sing sunlight, water, air, and minerals fromtheir environments. Animals eat the plants and in turnare often eaten by other animals. Food chains andfood webs describe the systems of energy flowthrough ecosystems. Energy is transferred upward bypredation through the levels of food chains and foodwebs and back down to the base of the food chainwhen organisms die and are decomposed. Nutrientsare recycled as living things die and decompose.

C-2 How does energy flow within an ecosystem?

Grades Six Through Nine

Energy and matter are transferred among organismswithin each ecosystem. Matter needed to sustain lifeis cycled and recycled within ecosystems; however,energy is eventually lost to the ecosystem and mustconstantly be renewed. Because energy is either usedby the consumer or lost to the environment as heatenergy, its flow through a food chain can be repre-sented as a pyramid. The efficiency of energy transferdecreases upWard through food chains and food webs.[Patterns of Change, Systems and Interactions]

The stnicture of ecosystems varies, as food chainsand food webs differ in complexity. Not all biomeshave secondary carnivores or even any carnivores atall. Decomposers use organic material from produc-ers, herbivores, and carnivores, and themselves de-compose. Matter and energy are thus partly recycledin the environment. [Energy, Scale and Structure,Systems and Interactions]

C-2 How does energy flow within an ecosystem?

Grades Nine Through Twelve

Organisms are adaptable, dynamic systems thatcontinually exchange energy with their environments.Matter needed to sustain life in an ecosystem iscycled and reused. Some of the cycles arc the carboncycle, the nitrogen cycle, the water cycle, and variousmineral cycles. The presence of varinus species inecosystems is largely limited by these cycles. [Pat-terns of Change]

The biomass production of ecosystems is generallyhigher nearer the equator than it is toward the poles.This is because more sunlight allows greater plantproductivity, which in turn permits more complexfood chains and food webs. [Energy, Systems andInteractions]

Through the absence or extinction of species, foodchains and webs may become simpler, and energyflow may change through an ecosystem. The prolif-eration of sPecies makes food webs more complexand also affects the flow of energy. [Energy, Systemsand Interactions]

Ecosystems are often characterized as being inequilibrium. This concept : invalid with respect tothe flow of energy, which is only inefficiently usedby consuming organisms. It is valid with respect tothe cyclical flow of nutrients through trophic levels ofan ecosystem, because there is a more or less constantamount of matter available for cycling through eco-systems. [Energy, Stability, Systems and Interactions]

How do ecosystems change?

Kindergarten Through Grade Three

As seasons change, living things also change. Eachspecies has its own life cycle. Events in its life cycleare matched with particular events in its surroundings(e.g., winter dormancy, the fall of leaves, the dailycycle of opening and closing of many flowers, matingseasons). [Patterns of Change]

Ecosystems have changed through time as theliving things in them have also changed. New kindsof organisms have appeared, and others have becomeextinct. In this way ecosystems have changed throughtime. Recently, changes in ecosystems have beencaused or accelerated by human intervention. Someof these changes have been destructive to ecosystems,causing the extinction of species and the disappcar-ance of their natural habitats. [Systems and Interac-tions]

C-3 How do ecosystems change?

Grades Three Through Six

Ecosystems and the organisms in them changc withdaily, seasonal, and annual cycles of environmental

; Chapter 3Life Sciences 139

Global change has also occurred in the past. Humans, for example, have caused extensive waves ofhabitat simplification and deterioration in Europe, the Middle East, and the Mediterranean and havecaused massive extinctions of species in New Zealand, Hawaii, and other places.

change. Organisms have their own cycles of life,from birth to death, and also cycles of growth,feeding, and reproduction. [Pattems of Change]

Changes in one part of an ecosystem (such as theintroduction of a new predator or the extinction of aproducer species) affect other parts of the ecosystem.Populations naturally increase and decrease accordingto changes in the food chain, particularly changesrelated to available resources. [Systems and Interac-tions, Pattems of Change]

Changes in the physical environment of an ecosys-tem, such as moisture and temperature, can drasti-cally affect the entire system. Some of these changes,such as El Milo, are a natural part of the environ-ment; other changes, such as depletion of the ozonelayer, are caused or accelerated by humans. Thesechanges are frequently detrimental and have far-reaching consequences.

In an ecosystem species move in and out, die, andevolve to adapt to changing conditions. Changethrough time is a natural process of ecosystems, butin the recent past humans have quickened this changeby overfaiming, overhunting, and clear-cuttinghabitats for human use. As a result, many specieshave been wiped out, and others am threatened.[Evolution]

The diversity of species at the lower levels of foodpyramids generally deteimines the diversity andcomplexity of interactions at higher levels. Forexample, an ecosystem with few green plants mayhave a limited number of herbivorous predators.

C-3 How do ecosystems change?

Grades Six Through Nine

The cycles of matter, such as oxygen, nitrogen,water, and minerals, are crucial to sustaining ecosys-tems. [Patterns of Change, Energy, Systems andInteractions]

Relationships among species also change throughtime. Examples are the evolution of parasitic systems(parasite and host), mutualistic systems, and corn-

140 Part IIThe Content of Science

mensal systems. Habits such as browsing, grazing,camivory, and herbivory have evolved many timesover. For example, herbivorous dinosaurs evolvedfrom carnivorous ones, and the diet of bears rangesfrom entirely carnivorous (polar bear) to omnivorous(black bear) to herbivorous (giant pandas).

Populations may stabilize over a period of time in abalanced ecosystem, where relationships amongspecies are in a dynamic stability. Ecosystems aredynamic, and they change through time as climateand species compositions change. Speciation, extinc-tion, immigration, and emigration am four ways inwhich the species composition of ecosystems canchange. These changes affect the availability ofsources of food and other resources (e.g., trees forshelter), and they also affect the flow of energythrough ecosystems. Ecosystems have changedthrough time as new species and adaptations haveevolved and others have disappeared. (For example,dinosaurs and giant horsetaillike trees once were thedominant land plant and animal species, but nowhoofed mammals and flowering plants occupy thesimilar environments of today.) Recently, humanshave accelerated the rates of extinction of species andalso the rates of emigration of species from theirnatural habitats, but the rates of speciation have notincreased to keep up with the very high rate ofdestmetion of species due largely to human interven-tion. [Evolution]

Natural catastrophic changes in ecosystems (e.g.,fire, hurricanes) can wipe out many species in an arcaand reset natural cycles of succession (e.g., fromgrasslands to shmblands to low forest to high-canopyforest; or underwater storms that can bury sedentaryorganisms and open an area to new colonization). Notall ecosystems have a single inevitable sequence ofsuccession. Fire and other catastrophic agents are anatural part of most ecosystems. [Patterns of Change,Evolution, Stability]

Changes in the environment can affect the size of apopulation, which may lead to its locai or globalextinction. Species must be sufficiently adaptable to

absorb these changes and respond to them. Optimalpopulation size helps to ensure variations in theorganisms necessary for the population to survive.[Systems and Interactions; Stability]

C-3 How do ecosystems change?

Grades Nine Through Twelve

Because of the innicate relationships that existamong species in a community and because of abioticfeatures of the biome, a change in one part of theecosystem may have Tar-reaching consequences to thesystem. These changes are difficult to predict and tocontrol. For example, the introduction of a pike into aSouth American lake or of rabbits into the Australianoutback may have very detrimental consequences onthelocal natural flora and fauna. [Systems andInteractions, Evolution]

Various periodic cycles of organisms in an ecosys-tem, as well as cycles of nutrients and other neccssarymaterials, are important controls on the diversity ofecosystems thmugh time. Quite frequently, ecosys-tems have a carrying capacity for each species thatthey can sustain. When these conditions are ex-ceeded, overpopulation can lead to depletion ofresources, and local extinction can result. [Patterns ofChange, Systems and Interactions]

Species diversity (the number of species in anecosystem) and species richness (relative numbers ofindividuals of various species) are both important com-ponents of diversity and how it changes through time.Organisms tend to be dispersed through their environ-ment according to the availability of crucial resources,which fluctuate seasonally and annually. [Evolution]

Succession is a predominant but not universalpattem of ecosystems; the dynamic stability ofspecies composition in ecosystems is maintained bylocal biotic and abiotic conditions. Fire, disease,storms, and prolonged extremes in weather conditionsare all natural features of ecosystems that constantlyreset ecological conditions and contribute to thedynamic flux of biomes. [Evolution, Stability,Patterns of Change]

Ecological relationships among species changethrough time, as species evolve, become extinct,immigme, and emigrate. This affects the flow ofenergy and of nutrients through the ecosystem. Someimportant ecological changes (such as the evolutionof grasslands) open new resource zones (e.g., food forherbivorous mammals), promote the evolution of new

adaptations (e.g., grazing dentition from browsing),and create opportunities for the diversification ofspecies (e.g., horses and other herbivores that movedfrom wooded to open environments in the earlyTertiary period). The introduction of predators oicompetitors, long-term and short-tenn changes inclimate, and environmental catastmphes are allchance factors that shape the history of ecosystems.[Energy, Evolution]

What are the responsibilities of humans towardecosystems?

Kindergarten Through Grade Three

Human practices can often affect the well-being ofother species in the environment. Humans shouldrespect living things and foster their survival. Be-cause we depend on other species for food, clothing,shelter, and other needs and will continue to do so, itis important for humans to respect nature and con-serve natural habitats, resources, and species.

C-4 What are the responsibilities of humans towardecosystems?

Grades Three Through Six

Waste disposal, the use of land (particularly theelimination of feeding and breeding grounds of manyspecies), imprudent collecting, pest control, hunting

The current attention to tropical deforestation,acid rain, ozone layer depletion, and the green-house effect is not a mere fad; these processesare evidence of the stresses that human activitiesplace on the global ecosystem. Such problemswill increase in number and degree well into thenext century. Instructional materials in sciencemust address these issues in an integrated waynot as isolated symptoms but as facets of thesame overarching issue. In some areas, humanshave surpassed the carrying capacity of theirregions, which has caused widespread famineand further deterioration of atmospheric, oceanic, and ecological systems.

/1)0 Chapter 5Life Sciences 141

practices, and the destruction of natural habitatsthrough human-caused disasters have contributed tothe extinction of species and to the loss of theirnatural geographic and ecological ranges and havethttatened or destroyed ecosystems.

C-4 What are the responsibilities of humans towardecosystems?

Grades Six Through Nine

Ecosystems often exist in a fragile balance. Theextinction of a species by human contribution oftenaffects the weii-being of the ecosystem. Pollution,which can be defined as an unnatural excess of(usually) abnormal materials in an ecosystem, is aprimary human cause of local extinction. The destruc-tion of natural habitats, such as the tropical rainforest, and the elimination ofnecessary resources,such as bmeding grounds turned into areas forrecreation, agriculture, or housing, are the primarycontributions by humans to the destruction of otherspecies. With careful planning, humans can manageecosystems to preserve their diversity and naturalbeauty, while allowing human use.

C-4 What are the responsibilities of humans towardeco'dystems?

Grades Nine Through Twelve

Land use, pollution, energy use, and application oftechnology all involve ethical considerations forindividuals and society. Conservation is not simply anethical question; it is in the vested self-interest ofhumAns to conserve and respect nature. Un.lerstand-ing life cycles, predator-prey relationships, metabo-lism of organisms, and other biotiCand abioticinteractions makes it possible for humans to contrib-ute to the well-being of species in natural ecosystems.The control or eradication of populations of destruc-tive or disease-causing organisms is also madepossible. Such activity always has some effects on therest of the ecosystem. (See further discussion inChapter 1, The Nature of Sciente.)

HuMans are unique among the earth's organisms intheir intelligence and adaptability. Humans canchooce to change their behavior and plan to providefor the needs of future generations. These considera-tions extend beyond those ofenergy sources, miner-als, and agriculture to areas of natural beauty andrecreation and diverse floras and faunas of the world.[Systems and Interactions, Evolution)

142 Part IIThe Content of Science

Pollution comes in Many forms: the introduction ofunnatural substances into an ecosystem; an excess ofnatural substances; or the acceleration ofnutrientflow through an ecosystem, bypassing natural pro-cesses and patterns (e.g., eutrophication of ponds andlakes). In addition, visual, auditory, and thermalPollution not only detract from human appreciation ofnatural ecosystems but also affect adversely otherorganisms living in them.

The environmental impacts of unregulated defor-estation have serious global consequences andare often devastatingly irreversible. Deforesta-tion is the permanent removal of forest andundergrowth. In the late 1980s, thousands ofacres of virgin tropical rain forest were burnedevery day in order to clear land for grazing andcrop production. Forest acreage equivalent to theentire state of Maine was destroyed every year.This massive combustion of carbonaceous mate-rial released enormous amounts of carbon diox-ide imo the atmosphere, thus exacerbating thegreenhouse effect already created by petroleum-consuming countries.

Given the rate of deforestation in Third Worldcountries to obtain lumber and food, the forestsin the southern hemisphere could all but disap-pear within the next few decades. In a study ofthe effects of deforestation on species diversity,coordinated by former President Jimmy Carter,scientists predicted that 20 to 30 percent of theworld's species were in jeopardy. In Colombiadevegetation rendered a hydroelectric generatingplant completely useless because its reservoirfilled with debris. To slow these disturbing trendsof erosion, forest devastation, and species annihi-lation, American corporations have purchasedacreage in the threatened forests of the Amazonbasin and elsewhere. But additional interventionis vdally needed to prevent what mightbe animminent global disaster.

.154

Part III

Achieving the DesiredScience Curriculum

143

Chapter 6

Science Processesand the Teachingof Science

MO chapter explains the processes of science thatfonn the core of science pedagogy: observing,communicating, comparing, ordering, categorizing,relating, inferring, and applying. As scientists usethese processes in their everyday work, so scienceteaching should center instruction, particularly hands-on instruction, on these fundamental processes.Expository instructional materials should show howscientists actually use these processes in their work.This chapter also considers the values and ethics ofscience that should be taught to students, the role ofscience and technology in society, and guidelines forconstructing the best possible science curricula inelementary, middle, and secondary schools. Ofparticular importance are the efforts necessary toreach the historically underrepresented or disenfran-chised students, including those for whom considera-tions of gender, ethnic and cultural backgrounds, andphysical disabilities are of primary importance.

This chapter opens with a recapitulation and elabo-ration of the thinking processes formalized in the1984 Science Framework Addendum. These mentalfunctions are referred to as processes, not skills. Thisconvention helps to avoid the educational connotationthat skills imply routine, low-level procedures. Theterm thinking skills has unfortunately become anoxymoron; however, the term processes suggests thedynamic, higher-level effort required in thinkingscientifically.

Much of Section A is devoted to building thinkingprocesses based on prior experience; SPetion C tellshow to develop science concepts for students. Sec-

144 Part IIIAchieving the Desired Curriculum

tions D and E consider hands-on science learning andthe role of ethics and values in science classes.Section E treats the need for showing the interrela-tionships of science and technology to society.

This chapter is oriented toward helping studentsbuild their understanding of the natural world andhelping them understand its connection to our techno-logically advanced society. It also advocates astudent-centered science program created by teacherswho are free to design the types of experience thatbest fit their students.

Section. A Scientific ThinkingProcesses

SCIENCE is an active enterprise, made so by ourhuman capacity to think. Scientific knowledge growsas scientists think about the natural world, act on thatknowledge in planned ways, and then developthoughtful explanations of the results. The knowledgeof science is its content. There is continual dynamicinteraction between the content of science and thethinking processes that characterize the scientificenterprise.

The content of science consists of a highly struc-tured, complex set of facts, hypotheses, and theoriesin a context where many observations have meaning.Theory development is progressive; theory suggestsfurther observations that often make possible furtherelaboration and testing of the ther)ry.

5 6

Scientists use their senses and extensions of theirsenses to see, touch, and otherwise view the world,observing its characteristics and behaviors as objec-tively as possible. Scientists describe and picturewhat they observe in various ways, thus communicat-ing their ideas to others so that they can exchangeviews and interpretations and pass along information.They test what they know against what they do notyet know, comparing features and behaviors forsimilarities and differences. Scientists organize theirunderstandings, ordering and categorizing them intobroader, more general groupings and classifications.They study the interactions among objects anddescribe the events, relating factors that reveal deeperinsights into causes and effects. Scientists hypothe-size and predict what will happen based on accumu-lated knowledge and on the events they expect to takeplace, inferring something that they have not seenbecause it has not yet happened or because it cannotbe observed directly. And as knowledge growsthmugh the use of these scientific thinking processes,scientists develop expertise, applying both knowledgeand processes for useful purposes, to make stillfurther extensions of the explanatory power of theoryand to perceive fresh possibilities.

OBSERVING

The scientific thinking process from whichfundamental patterns of the world areconstructed

The most fundamental of the scientific thinkingprocesses is that of observing. Only through thisprocess can we acquire infomiation from our environ-ment. Given objects to play with, the young childobserves them by looking, touching, tasting, smelling,

Teachers statements and questions that facilitate theprocess of observing:

"Tell us what you see.""What does this feel like?""Give us information about its shape and size.""What do you hear?""Point out the properties that you observe.""What characteristics seem to be predominantr"What properties can you find?"

and listening to them. These senses enable the childto construct a view of the world and how it works. Ina similar but more structured manner, adults place aspace probe on the surface of Mars to measure andrecord data. A mechanical hand touches the surfaceand crumbles the soil. Automated chemical "laborato-ries" analyze the material. Sensors "smell" the atmos-phere. With each of these actionsthe youngster'sfirsthand, sensory experiences and the adult's in-formed, inventive extensions of the senseshumansgather information as raw material for constructingfundamental knowledge.

Sometimes when we observe, we do not see verymuch. If we do not know how to look, we will not seeanything of importance. Knowledge from priorobservations enables us to extract more useful infor-mation from a new situation. For example, we mighthear the songs of birds and recognize only that some

The capacity for deriving patterns is more highlydeveloped in humans than in any other animalthat we know about. Most organisms exist in astimulus-response relationship with their envi-ronment. Birds respond to danger by acting inways that have a high probability of helping themescape. Frogs sit motionless and unseeing untilan insect passes by; then the frog thrusts itstongue toward the insect to take it in as food.Plant growth is stimulated by sunlight or inhib-ited by the lack of it. Humans learn about envi-ronments by realizing patterns within them andthen act on the environment to adjust or change itto suit their purposes. They are playful patternseekers when they daydream, doodle, or justenjoy an observation; and sometimes they arepurposeful pattern seekers as when they try tocomplete a puzzle, make sense out of something,or resolve problems. Because of this pattern-seeking capability, humans can live successfullyin virtually any environment on earth. No otherspecies is able to do so. Although all of us bynature are pattern seekers, the scientist is anexpert, well-practiced pattern seeker.

.1 5 "i'Chapter 6Science Processes and Teaching 145

"The whole thinking process is still rather mysterious to us, but I believe that the attempt to make athinking machine will help us greatly in finding out how we think ourselves."

Alan Turing

birds are singing. Knowing more about the character-istics of bird sounds, another person might recognizethree different types of birds singinga sparrow, arobin, and a blue jay. Even without seeing the birds,this person has a richer view of the event. Stillanother person might recognize that one bird is givinga warning signal and another is giving an aggressiveterritorial call. This expert, using both hearing andprior knowledge, "observes" something much deeperabout the event than other two listeners.

The scientist, as observer, systematically gathersinformation of the world through direct and creativeindirect use of the human senses. With an initial bodyof data, the scientist refines information by usingother scientific thinking processes such as comparing,categorizing, and inferring, all in an attempt tounderstand and explain what was observed.

As much as possible, the scientist adds a practical,trained objectivity to the process of observing. Afallen leaf is described in terms of its observable,verifiable propertiessize, shape, tip, base, venation,serration, and so on. It is not described as diseasedunless there is some evidential basis for doing so.Because of the importance of objectivity in thesciences, there has arisen, over the years, a myth thatscientists are completely objective individuals whocan remain independent of the information beinggathered. The scientist is every bit as human as otherpeople and is influenced by factors similar to thosethat influence anyone's objectivity. But prior experi-ence and training are crucial factors. As noted,knowledge gained from prior experience can enable aperson to "see" more in a situation. In schools,students bring with them a variety of previous experi-ences. Teachers can expect students to exhibit a widerange of observing behaviors, depending on thecultural background and values that each brings to,and imposes on, the objects and events that they areasked to observe. Teachers should encourage studentsto share their differing perspectives and welcome thediversity of the students' background.

Some students are highly influenced by what theyanticipate the teacher wants them to observe. Other

146 Pad IliAchieving the Desired Curriculum

students may be influenced by what they feel are theexpectations of their peer group. Being objective isdifficult, yet scientists try to observe as objectively asis humanly possible.

Science activities that involve students in thr;process of observing provide them with a repertoireof concepts about size, shape, color, texture, andother observable properties of objects. As it grows,this repertoire enriches the student's ability to ob-serve and apply concepts. This development isessential for the understanding of more complex andmom abstract ideas in the sciences.

COMMUNICATING

The scientific thinldng process that conveysideas through social interchanges

Most animals are able to communicate in some waywith other members of their own species, but humans,more than any other organism, are unique in theability to create and use language and symbols thatconvey ideas in the present and preserve those ideasin order to communicate with others in Cie future.

Scientists communicate through published works,lectures, and conferences. The community of scien-tists in a given field, redding and studying eachother's works, provides a check on the objectivity andaccuracy of a scientist's work. Published research isreplicated or extended by others interested in the

Teacher's statements and questions that facilitate theprocess of communicating:

"What do you see?""Draw a picture of what you see through themicroscope.""Plot the data you gathered on a graph.""Make a histogram of the number of raisins in slicesof raisin bread.""Write up your experiment so it can be replicatedby someone else.""Summarize your findings and plesent them to theclasS."

topic. Inaccuracy or error in the work is quicklydiscovered.

A histogram, for example, communicates a distri-bution along a continuum, as in tallying the heights ofyoungsters in a classroom. A Cartesian graph com-municates information that relates one factor toanother, as in using the height of a burning candle asa function of time.

Language arts activities and mathematics, with theirways of depicting data, should not be separated fromscience instruction. The communication skills of onecontent area enhance the skills of the other.

COMPARING

The scientific thinking process that dealswith concepts of similarities and differences

The process of comparing builds on the process ofobserving. Unfortunately, some people confuse thetwo: "Observe the similarities and differences be-tween these two animals." What they mean to say is:"Compare the similarities and differences."

We can learnabout the shape (or color, sin,texture) of an object by comparing its shape to thoseof other objects. Objects are separated or put togetheron the basis of comparable differences or similarities.When we do this, we develop more complex conceptsthan with simple observations of these objects. Forexample, youngsters can conceptualize two distincttypes of measurement involving length: (1) length asa property of an object; and (2) length as a lineardistance between two objects or points.

To find out more about an unfamiliar naturalphenomenon, scientists often compare it to somethingthey know well. They learn more about the un-knownthe ways in which it is similar and the waysin which it is differentfrom the known. All scien-tific measures (length, using rulers; mass, usingbalances; temperature, using thermometers; volume,using containers; time, using a stopwatch; and soforth) rely on the process of comparing an unknownto a known. Thus, when scientists use a ruler tomeasure an object, they are comparing the knownlength of the ruler to the unknown dimensions of theobject. When they are finished, they know somethingabout the object that was not known before (e.g., itslength and width).

The scientist adds a dimension of objectivity to thisprocess of comparing. While people often make

Teacher's statements and questions that facilitate theprocess of comparing:

"How are these alike?""How are these different?""Compare these on the basis of similarities anddifferences.""Which is larger/smaller (softer/louder, smoother/rougher, wetter/drier)?"

broad, sweeping comparisons, scientists attempt to beexact in their comparisons. The reason is that theoriesand experiments have reached high levels of preci-sion, and old standards of measures may be inade-quate. For this reason the standard meter bar, kept ina temperature-controlled room in France and useduntil 1983 to calibrate secondary standards all overthe world, was replaced by a combination of the exactknown speed of light in vacuum and a very preciseatomic clock. Today, one meter is the distance that apulse of light travels (in a vacuum) in a specified timeinterval. Secondary standard bars are calibrated interms of this fundamental distance. According to thetheory of relativity, the speed of light in a vacuum isknown to be exactly the same for all observers. Timeis now measured by atoms rather than by the lessuniform revolution of the earth.

)

ORDERING -The scientific thinking process that dealswith patterns of sequence and seriation

Ordering is the process of putting objects or eventsin a linear format. As such, there are two kinds ofordering: sedation and sequencing.

When scientists use sedate objects or phenomena,they place them in order along a continuumfromsmall to large, rough to smooth, soft to loud, light toheavy, sharp to dull, dim to bright, and so on. Theextremes are determined and ranges are established.Examining frequencies within ranges often revealspatterns that could not be seen by casual observa-tions. For example, counting the number of peas ineach pod in a sampling of pods is a way of determin-ing the range of the number of seeds produced by peaplants. With a range established and appropriate unitsplaced between them on a histogram, tallies for all the

Chapter 6Science Processes and Teaching 147

Teacher's statements and questions that facilitate theprocess of ordering:

"Which came first, second, last?""What is the range in the data you gathered?""In what order did these events take place?""Where in the order would you place these (forinserting in a range)?""Give evidence e when the pattern repeatsitself."

sample pods provide a frequency distribution withinthe range of the seeds produced. Looking at thedistribution reveals information that could not beknown by simply looking at peas in pods (e.g., thenatural distribution curve indicates the most and leastlikely number of peas in pea pods).

Seriating objects can involve an almost limitlessnumber of properties. Many are evident in scientificscales: windspeed scales (e.g., Beaufort's windspeedscale); temperature scales (Celsius, kelvin, Fahren-heit); elevation scales (below or above sea level);brightness scales (star magnitudes); tensile strengthscales; decibel scales; and the electromagneVe spec-trum. All of these scales were derived by seriallyordering information along a continuum.

When events are ordered, they provide a sequencethat tells a logical story. When scientists sequenceevents, they order them along a continuum of timefrom earliest action to latest action, from the first mo-ment to the latt moment. Sequences often tell stories,usually of two typeseither linear or cyclical.

Linear stories tell us about the growth and decay ofa plant or animal, the motion of an object, or thecause and effect of an event. The ordered layers ofsediments containing fossils tell a story of the historyand evolution of life on earth. The order throughwhich an insect passes through stages tells the storyof the life cycle of an insect.

Cyclical stories tell us about recurring events. Thewater cycle is the story of how water comes to theearth as rain, snow, and so forth; rises into the atmos-phere; and is returned again to the earth. A descrip-tion of the seasons and the changes which occurthrough them is a cyclical story. The motions of theplanets around the sun are repeating cyclical se-quences.

148 Part IIIAchieving the Desired Curriculum

CATEGORIZING

The scientific thinking process that dealswith patterns of groups and classes

Categorizing is the process of putting objects orevents together using a logical rationale. There aretwo kinds of categorizing: grouping and classifying.

When scientists categorize objects or ideas, they doso in order to compare and communicate informationabout them. Leaves, for example, can be groupedtogether on the basis of some commonality, such astype of venation, serration, tip, base, and so forth. Auseful grouping is one that increases understanding ofthe individual items by recognizing a commoncharacteristic among different items. Yellow flowerswith five petals, for example, can be placed with allyellow flowers, regardless of the number of petals onthem; they can be placed with different colotedflowers that have only five petals, or they can beclassified only with other yellow, five-petaled flow-ers. Through comparing different systems of classifi-cations, scientists can recognize those that are mostlogically consistent, best reflect the history andpattern of nature, or best explain natural propertiesand relationships.

Conceptualization of principles and laws almostalways follows a systematic compiling, ordering, andcategorizing of data. Bodies of knowledge grow fromlong-term organizing processes. The botanist, forexample, works with identified characteristics thathave been corapiled by many botanists for more thana century. By observing many different leaves,comparing them, and describing their characteristics,botanists have identified groupings useful in theidentification and study of leaves.

Teacher's statements and questions that facditate theprocess of classifying:

"On what basis would you group these objects?""Put together all those that you think belong to-gether.""What is another way in which these minerals canbe categorized?""Identify several characteristics you used to classifythese rocks.""What grouping best reflects the evolutionaryhistory of these animals?"

1 C 0

Scientists in aI fieldsfrom chemistry, to physics,to astronomy, and so forthuse the categorizingprocess to group and classify the objects in theirdomain of work.

Young children generally develop in their ability tocategorize by first sorting and grouping; that is, byputting items together on the basis of a singleproperty (e.g., color blues in one pile, reds in an-other, and yellows in a third pile). Experience isnecessary for them to be able to put objects togetheron any given characteristic (e.g., the leaves picturedcan be grouped on any one of the listed characteris-tics). As they grow older, gain experience, anddevelop more'advanced cognitive capacities, young-sters begin to classify items, by putting them togetheron the basis of more than a single property at a time(e.g., rocks that contain iron and are volcanic mightbe grouped together on these two common character-istics and separated from rocks that contain iron but3re sedimentary in origin, and rocks that arc volcanicbut do not contain iron).

RELATING

The scientific thinking process that dealswith principles concerning interactions

Seeing relationships between and among things inour environment is quite different from comparing orcategorizing objects on the basis of their characteris-tics. Relationships involve interactions, dependencies,and cause-and-effect events.

A zoologist might study lions and learn somethingabout the characteristics of the animal, the environ-ment in which it lives, and the animals it cats. Butzoologists go beyond the characteristics by determin-ing relationships among them. The lioness is the mainfood gatherer in a pride of lions (a characteristic of apride). She sees only shades of gray, no colors (acharacteristic of the carnivorous mammals). She sitsin the tall grasses of the savannah, and through thegrasses she watches her prey, the zebra, and decideswhen to make her move (a characteristic behavior ofstalking carnivores). Zebras have black and whitestdpes (a characteristic of the zebra). The zoologistasks, "Is there a relationship between what the lionesssees through tall grasses and the zebra's colorationand stripe configuration?" The zebras travel in herds,placing sentinels at appropriate places in the herd togive warning of danger (characteristic behaviors of

Teachers statements and questions that facilitate theprocess of relating:

"What factors caused the event to take place?""Explain why this is a good or inadequate experi-mental design.""State a hypothesis so that it is testable.""What is the relationship between the coloration ofan animal, its environment, and its predators?""Using this line graph, tell the relationship betweendistance and time.""Design a study to compare the evaporation ratesof different liquids (e.g., alcohol and water)."

zebras). The zoologist wonders, "Is there a relation-ship between the coloration and its configuration andthe behavior of traveling in herds?" To bring down azebra, the lioness must pounce on its back near theshoulders, sink her fangs into its neck, then roll off,snapping the neck as she falls (a characteristicbehavior of the lioness). The zoologist finds that thelioness accomplishes her task about once in everyfive tries. If she does not land properly near theshoulders, she is thrown from the zebra. The zoolo-gist wonders, "Is there a relationship between hersuccess rate and the behavior and coloration patternof the zebras?" Clearly, the principles derived fromthis setting come about by using one's ability torecognize and comprehend relationships amongseveral thingsin this case, the behaviors andcoloration of the pmdator and prey, and factorsinherent in the environment. Scientists look forrelationships among characteristics and behaviors inorder to understand events that take place.

A physics student has a metal ball and a long,inclined grooved track. Having a way to measure thespeed with which the ball reaches the bottom end ofthe track, the student wants to investigate the factorsthat influence the speed. First, fixing the angle ofincline of the track and varying the starting point ofthe ball, the student fixes the starting point and variesthe incline angle. The speed is measured each time.The student finds that the speed depends on both thestarting point and the incline angle. But then thestudent discovers that a long roll along a gentle slopegives the same terminal speed as a shorter roll along asteeper slope, as long as the starting point has thesame height in both cases. What really counts, then, is

Chapter 6Science Processes and Teaching 149

is.=xlmiammill11=1111

We cannot experiment directly with galaxies,black holes, quasars, or quarks, but we still knowa great deal about them. Scientific descriptions ofrelationships are always based on the logicalarguments that encompass all the data on hand.

thc height of the starting point. Thc direct dependenceof speed on height and the less direct relationshipbetween starting point or incline angle and speedestablish a basis for understanding conservation ofenergy.

In the sciences, information about relationships canbe descriptive (as in the lioness/zebra example) orexperimental (as in the inclined plane example).Many ideas in astronomy are based on description.We cannot experiment directly with galaxies, blackholes, quasars, or quarks, but we still know a greatdeal about them. Scientific descriptions of relation-ships are always based on the logical arguments thatencompass all the data on hand.

Knowledge derived from experimentation requiresthat the scientist use the relating process throughPypothesizing and controlling and manipulatingvariables. For example, a scientist might determinethe factors that influence the rate of swing of apendulum by isolating possible factors and testingthem one at a time while holding all others constant.The dentist might consider only the variables of. (I)the weight attached to the pendulum, heavy and light,and (2) the length of the pendulum, long and short.The scientist might then set out the four combinationsof possible variables: (1) heavy and long; (2) lightand long; (3) heavy and short; and (4) light and short.

The ability to separate variables by exclusion (thesystematic testing of each variable individually whileall others are held constant in order to determinewhich are relevant and which have no effect) is verypowerful. Instead of being closely bound to theimmediate experience, the scientist thinks, "Maybe ifI changed this, such and such would happen," andthen performs the necessary actions to confirm orreject the supposition. What the scientist tests is a

hypothesisa reasoned description of relationships,stated so that it can be tested. The test is thescientist's deliberate and systematic manipulation ofvariables.

150 Part lllAchieving the Desired Curriculum

INFERRING

The scientific thinking process that dealswith Ideas that are remote In time and space

Inferences deal with matters that an.: often beyondthe here and now. They are not experienced directly.The events of interest are distant in either time (suchas the inferences paleontologists make about life onearth in the Paleozoic era), or space (such as are theinferences astronomers make about the origin of theuniverse), or scale (such how electrons behave inatomic systems). They are established throughinferential reasoninglogical conclusions made froma chain of reasoning or answers derived throughreasoning from evidence and premises.

Long before we sent a probe to Mars, scientistsmade inferences about the planet. A century ago, theonly data from which inferences could be made camefrom telescopic observations. Mars was described asthe red planet with markings mat some observersthought lookal like canals. Because of the perceivedcanals, some inferences were made about life onMars. More recent technology led to the detection ofan atmosphere and the presence of water. And,among other things, it was inferred that Mars has oroncc had life on it. Today, our descriptions of Marshave become more complex and still more extensiveinferences about the planet have been made. Theinference about life on Mars has not yet been con-firmed or rejected.

The establishment of preliminary inferences in anew context (e.g., Mars) from knowledge alreadyobtained in another context (e.g., Earth), is one of thebasic reasoning patterns humans Ube to understandremote places and events.

Teacher's statements and questions that facilitate theprocess of Inferring:

"What can you infer from these data?""What arguments can you give to support yourprediction?""Explain how we know about quasars.""Under what conditions are we able to extrapolateor ioterpolate from data?""How would you determine how many frogs live ina pond?"

e ... ...s

. -- . .` r .

_

Gradelevel Science processes Descriptions of content Principles/Examples

K-3 1. Observing Focuses on one-word Static-organizational principles2. Communicating descriptions, discreet Sea water is salty. Water in most lakes and3. Comparing ideas rivers is not salty (def-mition by class).4, Ordering5. Categorizing

Flowers produce seeds that grow into newplants (definition by function).Machines are devices that make some taskseasier (definition by function).

3-6 1-5 above, plus

6. Relating

Focuses on principles,generalizations, laws

Active-relational, interactive principles

A force is a push or pull (relational).Poikilothermic (cold-blooded) animals havebody tempetatures that vary with surroundingtemperatures (relational).Heat changes water from liquid into gas(interactive).

6-9 1-6 above, plus Focuses on ideas that Explanatory-predictive, theoretical principles7. Inferring are not directly observ-

ableMatter is composed of tiny particles that are inconstant motion. In many substances these arecalled molecules (inference).The characteristics of mineral crystals are theresult of the way their atoms are bonded to-gether in geometric patterns (inference).When male and female sex cells combine insexual reproduction, equal numbers of chromo-somes from each parent determine the charac-teristics, irzluding the sex, of the offspring(prediction).

9-12 1-7 above, plus Focuses on inventions Usable-applicational principles8. Applying and technology; con-

cepts, generalizarions,principles, laws re-

Selective breeding of plants and animals withdesirable characteristics results in offspringwhich display these characteristics more

- phrased to suggest useand application

frequently (application).Use of the oceans and ocean resources is afocus of international conflict as well asinternational cooperation (application).The development and use of more efficientlighting sourcesfluorescent instead ofincandescent, for exampleis one way ofconserving energy (invention; use).

eChapter 6Science Processes and Teaching 151

Through evidence and rcasoning, we can makeinferences about the movement of continents. Withthose inferences and other inferences from observedphenomena, such as magnetic anomalies, we candevelop a theory of plate tectonics. From inference4about events in the universe comes a big bang theory.We cannake inferences about the shared characteris-tics of animals and plants and establish a hierarchicalclassification scheme that gives evidence ofevolu-tionary relationshipsa classification scheme of ahigher conceptual order than one created only fromobservation. But inferences, no matter how orderly intheir derivation, are never final; they must be tested todetermine whether they are true. A valid test involvesobservations independent of those used to generatethe inference.

Educators must be concerned with implications andvalid inferences in science because inferences involveorderly, connected thinking. Using the inferringprocess, studeills learn that the conclusion of anargument is an explicit statement of something that isimplicit in the premises. Its validity, or consistencycan be certified by logical considerations alone. Tothink well, students need experience in tracing theirthoughts to the sources and then determining the truthof the source in order to judge its validity.

APPLYING

The scientific thinking process by which weuse knowledge

The building of the Golden Gate Bridge in the SanFrancisco Bay Area was a spectacular accomplish-ment. It required hundreds of experts working coop-eratively to put the bridge in place. Structural engi-neers who knew about expansion and contraction ofmetals planned how to construct components so thatthey would not warp during the heat of the day norbuckle during the cold of the night; the bridge neededto move by expansion and contraction withoutdisrupting the movement of travelers. Geologists whoknew about the local land formations and the place-ment of bedrock planned where and how to place thepilings on which the weight of the bridge was sup-ported. Meteorologists who knew about the extremesof local weather conditions contributed the dataneeded to accommodate the sway of the bridge fromwinds in any direction. Building the bridge was acooperative effort among experts who applied theirknowledge to the task.

152 Part IIIAchieving the Desired Curriculum

Teacher's statements ano questions that facilitate theprocess of applying:

"See who can invent a glider that will stay aloft thelongest time.""Design a way to keep an ice cube on your desk allday without melting.""What political points of view must be considered itwe are to protect the migration flight paths of birdsover several countries?""What factors must be weighed if experimentationon animals is to take place?""How did different lines of evidence confirm atheory of continental drift?"

Applying is a process that puts extensive scientificknowledge to use. Sometimes that knowledge is usedin a practical sc:-,se as in the building of a bridge.Sometimes it is used :a tie together very complexdata into a comprehensive framework or theory. Andsometimes, the goal is to elaborate and extend thetheory.

Each scientific field of endeavor produces newknowledge and understanding. Darwin organiudmany observations and formulated a theory thatexplained how living organisms change through time.Einstein showed how the physical world could beunderstood on the basis of relativity theory. Men-deleev logically ordered the more than 50 differentelements known in his day. His first Periodic Table ofthe Elements clearly implied the existence of ele-ments not yet identified, and he predicted their atomicweights and other important properties.

p. -

ALL the scientific thinking processes can be used tosome extent by individuals of all ages. However,there are periods in child development in whichparticular processes have a higher payoff for learning,and there are periods when some processes seem tocontribute little. For example, elementary schoolyoungsters are superb at observing, communicating,comparing, ordering, and categorizing. However,

l-$

although they can make simple inferences (If theground is wet everywhere, it must have rained I stnight), major inferential ideas (structure of atoms,movements of planets and stars) and comprehensivetheories (evolution, relativity) elude many of*hem.The major inferential ideas are best taught at theonset of adolescence or beyond. In view of thesedevelopmental stages, the parts of the scientificthinking processes are best introduced in a particularsequence, as Table 1 illustrates.

Kindergarten Through Grade Three

The most valuable processes for these grades areobserving, communicating, comparing, ordering, andcategorizing. Young students are still buildin3 a basicmental picture of the world in which they live, andthey arc quite adept at identifying the characteristicsof objectC-determining similarities and differencesamong objects and events, grouping items togetherthat belong together on some rationale, and communi-cating to others about what they have done. Studentsreadily recognize characteristics inherent in objects.This fimdamental content matter becomes the basisfor more advanced ideas. In general, the characteris-tics of objects in any scientific field of endeavor canbe learned quickly and easily by youngsters at thisagc. Thus, the curriculum in kindergarten and gradesone through three should emphasize the developmentof descriptive language through the first four scien-tific thinking processes across all fields of science.

Examples of content derived by using the processesfor kindergarten throug.i grade three:

Insects haye three body parts and six legs as adults.

Leaves h ve identifiable characteristics: tips,bases, margins, veins, and shapes.

Sounds can be classified on the basis of their char-acteristics: volume, pitch, quality.

Light travels in all directions from a source.

Motion can be a source of electricity.

Grades Three Through Six

In addition to the processes at which they are soept in the earlier grades, youngsters begin to

develop the process of relating. Using this processand building on the facts teamed earlier, youngsterswill derive many principles of science.

1e5

Examples of content derived by using the processesfor grades three through six:

Some plants have been naturally selected andretain camouflagic characteristics.

Heat causes solids to expand.

The motion of a particle is in a straight line unlessacted on by external forces.

Light can be diffracted or refracted.

Current electricity travels through some materialsbetter than others.

Physical weathering can break rocks into smallerpieces.

Grades Six Through Nine

As youngsters move into adolescence, they becomemore able to make inferences. They think more aboutthe future and understand more about the past. Theycan comprehend concepts that are not represented byobjects and materials. If their earlier activities haveprovided them with appropriate experiences, they canhypothesize, design experiments, predict, and concep-tualize the laws of science.

Examples of content derived by using the processesfor grades six through nine:

Evolution has been going on so long that it hasproduced all the groups and kinds of plants andanimals now living, as well as others that havebecome extinct.

Momentum is directly proportional to both massand speed.

Sound energy is thought of as vibrations Ciat transfer energy in wavelike patterns through molecules.

All matter is made up of atoms containing tinyparticles that carry electric charge.

Grades Nine Through Twelve

As students reach the end of their basic schooling,the knowledge they have gained can be applied invarious ways. They are able to read about and under-stand new development in the sciences; they compre-hend the essence of theories, such as evolution,relativity, kinetic/molecular theory, and so on, theyunderstand the issues related to scientific decisionmaking, and they appreciate the value of scientificand technological endeavors and, depending on the

Chapter 6Science Processes and Teaching 153

endeavors, can build a reasoned case for supportingor not supporting them. As adults they can votewisely on scientific issues, and they are flexibleenough to adapt to new technologies and new ideasthat take place in their lifetime. As future voters andmembers of an informed, literate public, they canapply their knowledge in making wise decisions.

Examples of content derived by using the processesfor grades nine through twelve:

Decision making about scientific endeavors (e.g.,animal experimentation, expensive research en-deavors, DNA alterations, genetic engineering)must be viewed from several perspectives at thesame time (e.g., economic, political, ethical,environmental).Science alone cannot resolve the problems inherentin modem society (e.g., conservation, waste man-

agement, and pollution control), but it is an essen-tial component of any such resolutions.Worldwide dialogue is needed concerning preser-vation of resources, wildlife, and so forth for thewelfare of all humankind.

With the scientific thinking processes in place,appropriate content can follow. This arrangementprovides an important way for content to progres.through the grades. Repetitious instructiontopicstaught in essentially the same way with the samepurpose and content every few yearscan be elimi-nated, and a foundation for advanced knowledge builtwhich, in turn, provides the basis for still moreadvanced knowledge. The progressive introduction ofprocesses and content through the grades movesstudents toward adult understanding of the importantthemes and content inherent in the sciences.

'Example Of a theme progressing through the grades:

Opt,Kindergarterrihrough Grade-ThreeTh-'000ejsres!..00miting,,CommUnicating, CoMparing, Ordering, CategorizingSA Mpli:Coritent:Liiiing things have identifiable characteristics; thereis great diversity among living

thiOgt

Gia001.1hree Ibrough sixThe rrocetwONetving, Communicating, Comparing, Ordering, Categorizing,,plus RelatingSO* Conter44.4vinithings are adapted to their environment forsurvival; various structures of living

things:Operatein Ways Oiat keep them alive and,growing.

Grades:SIX ThroiiihltIline,

TI*EtOcessf*:0110Miti:Cominunicatirig, domparing, Ordering, Categorizing, Relating, plus InferringSamPle'foift*:TOktioninchides-g process.*herebY.living things Are naturally selected frongeneration

glierittajiotkplOduiingdeteendints-Wiih different characteristics;.,through geologic time, evolutionary:proceisOhaveshaPecOhe forms -and glaptations of all the species of plantt arid animals now living, as,WeltatothekslhathavebeCopeextinet.

A04084110- through tvielye,,Thi,Prpcotick:Obserirink;:Cornmunicating, Comparing, Ordering,-Categorizing, Relating, Inferring, plusIying. .Saimle *id; Worldwide- Ogreernents must be made for the preservation of resources and species. The

eharacieristicsofliving things can be altered through manipulation of the DNA structure.

154 Part IIIAchieving the Desired Curriculum

166

CHILDREN create meaning for themselves; conceptu-alization is promoted and made more useful whenpresented in the context of an appropriate theoreticalstructure. Students construct representations of manytypes of knowledge, but these mental maps areespecially powerful in the ways students learn (or failto learn) science concepts. Teachers should considerwhat concepts students hold about science for at leastthree major reasons: (1) to ensure that all studentslearn science, they must have conceptually rich ideaswith which to build new knowledge; (2) conceptions(and misconceptions) about the natural world areresistant to casual challenges unless new models arebuilt; and (3) ultimately, students will be usingWhatever conceptual models they have to make senseof the world around them. The following recommen-dations will help teachers use students' backgroundinformation as a springboard for leaming new con-cepts:

i. Pose questions to determine what iaeasstudents hold about a topic beforebeginning instruction.As a first priority, teachers are encouraged toelicit from students their prior knowledge aboutthe subject of study. This procedure will givevaluable information about students' readinessfor a given idea, and it will also reveal what con-ceptions they have about the way things are orhow things work. It is important for teachers toprobe deeply for students' understandings, aswell as misconceptions, as their first responsesare usually intended to get the answer right.

2. Be sensitive to and capitalize onstudents' conceptions about science.

In all science classes, but especially in those atthe elementary grades, teachers can count onstudents to hold diverse world views aboutnature. Students from a variety of cultural back-grounds will bring different experiences and ex-planations for natural phenomena to the class-room. Their ideas should be elicited, discussed,and respected. Some students will think that the

earth is round, some will have observed that the_rth is flat with occasional hills, and some will

not have thought too much about the character ofthe planet's shape at all. For a teacher to reach allthe students in the class, a unit on the shape andstructure of planet earth might be started with anactivity that brings all the students to a concep-tual understanding of planetary shape. For ex-ample, students could be shown NASA's videoclips of the earth from space twice: beforeleaming about the observations and competinghypotheses of sixteenth-century seamen andastronomers, and again afterwards. In the longrun, grounding students' conceptions throughactivity-based science lessons will work well forall children, including the historically underrepre-sented.

3. Employ a variety of instructionaltechniques to help students achieveconceptual understanding.

The resistance of students' subtle misconceptionsor naive theory, as some have referred to it, aboutthe natural world to educational intervention isbecoming better documented and understood.Generally, students' misconceptions need to bechallenged through direct experience with situ-ations that the existing misconception cannotreadily accommodate. Students who do not thinkdeeply about the evidence before them oftenignore or discount results that do not conform totheir existing model.

Small-group work, direct-leaming activities, andsophisticated questioning strategies are shown tobe effective tools for replacing the misconcep-tion; traditional science classes consisting oflectures and reading are likely to be ineffective,especially for the historically underserved studentpopulations. For example, students with anincomplete view of how gases behave undercertain conditions are likely to maintain thosemisconceptions if the only instruction theyreceive is reading several pages about the ten-dency of hot air to rise. On the other hand, ifstudents raise questions they have about air andhelp design and perform investigations thataddress the relationship of temperature andpressure, the teacher can use this opportunity toensure that all students not only learn more about

Chapter 6Science Processes and Teaching 155

_TT,

air as a gas but also learn something aboutmeteorology and space science.

4. Include all students in discussions andcooperative learning situations.

Because there are many ways to represent theworkings of the natural world, the teacher mustsee that all students are free to express their con-ceptions in different ways. Discussions amongsmall groups should be closely monitored so thata dominant voice does not take the opportunity ofanother student to express a similar (correct)understanding in another manner. Studentsshould be encouraged to challenge and reformu-late observations and statements that are madeabout the subject at hand. The open, honestexchange of ideas must be as readily acceptableto the teacher as to the students (and their par-ents).

Section II The Role othire-Ct.6 Experience in Science

Learning'

MUCH has been written about the need for studentsto conduct hands-on investigations in learningscience. The reasons are many, but they essentiallyfall into three major categories: (1) many studentswill not truly understand the science they are sup-posed to learn if the exposure is solely verbal;(2) students learn the processes and techniques ofscience through the replication of experiments; and(3) students will enjoy and retain the science theylearn front a laboratory activity iiore than from a

'Two excellent references arc available to help teachers involveallstudents in activity-based science. The California Department ofEducation publishes an Enrichment Opportunities Guide: Resource forTeachers of Students in Math and Science (1988). This guide listsactivides for studenti(and teachers) interested in participatory sciencelearning. 03pies of the guide are available from the Bureau of Publica-dens, Sales Unit, California Department of Education, P.O. Box 271,Sacramento, CA 95802-0271. The National Science ResourceCenter, acollaborative effort of the Smithsonian Institution, and the NationalAcademy nf Science have recently published Science for Children.Resources for Teachers. This anthology of curriculum materials,supplemmtary resources, and information sources is available throughNational Academy Press, 2101 Constitution Avenue, NW, Washmgton,DC 20418.

156 Part 111Achieving the Desired Curriculum

textbook. These reasons underscore the educationalmaxim that learning by doing is the most effectiveinstructional paradigm. However, our best scienceteachers know that experiential lessons must beplanned more carefully than passive modes of in-struction.

1. Engage students in science activities byplacing them In a position of responsibil-ity for the learning task.

Many teachers describe their best hands-onactivities as "minds-on." Minds-on lessons gripstudents in a way that makes them truly engagedin the action. Students actively process the infor-mation revealed to them in direct experiences,and they demonstrate their new understandingiindiscussions with other students. The most directlyobservable clue that students are engaged in thetask is that they control the learning episode.Whether the minds-on activity is hands-on or asimulation presented through electronic (or someother medium of) learning, the engaged soldenthas the power to manipulate some aspect of whatis happening. The test for an engaging hands-onexperience is whether the student is controllingthe situation or vice versa.

For example, upper elementary grade studentsmight be asked to build a model house frompaper, including windows madeof clear cello-phane. With some of the windows covered andothers open, students place their houses in directsunlight to determine which students' houses heatmost rapidly. The task itself requires manipula-tion of scientific instruments (thermometers),control of variables, data collection and interpre-tation, and small-group discussion. Students'engagement in the task can be assessed byproviding one or more open-ended investigationsinto the effect of other variables. Students can beasked to identify those variables, then given theopportunity to design and conduct independentinvestigations to test the various factors involvedin the process of passive solar energy.

2. Provide students with experimental prob-lem solving when the result has directmeaning for them.

Along with the issue of student activity comes thenecessity for students to care about the hands-on

I h

activity in which they participate. Students whoare working to solve problenis in which they havesome Mvestmenr are more likely to learn andretain important concepts. Science education hasan enormous opportunity to invite students tolearn about their world so that students can cometonnderstand what is important for them to learnand why.

Seciton E Values and Ethics2

As a human endeavor, science has a profoundimpact on society. Values and ethics are importantcomponents of science teaching and must be consid-ered by teachers, textbook authors, and curriculumwriters. Students can become scientifically literatecitizens responsible for themselves and the world'sfuture only if they are well prepared to assume thatresponsibility. In a scientific and technologicalcontext; their ethical judgments will result in respon-sible decisions using sound values and scientificknowledge to make those decisions. In a personal andsocietal context, their ethical judgments will followthe search for knowledge demonstrated repeatedlythrough the history of science. The State Board ofEducation avers in Moral and Civic Education andTeaching About Religion:

Telling the truth and expecting to be told the truth areessential to the development of (1) personal self-esteem and basic friendships; and (2) genuineunderstanding of our society, its history, and thedemocratic process. A commitment to telling thetruth embraces the conscientious pursuit and scrutinyof evidence. Students must learn to respect theprocesses involved in the search for truth. Theyshould learn to identify and assess facts; distinguishsubstantial from insubstantial evidence; separate theprocess of searching for truth from the acceptance ofpropaganda; and examine in a constructive andunbiased manner controversial subjects such as poli-tics, ethics, and religion. School personnel should

2In dealing vnth issues of values and ethics in the saence classroom,teachers and other readers are referred to the State Board of Education'spublication Moral and Civic Education and Teaching About Religion. Thisdocument examines the legal and educational responsibilities for addressing moral values (and ttlated topics) in the classroom and is availablefrom the Bureau of Publications, Sales Unit, Califomia Department ofEducat ice, P.O. Box 271, Sacramento, CA 95802-0271.

assist students to develop their abilities to communi-cate effectively as they accumulate knowledge andreach conclusions.

For these beliefs and actions to be developed,values and ethics must be an integral part of the sci-ence curriculum. Science teachers should be sup-ported with instructional Materials and curriculumthat help students:

1. Idently.theoommonly shared values ofthe scIrtlfIC}communIty.The dis9iplinekaf=science constitute a communityof indiyiduals Sharing a general set of commonvalues:The research geneticist, the chemist, andthe oceanographer all practice science, using thesame generally shared scientific values. The setof shared values is likely to include the scientificvalues Of curiosity, open-mindedness, objectivity,and s Jcepticism.

For example, the value of objectivity often ariseswhen immature students (regardless of grde1ey4),fmd.it easier to ignore data they have'collected if they conflict with those collected bythe majority of other students, especially if, in soignoring, they are able to arrive at the "correct"answer to a problem. If students are expected toroll marbles down an inclined plane covered withdifferent materials, one can expect a certainregularity in reported results. One student,however, might observe and record discrepantdata. If the student misrepresents the data (origpores them in reporting) in order to conformwi1iclassmates, hot only has that student missedthe: int of honest scientific reporting, butPerlidps the entire class has missed the opportu-niryito investigate the effect of differing angles ofinClinktion, differing effects of applied force, or*.iateVer other variable might account for the

AfierepasLesults. Students must be encouraged, to report all data they collect in an activity and to

explain them inian honest and ethical manner7c(eyen if it means admitting to procedural error).

Proiiidtd iclentlflc values In the class-

'Students best understand a scientific value andhow it is applied when they recognize and applyit themselves. For example, it would be hypocriti-

Chapter 6Science Processes and Teaching 157

Students must learn to respect the processesinvolved in the search for truth. They shouldlearn to identify and assess facts; distinguishsubstantial from insubstantial evidence; separatethe process of searching for truth from the accep-tance of propaganda; and examine in a construc-tive and unbiased manner controversial subjectssuch as politics, ethics, and religion.

cal for teachers to laud efforts to protect nativehabitats and then use rare wild specimens in theclassrooms. Science teachers should not create amarket for animals that are collected from thewild; rather, they should insist that supply housescertify that dissection specimens are raisedexplicitly for that purpose. In class, teachersshould take time to present their position on thisissue and other sensitive issues related to thehumane-treatment of all living things.

3. Develop rational decision-making skillsapplicable to major issues of personaland public concern.Any thorough learning experience regardingvalues and ethical considerations makes use ofrational decision-making skills. Students need toanalyze issues by resolving ambiguities, takinginto account the most relevant values of thedecision makers, balancing the advantages anddrawbacks of alternative solutions, and project-ing the likely consequences of a particularchoice. By combining such a decision-makingprocedure with pertinent scientific and techno-logical information, students move towardachieving scientific literacy.

A major purpose of experiences in decisionmaking is to stimulate students to become notonly lifelong learners but also scientificallyliterate citizens, seriously concerned with theinterrelationships of science, technology, andsociety. For example, the topic of heart trans-plants could challenge students to research avariety of issues, including the latest surgicaltechniques, host rejection and other technicalcomplications, trends in patient prognosis, and

158 PartinAchieving the Desired Curriculum

economic and societal constraints in caring forpatients. The central issue could be h mi anindividual and society make decisions aboutgoing forward with heart transplants.

SCIENCE is directed toward a progressively greaterunderstanding of the natural world. Technology isrelated to science as a human endeavor, but thedirection is toward using accumulated human knowl-edge from science and other fields in order to controland alter the way things work. Technology is a meansby which society develops and advances. Teachingwith a Science, Technology, and Society (STS)approach is invariably interdisciplinary, with strongconnections to historysocial science, mathematics,literature, and the arts.

Just as the thematic approach (see Chapter 2)brings together disciplines within the sciences, anSTS approach unites larger fields of study. Studentswho learn with peers and teachers about the inextri-cable connections among science, technology, andsociety have a very different experience from thosewho learn out of context. Imagine the English classthat teaches rules of syntax and never sees themapplied in literature or joumalism; a mathematicsclass where algorithms are drilled outside meaningfulproblem-solving situations; or a history class filledwith events, but without the cultures and charactersthat make them come alive. These subjects would belittle more than skill-driven shells of the rich disci-plines that arc their heritage. Teaching science in thecontext of STS helps reveal the situations in whichscience has meaning. Science teachers should:

1. Demonstrate how the enterprise of sci-ence operates in the United States andelsewhere in the world.The scientific enterprise embodies societal con-cern for advances in understanding the naturalworld. Highly technological nations, like Japan,place a high priority on scientific and technologi-cal advancement. This priority is evident in boththe private and public sectors, where huge invest-ments are made to ensure the expansion and

i 70

refinement of scientific and techrllogical devel-opments. Much can be learned about the valuesof a society by investigating the relative prioritiesand tradeoffs in these large-scale investments.

Students can experience how society makes deci-sions among competing alternatives by simulat-ing complex decisions involving space explora-tion. Students can form groups representingdiverse constituencies for and against expandingfunding for the development of space technolo-gies. By rehearsing their group's own point ofview, as well as those of competing groups, theycan learn the interrelationships and tradeoffs forfuture investments in space exploration.

2. Examine the array of job prospects andinterest areas within the science andtechnology arena.

Science and technology will have an increasinglysignificant impact on careers and avocations inscience-related fields. Every major projection ofemployment markets predicts the need for scien-tifically literate job seekers. The Department ofLabor estimates that 50 to 60 percent of the newjob opportunities will be in information andscience/technology (sci/tech) fields.

Because California has about 12 percent of theU.S. population and employs over 20 percent ofthe science and technology labor force, well over60 percent of our students need to be educated toparticipate in that job market. The diversity of

California's science and technology economyensures a range of opportunities for students whograduate with the interest and appropriate back-ground. In fact, for California it is imperative thatall students be given an opportunity to competefor the types of jobs that are and will be available.In addition, there are many hobbies, avocations,and interests that relate to studies in science andtechnology. Regardless of our students' back-grounds, there is likely to be some outlet forcreativity, aesthetics, and enjoyment that appealsto each of them. Such interests should be high-lighted and nurtured as part of the comprehensivescience curriculum.

Using civil engineering as an activity base,students could form design teams that wouldsimulate the planning of some large (or signifi-cant) construction project. It could be construc-tion of a local dam (where they would do anenvironmental impact study); a bridge (wherethey would investigate span designs); or a multi-purpose sports stadium (where they wouldconsider seating options, traffic patterns, and soforth).

3. Describe how the products of scienceand technology change society.The products of scientific endeavors are readilyavailable to people in our culture, and studentsshould understand the origins and implications ofthese products. Developments in agriculture,transportation, allied health fields, and design and

"Science and technology spring from two different but equally important activities. One Ls the searchforknowledge and understanding, the second is the application of knowledge to satisfy human needs."

Albert Baez

"Aviation and space technologies have unlimited potential, not only for meeting industrial, commercial,

and leisure needs, but also for offering insights and solutions to scientific problems and challenges. Byexpanding our knowledge and understanding, aerospace and aviation education can extend our reachand inspire our young people, the builders and inventors of the future."

President Ronald Reagan, July 8, 1983,in a statement to the Third Biennial World Congress on Aerospace Education

; 'al ....r. 1 1 Chapter 6Science Processes and Teaching 159

The waterproof properties of the sap extracted from the rubber tree was known for centuries by theQuechua Indians of SouthAmerica. While heating the sap, the Indians added sulphur to make therubber stronger and more resilient and remove its stickiness and foul odor. This same process of vul-canization was accidentally rediscovered by Charles Goodyear in 1839, and a multiplicity of newinventions and practical applications followed.

manufacturing are all part of the sci/tech land-scape. The benefits and costs of these fields areimportant areas of investigation for the sciencestudent. The standard of living we currently enjoyis a direct product of science and technology. Thetradeoffs for such a highly consumption-orientedculture must be understood and appreciated forall those who live in this society. Failure tounderstand science results in the type of illiteracythat leads to educational, economic, and politicaldisenfranchisement.

Section G 'Elementary School Science

THE elementary school science curriculum holdsgreat potential for exploring natural phenomena andtechnological applications in science. At a time whenchildren are most curious about the world, teacherscan capitalize on this joy of learning in ways thatmake science enjoyable, interesting, and meaningful.Elementary science programs, as far as possible, must:

1. Provide a balanced curriculum in thephysical, earth, and life sciences.All three disciplines should have laboratoryactivities that involve students in "doing science."Each subject should receive roughly one-third ofthe total class time for any given year.

2. Show students that science is enjoyable.If the joy of learning permeates science classes,students will be eager to learn. The motivationprocess begins with teachers modeling a fascina-tion with scienc_ and its dynamic presence in ourdaily lives. The motivation process continues andexpands as students are given more and more op-portunities to explore the natural and technologi-cal world.

160 Part illAchieving the Desired Curriculum

3. Reinforce conceptual understandingrather than rote learning.

Conceptual understanding requires higher-levelthinking processes than lower-level recall andthus requires more in-depth experience andreinforcement in the classroom. Larger scienceconcepts can be embedded in longer-term instruc-tional events (two- and three-week units) wheredaily lessons include experiential Icar.l.g andcontinually reinforce the overarching theme(s)and related science concept(s). Conceptualunderstanding is strengthened when studentsdraw connections from concepts being studied todaily experience, novel situations, and previouslylearned ideas.

4. Organize an articulated scope and se-quence at the school level.

Principals, other school site leaders, teachers, andparents should jointly plan a sequence of scienceunits according to which each grade level treatssome significant portion of the total sciencecurriculum for kindergarten through grade six.Once the curriculum has been divided amonggrade levels, and teachers are clear on theircurricular expectations, adequate planningensures that teachers have the professionaldevelopment, instructional materials, and classtime to teach the agreed-on science curriculum.Of the total time spent learning science, at least40 percent should be involved in activity-basedlessons.

5. Arrange the classroom setting and stu-dent grouping to optimize positive atti-tudes for learning science.There are many accommodations that can trans-form the usual classroom setting into one that en-courages curiosity and motivates students to learn

more science. Classroom tables can be arrangedto facilitate small-group work on dnect scienceexperiences. Science equipment and materials, aswell as reference books and periodicals, shouldbe visible and within easy reach of the students.Bulletin boards can display the results of the mostcurrent unit of study, from student work to relatedarticles, including science careers and technol-ogy. A number of study areas in the room can bedevoted to,science learning, making it clearlyevident that this is an environment that encour-ages questioning and inquiry. Students shouldhave opportunities to work in cooperative groups,perform investigations, manipulate scienceequipment, and follow safety precautions. Thesegroups can be organized to assume responsibilityfor their learning.

6. Integrate science with other subjects.Scientific literacy could receive a considerableboost if science were used as a vehicle toenhance reading, mathematics, and the arts. Theuse of sciencc to teach other fields has beenshown to be quite successful in many exemplaryelementary science programs. Science readingshould be encouraged and integrated in theoverall cuniculum. During these integratedlessons featuring two or more subjects, it isessential that science maintain its rigor anduniqueness as a field of study. For example,students who sketch for the dual purposes ofrefining their artistic skills and furthering theirbotanical knowledge need to observe (andperhaps classify) several types of leaves care-fully before rendering them in an aesthetic man-ner that is also botanically correct.

7. Make full use of community resources.Community resources should be enlisted to par-ticipate in elementary sciencelessons. Studentswho may have less outside experience to drawon are enriched by community resource agen-cies and their personnel. The local grocer, firefighter, florist, or farmer can add a real-worlddimension to a science experience. Field trips tolocal parks, gardens, streams, or other sciencerelated settings can illustrate concepts or ideasintroduced in science lessons. As with othertypes of science study, students should be

7r;

encouraged to ask volunteers questions thatbuild on what the students already know or havelearned in classroom science activities. Califor-nia offers an array of science museums andother informal science education settings wherestudents can revel in the many areas of inquiryand examination. Outdoor schools offer a won-derful resource for science instruction; all upperelementary students should have the opportunityto spend a week in these outdoor settings.

Section H Middle School Science

THE most effective middle school science program iscomposed of five semesters of science coursework(during grades six through eight). There should alsobe another semester of health and other importantadolescent topics as well as electives for interestedstudents. According to the most common middle-school configurations now in use, them should be:(1) four semesters in traditional seventh and eighthgrade junior high schools; (2) six semesters in a sixth,seventh, and eighth grade pattern; and (3) six semes-ters for schools using a seventh, eighth, and ninthgrade pattern. In short, all middle grades studentsshould be taking science each year.

In most curricular areas, middle school programsare seen as transitions from a sound basis providedduring elementary grades to the specialization of thehigh school years. Articulation through regulardiscussions among staff and administrators fromelementary and middle schools is strongly recom-mended. Middle school science programs, as far aspossible, must:

1. Introduce students to the connectionsamong the disciplines of the physical,earth, and life sciences.During the middle school years, students shouldhave the cognitive ability to understand that de-velopments in one field can have major implica-tions for another. Nowhere is this more true thanin the natural sciences. For example, if a localbusiness causes a toxic spill in a nearby creek,students can examine what effects toxic chemi-cals will have on the soil, plants, and animals ofthe area.

Chapter 6Science Processes and Teaching 161

Often, the physical sciences are not well devel-oped in middle school science programs. It is es-pecially timely to introduce basic concepts inchemistry and physics to these students. Instruc-tional materials can provide helpful hints to themiddle school science teacher on how to addressa more integrated science program in both lectureand laboratory activities.

2. Expand the role of the science processes.As students mature during this period of adoles-cence, they become ready to tackle mom sophisti-cated thinking prwesses than was possible earlierin their education. Activities should raise stu-dents' expectations for the level of thinking ofwhich they are capable. Students should be ableto appreciate the connections among disciplinesand to apply higher-level thinking processes intheir study of science.

3. Motivate students to take and learn morescience.A major goal of middle school science is tomaximize students' exposure to high-interestscience topics so that they will be eager to enrollin a variety of science classes in high school.These students, more than those in any other agegroup, need to see a direct relationship betweenscience educaticn and their daily life. Coursesdesigned to help students leam about themselves(adolescence in human biology) and their world(environmental/earth science) are highly motivat-ing to these students. Science lessons should behighly experiential, manipulative, and laboratoryoriented. Students should be working in smallgroups, cooperating on peer-group projects, andsolving laboratory-oriented problems.

4. Create long-term projects with students.Consistent with the recommendations fromCaught in the Middle,' students in the middlegrades are ready to assume responsibility for alarger share of their learning. Middle gradescience teachers can offer students the opportu-nity to select projects that are consistent with thecurriculum for the course and involve consider-

Me California Department of Education published Caught in the Middle,a description of the middle grades reform initiative. It is available from theBureau of Publications, Sales Unit, California Department of Education,P.O. Box 271, Sacramento, CA 95802-0271.

162 Part IllAchieving the Desired Curriculum

able out-of-class work. Science projects increasethe possibility that students will take responsibil-ity for what they learn. As they develop thisgrowing sense of responsibility for learning, theyshould be encouraged to seek assistance frompeers, parents, teachers, and others in the commu-nity. Whether schools adopt a project orientationto their science program or not, at least 40percent of the class time should be spent onactivity-based lessons.

5. Make full use of community resources.Middle grade students are also capable of creat-ing their own field trips. From the physics ofskateboarding to the design and manufacture ofnew devices or inventions or to the study of localfauna in a natural environment, these students canand should be challenged to learn what they wanton their own, as extensions of material leamed inclass. They should be encouraged to visit the highschool they will attend and sit in on laboratoryactivities to get a sense of what type of sciencestudy lies ahead. And, of course, these studentsshould be given responsibility for selecting andinviting guest lecturers on topics of interest.Many community agencies are open to participat-ing in classes where adolescents care about whatthey learn. As students take initiative in learningscience, they will learn more about their commu-nity and possible future vocations.

6. Establish the relevance of science les-sons outside the school context.Middle grade students often challenge teachersabout the relevance of a particular topic orconcept. These challenges ought to be seen as re-quests for the relevancy of science to students'daily lives, and students should not be put offwith an answer like, "You will need to know thisin order to do well in high school."If students are to take responsibility for theirleaming, they ought to be given reasonablejustification for what they are learning. Fortu-nately, the middle school science curriculumabounds with material of high interest. It may)rove useful to entreat these students to developthe rationale themselves. In this way, they canbegin to model the self-sufficiency towardsleaming they will use throughout their adult lives.

-'* ''1 1.1, I ,i

Sedon I High School Science

THE secondary science curriculum is less subject tomandate than that of the elementary school. Manystudents take a minimum of science courses in highschool, and no textbook adoption process, beyondlegal compliance criteria, is used beyond the gradeeight. Strong traditions exist regarding what highschool biology, chemistry, and physics coursesshould be like. Regardless, many excellent optionsfor teachers and students have been developed.Science teachers, with support from administrators,must reexamine all portions of the program in thelight of modem trends, and needs.

An effective science program is more than acurriculum or a textbook or a set of laboratoryexercises. It is science as experienced and understoodby the students and taken by them beyond the class-room. The science department should be concerned,of course, with the curriculum offerings and thepathways that individual students follow throughsecondary school, but also with the effectiveness ofthe instruction and the degree to which attempts tointegrate within and beyond the discipline of sciencebecome part of the student's life and experience.

The process of science as an aesthetic pursuit andan effective tool with the power to both create andsolve problems must be apparent to graduates fromhigh school. At each school, science teachers (andother faculty) must ask for the leadership, time, andbudgetary resources to perform ongoing review andimprovement of the program. A secondary schoolscience program will accomplish the following:

1. Build on a solid foundation of science in-struction in kindergarten through gradeeight.In an exemplary school, science teachers worktogether within the department with school ad-ministrators and with district curriculum commit-tees and administrators, to create articulatedscience programs. Secondary science instructionand what precedes it are seen to be working inharmony to create a steady accumulation ofscience knowledge,science processes, andconceptual understanding. Such a curriculum isdesigned to revisit all the concepts and providefurther experience with processes introduced in

175

the elementary schools. At the higher gradelevels, a much greater degree of understanding,performance, and descriptive ability is expected,as well as a far greater emphasis on quantitativereasoning. For example, secondary students studythe melting of ice, which they saw first in theearly grades, by investigating how water purityaffects the freezing point, how energy changesmay be measured, how different forms of ice mayexist at different temperatures, and what effectsare caused by trapped gases.

2. Lead In a coherent fashion to greateropportunities for all students.All science coursos should encourage students tounderstand that there are yet more exciting thingsto discover and important concepts to learn. Bothcollege- and employment-bound students shouldtake courses beyond the state-mandated two yearsbecause all courses have been designed to en-courage students to become involved in more ad-vanced science. Technology-based programs arepart of the advanced curriculum and have beendesigned to reinforce basic science understandingas well as to explore specific technological areas.

The science department should work closely withthose responsible for special groups of students tobe sure that all students have the opportunity toexperience a challenging and developmentallysignificant science curriculum. Possible organiza-tion plans for science programs in high school arepresented in the chart that follows. Courses in thehigh school science program should be designedspecifically to allow students to shift from onesequence to another. For this to happen, sciencedepartments must be more detailed in the rela-tionship of one course to another. For too longonly students in the four-year mathematicssequence met prerequisites for physics enroll-ment. As a consequence, physics enrollment inCalifornia in the 1987-88 school year laggedbehind the national physics enrollment pattern byabout 33 percent. Nationally, about 20 percent ofgraduating seniors have taken physics, while inCalifornia only 13 percent have taken physics.

Science departments are encouraged to developpathways for all students to be able to takephysics and chemistry, even if the pathways arenonquantitative. In fact, many science educators

Chapter 6Science Processes and Teaching 163

at the secondary and college levels prefer concep-tual physics and chemistry courses over the morequantitative courses. The following chart demon-stratcs connections among pathways for studentswith diffeting entry points. (Ofcourse, there aremany other possible combinations within andbeyond thc current tradition of single-subject,five-hours-per-week science classes.)

GradsGeneral

sequenceOuantitativesequence

Conceptualsequence

9 Physical Earth science Earth sciencescience or elective* or elective*

10 Life science Biology Conceptualphysics

11 Conceptual Quantitative Conceptualchemistry chemistry chemistry

12 Conceptualphysics

Quantitativephysics

Biology

*Science electives might includeoceanography, astronomy,ecology, and so fOrth.

An even broader xeform of thc high school cur-riculum has been proposed by the NationalScience Teachers Association. In "EssentialChanges in Secondary School Science: Scope,Sequence, and Coordination," NSTA ExecutiveDirector Bill Aldridge writes:

The fundamental problem with high schoolbiology, chemistry, and physics courses is thatthey are not coordinated, are highly abstract andtheoretical, do not spend enough time on eachsubject, and do not use correct pedagogy. Inshort, we never give students the chance tounderstand science....By contrast, consider the secondary school levelscience courses offered in the USSR and thePeople's Republic of China. In both countries,allyes all students take several years ofbiology, chemistry, and physics. And essentiallyall children learn these subjects successfully....As you can see in [the accompanying table], theaverage student in the USSR and China [PRCIspends almost twice as much time studying

164 Part IIIAchieving the Desired Curriculum

biology and chemistry and more than three timesas much time studying physics as his or herAmerican counterpart. Notice that the ratios areeven higher when you compare years spent oneach subject:

Time Spent on Etiology, Chemistry, and Physics

US USSR PRC

Biology 180 hrs.321 hrs. 256 hrs.year 6.years 4 yarn

Chemistry 180 hrs. 323 hrs. 372 his.1 yea 4 years 4 years

Physics 180 hrs: 492 hrs. 500 hrs.1 year 5 years 5 years

In accordance with the NSTA proposal, a pos-sible scenario for redesigning the Californiasccondary school scicncc cuniculum is illustratedin thc table on the following page. This tableoutlines just one ofmany possible designs forchanging secondary school science. Coordinationis essential if thcsc components are to bc learnedproperly. And, of course, any such broad changesin curricula would pose significant staffing,scheduling, and other problems. But change cancome only from exploring what is ideal and pos-sible and working from there to what is practi-cable.

Science faculty should integrate the sciencecurriculum so that students fully understand thcinterconnectedness and interdependence of thetraditional disciplines. Less discipline-orientedcourses help students to understand that basicprinciples of physics, chcmistry, and biologyhave a common foundation, and that applicationsof these principles constitute most of modern-dayscience and technology. For example, a biologyclass examines the physics of motion and theconcept of work and machines when discussingbones and muscles; a chemistry class reviewsdigestion and biood chemistry when discussingacids and bases; a physics class investigates thestructure of the human and other animal eycswhcn discussing refraction, light, and color theory.

3. Help students understand the nature ofscienceIn particular, its experimental,nondogmatic nature and the methods bywhich progress Is made.Students should practice an ethical understandingof the responsibilities of science in their ownlaboratory and other investigations. Honest andclear observation and reporting are rewarded.Inadequate.recording, misrepresentations, or cleardishonesty are actively discouraged and areconsidered unacceptable in science. Dilemmasexisting in modem science are examined anddebated in the classroom. Students understand thelimitations of measurements and observations andlearn how to communicate clearly the truemeaning and limits of investigatory activities.

4. Develop in students a strong sense of theinterrelationship between science andtechnology and an understanding of theresponsibility of scientists and scientifi-cally literate individuals to both presentand future societies.In the exemplary school, teachers assist studentsto appreciate the implications of the powerand

limitations of science in addressing societalissues as they learn how to use their scientificknowledge and skills to make decisions andjudgments about important matters for presentsociety and the future of the planet earth.

Science and social science teachers work togetherto make science relevant for students by consider-ing the social impacts of science and technologyand the need for all citizens to be responsibleworld inhabitants. Major issues, such as theimpact of human population growth on otherspecies and on world resources and environ-mental deterioration, are to be discussed in anopen manner by all students, not just thosechoosing science careers.

The science curriculum in all science courses,without exception, provides opportunities forinteraction; students participate in model debatesand forums on such public issues as water use, airpollution, gene splicing, and biological speciesconservation. These exercises employ properdata, gathering from both science experimentsand surveys. Teachers from valious disciplineswork together to help students learn valid meth-ods for data acquisition, analysis, and reporting.

A Proposed Science Curriculumfor Grades Seven Through Twelve In California

.

0 Hours per week,.by gracle level

Total hours spent

Subject 7 8 9 10 11 12 on science

Biology 2 2 1 1 1 1 288

Chemistry 1 1 2 2 1 1 288

Physics 1 1 1 1 2 2 288

Eatth science 1 1 1 1 1 1 216_.

Total hOuts per. week 5 5 5 5 5 5

Emphasis Descriptive, Empirical, Theoretical,phenomeno- semi- abstract flogical quantitative

177 Chapter 6Science Processes and Teaching 165

5. Foster each student's ability to act as anindependent investigator and thinkerrather than a "recipe follower."High school students should be responsible fortheir own science education. Students shouldleave class with questions as often as with an-swers and learn to optain answers from a varietyof sourceslibrary books and journals, video-tapes, computer data bases, parents, communitymembers, and other students. They should learnto work effectively alone and as members of co-operative learning groups, where they have hadopportunities to play different roles. In the labora-tory they can organize work in groups, arc moti-vated to complete experiments, create profes-sional-looking records of what happens, and areresponsible for their own safety, understandingthe need for personal protection and maturebehavior. Students should spend at least 40percent of their time on practical activitiesdesigned to foster manipulative skill developmentas well as higher-order thinking.

6. Reinforce basic tools of language andmathematical communication.Science faculty within schools must work closelywith their colleagues in other disciplines to helpstudents see the overall plan in the high schoolcurriculum. Communication tools should beemphasized by having English teachers read andgrade science reports for grammar and style,while science teachers suggest topics for Englishclass assignments. Science and language artsteachers could create avenues for students to readand discuss literature relevant to science. Dramaclasses offer opportunities for students to explorehistorical figums in science: Galileo or MarieCurie, for example. In this way students learnabout the importance of environment and person-ality in science as well as the brilliance of discov-ery.

Lessors in algebra and science can be co-taughtso students see mathematics in action; at the ad-vanced levels, probability, statistics, trigonome-try, and calculus am presented in the context ofscience experiments. No student is expected touse mathematics beyond his or her level of under-standing, but science is uso' to motivate thepresentation of more advanced mathematics, and

166 Pait illAchieving the Desired Curriculum

the lack of specific mathematical power is notseen as an excuse or barrier to avoid exploringscience concepts.

Computers are used in a variety of ways in theexemplary science classroom. Mainly, they areperceived as a useful tool for students in expand-ing their ability to gather and organize informa-tion. Simulations and modeling programs are usedjust as they are in science investigations. Scienceclassrooms have access to data bases by computernetwork and a laser disk system that allowsstudents to observe experiments that cannot bedone in the classroom.

7. Provide an expanded view of science-related careers.Students should understand what science-relatedcareers are available to them and what coursesthey need to prepare for these careers. Science,English, and mathematics teachers, as well ascounselors, necd to work together to inform andplace students in science classes and to see thatfemale and minority students are equitably repre-sented, especially in more advanced scienceclasses. The importance ofeducation beyond highschool is emphasized for all students, whether at acommunity college, technical college, or four-yearuniversity. Students recognize that being a teacherof science is a worthwhile and rewarding experi-ence. To show students the wide range of opportu-nities in science, teachers have found ways to visitbusinesses, industries, and research laboratoriesand to arrange for visits to the classroom byscientists from academia, government, medicine,business, and industry. Students experience theenthusiasm of males and females of all ethnicbackgrounds working in careers at all levels, fromthe technician to the laboratory director.Teachers should recognize that reading aboutscientists in books in itself may not generate muchinterest or connection. Hearing only about sciencesuperstars may give too unrealistic a picture andimply that all persons working in science aregeniuses. Teachers can emphasize that manyindividuals, now and in the future, will make theirliving in science or science-related employment.Students in all science classes should have suchopportunities explained to them, not just thosewho major in science.

-teaching All 8ti.jdents75

THE demographic trend of the California schoolpopulation is on a collision course with the scientificilliteracy rate. The populations of minority and at-riskyouth are increasing, along with the number ofdmpouts and graduates without soli(' backgrounds inscience and technology. This state cannot afford acitizenry or woik force composed of individualslacking the scientific literacy to compete in a techno-logically sophisticated economy. While the economicincentives for scientific literacy are compelling, theyarc not the only force driving public schools toward 3greater emphasis on science learning. More than ever,voters are asked to make difficult choices betweendevelopment and environmental issues. Consumersarr, besieged by advertisements and counterclaimsabout energy efficiency, competing technologies, andother aspects of OX process of product selection.

In a technologically advanced culture, the scientifi-cally illiterate are disallowed entry into educational,economic, and political arenas. As women andminorities become larger segments of the Californiawork force, they are less well repiesented in the fieldsof science and technology. Science teachers are nowassuming greater responsibility for helping femalesand minorities learn to succeed in these fields (as wellas in mathematics). With co.,eems ofdomestic equityand international competitiveness, science educatorsmust help ensure that all students have an equalopportunity to succeed in science-related endeavors.

The two sections that follow show how scienceteachers can help overcome societal and culturalfactors that mitigate against success of the historicallyunderrepresented. In the first section, there aregeneral strategies for working with femaleb art1minorities (especially Olacks, Hispanics, and Ameri-can Indians). The second section presents strategiesfor working with linguistic minorities.

With concerns of domestic equity and interna-tional competitiveness, science educators musthelp ensure that all students have an equal oppor-tunity to succeed in science-related endeavors

1 79

Teaching Science to the HistoricallyUnderrepresented

By all reports and analyses, females, minoritygroups (with the exception of some Asian ethnicgroups), ar.i persons with disabilities are under-represented in undergraduate and graduate study,research, industry, and other scientific enterprises.The many reports addressing this situation documentthe shortcomings of the system but do little to treatthe problem or its causes. Fortunately, there areindividuals and pilot programs working to helpyoungsters overcome barriers that keep them fromsucceeding. The successes of dedicated professionalswho believe and regularly demonstrate that all chil-dren can achieve lead to the recommendation thatteachers should:

1. Model positive attitudes about all stu-dents' successes in mathematics andscience.

The most powerful force in helping the under-represented to achieve is the consistent belief thatthey can succeed. Teachers are especially effec-tive in promoting positive attitudes about stu-dents' abilities and achievements. From the start,teachers must demonstrate that every child in theclassroom can make a significant contribution toa lesson, and the conscientious classroom teacherdraws out students who may be reticent. Mean-ingful recognition from a caring teacher can sparkinterest and enthusiasm and reveal students'natural abilities.

Th,', use of role models in science instructioncannot be underestimated. While teachek and in-class speakers provide the most impact onstudents, videotapes and other supplementallearning materials can readily demonstrate theexpanding presence of females, minorities, andpersons with disabilities in science careers andavocations. Role models who speak of their earlymotivation and preparation are very effective intranslating personal experience into touchstonesfor students with interest in science and technol-ogy. Above all, role models prove that histori-cally underrepresented studerns can succeed inhighly technological fields.

Chapter 6Ccience Processes and Teaching 167

2. Prepare students well in the mathematicsand language arts.Comprehensive programs in English-languagearts and mathematics are much broader anddeeper than reading and computation tools, but atsome level students need to manipulate text andnumeric symbol systems in order for them tosucceed in science. The development of suchtools should not be seen as prerequisite to sci-ence, any more than they are prerequisite toliterary appreciation or problem solving. Learn-ing science can occur simultaneously with suchtool development. And, in fact, science is often asource for this development because it capitalizeson students' innate curiosity about the naturalworld and how things work. Females, minoritystudents, and students with disabilities should begiven frequent opportunities to learn science inthe context of developirg other skills.Historysocial science and the arts bring specialskills and understandings that further thesestudents' general and science education.

3. Provide enrichment opportunities inmathematics and science for females,minority students, and students withdisabilities.

Often, students who could benefit the most fromextracurricular activities do not gct a chance toparticipate. And, often they are not aware of orare precluded from participating in the extra pro-grams available to others. Some special programslike science fairs, Invent America!, and thcScience 01.npiad allow students to dcmonstratcthcir creativity and interest in science-relatedareas during tegular school hours. Opportunitiessuch as the Mathematics, Engineering, andScience Achievement (MESA) program provideextended assistance for students who demonstratean early interest in and motivation for technicalcareers. Other programs require some involve-ment from home or community in order forstudents to participate fully. Before students canactualize thcir interest in science enrichment ac-tivities, they must be made aware of the opportu-nities, they must be encouraged to participate,and they need to achievesuccess. No studentsucceeds without awareness and participation.

168 Part IllAchieving the Desired Curriculum

4. Build parent involvement and peer recog-nition programs.The same sociocultural forces that create barricrsto the interest in science of females, minorities,and studcnts with disabilities can be turnedaround to help them succeed in scientific andtechnical fields. Perhaps the most persuasive in-fluences for and against learning science are thenormative mores and values about science andtechnology. Homes and neighborhoods that aredisenfranchised from the world of science andtechnology pass along this indifference andignorance to children. This trap is especiallydestructive to the opportunities of females who, ifthere were no cultural stereotypes about science-related fields, might follow their own interestsand abilities and pursue more science education.When parents and peers show an interest in andacceptance of science endeavors, there is moreroom for these students to participate and suc-ceed. Local PTAs and PT0s, othcr communityaction groups, university incentive programs, andafterschool clubs and enrichment programs allwork to build more healthy attitudes about accept-ance and success in scientific and technical fields.

5. Capitalize on students' prior knowledge.In the section on concept learning, we saw thatstudents learn more effectively in all areas (butespecially mathcmatics and science) if ncwmaterial is incorporated within the existingknowledge base. For the historically underrepre-sented populations, this presents two challenges:(1) the prior experience students bring to schoolmay be fundamentally different from the main-tream culture; and (2) thc prior knowledge

students have may be incomplete, especially inthe physical and earth sciences. The first chal-lenge can be mitigated through large-groupdiscussions or background information for allchildren in thc classroom. To do so is moredifficult than might be thought because discuss-ing or passively viewing and listening (in the caseof video background information) alone may notdevelop rich experiences for all students. Hereagain, direct experience with concrete materialsmay bc needed to further cnrich students' worldview. Thc sccond challengl is best overcome byworking in smaller, heterogeneous groups.

lao

All students with limited-English proficiency,regardless of their primary language, shouldhave rigorous English-as-a-second-language(ESL) lessons. A strong ESL component is neces-sary to build a foundation in English for accessand success in content instruction that will laterbe taught solely in English. ESL classes,especially for intermediate level speakers ofEnglish, might integrate science vocabulary andscience concepts as part of language develop-ment activities.

6.

Cooperative learning offers the possibility thatdirect experience of workhtg with others allowsall students to develop an understanding of theconcepts of science. Care must be taken in thesesituations to ensure that historically underrepre-sented students are not dominated in discussionsby students who claim to know more or havebroader experience. The diversity of experiencesthat students bring to the classroom should beaccepted and respected; teachers should makeevery effort to encourage students to share theirperspectives. Both these challenges require closeobservation by the classroom teacher and otherinstructional staff; both the process and substanceof learning need to be watched closely to ensurethat all students have similar cognitive constructsbefore new concepts are introduced.

Maintain the same standards for allstudents.Learning any subject deeply requires hard work.In fact, the root of the word tuition comes fromthe effort (not the money) required to learn. It isessential that females, minorities, and studentswith disabilities experience the challenge andhard work it takes to master mathematics, sci-ence, and technology. With positive attitudesabout their abilities to succeed, they can and will.It does no good (and may do irreparable harm) toinflate the grades or successes of one grouprelative to others. The standards for success mustbe equivalent so that a common metric is under-stood and appreciated by all students.

Teaching Science to Limited-English-Proficient Students

The rapid changes in California's populag ,n aredirectly reflected in our schools. More and more stu-dents come to class with primary languages otherthan English. Limited-English-proficient (LEP) stu-dents lack the English language skills to benefit frominstruction which is designed for native Englishspeakers.

While providing comprehensible science instruc-tion for students who are not fluent in English hasimdlications for instruction, so does the amount ofprior schooling these children have had. Some of thesame students new to English have never been toschool in their homeland, coming from rural back-grounds in countries with educational systems thatare less developed than ours. Many of these young-sters come to our schools preliterate. Other children,while not proficient in English, have had schooling inadvanced educational systems and are highly literatein their own language. Students proficient in lan-guages other than English can learn the sciencecontent applopriate for their grade level as outlined inthis framework. The problem is not one of cognitivecapability; it is a problem of delivery.

All students with limited-English proficiency,regardless of their primary language, should haverigorous English-as-a-second-language (ESL) les-sons. A strong ESL component is necessary to build afoundation in English for access and success incontent instruction that will later be conducted solelyin English. ESL classes, especially for intermediatelevel speakers of English, might integrate sciencevocabulary and science concepts as part of languagt,development activities. The critical variable here issecond-language acquisition (English) and notscience per se. Experiences in advanced-level ESLclasses may also include readings from the basicscience program textbook.

When the ESL teacher and science teacher worktogether to develop vocabulary and assign readings inscience, students come to science classes with enoughEnglish language skills to make science instructionsuccessful. This is not to say that students must be asfluent in English as they are in their primary lan-guage. In addition to providing support in the primarylanguage for limited-English-proficient (LEP) stu-dents, science instruction can be meaningful for LEP

Chapter 6Science Processes and Teaching 169

students if appropriate techniques are used to makethat instruction comprehensibletechniques whichare based on good teaching in general and goodscience teaching in particular.

All children in California, including those whoseprimary language is other than English, should haveaccess to high-level science instruction. Thesestudents who are limited-English proficient can haveimmediate access into science via their primarylanguage while acquiring English. As snidents reachintermediate fluency, they depend less on primarylanguage support. Intermediate speakers ought to beable to string sentences together, even though theirsentences may be grammatically incorrect. Thesestudents can gain comprehension skills when thecontent is delivered orally with context clues. Contextclues help to lower the lirguistic barriers to high-levelscience instruction.

The important task of modifying science instructionto remove barriers comprehension will have to bemet by all teachers of science, not only those trainedfor ESL or bilingual programs. These teachers havewithin their teaching repertoire strategies that can beused to lower the linguistic barriers preventing accessto their disciplines. The following strategies are not toimply a simplification of science; rather, they areused with the same content as for English-proficientstudents. We are not to create two science curricula.Perhaps the most powerful teaching tool is theexpectation that all students can and will succeed.Using techniques founded in sound teaching prac-tices, teachers should:

1. Simplify the input.Use a slower but natural speech rate with clearenunciation. A modified, controlled vocabularymay be appropriate. Science teachers shouldresist the temptation to make science a vocabu-lary development course. Use proper scienceterms when necessary, but avoid obfuscation. Domake attempts to restate, redefine, providefamiliar examples, and draw on students' priorbackgrounds. Define words with multiple mean-ings and avoid the use of idiomatic speech.

2. Provide context clues.Be animated, use gestures, and when possible actout the meaning. Use props, graphs, visuals, andreal objects. Hold up the mortar and pestle and

VW.' Part HIAchieving the Desired Curriculum

domonstrate how to grind leaves in preparationfor extracting chlorophyll. Make frequent visualand word associations. Show students the fin-ished product when possible.

3. Draw on prior background.Have students brainstorm, list things they alreadyknow about the topic at hand, and be prepared forand accept single word or limited responses.Categorize their responses to show associationsand relationships. Use graphic organizers, mich aschapter or concept maps. Provide multisensoryactivities and ask open-ended questions to elicit avariety of responses and record the students'responses when possible.

4. Work to ensure understanding.Repeat ideas or concepts frequently. Expand,restate, and reinforce important points. Do regu-lar comprehension checks to confirm that stu-dents really understand the concept under investi-gation. Frequent interaction between teachers andstudents and among students are strategies, alongwith others, for formative evaluation.

5. Make sure instruction is content-driven.Identify a few key concepts. Attempt to ensureunderstanding of fewer, larger ideas rather thanmany factoids, those isolated facts and definitionsthat have long dominated science instruction.Make sure those few concepts are learned wellrather than many ideas developed superficially.Select essential vocabulary, about five to sevenwords, but certainly not 20 or 30 per chapter.Teach the selected vocabulary through a varietyof interactive ways (avoid simply assigning themto be defined). Explain textual features such ;IFbold print, italics, and chapter summaries in orderto build comprehension. Show studentshow touse context clues in the text, such as pictures,graphs, taLles, flow charts, and similar graphicmaterials.

6. Ensure that instruction Is student-centered.Use a variety of grouping strategies, such assmall-group, large-group, and cooperativelearning. Provide instruction with direct experi-encesabout 40 percent of instructional time-

2

which are appropriate to various learning modes.As much as possible, put material§, in students'hands; demonstrations are not as.effective as ma-nipulation. Provide opportunities for-students touse concepts rather than merely reiterate theconcept label and definition.

7. Use science text effectively.When using text materials, begin by establishingstudents' prior background and be prepared toadd background when necessary. Select theessential vocabulary and teachit through a

variety of interactive and contextual ways thatcapitalize on prior experience. Begin a chapterwith an activity; try starting with the first labora-tory activity even if it is located three or fourpages into the chapter.

All students in California deserve access to high-quality science instruction. Using techniques toreduce linguistic barriers will ensure access for stu-dents with limited-English proficiency. Rather thanuying merely to cover the content, we should uncoverscience content.

183 Chapter 6Science Processes and Teaching 171

Chapter 7

Implementing aStrong ScienceProgram

THis chapter deals with the implementation of strongscience programs at the school district and site levels.It includes considerations of organization, selection,and administration of curricula; the use of educationaltechnology in science classrooms; the physicalresources of the school and the community resourcesof the district; and guidelines for staff development,using resources available from state agencies andother sources.

I

A WELL-FORMULATED districtwide plan for scienceeducation provides the basic design for the establish-ment of an effective science program. The mosteffective programs result when administrators andspecialists provide leadership and support to teacherswith a collaborative spirit; and teachers who will beimplementing the plan need to.be involved at everystep of the process. One goal of an implementationplan must be the development of expertise amongteachers at WI levels; only then will the plannedcurriculum be taught. The definition of programs andthe adoption of textbooks provide some of the ele-ments needed to put that plan into practice. However,unless 1;;arners experience conceptual, sequential, andintegrated science in the classroom, all the best madepolicies, plans, and intentions become poor substi-tutes for success. Proof of the establishment of a goodscience program lies in student growth in understand-ing and enthusiasm for science.

172 Part IIIAchieving the Desired Curriculum

Implementation entails more than the disseminationof information, materials, and programs. If anadopted science curriculum is to result in knowledge,experience, and understanding for students, theprogram must be challenging, stimulating, and useful.Students should be doing science in their classrooms,not merely reading about it. Teachers need opportuni-ties to increase their understandingofscience bytrying out the activities or lessons they will use ininstruction. In order to be in a position to supportteachers, administrators need to gain experience byattending staff development workshops with high-quality science instruction, and the community needsto know enough about the science curriculum so thatits many members can contribute their expertise andsupport.

The design of a district science implementationplan is a process that should involve all of the peopleidentified above over a sustained period of time. Tobegin, planners need to have a broad view of theentire implementation process in order to understandhow all the parts fit together. Once the process isunderstood as a whole, planners can concentrate onkey elements of implementationplanning, staff de-velopment, assessment, and resources (includinglearning environment, technology, and community).Planners need to be aware of the relationship betweenthis framework and those in other subject areas inorder to facilitate the integration among subject areasthat are increasingly seen as essential. The material inthis chapter follows the sequence described forplanners.

3_ S

Section Implementation Planninga

TIME, people, and resources are the main factors tobe considered when planning the implementation ofthe curriculum.

Time for ImplementationIt is not enough to focus on science for the one

adoption year out of every seven. The adoption ofmaterials should be preceded by extensive planningand staff development and followed by more staffdevelopment and assessment. The changes suggestedby this framework build on the preceding ScienceFramework and Science Framework Addendum andstrengthen the position that students should activelyexperience science rather than passively read about it.The changes in practice that are required to imple-ment this framework faithfiilly, however, are moreradicalthe shift from instruction that emphasizesaccumulation of knowledge to a program that devel-ops concepts and the understanding of the connec-tions among them. Teachers and administrators needto experience the changes themselves and have thetime to plan, to experiment, to revise their plans, andto implement the changes at a pace that allows foradequate reflection and internalization.

The California Department of Education issues eachyear a new framework in a different discipline, a sched-ule which may present districts, and elementary gradeteachers especially, with an overwhelming task: im-proving three or four curricula at once without pause.The changes called for in the various frameworks, asprofound as they are, are harmonic with one another.For example, the move to use cooperative groups todevelop the ability to communicate mathematicalthinking has made ready the way for the same kind ofgroup wolk called for in this framework. The need tofocus on the connections between ideas, rather thanon isolated facts, is emphasized in the HistorySocialScience Framework. An important benefit of thisinteftlisciplinary harmony in the frameworks is thatteachers and districts can, to a significant extent,accomplish critical improvements in several curricu-lar areas at the same time. A later section of thischapter delineates the relationships between thisframework and each of the other subject areas.

People for Implementation

Effective implementation involves administrators,school faculty at all grade levels and students, par-ents, and other members of the community in acontinuous, cyclical process that has evaluationelements throughout. The steps in this process aredetailed in Figure-8. A comprehensive needs assess-ment, as outlined in the first column, enables thedevelopment of a detailed plan, characterized in thesecond column, with a high potential for successfulimplementation, described in the third column.

Effective implementation incorporates both adistrictwide plan and plans for individual schools. Acommunication plan must ensure articulation amongvarious levels (e.g., state, county, board, districtoffice, school site, and classroom); within and amongelementary, middle, and high schools; and betweenand among teachers at different grade levels withinschools. A comprehensive communication structure,with teachers representing each school in planningand implementing committees, is a prerequisite tointegration and articulatioit across grade levels withinthe district. Such a structure should also identifylocally available resourcesilogether with theirappropriate contribution to the total program. Theseresources include mentor teachers and scienceeducation specialists; educators trained in technologi-cal applications; local college or university scientistsand science educators; community experts in science,medicine, and technology; and parents.

A whole range of people should participatethroughout the implementation processprincipals,governing boards, district and county personnel, andlocal college and university representatives. Theyshould be familiar with the goals of the frameworkand with implementation strategies so that they canlead and assist the process effectively, build enthusi-asm in the staff, and model informed, committedsupport. Knowledgeable administrators arc effectivemanagers of time, money, and supplies. They shouldbe selected in part for their ability to offer creativesuggestions for the use of existing funds, but theyshould also be well informed about special grants andmoneys that might become available. They shouldenhance their effectiveness by identifying individualswith science leadership itsponsibility and by piovid-ing necessary support to them.

Chapter 7Implementing a Strong Science Program 173

Plan revisions and'i-epeat the procegs.

'1***

Resources for Implementation

Resources are" available to assist the implementa-tioh planning process. See, for example:

Science Educat.lon for the 1980s (includes adv iceand an extensive checklist for conducting a self-evaluation at the local level) (California De-partment of Education, 1982)Quality Criteria for elementary schools, middlegrades, and high schools (California Departmentof Education, revised annually to reflect newframeworks)Recommendations of the California ScienceTeachers Association (Lawrence Hall of Science,Berkeley, CA 94720), the National ScienceTeachers Association (1972 Connecticut Ave.,Washington, DC 20009), and other professionalorganizations

AN effective science program depends primarily onteachers who are enthusiastic, informed, and providedwith adequate resources. We hope that teacherpreparation programs will be able to educate newteachers in the kind of science education called for bythis framework. Yet, teaching is a profession thatrequires ongoing professional development, andteachers need the opportunity ti experience the kindof instruction they are being asked to provide. A goodstaff development pmgram should:

Be ongoing, comprehensive, and based on theimplementation plan.Involve teachers in planning, conducting, andevaluating workshops.

Provide appropriate science content and scien-tific thinking and illustrate that scientific knowl-edge is a praluct of the scientific process.Provide opportunities to practice new activi-tieshands-on, laboratory, investigative, andfield activitiesin low-risk environments.Provide formal and infonnal opportunities forpeer coaching and feedback.Allocate additional released time for teachers toreflect, discuss, solve problems, and exchangeideas.

While generic workshops on teaching techniquesand classroom management strategies are of benefitto science teachers, it is important that substantialtime and resources be devoted to strategies for incor-porating these techniques most effectively in theteaching of science. Cooperative learning is a tech-nique of great value to science teachers; cooperationin laboratory work and student projects needs to beemphasized to achieve the most from this technique.

To encourage an articulated program, those respon-sible for staff development must ensure that someportion of the training of district and school level takeplace across the grade levels. It is important forelementary teachers to anticipate where the curricu-lum is going and for secondary teachers to gainfirsthand knowledge of where the students have been.In a collegial setting, the elementary teachers' exper-tise in a variety of teaching methods is as instructiveto secondary teachers as the secondary teachers'subject matter expertise and enthusiasm are to theelementary teachers. As the content is specified bygrade level, differentiated experiences are necessaryat some point for teachers at different grade levels toreceive enough specificity to carry out the program attheir level. At every point, however, participantsshould have an active role, experiencing the processes

A favorite problem for workshops is the following. "You have two glasses of liquid, one white and onered, each initially containing the same amount. You take a teaspoon of white liquid out of the white glassand put it into the glass of red liquid. After stirring thoroughly, you take a teaspoon of slightly dilutedred liquid from the red glass and put it into the glass of white liquid. After you stir it again, which glassis more contaminated, the red with the white or the white with the red? Or, are they equal?" This is afavorite problem because it elicits heated discussion and because it is easier to solve with a real modelthan with an algebraic one.

188

Chapter 7Implementing a Strong Science Program 175

If an evaluator comes into a science classroom to observe and finds that all of the students are workingin groups on projects of their own design and decides to return when the teacher is teaching, he or shedevalues this mode of instruction and discourages teachers from using it. Certain features of the clinicalsupervision paradigm, particularly a conference before the observation to discuss the teacher' s goalsand a conference after the observation to compare the observer' s and the teacher' s perceptions of thesuccess of achieving those goals, are valuable features that should be part ofany assessment ofinstruction. Other features, such as the requirement that all lessons should include considerable time forpractice, as if complex new ideas can be mastered through practice, are at odds with the idea ofstudents' constructing their knowledge through investigation.

of science, as leaders model better ways to teach forconceptual understanding.

,.SetiorLD Assesthnent

A TRUISM in education is, "What you test is whatyou get." Students will focus their attention on the ac-tivities that determine their grades, placement, andcareer opportunities. Similarly, teachers will guidetheir instructional decision making toward the criteriaby which they and their students are evaluated. Prin-cipals will provide instructionaLleadership that isconsistent with the basis on which their schools arejudged. The superintendent will emphasize the schoolboard's and stai.e's criteria for success in his or herinteractions with the principals and the district'scurricular leaders. Of course, each level must be ac-countable to the next, yet it is essential that each levelbe held accountable for the right things. In this con-text, the right things are the agreed-on goals for thescience program. If the goals of the science programait scientific literacy and the ability to make sense ofthe world, then tests of vocabulary and factualknowledge will not measure their attainment. Thedesign of an assessment program requires as muchcare and consideration as the design of the instruc-tional program itself.

Before an administrator can design and implementan effective assessment of science teaching at a givenschool, he or she must be familiar with the goals andmethods of the science cuniculum. Adequate assess-ment of teaching must reflect the same range of

176 Part IllAchieving the Desired Curriculum

teacher behavior as adequate assessment of studentoutcomes reflects the wide range of desired studentoutcomes. There is a temptation to limit assessmentof teachers to what can be most easily observed:direct instruction. This is as much to be avoided a:limiting student assessment to wnat can be mosteasily measured: factual recall. While direct instruc-tionthe teacher addressing the whole class from thefront of the classroomhas a role in science instruc-tion and has a well-described paradigm for assess-ment, its effectiveness is limited as a mechanism forgiving students direct experience with doing science.The assessment of instruction must meet the chal-lenge of the wide range of instructional strategiesproposed in this framework in the same way as theteacher meets these challenges in making decisionsabout instruction.

Administrators should begin the process of teacherassessment by asking teachers to assess themselves,using the following questions. At the same time,administrators need to ask themselves whether theyhave provided the teachers with opportunities todevelop positive responses to each question.

Am I using a variety of teaching methods? Arethey appropriate for the subject and the learners?Am I moving toward hands-on, active learningof science and away from passive, text-onlylearning?Have I made adjustments in addressing theneeds, strengths, and interests of my studentswhen direct observation and evaluation indicatethat particular methods are not succeeding?Am I acquainted with and employing specificinstructional strategies designed for students in

categorical programs such as bilingual education,compensatory education, special education, andgifted education?Am I aware of each student's perception of whatis being taught? Am I using a range of assess-ment techniques to determine student under-standing, including performance assessment,portfolio review, and the safe manipulation ofscientific apparatus?How do I handle controversial issues, and do Imodel positive attitudes toward important issuesin science and society?Does my classroom promote inquiry, ethicalvalues, and respect for others' opinions?Do my classroom and school provide a variety ofmaterials supplemental to the core program,resources for independent student work, and anemphasis on safety and humane treatment ofanimals?Am I involved in the school's and district's..overall science program? In addition to servingon committees, do I take advantage of the oppor-tunity to work on program development will'teachers at other schools and with teachers ofdifferent courses at my own school?Am I continuing my professional developmentthrough participation in professional organiza-tions, attendance at conferences, and active par-ticipation in staff development activities?

Assessment of school science programs at thedisuict, county, and state levels should incorporatethe following additional considerations:

Alignment with the framework and other cur-riculum documents such as the Science ModelCurriculum Guide, K-8, the Model CurriculumStandards, Grades 9-12, the Statement onPreparation in Natural Science Expected ofEntering Freshmen, and the Quality Criteria (forelementary schools, middle grades, and high

-11011.

schools). All major concepts and processes in theframework should be assessed. Local variationsin curriculum should be intentional and explicit;they should be reflected in local assessments.Modeling good instroction. Assessment criteriathat reward poor or unimaginative instroctionalmethods should not be used. Because instroctionis greatly influenced by the methods and criteriaof its assessment, only assessment criteria thatmodel good classroom practices should be usedat each level of assessment. In particular, assess-ment should be perfonnance-based whereverpossible; students should demonstrate under-standing and skill in situations that parallel priorclassroom experience.Design and administration of assessment bypracticing teachers who have been given specialpreparation to do so. Teacher involvement givesteachers a sense of ownership, improves teachingmethods, and helps to ensure the practicality ofthe assessments. Knowing what to obrerve andthe various strategies for administering perfor-mance tasks will require special preparation, particularly to ensure consistency among assessors.Coordination with the assessment of other disci-plines as appropriate. Skills and concepts inmathematics, Englishlanguage arts, historysocial science, and the visual and perfonniag artsshould be included in science performance tasksif they are integral parts of the tasks.Consistency with the developmental levels ofchildren.Inclusion of periodic surveys of students' atti-tudes towards science.Provision of timely feedback to teachers. Resultsof assessment programs should be available soonafter thc assessment is conducted so that teacherscan make appropriate adjustments in the program.Provision of well-explained qualitative andquantitative information to the public.

If an evaluator comes into a science classroom to observe and finds that all of the students are workingon hands-on activities, he or she should not assume that everything is fine. Questions that the evaluatorshould ask include, "Are students following a recipe or investigating?" "Do they know why they arefollowing the procedures they are using, what they are looking for, what the data mean?"

Chapter 7Implemnting a Strong Science Program 177

Section E Re

THE preceding sections have emphasized the humanresources of implementationstaff development andassessment effortsyet their success depends onadequate investment in physical resources thatsupport excellence in science teaching. Instructionalmaterials play a key role in defining and supportingthe science curriculum and are explicitly described inChapter 8, "Instmctior,al Materials Criteria." Theclassroom environment, the availability of equipment(particularly new technologies), considerations ofsafety, and the incorpratiou of community resources,including parents, arc discusF,ed in this section.

The Classroom Environment

The physical resources of the entire school plantand the community should be taken into considera-tion in planning the science instructional program.Optimal school facilities for science will provideflexibility to accommodate large- and small-groupinstruction, laboratory activities, outdoor experiences,demonstrations, audiovisual presentations, activitiesenhanced by educational technology, seminars, andindividual or small-group projects. Teaching alaboratory or activity-oriented program in the elemen-tary school does not necessarily require sophisticatedlaboratory facilities, but it requires at least tables andsinks. Adequate floor and storage space, lighting,ventilation, and chalkboard space must be provided.The availability of bulletin boards to permit displayof colorful posters and examples of student workenhances the classroom. Secondary science programsgenerally require more elaborate facilities, includinglaboratory stations equipped with runni-4, water, gas,electricity, and storage space for student equipment.Safe storage for volatile, flammable, or corrosivechemicals is mandatory. The number ofstudents inthe laboratory classroom should be determined byfactors such as safety, number of stations, and totalclassroom square footage, rather than school schedul-ing needs.

Equipment and materials must be made available toall teacherselementary and secondary. It is asimportant for a first grader to be able to manipulate ahand lens, a magnet, or other materials throughhands-on activities as it is for the high school student

178 Part IllAchieving the Desired Curriculum

to be able to use chemistry equipment. A substantialyearly science budget must be available to teachers sothat they can replenish the consumables and purchasethe essential additions that encourage the expansionof an effective program and experimentation withnew ways to present concepts.

When adopting instructional materials, disnict staffmust consider the cost of equipment and consumablematerials along with the cost of textbooks, software,videotapes, videodisks, and so forth. Evaluators at thelocal level should decide what program is best fortheir students, determine the cost of implementingthat program, and present their recommendations tothe administration or governing board. While it maynot be possible to purchase and ,:quip the optimalprogram, decision makers need to know what isconsidered best, next best, and so forth.

Safety is a particularly important component of thelearning environment in science. A safety policy mustdelineate the roles and responsibilities of students,teachers, site administrators, and district administra-tors. The Education Code places responsibility forcertain safety practices, such as the provision of eye-protection devices, on the local governing board andresponsibility for the implementation of these prac-tices on teachers. Districts need to develop proce-dures so that each person is aware of his or herresponsibility and is given the resources needed toenact it. The California Department of Education hasdeveloped a handbook, Science Safety Handbook forCalifornia High Schools, to assist districts in carryingout this aspect of the implementation of an effectivescience program. Safety concerns should be ad-dressed directly and not used as a rationale for theelimination of activity-based scier.ce.

Teaching Technologies

As indicated in the preceding section, equipmentand materhils are essential components of scienceprograms at all levels. Traditional equipment, such astest tubes, scales, meter sticks, and microscopes, havealways had a prominent role in effective seienceprograms. As newer technological devices, such asscientific calculators, computers, videotapes, andvideodisks, become less expensive and more signifi-cant as mechanisms for teaching and learning, theirrole should be constantly evaluated for their contribu-tion to an effective science program. These technolo-gies can support teachers in administrative tasks and

..,

can be used in obtaining new information and ideas.The effectiveness of the newer technological devices,of course, depends on teachers receiving adequatepreparation in their use and time to incorporate themin their work. This section considers the rationale forusing newer technologies in teaching, the mecha-nisms for incorporating them in the curriculum, andsome criteria for evaluating the use of technology inthe science curriculum.

Technology can provide conduits to new informa-tion, new experiences, and an opportunity to experi-ment and fail in a supportive environment. Thestorage and computational capacities of computerscan help to eliminate the misconception that scienceis merely a collection of facts to be memorized anddata to be manipulated. Used properly, they serve as abridge that permits students to concentrate theirattention on making connections among the facts andmaking sense of the results or numerical computa-tions. While computers can be deployed as electronictextbooks and programmed to provide drill andpractice, their most important contributions are tosimulate simple and complex systems, assist in thecollecting and interpreting of laboratory data, andserve as adaptable reference stations. Computers canalso be used as part of a telecommunications networkin which students and teachers sham data and ideaswith one another, comparing the pH of rain across thenation, for example, or the results of a classroomsurvey of genetic traits. For the teacher, they are alsoan invaluable relief from administrative burdens, suchas maintaining student records and preparing exams.

Videotapes and videodisks extend the range ofexperiences available to students and teachers.Experiments that are too dangerous or costly toconduct in the classroom, historical or one-timeevents, and activities at a distance can all come intothe classroom environment. Use of a video camera isalso a way for students and teachers to bring theirown projects and experiences outside the classroominto the arena for discussion. The ability to preview,review, and stop and discuss that is offered by avideocassette recorder increases the range of thisteaching technology; the ability to program the inter-face with a videodisk offers even greater potential forthe individualization of materials to the teacher whohas the time to take advantage of this technology.

In each of these casescomputer and video--theperson who benefits most from the experience is the

person who designs it. Therefore, as far as possible,students shoz.:ld be involved in the control of thisexperience. They can be involved in selecting thetechnology for the instructional purpose, previewingit, explaining it to other students, predicting what willhappen next, forming generalizations, and summariz-ing the experience. This mode of using technologiesis analogous to the use of laboratory experiences; itmust be thoroughly integrated in the instructionalenvironment in order to contribute to it. Passive uses,such as watching an hour-long video, should be madeactive threugb preparation, discussion during,Fatch-ing, and expectations for follow-up acti ities. ,

A likely msult of the incmased use of technology inthe classroom is the evolution of the role of theteacher from disseminator of information to facilitatorof the students' learning. As individual students go indifferent directions with a wide array of informationand resources, it is not possible, nor desirable, for theteacher to anticipate every path taken by everystudent. Teachers need to gain sufficient experiencewith this style of learning themselves that they feelcomfortable with the perceived lack of disciplinedcontrol. They will soon discover that the technologyfrees them from the management of information andallows them to devote mom time to one-on-oneinteractions with the students. From these discus-sions, the student acquires an understanding andappreciation for the fact that science results frommaking sense of information rather than from theinformation itself.

Mechanisms for changing the way teachers teachwill have to incorporate this view of technology'srole in instruction. Just as mechanics must learn howto use a tool in the context of their work, teachersmust learn to how to use technology as a pedagogicaltool in the context of their classroom. The appiicationof technology to teaching is more than a skill, it is anart that requims practice. The introduction andcontinued use of technology requires:

Support for people at all levels of the educationalstructum, from the teacher through the academicadministration, including opportunities for sus-tained experience

Support from the administration and the commu-nity for long-term investments in staff develop-ment and acquisition and maintenance of equip-ment and instructional materials

..,

1 92Chapter 7holementing a Strong Science Program 179

Reevaluation of educational goals and methodsas teachers evolve new teaching strategies usingtechnology

Consideration of technology-based educationalmaterials in the curriculum planning, adoption,and implementation cycles

Criteria for evaluating materials in science havebeen presented in the Technology in the Curriculum:Science Resource Guide, distributed by the CaliforniaDepartment of Education to all public schools inCalifornia in 1986. Instructional technology programsshould be used to (1) provide experiences that cannotbe provided better through other means; (2) promoteactive involvement by relating content to approprian:.science processes; (3) contribute to the developmentof a positive attitude toward science; (4) overcomebias and singular points of view; and (5) support andbe integrated into the science curriculum.

Other Valuable ResourcesParents and the community offer tremendous

potential for supporting and enhancing the school'sscience program. Parents should be regularly in-formed about the science program, teachers' expecta-tions, homework policies, and the student's progress.Active parent involvement can be encouraged as ameans of supplementing classroom science instruc-tion. The teacher can:

Encourage parents to visit the classroom toobserve and discuss the student's interest,assignments, and skills in science.Provide a listing to encourage family visits toscience resources in the communitymuseums,planetariums, libraries, research labs, zoos, andother loeadons with interesting ecologicalfeatures.Provide information regarding science-relatedtelevision programs, books, magazines, andnewspaper articles. Encourage parents to view orread and discuss the content with the student.Invite parents to become volunteers in theclassroom or resource persons to share informa-tion regarding their science-related careers orhobbies.Extend the science classroom to the home bydesigning homework involving experiments orsurveys to be carried out with family involve-ment.

180 Part illAchieving the Desired Curriculum

The community also provides a rich resource forextending the science program. In addition to visits tofacilities where science is practiced and exemplified,the people in the community who work in science-related occupations are frequently interested in publiceducation and willing to visit classrooms to discusstheir work with students. Role models motivatestudent interest in science careers. It is especiallyimportant that such role models include representa-tives of groups Taditionally underrepresented inscience, such as women and minorities. Scientists andothers who use science in their jobs should be encour-aged to bring slides, photographs, and the tools theyuse so that students can better envision the experienceand excitement of being a scientist.

I

THE California Science Implementation Network hasdeveloped a school-based model that many teachersand principals have found useful. The planningprocess, which involves the entire school staff, hasthree steps: (1) complete a matrix for programelements and one for content; (2) conduct indicatedstaff development; and (3) monitor individual teacherprogress.

Program Elements MatrixFilling in the program elements matrix is a whole-

staff activity. The staff should decide what elementsare important to put in the first column of the matrix;the list in Table 2 is simply a starting point. The othercolumns represent steps in the continuum from wherethe staff is to where they would like to be.

The columns in Table 2 are to be filled in with athree-year perspective. The bare minimum of scienceinstruction in grade one might be 60 minutes perweek, and the goal might be 120 minutes per week,with entries in the first and third columns. The mid-point, a reasonabde transition goal, would be 90minutes per week. Similarly, the values for grade fivemight range from a starting point of 120 minutes perweek, transition of 150 minutes per week, and a goalof 200 minutes per week. The amount of contentcovered might range from three units per year at thestart to five units per year as the goal. The way in

.) 3A

TZA )q0r1Yroitram: fit*InScieticeNapation.

Element Starting point Transition Attainable goal

Time

Content

Instructional strategies

Integration

Materials

Resources

Assemblies

Science fairs

Family science

which teachers present information might range fromteacher demonstrations to teacher-led activities tostudent investigations. Once the entries are agreed on,teachers can locat t. thcir current programs on thcchart and set personal goals for moving over onecolumn each year. Thus, if a teacher is alreadytcaching science 90 minutes per wcck, hc or shewould aim for 120 minutes per week the followingyear and 150 minutcs per wcck the third ycar, ecnthough it is off the chart.

Content MatrixA goal in dcsigning a schoolwide articulated

contcnt matrix following the mandatcs of this frame-work is to balance the three science disciplines(physical, earth, and life) so that the curriculumspirals through the grades and is united through theuse of the themes of science.

There are many approaches for developing such amatrix; somc are more effective than others inreaching thc goals of thc framework. Themes mightbe included in the curriculum on an awareness level.Although this is better thaii no attempt at conceptuali-zation, it does not incorporate the thrust of thcframework. Themes can also be introduced in thccurriculum. This is a more sophisticated goal towardwhich the matrix might be directed. A third approachto building the matrix involves theme induction. This

process uses known t.ontent to build discipline-specific strands that are organized around unifyingconcepts. The content of the strands is then analyzedfor themes that emerge as commonalties in thc disdplincs. This method is presented in detail in thisscction.

Onc mat remember that building a content matrixis like playing with a Rubik's Cubc. All of the pieceseventually fit togcthcr, but they may need to bcjuggled or fine-tuned to create thc best fit of ideas.The fluidity of thc matrix allows for many differentexamples to be developed using the same contcnt.Thc amount of variety depends on the emphasis ofthe componcnt parts of the matrix (Lc., unifyingconcepts, grade level concepts, subconcepts, themes).Planners are encouraged to design their own planningmodel. (Two examples arc presented later in thissection [tables 4 and 7). Thcy are not mandates forhow a curriculum should look, but rather a process bywhich a curriculum is designed.)

General Structure of the Matrix

Table 3 represents a pattern for a content matrixthat is to bc filled in with conceptual and thematicidoas. It is used by the staff to design thc scope andsequence of the curriculum ()Nes a thm year period.Implementation of the matrix can thcn bc done in"little steps":

Chapter 7Implementing a Strong Science Program 181

3 units x7 grade levels = 21 units for year one4 units x 7 grade levels = 28 units for year two5 units x 7 grade levels = 35 units for year three

Schools that include grades seven and eight wouldexpand the matrix to include the additional grades.

The matrix in Table 3 consists of five columns andseven rows (for grade levels kindergarten throughgrade six). Grade-level themes are to be inserted inthe second column. The third, fourth, and fifth col-umns represent the traditional disciplines of scienceand might be considered by some districts as the corescience curriculum. The next two columns take intoconsideration the diversity found in California'sschool system and are purposely left open for deci-sion making at the district and school site levels. Wesuggest that these columns be filled with units ofstudy that either complete the core curriculum orenrich it and that they be organized to be consistentwith the themes driving the other units found in thatrow (grade level). Columns are organized throughunifying concepts that are discipline-specific and tiethe grade levels together. The rows of the matrixrepresent curricula at successive grade levels, kinder-garten through grade six. Units in a row are united bythe themes of science and inten-elated content.

Building the Vertical Columns of the Matrix

Unifying concept(s) and grade-level concepts andsubconcepts are developed for each discipline:physical, earth, and life science. (Subconcepts are il-lustrated in more detail in tables 5, 6, 8, and 9.) Stepsfor defining and identifying these components in eachdiscipline follow:

Unibing concepts. The unifying concepts helpteachers answer the question: "What do you wantyour students to know after they leave grade six(grade eight) in science?" These concepts:

Are broad enough that students at each gradelevel can learn from them.Are discipline-specific; i.e., they explain thenature of the discipline and help to organize andunderstand it.Provide a framework for the developmental se-quence of traditional content.

Process for identifying umfying concepts. Theprocess for ident;fying unifying concepts includesfour steps:

182 Part IIIAchieving the Desired Curriculum

1. Brainstorm about the most important things for astudent to know and experience in a given disci-pline. A resource for doing this is the contentsection of the Framework, which is arranged bycentral organizing principles and organizingquestions.

2. From the brainstorm session, cluster topics ofideas and activities that seem to fit into biggeridels. It is very likely that traditional topics canbe categorized several ways. For example, rockscan be included as pmducts of the changing earthor can be discussed from the perspective of thestructure of the earth; body systems can beincluded in a structure/function relationship, butalso to explain the diversity of life; and mattercan be described from the energy required tochange it or from the relationship of microscopicto macroscopic interactions.

3. From the cluster, select a unifying concept orconcepts broad enough to be developed for kin-dergarten through grade eight by the use ofgrade-level concepts.

4. Express the unifying concept in a sentence toclarify its meaning. Here are some examples:

The earth, within its universe, is changing.Life is diverse.Matter and energy can be changed but cannot

be created or destroyed.

Grade-level concepts. The grade-level concepts arecharacterized as:

Supporting the unifying concepts (similar todeveloping a topic sentence and its supportingdetails).Describing content from a conceptual basis,rather than presenting isolated facts. For ex-ample, if the unifying concept is that the earth ischanging, then the traditional subject of ocean-ography would be addressed from the standpointof how oceans affect or arc affected by thechanging earth, rather than presented as unre-lated bits and pieces.Being arranged in a developmentally appropriatesequence.

Process for selecting grade-level concepts. Wesuggest two methods for developing and selectinggrade-level concepts: (1) brainstorm supportingconcepts for unifying concepts, or use content de-

i % 5

,,,-

-7:- --; ..-. L.:::

.:,--.--,,,:.---';' '.e-, ,,...-

.-,-:ei.A:;i:-,i.::-.,_ -.---e- .-11171:-7"...!-=3:f. . - --- --.--_:. , ";-..:.;._ "5 '''; ...,

.

OW*

.. -...

_ .. . .

. Unififing-

__ _.

.

.-. .

._.... .--......- . .,

concefits

.,Local -Os .

i..,....-- ---......

t .

_

.. _

-llhaiiii*.z.

-grade-levettonOpts_and$aopiicepts.

. ,_ 0

.

. ...

,

,

_

.

..

. ,.. .

.. .

.

,

-

,

scribed in the appropriate grade-level span of theFramework, or (2) brainstorm the content that iscurrently taught at each grade level and rephrase it inthe focus of the un!fying concept. For example,traditional content for grade two might include theideas that plants have roots, stems, and leaves andanimals have body systems. If the unifying concept isthat life is diverse, then this content can be refocusedas a grade-level concept to read: Living things havesimilar needs but diverse structure to meet their needs.If the content that is brainstormed does not seemappropriate to the unifying concept, set it aside forconsideration in ..ither areas.

After completing method (1) or (2) for selectinggrade-level concepts, place the sentence describingeach grade-level concept in sequence so that thesequence is developmentally appropriate.

Subconcepts. Subconcepts exhibit the followingcharacteristics:

They support the grade-level concepts by identi-fying the content to be taught at each grade level.They describe the how and why as well as thewhat of the content. For example, if the unifyingconcept for earth science has been identified as"The earth, within its universe, is changing," andthe concept for grade five has been identified as"Forces that work on the earth are responsiblefor the changes that we observe," then traditionaltopics such as erosion deposition, rocks, tectonics,layers of the earth, and so forth can be organizedby three subconcepts: (1) forces change the earth;(2) products result from these changes; and(3) change occurs over time.

Process for selecting subconcepts. (Treatment of sub-concepts in the process is illustrated in tables 5, 6, 8,and 9.)1. Brainstorm the stuff that is taught. Sources include

the Framework's content section, previous experi-ence, textbooks, and other reference materials.

2. Combine similar subconcepts, eliminate those thatdo not address the grade-level concept, and selectthree to five that meet the above characteristics-forsubconcepts.

After completing the process for identifying the uni-fying concepts for physical science, repeat the processfor earth science and life science. We suggest buildingeach strand with reference to the other strands. In thisway, one can start to look for thematic connectionsfrom the subconcepts across a grade level.

184 Part IIIAchieving the Desired Curriculum

Building the Horizontal Rows of the Matrix

The goal in constructing a horizontal row is tomake the subconcepts of the units match and relate toeach other and be unified by the themes of science.This can be done using the following steps:

1. Analyze the subconcepts of each column toidentify which themes seem to be expressed.

2. Identify commonalities of themes across a row(some literally pop out at you).

3. Correct for mismatches of themes by makingalterations, including slight rephrasing of subcon-cepts, modification of focus, movement of grade-level concepts to another row, or identification ofadditional themes.

4. Review the entire matrix to ensure that all themeshave been presented in the curriculum for kinder-garten through grade six or eight. We recommendtwo to three themes per year and that the themesbe repeated.

Sample Matrices

Tables 4 and 7 illustrate two models of matricesthat have been developed using the aforementionedprocesses. Each of the models is different in the sensethat each develops a proposed curriculum at onegrade level and for one discipline: Example A (Table4) for grade four in the earth sciences; Example B(Table 7) for grade one in the physical sciences. Thegrade-level choices are a slice of what the curriculummight look like for primary and upper elementarygrades. The matrices are also different in the selectionof imifying concepts and the emphasis on differentthemes. Both, however, use traditional contentknowledge as a basis for the matrix.

Note that two units, grade one "Water in theWorld" and grade four "Energy Transformations,"are presented in both models. These units are orga-nized under different unifying concepts in the twomodels so that planners can see how the same topicscan be approached from different points of view.When referring to the matrix, notice that the grade-level concepts (which were identified using theaforementioned process) are listed, follOwed by a unittitle in italics. In order to avoid repetition, the grade-level concepts are referenced in this section by theunit title. The themes are italicized in the narrative.

Example A. Explication. This example (Table 4)looks at the earth science strand and the grade-fourslice of a curriculum. Consider first the earth science

dr -If)1 ,-)C.)

column. In the development of this strand, it isdesired that students first experience and describe theworld immediately around them, expand their hori-zons to talk about the larger world, and then considertheir place within the universe. They will do so withinthe context of the unifying concept "The earth, withinits universe, is changing."

Kindergarten students need to explore the immedi-ate. They can talk about observable changes in ',heirworld (day and night, seasons, the weather, and soforth), the landforms with which they are familiar,and the world of their community (which integratesnicely with the History-Social Science Framework).

In "Water in the World," students in grade one arcprepared to take on slightly more challenging investi-gations. This unit addresses several themes thatappear in all grade-one units in this matrix. Studentscan be introduced to several related concepts: (1) thatthere is stability in the forms and content of theearth's water by looking at oceans and other bodies ofwater, (2) that energy from the sun warms the earthand its water, driving the water cycle; (3) that waterchanges its statc; (4) that clouds arc a part of thewater cycle; and (5) that this water cycle is a majorfactor in the creation of local weather. Patterns ofchange in the local weather can be experienced asstudents collect and report daily weather data.

In "Changing Earth," students in grade two caninvestigate the macroscopic products that come fromthe earth (rocks and soils, for example). They canalso come to an understanding that certain forms ofenergy are at work in the earth, creating and reshap-ing those products. Patterns of change in the earthinvolve processes that occur over long periods of time.

A broader background with geologic processesenables grade three students to examine "Changes inthe Ocean." Landforms and ocean basins can bcdescribed and defined and shown to have changedover geologic time. [Evolution] The energy of wavepatterns can be investigated, and their relation tochanging landforms studied. The mechanics of wavemotion itself can be introduced or reinforced at thislevel. Connections to other disciplines can also bemade as students examine the influence of oceans onweather and cHmate and the effect these have onliving organisms and ecosystems. [Systems andInteractions]

These discoveries prepare students to revisit"Meteorology" in grade four. A review of the watercycle prepares them to understand how the energy of

199

heat transfer interacts with and affects atmosphericpressure, wind patterns, and precipitation. The effectof weather and climate on ecosystems can also bestudied. [Systems and Interactions]

In grade five, students return to a study of "Chang-ing Earth," but at a more sophisticated level. They areprepared to begin a deeper investigation of geologictime and the changes it has brought. [Evolution] Theyare ready to look at the various patterns of changethat can be observed in river systems, crystals, androck formations. They might also examine the effectthose changes have had on both landforms andorganisms. [Systems and Interactions]

Having concentrated on the earth, students areprepared in grade six to look at the universe from theperspective of the earth. In "Astronomy," they caninvestigate the changes wrought by the sun and moonand examine the earth's place in the solar system.[Systems and Interactions] They can also begin tounderstand the clues provided by the stars of theevolution of the universe. This study, in turn, preparesstudents for a more sophisticated look at similartopics in the middle school years. For a more detailedlook at the subconcepts that make up each of thesegrade-level units, see Table 5.

Table 6 is the grade-four row of this matrix. It isdetailed to show the relationships among the unifyingconcepts, grade-level concepts, subconcepts, andthemes. Analysis of the subconcepts reveals thecontent of each unit, suggests connections among thathree disciplines, and forms the basis for the identifi-cation of the themes. Notice that the themes arc keyedto the subconcepts.

Two optional units for grade four arc "Food andNutrition" and "California Landforms." (Seelable4.) They arc presented as possible choices to coin-plete the thematic approach. In the first unit, focusshould be directed toward clarifying the energy needsof the human body and how adequate diet, caloricintake, and balanced nutrition meet those needs.Students can also investigate the role of humans ;r1the food chain. The second unit might fulfill a "localoptions" need and provide an integration with thetopics of California history and geography that ismandated by the History-Social Science Frameworkfor grade four. This unit might be a multidisciplinarystudy that looks at the interrelationships amongenergy transformation, meteorology, and geology onthe specific landforms in our state and the ecosystemsthat have de tieloped as a result of that interaction.

Chapter 7Implementing a Strong Science Program 185

'MMUS.

2

it

* :

1 54

5

' : 1

I

DIll I I: r

Unifying concepts

I

I I 1

: I

I

.4

.1 I I

I

t .5_1 I * S 1 II

I St

3 I . I 11 :4

t I

I " I

:4

, 11

I I I

l.a I

I

I

I 6 11

. . h. _ ..

-;,. .,....,. -,---°:..--.4,S*11)10.4.0 .... ,and w me

.,. ........ .. _ _ , - . ,.

Unifying.Concept: The earth; within its universe, is comstantly changing.

Grade Theme(S) Grade-level concepts and subconcepts

K

Me in My World There are observable changesbil.the earth..I see changesin the world around me.,Weather--Day and nightSeasonsI see different landforrns (mountains, valleys, plains, hills, deserts,oceans, and so forth).The world of my community is oade of different things (living andnonliving; integrated.with hisitirysocial science).

1

StabilityEnergyPatterns of Change

Water is an important element of change on the earth..

Most of the earth's water is found in the ctleans and is salty. Freshwater is found in lakes, river systems, streams, creeks, and otherdrainage systems.Water undergoes changes.The sun warms the earth and the sea and drives the water cycle. Cloudscan be observed and arc part of the water cycle.The.water cycle, in conjunction with other factors, creates the earth'sweather.Weather data can be collected and reported, zed the patterns can bedescribed.

2Patterns of ChangeScale and Structure

Different forms of energy reshape products of the earth.Forces at work in the earth create and reshape it.The earth (and its forces) work change over long periods of time

3

EnergyEvolutionSystems and Interactions

Oceans affect or are affected by the changing earth.Landforms and ocean basins can be described and defined.The energy of wave patterns in the ocean changes landforms. Wavepatterns can be studied as mechanical motions.The oceans have a profound influence on weather and climate, which,in turn, affect living organisms.Diverse life forms are found in the ocean habitat.

4

Systems and MteractionsEnergy

Changes in the atmosphere affect and are affectcd by changes in theearth.

The sun warms the earth, sea, and air and drives thewater cycle.Uneven heating of the earth affects air pressure and gives rise to windpatterns that move locally and around the globe.Moving air masses of different temperature and different moisturecontent come in contact, resulting in precipitation and other identifiableweather phenomena.Weather data can be collected and reported.Weather has profound effects on climate and life forms.

Chapter 7Implementing a Strong Science Program 187

tgble'5' (eOntinued)

Grade Theme(s) Grade-level concepts and subconcepts

5

EvolutionPatterns of ChangeSystems and Interactions

Forces that work on the earth cause the changes we observe.The earth is very old and has changed over geologic time.Forces arising from heat flow in the earth have caused it to change.The changing earth has had a profound effect on landfor ns and livingorganisms

EvolutionSystems and Interactiom

6

The changing earth is part of a changing universe.Both the sun and the moon, bodies within our solar system, have ob-servable and identifiable effects on the earth:The sun is the source of all energy.The moon and the sun are responsible for tidal movement.Seasons are related to the earth's orientation the sun.The earth is a part of the solar system; it is both like and unlike otherplanets.Stars provide information about the history of the universe. The earth isbut a small part of the universe.

188 Pan IIIAchieving the Desired Curriculumr:

_

'Tbe ultimate source-of niost cir.the-energy we use the

*8 Energy can be &inverted from oneform to onothei; the= axe Many foriniof enety.

In food chains the sun's radiant energyis converted throughihotosynthesis tochemit=i enagy which, 3r1I non, istrarisfonnectbuo Mechanical energy.Some of this energy is kit as heatenergy.

* In physical systems energy from anumber 9f sources is used to do work.Heat energy is often a by-product ofthis transformation.

Heat energy moves through the envi-ronment from warmer to coolerregions by processes calledeo-nduc-don, cohiection, and radiation. Thismovement has an effect on meteor-ologic and geologic procsses and onecosystems.

* The stinwarms the earth ar4 air and&Wei are water cycle.

Uneven, heating of the earth affectspressure andternperature, creatingwind patterns that mcive locally andaround-the globe.

**Moving air masses of differeactem-perature and differm moisturecont..= come in contact, resulting inprecipitation and other forms ofweather phenomena; weatt,:r dataczn be collected and used to makepredictions.

Different kinds of weather haveprofound effects on climate and onliving organisms and contribute to thestructure of ecosystems.

- There are Strucninis of and identifiablerelitienshiPS__Within_zi ecosystem-Thes:Elnr:lotic/abiotic, niche/coriunialiOtsbitits, producer/

_ _corsmTleildeOrnPosei-

*5 Energy is transferred through an coo-syst= from the nonliving to the living(food chains, food webs, and food pyra-mids).

Components of ecosystems interactand are interdependent.

Human beings (people) affect the eco-system.

204I t.)

Example B. Explication. In this example (Table 7),the physical science strand is organized around theunifying concept, "Matter and energy can be changedbut not created or destroyed." In the development ofthis strand, it is desired that students first experienceand describe the world immediately around them.Doing so will allow them to explore the macroscopicproperties of matter, energy, and motion. Understand-ing these observable properties prepares students tobegin investigations into ever more discrete conceptsrelated to energy transfer and the structure of matteritself.

Kindergarten students need to explore the immedi-ate. In "Matter Around Me," they can observe anddiscuss the properties of the stuff around them (color,size, texture, shape; whether it sinks or floats inwater, the state in which it is found; and so forth).They can also examine things to observe that every-thing is made of smaller structures. The things thatthey observe can, in part, be drawn from materials inthe other two core units of this grade level.

In "Kinds of Energy," grade one students observe,classify, and describe the unique properties of differ-ent forms of energy as observed at differing levels ofobservation. [Scale and Structure] Students investi-gate such important concepts as :ransmission, reflec-tion, and absorption of energy. I . ..idition, they canexplore the idea that energy can be used to do Wolkand make changes in matter. [Systems and Interac-tions]

"Matter," in grade two of this model, continues todeal with the properties of macroscopic things, butstudents can approach their study in a more formal-ized manner. They can review previous learningsabout phase changes and sinking/floating and can beintroduced to the concepts of matter occupying spaceand having weight and substance. In addition, gradetwo students can begin to use tools of measurementand observation to examine the differing scale andstructure of all matter. They can also conduct investi-gations into simple physical and chemical changes[Systems and Interactions], with an emphasis onunderstanding that changes in matter sometimesrequire energy and sometimes release energy.

In grade three, students examine forces that act onmatter and affect its motion. After investigating thoseforces, students measure and observe the patterns ofchange in moving objects in terms of distance, time,and weight. They can apply forcc to objects in order

190 Part IIIAchieving the Desired Curriculum

to move them through a distance, and they can con-struct simple machines to do work and tocreatc changein their environments. [Systems and Interactions]These simple energy transformations form the basisfor understanding the concepts of mechanical energy.

The grade-four unit, "Energy Transformation," isorganized around the major themes of systems andinteractions,and energy. Students will investigate avariety of conversions from one form of energy toanother, recognizing that the total energy in thesystem is conserved. They will expand their studiesof mechanical energy in an understanding that energyconversions from a number of sources are used to domechanical work, often with heat energy as a by-product of the transformagon. Processes that transferthis hcat energy will conclude the unit of study.

"Waves, Light, and Sound" provides grade fivestudents with a look at some of the microscopicproperties of matter and energy transfer. [Scale c.hdStructure] They can investigate the similarities anddifferences between electromagnetic and mechanicalwaves. They can also explore the unique poperties oflight and sound energy. This unit has a variety oftopics suitable for integration with other sciencedisciplines, as well: infrared radiation and heattransfer (geology and meteorology), photosynthesis(ecosystems and food chains), sight and hearing(anatomy and health), and the effect of concussivewaves (earthquakes), to name a few.

The grade-six unit, "Matter," looks at the scale andstructure of atoms and demonstrates how chemistry isdevoted to understanding the properties and interac-tions of atoms and groups of atoms. [Systems andInteractions] Students can investigate such conceptsas mass, displacement, and density. They can explorephysical changes in matter and chemical reactions.They can also come to a fuller understanding ofvarious energy transformations involved in chemicalreactions. As such, this is a Ping summarizing unitfor the learning that has gone before and a challeng-ing introduction to the concepts needed for a richmiddle school experience.

For a more detailed look at the subconcepts thatmake up each of these grade-level units, sec Table 8.

Table 9 is the grade one row of Example B. As withExample A, the subconcepts for this row are detailed,and the themes are keyed to the subconcepts.

The fourth and fifth columns in the grade-one rowon Table 7 :dentify an outdoor education strand and a

ri

, .

eii 10 .itoti: Sx

Giade Therne(s)-

Physical sciencei

Earth science! Life science

,.._

Local Options

Ecology,lechnology,,health.,:--..

.

.

:..

.

Unifj:fing concepts

iviation/space science -

rilit.aer.iiid eiititZt_in bechangefibut nolcfreate4-or-destiOyed.

' -gert Pike 1!). r hitiOet in -'cycliCal Piiterni

!,ife. ii diverse. ' Respect for natMe.develops*om under-standing how naturewOrks.

"The application ofscientific knowledgechanges the world.

Grade-level concepts (with unit titles)

f Me in My World -Macan be observedincf classified."Matter Around Me"

... ..

.

Systems and InteractionsScale cad Structure

Energy comes inditferent forms."Kinds of Energy"

Water affects life on earth."Water in the World"

There are similaritiesand differences in livingthings."Diversity of Life"

Human beingsaffect the environ-merit."Conservation"

Resources arc limited;some can be recycled."Recycling"

Scale and StructureEnergy

Matter has propertiesand csat be changed....matter

Systems and InteractionsPatterns Of ehange

Forces set on matter andcause motion."Changes in Motion;SimpliMachines"

EnergySystems.and InteractionsScale and Structure

Energy can be convertedfiont one form to another."Energy Trans fonnation"

EnergyScale and InteractionsSystems and Interactions

-

Mauer and energy interactat tmicrescopic level."Waves, Light, Sound"

EnergySystems and Intee-actioniScale and Structure

The structure of matterata Microscopic level affectschemical reactions."Matter"

21171

c)

,.. 1 '.;1-' ---. ... t . .

,. . .,,,,' .5,

.

,iciwat..,.:..-

. .. . ..,_

and energy can be changed but not created or destroyed.Unifying Concept: Matter

Grade Theme(s) Grade-level concepts and subconcepts

K

Me in My World Matter can be observed and classified.Everything around me is made of "stuff." The stuff can be described andclassified by many characteristics:Color, texture, shapeHardness, flexibilityTaste, odorSound or light that might be emitted or reflectedState-(solid; liquid, or gas)Tendency tofloat or sink in waterAll things are made of similar structures.

1

Systems and InteractionsScale and Structure

Energy comes in different forms.At the macroscopic level, each of the various forms of energy hasunique characteristics. Observe and compare the properties of differentmanifestations of energy (light, sound, static electricity, magnetism,heat., wave motions, and so forth) in order to classify and describe.Energy can be uansmitted, reflected, and absorbed.Energy can be used to do work and to make changes in matter. Changesin matter sometimes require energy and sometimes release energy.

2

EnergyScale and Structure

Mauer has properties and can be changed.Matter has definable properties that can be described and reported:It occupies space.It has weight and substance.It sinks and floats.It exists in three states.Matter is made of smaller structures. We use tools to measure, perceive,and better understand these structures when they exist at a scale toosmall, too fast, or too far away for normal perception (telescopes,microscopes, thermometers, scales, clocks, and so forth). The more weunderstand the structure and function of matter, the better we understandliving organisms and how they intelact with their environment and thebetter we understand the changing earth.Matter undergoes physical and chemical changes.

3

Patterns of ChangeSystems and Interactions

Forces act on matter and cause motion.Forces act on matter. Forces include:Pushes and pulls by direct contactGravityFrictionMagnetismThese forces can affect the motion of matter.Motion can be measured in terms of distance, time, and weight.Speed is the distance covered divided by the elapsed time.

192 Part IIIAchieving the Desired CurriculumAo.'

,.. .

Grade Theme(s) Grada4ev:11 concepts and subconcepts

3(Continued)

Patterns of ChangeSystems and Interactions

The weight of an object is related to the amount of force necessary tochange its motion.

Work is done when a force is applied to an object that moves it through a

distance.Simple machines help people do work and change their environment.

4

Systems and Interactions

Scale and Structure

Energy can be converted from one form to another.The ultimate source of most of the energy we use is the sun.Energy can be converted from one form to another. In the process thetotal energy in the system is conserved but not necessarily in the sameform. We use energy from a number of sources (the sun, water, heatwithin the earth, nuclear reactions, and so forth) to do mechanival work.Heat energy moves through the environment from warmer to coolerregions by processes called conduction, convection, and radiation. Thismovement affects meteorologic and geologic processes and ecosystems.

5

Scale and StructureEnergySystems and Interactions

Matter and energy interact at a microscopic level.Light and sound energy arc similar in many ways, but they are not the

same thing:Both travel as waves and can be reflected, refracted, and absorbed.

Both have frequencies and wavelengths.Light is an electromagnetic form of energy.Sound is a mechanical wave arising from vibrating objects.Infrared radiation is an electromagnetic form of energy. Light carries heatin the form of infrared radiation. When infrared radiation is absorbed bymatter, it releases heat energy.As a mechanical wave, energy can be a force that can do severe damage

(earthquakes).Animals perceive their environment by means of light and sound energy:Electrochemical impulses arise from light striking the retina and are

processed by the central nervous system.Electromechanical impulses arise from sound in the middle ear and

are processed by the central nervous system.Plants use electrochemical processes in photosynthesis to manufacture

food from sunlight.

6

Systems and InteractionsScale and StructureEnergy

The strecture of matter at a microscopic level affects chemical reactions.All matter has unique properties that can be observed and measured:

It has weight and mass.It occupies space and displaces other matter from the same space.It has density.The properties of matter depend very much on the scale at which welook at them. Properties of matter at the large scale (macroscopic)depend on its properties at the small scale (microscopic).Chemistry is the study of the properties and interactions of atoms andthe study of groups of atoms as they combine to form compounds and

mixtures.

r Chapter 7Implementing a Strong Science Program 193

LC)

'.Physical SciOrica

tnergyiranifocmnOnnt bring aboutmany changes in the physical %VOrld,but, overall, energy is Conserved.

Cycles'arese-peatable pasterns in nature. Diversity is the concept that representsthe panoramic variability in the naturalworld.

Grade Theme(s)

Systems andInteractionsScale and'Structure

Energy comes in different-forms, eachwith its own.characteristics."Kinds of Energy"

Grade-level concepts (vith unit titles)

The water cycle govems much of theenvironmental conditions on earth."Water in the World"

The diversity of life arises from theintersection of evolutionary mecha-nisms with environmental conditions."Diversity of Life"

Subconcepts

At the macroscopic level each of thevarious forms of energy has uniquecharacteristics that can be observed,described, and classified.Energy can be transmitted, reflected,and classified.Energy can be used to do work andto make changes in matter. Changesin matter sometimes require energyand sometimes release energy.

Water is essential for life on thisplanet.Water undergoes changes when heatenergy is added or removed.The sun warms the earth and drivesthe water cycle. Clouds can beobserved and are part of the watercycle.The water cycle, in conjunction withother factors, creates the earth'sweather.Weather affects the earth and livingorganisms.

Living things need food, water,shelter, and space. Living thingsshare characteristics, includinggrowth, reproduction, response to en-vironmental stimuli, and so forth.There is utmendous diversity inliving organisms and between them.There is great diversity in the homesand habitats of living things.Within diverse habitats, plant. andanimals secure their needs in differ-ent ways but often depend on oneanother.

technology strand as optional topics to be developed.In this row, the first unit is entitled "Conservation"and deals with the primary ideas of conserving thingsand littering. "Recycling" takes these ideas a stepfurther, illustrates what we can do with the things wecannot conserve, and helps to awaken student concemover social issues.

Sect,fon 6 t RelAionshiRyvith Other'FrameTlrks

THE reforms in science education that are reflected'n this Framework are part of an overall reformstrategy to transform education for all students so thatit promotes thinking and reasoning. As described byLauren Resnick in her monograph, Education andLearning to Think, there is nothing new in a curricu-lum that promotes thinking; there has always been thetradition of the academy in which students werechallenged to read demanding texts, to write criticalessays, and to understand the basic tenets ofscientificand mathematical reasoning. What is new about thepromotion of higher-order thinking skills in thereform of the 1980s is the expectationAhat all stu-dents can and must be involved in such a demandingcurriculum. As Resnick points out, the definition of"higher-order thinking skills" is elusive, but wc canrecognize it when it occurs. It is nonalgorithmic andcomplex, it involves multiple solutions and judgment,and it often involves uncertainty. The thinker mustexamine his or her thinking and must impose mean-ing on the situation. Such thinking is required by allof our citizens, not just the elite, and must be theoutcome of schooling.

The manifestation of the attempt to cultivatehigher-order thinking takes different forms in differ-ent subject areas. Mathematics educators are inclinedto talk in terms of problem solving; history and socialscience educators speak of critical thinking; scienceeducators talk about the nature of science, as illus-trated in Chapter 1. In each case, the details andmechanics of the discipline are being subordinated tothe goal of a meaning-centered curriculum with theaim of increasing the thinking and reasoning in whichstudents are engaged.

The focus of the Mathematics Framewor:c, approvedby the State Board of Education and published in

1985, is "mathematical power, which involves theability to discern mathematical relationships, reasonlogically, and use mathematical techniques effec-tively. . . ." It emphasizes teaching for understanding,instead of teaching rules and procedures for their ownsake. The consistent call to relate mathematicaltechniques to the solution of problems that aremeaningful and aexessible to students makes thebridge t science instruction a natural alliance. Thepractice of computational, measurement, and graph-ing skills makes obvious connections betweenmathematics and science. Science educators shouldbe particularly conscious of the MathematicsFramework's emphasis on selection of the appropri-ate method for achieving numerical resultsestima-tion, mental arithmetic, paper-and-pencil, or calcula-tordepending on the nature of the problem and thenumerical information involved. Students shouldlearn to select the method and the appropriate level ofaccuracy of the result. They should be making theirown selections, both on class assignments and ontests, by the end of grade six. Use of scientificcalculators, advocated in mathematics for secondarystudents, should also be incorporated in secondaryscience programs.

Beyond computation, however, the mathematicscurriculum also includes the important strands ofstatistics and probability, patterns and functions, andlogic. The statistics and probability strand includesthe formulation of questions, collection and organiza-tion of data in a variety of representations, and com-parison of empirical results with theoretical probabili-ties. The patterns and functions strand includes thesearch for patterns in data and the representation ofthese patterns in verbal, visual, numerical, graphical,and algebraic forms. The logic strand includes theorganization of ideas with an accurate use of termssuch as all, some, and, or, i f . . . then, and not, andmaking valid inferences. These skills are both re-quired by and developed in the science curriculum, socoordination with the mathematics curriculum isessential for science and mathematics.

The theme of scale and structure is particularlywell suited to integration of mathematics with sci-ence; developing the number sense for very large andand very small numbers and the scientific notation toexpress them, ratio and proportion, and even the ideaof scale itself are central concepts for both disci-plines. Patterns of change is another important

Chapter 7Implementing a Strong Science Program 195

The matufestation of the attempt to cultivate higher-order thinking takes different forms in differentsubject areas. Mathematics educators are inclined to talk in terms of problem solving; history andsocial science educators speak of critical thinking; science educators talk about the nature of science,as illustrated in Chapter I .

bridge, as quantitative analysis is often the methodused to differentiate among cycles, trends, andrairdom changes.

The EnglishLanguage Arts Framework wasapproved by the State Board of Education in 1986and published in 1987. Also centered on the construc-tion of meaning, its focus is an integrated curriculumin which the language arts of reading, writing,speaking, and listening are treated together in mean-ingful contexts rather than treated separately, apartfrom context. With an emphasis on a literature base,it exposes students to significant literary works, ratherthan brief narratives constructed to teach skills. Thisapproach is particularly well suited to coordinationwith science instruction, as science investigationsprovide meaningful contexts for reading, writing,speaking, and listening and help students to developtheir language arts skills related to nonfiction. Ofcourse, science fiction and literature about sciencethemes are additional avenues for coordination of thescience and Englishlanguage arts curricula.

The HistorySocial Science Framework wasapproved by the State Board of Education in 1987and published in 1988. One of its themes is theimportance of "history as a story well told." It empha-sizes depth over breadth, using the opportunity toexamine in deput the connections among history,geography, and culture, particularly the literature ofand about a period. The notion that science is ahuman activity and that it takes place in certain placesand certaln times due to the conditions that have gonebefore as well as current circumstances is certainly inaccord with such study. In fact, the role of scienceand technology in societal development is an impor-tant component of history, particularly as it relates tocontemporary issues and events. Incorporating theachievements of people from diverse cultures in thehistory of science, whether it be discussed in historyor science or both, is a particularly appropriateapproach. Care should be taken to ensure the accu-racy of the portrayals of historical figures. The

196 Part IIIAchieving the Desired Curriculum

HistorySocial Science Framework also makes clearthat controversial topics and discussion of values areto be embraced rather than avoided. As discussed inChapter 1 of the Science Framework, "The Nature ofScience," controversy and values are not the provinceof historysocial science alone and must be handledas legitimate concerns of the science curriculum aswell. Finally, the themes of evolution, which isdirectional change, and patterns of change, whichincludes cyclical change, are important bridgesbetween historysocial science and natural science.The ideas of systems and interactions and stability arefurther links between these fields.

The Foreign Language Framework is the mostrecently developed framework, approved in 1988 andpublished in 1989. Its emphasis is on communication,again subordinating skills to the meaning that isnecessary for the development of understanding.While particular connections with the science curricu-lum are few, the general trend toward meaning andaway from vocabulary fot its own sake is certainly asvalid in science as it is in foreign language. It hasbeen estimated that some high school science text-books introduce more new vocabulary words than atypical first-year foreign language textbook. Suchpractices should be compared with exemplary prac-tice in foreign language instruction and abandoned.

The Visual and Performing Arts Framework,aproved in 1981, published in 1982, and reissued in1989, is constructed around four components of artseducation: aesthetic perception, creative expression,arts heritage, and aesthetic valuing. The relationshipbetween science and the arts should not be limited toan "arts and crafts" approach but should extend to thecommon intellectual processes and content of thesefields. The critical-thinking processes ,ssociated withscience are paralleled in the arts, as students use all oftheir senses to observe, analyze, and synthesize thesights, sounds, and movements in the world aroundthem. The work of both scientists and artists includescommunicating their impressions, evaluating their

2 1 4

own work and the work of others, and maldngthoughtful and informed judgments. Certain scientifictopics, such as light, sound, and perception, areparticularly appropriate areas of integration betweenscienee and the arts. Certain arts skills, such asobseiving, drawing, and.acting, can also enhance thestudy of science. Most of the major themes of scienrxfind their representation in the visual and performingarts curriculum, but certainly scale and structure,systems and interaction, and energy am likely ve-hicles for connecting the arts and the sciences.

Tile next framework to be revised, with &commit-tee established in 1989 and a product anticipated in1990, is the Health Framework, the current edition ofwhich was approved by the State Board of Educationin 1977 and published in 1978. The old documentexplicitly avoided any commentary about relation-ships with other subject areas, defcrring to "theprerogative of local school districts." The new healthframework will reflect the thrust of the "HealthyKids, Healthy California" comprehensive healtheducation initiative in which the various aspects ofschool life that promote healthincluding healtheducation, nutrition, health and psychological ser-vices, and physical educationare coordinated witheach other and with the total school program. Whilehealth education will maintain its distinctive role inthe curriculum, consistent with Educzdon Coderequirements to offer health education at elementaryand secondary levels, it is likely that connections withother subject areas, including science, will be definedand encouraged.

In addition to the conceptual connections amongthe frameworks, certain pedagogical techniques, suchas cooperative learning and writing across the cur-riculum, are appearing with increasing frequency.Broader notions of assessmentaway from multiple

215

choice and towards student-generated work, projects,and portfoliosare also becoming increasinglyprominent. These teaching and assessment strategiesare required by the attention to higher-order thinking,as it is necessary to develop one'a ideas by discussingthem with others and by writing abaut them, and it isnecessary to assess a student's progress by usingconditions similar to the learning.

When the curricula emphasized mastery of narrowskills, such as long division, spelling, historical dates,and science vocabulary, individual students practicingisolated exercises in quiet rows of desks may havebeen an efficient and effective strategy. The curriculaare moving toward attention to skills in order to makemore meaningful activiq possibledivision for thepurpose of solving a complex problem, perhaps usinga calculator; spelling for the puipose of publishing anessay, possibly using a computer spell-checkingprogram; dates for the purpose of a historical argu-ment, maybe using a reference book; and vocabularyfor the purpose of communicating about a scientificinvestigation.

These meaningful activities are characterized bycommunication about thinking with others, enrichedby intcraction with other students, and less likely toproceed effectively in quiet rows of isolated students.The groups of four that are assembled for mathemati-cal problem solving become the peer response groupsfor revising writing, the debate team for enacting ahistorical argument, and the research group forinvestigating a scientific question. This is not to saythat there am not some things that need to be learnedindividually or quietly; merely that the movementtoward meaning-centered curriculum is coming in allsubject areas and that somc of the changes in teachingand assessment that support one subject will prove tobe valuable in others.

Chapter 7Implementing a Strong Science Program 197

Chapter 8

InstructionalMaterials Criteria

THIS chapter summarizes the criteria that Californiawill apply to thtadoption of science instmctionalmaterials in 1992, bastd on the philosophy, content,and guidelines of the foregoing chapters. Of panicu-lar importance are (1) the.shift of emphasis on con-tent, away fnim inclusion of topics and toward cover-ing fewer topics in depth and thematically; (2) the'emphasis on representing science accurately andhonestly, particularly the nature of science, its philo-sophies and methods, and its language; and (3) thefbrsaking of disconnected, vocabulary-driven chap-ters and units that merely pile facts on definitions, infavor of a considerate narrative prose that cares lessabout readability formulas and more about readabletext.

CALIFORNIA is one of 22 states in the United Statesthat conducts state level review and adoption ofeducational materials. According to procedures setforth in the Education Code, the State Board ofEducation selects from five to 15 programs for eachsubject area at each level, kindergarten thmugh gradeeight, that can be purchased with money in theInstructional Materials Fund (IMF). Each year, schooldistricts are fmanced from the IMF on the basis of thenumber of students they serve. Currently,18% of theIMF funds for materials for students in kindergartenthrough grade eight are restricted to programs' that

'By "program" is meant the sum of instructional materials purchued foruse in the classroom, including but not limited to textbooks, software,charts, maps, equipnent, and supplies. Also included in a good cuniculumare features such as field trips, extramural visits and speakers, and otheraudiovhual aids.

198 Part RIAchieving the Desired Curriculum

are listed on the adoption list (often called "thematrix") for the particular subject area, unless thedistrict completes a waiver process demonstratingthat different materials are necessary to meet thedistrict's needs. (The remaining 30% of the fundsmay be spent on any materials that meet the state'slegal compliance requirements. Districts ate alsopermitted to use their own funds to purchase anymaterials that they select.)

The purpose of state adoption is to ensure that statefunds are used for materials that are consistent withthe state's curriculum guidelines, as set out in theframeworks for the subject areas. Critics have pointedout that some of the problems with current instmc-tional materials can be traced to the adoption process.The fact that 22 different states develop differentcriteria for acceptance, including specifications of thecontent to be covered, has forced publishers toinclude ever-increasing numbers of topics andconsiderations. This has led to the pracdce of men-tioning, mating many topics superficially rather thana smaller number of the most important topics indepth, and has resulted in textbooks that are encyclo-pedic collections of vocabulary that correspond to thecontent on every state's list. Local selection agencieshave often exacerbated the situation by applyingreadability formulas that judge the trading level ofthe text by characteristics such as sentence length andvocabulary used, regardless of the actual readabilityof the material. The stress on readability formulas incontent areas has favored choppy sentences and theevasion of appropriate vocabulary, especially inelementary science textbooks.

Most educators, including authors and editors,agree that mentioning and the use of readabilityformulas make it very cliff' ;ult to produce goodeducational materials. These practices, however, are

not inherent in the adoption process, and it may evenbe possible to use the adoption process to discouragesuch practices. California's State Board of Educationhas begun to use the adoption process as a way ofsupporting the curriculum reform reflected in itsreceht frameworks and standards. In 1985 the Boardrequired science textbooks before they were acceptedto be strengthened in certain topics that had been P

treated too superficially. In 1986 the Board requiredmore substantial rewriting of mathematics books toalign them better with the Mathematics Framework.

With recent English-language arts and history-socialscience instructional material criteria, the Board hasalso taken a leaduship position; instead of selectingthe best of what has been available, the Board hasasked for improvements in what the publishers haveoffered.

These more stringent criteria place additionaldemands on publishers and teachers alike. In onesituation the materials requested will bo appropriatefor the best prepaied teachers in the state but willprovide too great a challenge to the teachers who are

Content(50%)

1. Material discussed in Content sections is presen(5%).2. Material is treated accurately and correcdy (15%).3. Material is treated thematically115%).4. Depth of treatmentis adequate.(10%).5. Eniphasis is placed on how scientific knowledge is gained (5%).

Presentation (25%)

6. Language is made accessible to students (5%).7. Prose is considerate and engaging; scientific language is respected

(10%).8. Science is open to inquily and controversy and is presented non-

dogmatically (5%).9. Science is shown as an enterprise connected to society (5%).

Pedagogy (25%)

10. Hands-on experience is emphasized; there is an explicit connectionwith real experience and problem-solving; textbooks and othermaterials are not the sole source of information (15%).

11. Instructional materials recognize cultural diversity (5%).12. Assessment reflects experience, integration, and creativity (5%).

2 t 7 Chapter 8Instructional Materials Criteria 199

not so familiar with the content and instnictionalstrategies advocated in the new frameworks. Almosteveryone would agree that more staff development isnecessary and that we may never have adequateresources to do:the job. Clearly, staff developmentand instruclional materials are intimately related, andstaff development programs are essential to supportthe entire science program, as indicated in Chapter 7,Section C. Yet we feel that fine instructional materi-als can themselves instruct teachers while theysupport student learning. Further, improvement ininstructional materials cannot afford to wait untilsuch time as all of the teachers who will be usingthem are optimally prepared. With the view thatimprovements in science education must proceed onall fronts, including both staff development andinstnictional materials, we present the criteria in thischapter.

The instructional materials criteria that follow aredifferent from past criteria in a number ofways. AsTable 9 summarizes, the list is short and to the point.

Content is treated dynamically, including a the-matic approach that makes connections among ideasand that values depth over breadth of coverage. Theseideas are consistent with the national calls for changein science education, exemplified by the AmericanAssociation for the Advancement of Science (AAAS)report, Science for All Americans, which suggests thatwe should teach less material, teach it better, andspend more time on it. The presentation of materialshould be open and engaging, with vocabulary usedto facilitate understanding rather than as an end initself. Finally, students must expelience science as itis connected with real experience and problemsolving, and the materials that support these expe..-ences must be considered part of the basic program(i.e., in the 70 percent category).

Many of the criteria that follow address the particu-lar issues of text. To some this will imply a text-basedprogram. Although it is likely that many scienceprograms will have a variety of print materials,including a basic textbook, this in no way is meant todiscourage the use of other media such as film,videotape, and videodisk; software and other com-puter tools; specimens, equipment, and other objects;reference books, readers, glossaries, and other printmaterial. In fact, criterion 10 expLitly calls forhands-on experiences to be integral (40 percent) tothe science program.

200 Part IIIAchieving the Desired Curriculum

Following the criteria, which will be used to guidethe adoption process for kindergarten through gradeeight materials at the state level, suggestions areoffered to guide the local selection process.

The following three sectionson content, presenta-tion, and pedagogydevelop the 12 criteria listed inTable 10.

a

CONTENT refers to the subject matterhow well itrepresents what is currently known of science;whether it uses themes to integrate information;whether it provides deep discussion of topics, inte-grating ideas and facts, instead of shallow, éncyclope-dic coverage of topics that become little more thandefmed tenns; and whether it messes how we cometo know what we know in science and how scientistsdo their work.

In examining adopted materials for local selection,committees should assume that the state-adoptedmaterials have satisfied minimal requirements for thequality of content. This is not the same as assumingthat the content is optimal and equally good in alladopted materials. Local selectors areurged to readand examine printed materials and directed activitieswith an eye toward seeing how well the material istreated. One good appmach is for an evaluator tochoose a unit or several units with which he or she ismost familiar and judge how well these materialsmeet the criteria explained here, as well as the needsof the students in a given district.

The topics discussed in Part II of thisframework are treated in the instructionalmaterials under consideration.

The three chapters on physical, earth, and lifesciences g;ve the broad outlines of a content curricu-lum in natural science. Not all possible topics arementioned by name, nor does the vocabulary in thesesections necessarily correspond to the vocabulary thatappears in instructional materials of the correspond-ing grade level. However, the concepts given at

particular grade levels in this framework should betreated at those levels in the instructional materialsunder consideration. For example, the concept oflithification (how rocks are formed) should beintroduced in materials intended to discuss earthscience in grades six through nine, and not earlier crlater; but it is not necessary to use the term lithifica-don in these grades.

Experienced educators and producers of instrue-tional materials will note our relarive deemphasis onthe presence of content (5 percent). This is becausewe emphasize that it is more important to treat certaintopics well and to integrate them with other conceptsand ideas than it is to provide encyclopedic coverage.Consequently, we strongly recommend deempha-sizing or eliminating checklists in selecting materialsfor local use. Rather than enumerating whether everytopic is covered, it is more important to considerwhether what is included is considered well, in detail,and accurately. We urge the use of qualitative ratherthan quantitative criteria when considering instruc-tional materials for local adoption.

Content is treated accurately and correctly.

By accurately and correctly we mean that instruc-tional material should present what is currentlyunderstood in science, not simply rehash traditionallycovered materials. Content should also be presentedas what is understood in science, not qualified withmodifiers ("many scientists believe") when dealingwith robust scientific conclusions.

Considerable improvement is needed in the validityof scientific content presented in instructional materi-al& In general, them are three classes of problemswith the content in typical science materials. First,there are simple errors of fact (such as "most muta-tions are harmful," when it should state that the effectof most mutations on organisms is, in fact, neutral).These are generally easy to correct, but remainnagging problems if not corrected. Local selectioncommittees are encouraged to contact the Mathemat-ics, Science, and Environmental Educatier. Unit ofthe Department of Education if they have questionsabout content presented in instructional materialsunder consideration.

219

Second, there are errors in interpretation. Forexample, the principle of uniformitarianism in earthscience should not be presented as the "Law ofUniform Change" and interpreted as a doctrine thatsays that things now happen pretty much as rimyalways have. (Unifomritarianism is nothing morethan the operating principle that the laws of theuniverse have not changed since the beginning oftime; but that differs from inferring constant rates oferosion, sedimentation, and so forth.)

Third, there are failures to integrate obviouslyrelated concepts, such as continental drift, changes inthe fossil record of continents through time, and thegenetic mechanisms that underlie changes in speciesthrough evolutionary history. It is as important tocorrect these kinds of errors as it is to correct thesimplest error. The reason for this is explained in thenext criterion.

Instructional programs should be organizedaround thejnes, not aroundfacts.

The big ideas of science are what hold it together asa discipline, united in its methods and in the continu-ity of its evidence. Science programs no longer can becompilations of disjointed trivia, even if such compi-lations achieve high success in training students topass standardized tests. Concepts and ideas should beintegrated, and their connections made explicit,within and among chapters and units. Instructionalprograms should not be written or marketed as if theunits in them could be presented in any order. That isunrealistic. Material in the later units of scienceprograms should refer to material learned in previousunits, because that is how science builds on itselfjust as a person's education builds on itself. State-ments like "Remember this concept from Chapter 4?"and "You will see how this fits into earth science inChapter 11" are to be encouraged.

As one example, consider the parts of a flowec thesepals, petals, anthers, stamens, pistil, and so on.These can be taught in a perfectly straightforward anddry fashion, as a series of boldfaced terms to bememorized and labeled on a diagram. But in thecontext of a theme such as structure andfunction, orevolution, the student is able to realize that the factsfit into a larger picture; there is a reason for learning

Chapter 8Instructional Materials Criteria 201

them, and the larger picture may even be interesting.Sepals and petals, for instance, look very similar andmay arise from the same kinds of tissues. But scpalsoften support the flower, whereas petals often attractvignally oriented pollinators such as bees and moths.The larger picture of structure and function, ofsystems and interactions, integrates the facts andmakes them relevant.

As another example, consider the vital interrelation-ship of genetics, evolutionary biology, and the fossilrecord. Inmost science programs, there are separateunits on these three topics. And in many such pro-grams, no connection is made among the three. Butthe genetic code determines the development of theindividual, which must survive to reproduce its genesin the next generation. As it does so, its geneticmaterial combines with the genes of its mate todetermine the composition of the next generation.Natural selection plays a vital part in the differentialsurvival of these individuals, and it fosters the changein composition of populations that is the raw materialof evolution. The track of evolution is seen not onlyin the living world but also through more than 600million years of the fossil record. The succession ofrock beds that encase these fossils and the geochemi-cal means of determining their ages bring physics andchemistry back into the process of understanding thehistory of life, just as physics and chemistry form thebasis of molecular biology of the gene.

No instructional program can be acceptable if itfails to treat these, topics or fails to show theirneces-sary interrelationship. The theme of evolution linksall the disciplines necessary to the study of life. Evenif genetics, evolutionary biology, and the fossil recordare accorded separate units; their connection must beexplicitly shown and cross-referenced in each sup-porting unit.

An important implication for the use of themes ininstructional materials and curricula is that thecomponent units of scientific curricula should betaught in a meaningful order, and this criterion will beof prime importance in evaluating instructionalmaterials:Interconnections among ideas and conceptsthat span several subfields mquire knowledge ofsome concrete facts and some abstract conceptsbefore others can be covered in a meaningful way. Indesigning curricula, attention must be paid to the-matic development as facts and concepts are intro-duced, and this meanc that the order in which material

202 Part InAchieving the Desired Curriculum

is presented is important. In the physical sciences,energy must be taught before the concepts of electric-ity, magnetism, and gravity are introduced. In thebiological sciences, evolution must be explainedbefore classification, because classification is based onevolutionary relationships. Then the diversity of lifeand its phylogenetic interrelationships can be-treated.

It is stressed at several places in this framework,notably in Chapter 2, that the themes suggested anddeveloped here are not to be regarded as rigid. Thereare many other possible configurations of thematicideas besides those suggested here. What is importantis that some thematic strands be selected and incorpo-rated in the presentation of science in all curricula.

Instructional materials in science shouldemphasize depth of understanding, notencyclopedic breadth of coverage.

Textbooks should not be encyclopedic. No textbookcan cover the entire discipline and do it well. Instead,instructional materials should take a major theme orseveral major themes or strands and interweave theminto a logical and coherent exposition of the disci-pline under study. This criterion has some direct im-plications for the adoption of instructional materialsand for the assessment of student performance.

It is dismaying that checklists are often the princi-pal way in which content is assessed. The coverage ofconcepts, terms, and subjects, when measured bychecklists, produces instructional objectives con-nected in prose. Mentioning or defining a topic doesnot cover it, and even covering it, regardless of thelength at which it is covered, does not ensure mean-ingful or readable prose. Often, it ensures only anopportunity to insert more definitions and mentions.These counterproductive criteria of the adoptionprocess drive the engine of mediocrity and makedictionaries of textbooks. We urge local selectionagencies to eliminate quantitative criteria for theassessment of instructional materials and to focus onqualitative evaluation of the coverage of key issues,fundamental concepts, and integration of ideas.

Clearly, a thematic orientation of textual materialrequires shortening or eliminating some mater:alcurrently found in most instructional programs if

rl ri4.A1

textbooks are not to grow excessively large. Buteducators can be confident that a great deal of mate-rial in current curricula can be scrutinized andabridged or eliminated without detriment to thescience program. This is discussed fiirther in Chapter2, The Major Themes of Science. Submitted instruc-tional Materials will not be penalized for omittingbreadth of coverage in favor of depth and goodintegration of thematic lines.

Explanations should embroider the accumu-lation of knowledge, with a detailed descrip-tion of how it is that we come to know thesefacts and why this information is important.

This approach is preferable to a recitation of trivia

that is not particularly worth knowing outside anycontext. For exampl% in discussing the features of theseafloor, the author of a textbook might state:

The land on the continents is primarily flat. There arealso mountains and valleys. These features providevariability in the land. Similarly, the seafloor is likethe surface of the land. Most of the seafloor is flat.

Near the middle of the oceans, there are mountainsand canyons. Here is where the seafloor is said to be

spreading.

The author could have presented the informationmuch better in this way:

After World War I, scientists developed sonar, so thatthey could see objects under water by bouncingsound waves off them and picking up the echo. It had

been assumed that the ocean bottom was largely flat,

but when sound waves were bounced off the floor in

the mid-Atlantic Ocean, they showed great mountains

and chasms. This is where the seafloor is spreading.

The relief features of the surface of the continents,described in the first passage, should be fairly obvi-

ous to most students. Teachers are eminently capableof filling in the context by contrasting the familiar(surface features on land) with the unfamiliar (surfacefeatures of the ocean floor). It makes more sense touse available space to tell them what they do notalready know and to motivate them by showing them

how discoveries are made.

ft

221

Section C Presentation

PRESENTATION means how science is described,organized, written, and illustrated.

Language must be made accessible to stu-dents.

As discussed in Chapter 6, Section J, students withlimited proficiency in English must not be excludedfrom the study of science until such time as they areproficient in English. Teachers' editions and refer-ence materials muSt suggest ways that instruction forlimited-English-proficient (LEP) students can bemade comprehensible to them, age appropriate, and ata level commensurate with their academic ability andtraining. Providing editions in the primary languageof the LEP students is one way of giving them accessto the curriculum. Providing glossaries and summa-ries of key concepts in the primary language of thesestudents is another way. The five largest languagegroups among LEP students in California, in rankorder, are Spanish, Viemamese, Chinese, Cambodian,

and Pilipino.

The prose style of instructional materialsshould be considerate and engaging, and thelanguage ancivocabulary of Science shouldbe respected.

Too often, the selection of instructional materials is

subjugated to constricting, destructive readabilityformulas, with no consideration for student interest orthe liveliness of prose. Just as important, the way in

which scientific terms are used, particularly those thatrelate to science as a method of inquiry, are distorted.Consequently, students never really learn whatscience is, or how it differs from other kinds ofinquiry, and how its terminology reflects this.

(a) Lively, Engaging Style. Instructional materialsshould be written in a lively, engaging style (referred

Chapter 8Instructional Materials Criteria 203

to as considerate text), rather than in choppy prosedriven by readability formulas, or in a passive voicethat talks down to the reader in a manner that createspassivity and boredom. It is dismaying that readabil-ity indices, some of which use vocabulary listsoutmoded decades ago, are still dominating determi-nations of grade-level suitability. For many years itwas popular to argue that content-area materialsshould be written one or two grade levels below ordi-nary reading levels to avoid frustration. This is partic-ularly disabling in content subjects, because usuallysome number of new and unfamiliar words must belearned in order to manipulate concepts and ideaseasily, and many of these words are polysyllabic. Butif a readability computation on a typical issue ofSpiderman Comics yields a twelfth grade readinglevel, are we to assume that the nine-year-old whosits enthralled with the book is not understanding it?

Readability formulas are injurious to publishersand, by extension, to students. Formulas force pub-lishers into what can be called a maximum-minimumbind; that is, they are obliged to use technical termsand so must compensate for their effect on readabilityformulas by using only very simple words and shortsentences in the rest of their prose. No one benefitsfrom this situation. Children, like adults, are mod-vated'to read what interests them. If the prose issufficiently interesting and the illustrations effectiveand appropriate, we need not underestimate thepotential interest of students. An engaging narrativeprose style can overcome the stultifying effect ofreadability formulas.

If text does not read well, it will probably notengage its readers. Try this exercise: read pessagesfrom a textbook aloud to yourself, to colleagues, andto students. You will know from their expressionswhether this book is effective in its prose style. If, asin one recent junior high life science book, theauthors require five sentences to convey to thestudent that trilobites, mammoths, and sabertooth catsare extinct, the prose is probably not particularlyengaging. Students who are old enough to be taughtscience are old enough to appreciate good narrativestyle and probably prefer Nancy Drew and the HardyBoys to The Cat in the Hat. Therefore, textbooksshould be written as explanations ofdiscovery, not asprimers.

(b) Respect for Language and Students. Instruc-tional materials should respect the language of

204 Fart 111Achieving the Desired Curriculum

science and should respect the intelligence of stu-dents. Modifiers such as "Some scientists believe"and "Many scientists agree" present science as aconsensus activity. Rather, textbooks should empha-size the fact that scientists base their conclusions ondata, which are valid at a given Point. We have takenup this issue in Section B of this chapter and inChapter 1. We restate it here in a-form that applies tothe construction of vocabulary in science materials.

(c) Vocabulary. Vocabulary should not be a mainfocus of text. Books that contain an inordinatenumber of boldfaced or italicized words may be moreintent on defining these words than on explaining andrelating the concepts to which they are germane.More than likely, such textbooks emphasize thememorization of terms at the experue of understand-ing and integrating ideas. Textbooks should empha-size vocabulary development only when the termsintroduced add to the abilities of students to under-stand concepts and communicate about the subject.Vocabulary loads should not occupy space betterdevoted to other, more meaningful scientific inquiry.It is less important to know the names of the threekinds of rocks than it is to understand how rocks areformed and how this came to be understood.

Consider, for example, the following samplepassage on levers:

A bar that is used for a lever always turns on afixed point called a fulcrum. The fulcrum is thespot where the lever is held in place as it moves.The fulcrum placement determines exactly howthe lever works. When a bar, used as a lever, hasthe fulcrum between the effort exerted and theobject to be moved, it is called a first-classlever. A second-class lever has the objectbetween the effort and the fulcrum. A nut-cracker is a second-class lever. When the leveraction is between the resistance and the fulcrum,it is referred to as a third-class lever. A shovel isconsidered a third-class lever.

The terms lever, fulcrum, effort, and object arearguably necessary terms to communicating ideasabout the transmission of force. But what is thepurpose of this passage other than to taxonomizevarious forms of a simple tool? When are variousclasses of levers useful or necessary? Why arc somenutcrackers second-class levers while others are first-class levers? Is a shovel always a third-class lever, or

can it also be a first-class lever? Which class of leverrequires the most force, and why would anyone wantto use a third-class lever, anyway?

(d) Glossaries. The glossaries of instructionalmaterials often misuse scientific vocabulary. Often,nouns are defined as if they were verbs; and verbs, asif they were adjectives; and the phonetic pronuncia-tions supplied are both incorrect and phonicallyinconsistent with the standairl practices of diction.These deficiencies are signs of a slipshod text. Moreimportant, however, defmitions of terms given inglossaries should not merely paraphrase the sentencesin the text in which these terms appear. (That is whatan index is for.) A student will not be enlightened byfinding an unfamiliar term with an inadequate de-scription in the text, then by looking it up in theglossary find the same words but rearranged: Those'who selecti ,structional materials will find it instruc-tive to spend some time with the glossaries of materi-als under review.

(e) SI Metric System. The metric system is used byscientists for units of measurement because of itssimplicity in calculations and its international accep-tance. Traditional units of measure, however, may bemore familiar io many students and thus easier forthem to use and understand. Although students shouldgradually become familiar with the metric system, itis more important for them to understand concepts ofmeasurement than to memorize unfamiliar termsprimarily because they are mom accepted in thescientific community. Thus, instmctional materialsshould reflect the use of measurement units that willbe likely to be understood by students. At the appro-priite pedagogical levels, students should be intro-duced to scientific practices and conventions ofmeasurement as well as to the masons why thesepractices and conventions are favored (e.g., ease ofcalculating in a decimal system; international accep-tance).

(f) Corruptive Euphemism. One of the most disturb-ing features of current instructional materials is thepractice of what could be called corruptive euphe-mism. This is the use of one word, usually a weakerpseudosynonym or a word with more neutral value ina social context, as a substitute for the genuinescientific tenn or concept.

Some corruptive euphemisms are used to accom-modate readability formulas. The law of uniformitari-

223

anism, already mentioned as an example, is fre-quently garbled as "the law of uniformity" or, worseyet, "the law of uniform change," which is preciselynot what uniformitarianism is about. (Uniformitarian-ism is a statement that the natural laws of the universehave always been in effect, not that rates and pro-cesses have always been the same.) In this example,the cormptive euphemism distorts and confuses thescience that it is supposed to present in the service ofinappropriate prescriptions of grade-level suitability.

Other corruptive euphemisms occur in the contextof historically sensitive terms. For example, sometextbooks use the term development, which refersspecifically to an individual's growth from one-celledstage to adult, as a false synonym for evolutIon in aneffort to avoid the social repercussions that the wordevolution evokes from some individuals. This prac-tice is reprehensible. The only way that publisherswill be fmed of this practice is for the correct terms tobe specified in frameworks, and for the use of weakor invalid alternative terms to be discouraged.

A third kind of corruptive euphemism involveswhat might be called special science. Frequently, oneencounters a passage in a textbook such as, "Desali-nation of seawater is done with special equipment,"with no further explanation. What does the wordspecial mean in that sentence? It means, perhaps, thesame as magic, a word that may as well have beensubstituted for it. It means, perhaps, "You're notsmart enough to understand this," and so the intelli-gence of the student is insulted. Why, then, includethe concept of desalination at all? Or perhaps the useof the term special in that sentence means that theauthor of the text could not find a way to explain it tothe audience, could not explain it with terms thatwould iit readability formulas, or did not have thenecessary space in the text to do so. The word specialhas no particular scientific meaning, and it shouldnevei be used in a text to substitute for an explanation.

Teachers and other selectors of instructional mate-rials at the local level are encouraged to monitorclosely the materials submitted for their considera-tion. We have provided here only a sample of thefaults of presentation frequently encountered intextbooks and other materials. We suggest that aclose critical reading of submitted materials, withthese ideas in mind, may help to discriminate amongpossible choices. We also suggest asking studentsthemselves how the books read to them.

Chapter 8Instructional Materials Criteria 205

The character of scienc. must be repre-sented faithfully. This means that It must beshown as open to inquiry, open to contro-versy, and nondogmatic by its nature.

These particulars are explained in the paragraphsthat follow.

(a) The Nature of Science. Instructional materialsshould explain and exemplify the nature of science asa form of inquiry and understanding. For a fullexplanation and examples of what this means, seeChapter 1, The Nature of Science. We stress here thatthis understanding iS not to be roped off in an intro-ductory chapter but is to be integrated thoroughly inthe narrative of the text. The scientific method is nota monolithic formula that can be reduced to hypothe-sis-materials-methods-observations-conclusions.Instead, examples of how scientists investigateproblemsexamples that delineate the processes,successes, and limitations of scienceshould appearin every chapter.

(b) Controversy in Science. Instructional materialsshould encourage responsible, science-based discus-sion of controversial or contentious issues. Scienceshould be portrayed as a vital, changing endeavorwith controversy and competing lines of intellectualdiscussionnot as a sterile, dogmatic discipline inwhich facts arc known and approaches are agreed on.The historical growth of science should be reflectedin controversy.

This desideratum must be explained carefully.History is usually written by the winners, but sciencethat survives does so because ideas and findings havewithstood constant further inquiry. In science, it is notthe struggle of individuais against individuals thatmatters, but of ideas and evidence against competingideas and evidence. Controversies in science shouldbe presented as matters of evidence, not of personali-ties. Historical figures are not to be trotted out simplyto suow the faults and quaintness of earlier workers.An example of this is Lamarck, whose theory ofevolution predated and wag challenged by Darwin's.Students are often presented with simplified explana-tions of Lamarck's ideas but arc seldom shown whatwork was done to falsify them. This is a disservice. It

206 Part IIIAchieving the Desired Curriculum

presents not the resolution of controversy but thesupplanting of apparently archaic ideas. That is nothow science works.

Above all, in discussing scientific controversies,attention should be focused on the weight of evi-dence. There are nearly always certain facts andobservations that can be interpreted in a light differ-ent from prevailing theories. The evidence of ourhuman senses, for example, would suggest that thesimplest explanation of the patterns of night and dayis that the sun, like the moon, goes around the earth.And indeed, it is difficult for the average person torefute this inference. But the weight of evidence doesnot accord with it, and undue significance should notbe given to isolated facts or inferences in responsibleclassroom instruction and instructional materials.Specific examples of controversial issues in scienceand how they should be treated arc given in Chapter1, Section E, Social Issues in Science.

(c) Understanding, Not Dogmatism. Instructionalmaterials should not be dogmatic or selectively dog-matic. The thrust of the text should direct the studenttoward inquiry rather than conclusions. Scienceshould not be presented as a corpus of settled dogmaor authoritarian statements. It should be shown to beauthoritative, but not authoritarian, and constantlyself-correcting (again, see Chapter 1, Section C,Teaching "What Science Is").

Moreover, sensitive issues in science, that is, thosewith some social relevance or controversy, should notbe roped off as conjectural or as matters of opinion.Certainly, some issues connected with science arecontroversial, but that does not mean that the scienceitself is controversial. The implications of issues onwhich science bears arc complex matters of publicpolicy and cultural interpretation, but this has nobearing on the science itself. Furthermore, no instruc-tional materials should ever convey the impressionthat science itself is a matter of guesswork, belief, oropinion.

We repeat here the fundamental conviction of thisframework: Education does not compel belief; itseeks to encourage understanding. Nothing in sci-.ence, or in any other field, should be taught dogmati-cally. But teaching about something does not consti-tute advancing it as truth. In science, there is no truth.There is only knowledge that tests itself and builds onitself constantly. This is the message that studentsshould take away with them.

224

Science should not be presented as anenterprise operating In isolation from societyand technology or from other fields ofknowledge.

Technological advances are based on fundamentalscience, including a proper appreciation of thephilosophy and methods of science. Integration ofscience and technology, where appropriate, is part ofany good science program.

As a corollary, emphasis on recent advances inscience should bc mandatory in every science pro-gram. For example, discoveries of Mendel andDarwin are important to explain, but the sciences ofgenetics and evolution have made considerableprop= since the mid-1800s. Students should bepmsented with these advances so that they canunderstand the intellectual vibrance of these fieldsand the ways in which science progresses, alwaystesting and building on what has gone before withnew ideas, new techniques, and new evidence.

In the same way, science should be explicitlyintegrated with other disciplines, especially thelinguistic, historical, and mathematical fields. Itshould not be seen as an isolated discipline estrangedfrom other fields of inquiry, such as the arts andhealth. The etymology of scientific words, theaccounts made by scientists of their own discoveriesand of their times, and the applications ofmathemat-ics and of numerical organization of information toscientific investigations are all examples of vitallyimportant features of a good science curriculum.

. o 9 -6 .6 66

PEDAGOGY refers to the instructional methods thatare employed. We stress several goals here. First,hands-on experience should be emphasized, and bothprinted materials and activities should be related toreal experiences. Second, the textbooks and otherinstructional materials should not be the sole sourcesof information for the students. Third, assessment oflearning should go beyond the level of recall andparaphrased mull to include assessment of howstudents can use the concepts learned and relate them

225

to other concepts. Assessment should also take avariety of forms, including activities, journals,recorded observations, problem solving, and portfo-lios of accomplished work.

Instructional programs must be connectedwith experience.

There are four major features by which instruc-tional materials should be evaluated in the context ofthis criterion.

(a) Student Involvement. Instructional materialsshould involve students in science through problemsolving and decision making. Programs shouldencourage active learning on the part of students inwhich they are actively-engaged in the doing ofscience, rather than treating students as passivelearners, the empty vessels into which accumulatedknowledge is poutud. Part of this approach is to usehands-on, manipulative experimental materials tosolve problems. This approach is canonical in mostscience curricula at the present time, so we do notexpect this criterion to be regarded as revolutionary.We do support the goal of increasing hands-on timein science classes to at least 40 percent of the totaldevoted to teaching science, and instructional pro-grams should reflect this goal.

There is considerable pedagogical benefit in havingstudents repeat experiments or investigations thathave become part of the basic understanding ofsciencesuch as manipulating the conditions ofwater, soil, and light under which bean plants grow.Most students could understand the conditions thatproduce the best growth in plants simply by havingthem explained verbally. But actually performing themanipulations validates and internalizes these ideasand makes them vivid to the student.

Experiment can also stimulate further inquiry of amore open-ended sort. (What happens if I plant mari-golds and beans together?) Instructional materialsshould suggest further investigations that can becarried lut in order to take the basic questions a stepfurther, not just to perform variations on a theme. Inaddition, instructional materials can show studentshow the kinds of experiments they are carrying outhave led to advances in science and technology. (Forexample, farmers rotate certain crops so as not to

Chapter 8-1nstructional Materials Criteria 207

deplete minerals in the soil; some plants used in thisway, such as clover, actually return vital nitrogenouscompounds to the soil.) Instructional materials shouldencourage students to explore the "what if?" questionsthat lead to creative, integrated, and applied learning.

The teacher's edition of instructional materials isoften the best place to suggest open-ended, hands-oninquiries and activities that can motivate studentinterest and learning. Districts should encouragescience supervisors and curriculum developers toemphasize hands-on units and activities in workingwith classroom teachers. Administrators shouldprovide and encourage the use of release time forteachers to attend in-service training designed tofamiliarize teachers with hands-on approaches toscience teaching. Elementary and middle schoolteachers should be encouraged in this effort as muchas junior and senior high specialist teachers.

(b) Interdisciplinary Approach. Scientific discover-ies should be presented in the social, political, andhistorical contexts in which they took place, much asthey are treated in the History-Social Science Frame-work. Vaccines and medical advances have histori-cally been developed in the context of a dire socialneed for them at a particular time and place. Darwinworked out his theory of natural selection because,although the fact of evolution was generally acceptedby scientists of his time, a mechanism for change inthe species of organisms through time was stillneeded. Kepler worked out an elliptical model of theorbits of the planets around the sun because he couldnot make any circular model fit the observationsavailable to him. The understanding of mechanics ofthe solar system was central to the natural philosophyof Renaissance knowledge on which so much intel-lectual, political, and cultural philosophy depended.The agricultural research that resulted in the GreenRevolution of the 1970s was stimulated by an im-pending crisis in the world's supply of foodjust asa tragically misguided effort, headed by Lysenko inthe USSR from the 1930s through the 1950s, wasdesigned to meet increasingly ominous food short-ages in the Soviet Union at that time. Nearly everytechnological tool has an important historical andsocial context that was vital to its development. Eventhe familiar microwave ovens ofour kitchens todayare the by-products of the need to develop betterradar facilities during World War II.

By bringing out these historical, cultural, and social

208 Part 111Achieving the Desired Curriculum

aspects as the context of scientific discoveries, the wri-ters of instructional materials can show students thatscience is put to work for people, that research is stim-ulated because of real needs of real people, and thatdiscoveries in science help us to make informed deci-sions about the critical problems that face humanity.

For example, many instructional prugrams on theenvironment have units in which conservation ofnatural resources is encouraged and waste is de-plored. These are commendiNe. However, to becomprehensive with respect to the scientific side ofconservation issues, instructional marials shouldprovide students with tables of estimates of represen-tative nonrenewable natural resources (coal, oil,aluminum, and so forth), together with estimatedrates of depletion. Students should also understandhow long it takes typical waste materials, such asglass, paper, styrofoam, and aluminum and steel cans,to degrade in the environment. For a hands-oncomponent, they should be encouraged to measurethe use of nonrenewable resources and energysources by themselves, their families, and theirschools. They should calculate the amount of yearlyuse by their community or region and compare this tothe use of such resources by other communities orcultures, and to the estimates of remaining stores ofthese nonrenewable resources. Only then will stu-dents be able to make informed decisions as adultcitizens about some of the scientifically based issuesthat will face them in their daily lives. Instructionalmaterials should encourage and suggest to teachersthe possibilities of including people from the commu-nity to provide information, insight, and bases fordiscuss;on of "real-world" problems connected withscientific knowledge.

(c) Meaningful Activities. Activities must be mean-ingful and integrative, not simply based on recall.Activities in science textbooks and supplementalmaterials frequently do not help teachers and studentsto internalize and manipulate the concepts and evi-dence presented in the units. Role-playing games andarts and crafts projects may be fun and are intrinsic tosome kinds of learning, but in the context of most ofthe ideas in which they are commonly employed intextbooks, they are irrelevant. "Make a model of theGrand Canyon," suggested one textbook to eighthgraders. And how many years would that take? Moresignificantly, what is a student supposed to learn fromthis exercise? The textbook provided no clue.

Rather than have students make casts and molds ofleaves and shells each year from the third through theeighth grade, it would be mom useful to explore thepreservation of fossil remains by leaving chickenbones in different kinds of local environments andchecking on them every few days until differentialdeterioration becomes noticeable. Rather than havestudents imagine how many carnivores and herbi-vores can coexist in an imaginary ecosystem, teachersshould bring well-done films on actual ecosystemsinto class, thereby increasing motivation, experience,and basis for discussion. Such resources are readilyavailable, and publishers need to find and 1" them intheir teachers' resources, instead of the repetitious,unimaginative works that often constitute suchrecommendations. (For suggestions, contact theMathematics, Science, and Environmental EducationUnit of the Department of Education.)

As an underpinning to this recommendation, thematerials and supplies (apart from expendablematerials that need periodic replacement) necessaryto instructional programs should be considered part ofthe basic program eligible for expenditure under the70 percent criterion of the State Board of Education.Basic instructional materials are those parts of aprogram without which the program could not becarried out effectively. In a program devoted in largepart to hands-on activities, which is the goal of thiscriterion of the framework, such materials wouldinclude experimental and other equipment andsupplies used in student participation and teacherdemonstrations, in addition to print and electronicmedia that am fundamental parts of the curriculum. Ifa concept or unit cannot be taught in the programunder consideration without a given piece of equip-ment (whether printed, electronic, or macipulable), itis considered necessary to the instructional programand should qualify for the 70 percent funds.

(d) Variety of Resources. Textbooks and otherprovided instructional materials should not be thesole sources of information for the student. As statedabove, instructional materials should not be encyclo-pedic in their coverage, nor can they possibly beexpected to satisfy all of a student's curiosity. Part ofgood education is to teach and encourage students toseek supplementary msources. Instructional, programswill be most useful when they do this conscientiouslyand effectively. This means that reading lists, activi-ties, and chapter reviews should be more creative,appropriate, and conscientiously constructed.

Great improvement is needed in the suggestions forfurther mading at the end of a chapter or unit in mostcurrent instructional p:ograms. Typical suggestions incurrent instructionat materials frequently list out-dated, nonauthoritative, or relatively inaccessiblesources. These features of instructional programsappear to promise much, but generally are not veryhelpful to teachers. Publishers and adoption commit-tees should work with content area experts to findbetter treatments that explain and expand topics in thechapters and that are engaging in their prose style tostudents and (for teachers' editions) teachers alike.These would also be of great useto school librarians.

Instructional materials could be greatly improvedby the inclusion of first-person accounts of scientificdiscoveries and the excitement of science. There aremany classic examples ranging from Beaumont'sstudy of the stomach processes of a wounded trapper,to Darwin's account of his discoveries on board theH.M.S. Beagle; to Richard Feynman's stories ofbuilding a crystal radio set as a child, picking thelocks at Los Alamos National Laboratories, anddiscovering how a flaw in construction of the 0-ringsdestroycd the Challenger spacecraft. Such acrountscould be framed in a few paragraphs in a "box"typical of features now present in all textbooks.Original source materials are vital to conveying theunderstanding and excitement of science. And, asnoted in Eyeopeners! reading levels should not beassumed to be a problem; good books are ageless.2

Instructional materials must recognize cul-tural diversity and reflect strategies that re-search and practice have shown to be suc-cessful in meeting the needs of all students.

Many of the suggestions in Chapter 6 that aredesigned for all students are especially important forstudents from groups historically underrepresented inadvanced science courses. Because it is imperativethat culturally different students succeed in scienceeducation, this criterion emphasizes the pedagogicaltechniques that enable them to be successful:

(a) Current Research. Instructional practices basedon current research on cultural learning styles should

'Beverly Kobrin. Eyeoperters! New York. Pcnguin Books. 1988,

2 2 7 Chapter 8Instructional Materials Criteria 209

be included in the content of teachers' manuals andintegrated in the design of the students' materials.

(b) Learning Goals. The full range of learninggoals, including the processes of science and appliedproblem solving, must be part of the program forevery student.

(c) Relevance. Connections with student experienceare made in several ways. First, teachers must begiven suggestions of ways to bring the students'environment and experience into the classroom sothat it connects in a meaningful way with the activi-ties that take place there. Second, the program shouldprovide activities in the classroom so that all studentshave a common experiential base. The more that theknowledge and processes are relevant in the students'everyday life, the more likely they will be able tolearn them.

(d) Successful Instructional Practices. Successfulinstructional practices are incorporated. Activeendeavors are more successful than passive ones.Thus, hands-on experiences are particularly importantfor students from diverse backgrounds. Heterogene-ous, cooperative groups are particularly effective withstudents of varied language backgrounds and achieve-ment levels who are working toward a commoninstructional goakOther successful practices includean integrated curriculum that emphasizes depth overbreadth and a multidimensional program that uses avariety of teaching methods.

(e) Reasoning, Not Drill. Certain practices havebeen shown to discourage students and to distancethem from cchool. These include excessive drill andpractice and pressure to get one right answer. Pro-grams that allow for reflective thinking value astudent's reasoning more than a single and quick rightanswer and provide for informal group work; suchprograms are to be encouraged.

Assessment should be integrative and ori-ented toward solving problems, not simplyrecall-based.

Reviews of chapters should expand on the text'spresentation, not just repeat its lessons and drillstudents in its minutiae. These failings characterize

210 Part IllAchieving the Desitod Curriculum

textbooks that are little more than dictionaries; a realtextbook with good narrative prose and true exposi-tion of ideas and concepts should elicit much morecreative and intellectually fruitful exercises at theconclusions of units. Questions at the ends of chap-ters should be less regurgitative and more integrative,pulling together the themes that should be woven intothe chapters. Thestandard response in a teachers'edition, "Answers may vary," is not particularlyhelpful for teachers.

There are many ways to assess student perform-ance. Objective tests measure recall and some inte-gration of facts, ideas, and concepts. In a largelyhands-on curriculum, other more creative tools ofassessment are necessary. Problem solving, particu-larly solving real-world problems, involve not onlyrecall but also integration of ideas and creativity ofsolutions. These means may be more appropriate foractivity-oriented curricula. For example, in learningthe basic methods of designing scientific experi-ments, students may want to test rival claims oflaundry detergent manufacturers. A real-world testwould have to take into consideration variables suchas type of clothing, amount of detergent, watertemperature, and so forth. Organizing students inpairs or teams can add to the creativity and stimulatemuch animated intergroup discussion.

Written work, particularly when not limited by thetime and response constraints of a classroom testsituation, can provide deeper insights in the creativeprocesses and integrated understanding of students.Projects and essays integrate writing skills andlanguage arts concepts in the science curriculum andmay be used to interface with those disciplines wherenonfiction literature is encouraged. Students shouldbe encouraged to assemble pertfolios of their work ina science class, including class exercises, team work,reports on activities, creative projects, designs forexperiments, and observational accounts of theirresults. By varying the fommt of assessment, teacherscan assess and appreciate the varied abilities of allstudents, and they can better plan how to help indi-vidual students improve their abilities in a variety ofcontexts.

It is dismaying that curricula in science are solargely driven by student performance on standard-ized tests. Teachers are thus forced to teach to theend-of-year evaluations or institutionalized examina-tions. There is no doubt that these tests measure

something, but what? Too often, the memorization ofminutiae can ensure at least above average perform-ance of a student population profile. It is arguable thatan ineffective teacher can remain undetected withoutsuch monitors. But standardized tests can only poorlyevaluate philosophical understanding, creativity,originality, and competence in approaching prob-lemsto say nothing of theindividual's ability toexpress himself or herself on subjects. Publishers areforced by these criteria to cram into their textbooksand other materials even more trivia, boldfaced terms,and jargon useful only for their own sake. We suggestthat if standardized tests are to be used at all, thattheir results be scrutinized with care and put intoperspective against other indicators of learning andteaching effectiveness.

Section E. Coiisiderations

THE criteria in the preceding section will guide theInstructional Materials Evaluation Panel (IMEP), agroup of approximately 40 teachers, curriculumspecialists, and scientists who will review the materi-als submitted for adoption and submit their recom-mendations to the Curriculum Development andSupplemental Materials Commission (CDSMC), thatwill in turn make recommendations to the State Boardof Education. Once the State Board has adopted thematerials for science, local districts and schools arcfaced with the challenge of making selections fromthat adopted list. Local reviewers should have thefollowing things in mind as they evaluate materials:

Be aware of the criteria used in and the results ofthe state-level adoption process. Reports from theIMEP's review are displayed at the InstructionalMaterials Display Centers (IMDC) in conjunctionwith the adopted materials, and a report from theCDSMC is sent to every district. Those reportsmay allow reviewers to see the characteristics ofmaterials that were judged similar and the onesthat differed among programs. This will savetime for the local panel, which can focus itsattention on the reported differences.

Do not turn the content evaluation into a check-list. The thematic approach advocated in thisframework should make the use of a checklist afrustrating experience, because ideas and topics

229

are meant to be interwoven and connected, notnecessarily listed under conventional chapterheadings. Vocabulary should be hard to find inboldfaced definitions, because it should be usedand defined in context. Indices to books make nodistinction between a mention and an in-depthtreatment of a concept, so to check the number ofentries is a misleading exercise. Finally, a check-list is likely to penalize the authors who took agenuinely thematic approach and to reward thosewho presented material in a bulleted, point-by-point fashion.

3. Do not apply a readability formula to the text. Asindicated in the introduction to this chapter, suchformulas reward choppy sentences and frustratecommunication. If reading level is an issue in thedistrict or school, the suitability of the text shouldbe determined by reading it aloud, or having astudent of the appropriate grade level read italoud or silently and answer questions. Thetextbook should not be the sole source of instruc-tion; students should have a variety of hands-onand other experiences. Thus, the challenge posedby the reading level of the text should be put inthe context of the rest of the curriculum and theproportion of time that students are actuallyexpected to be rcading.

4. Provide for students whose English is not yetproficient enough to understand instruction inEnglish. This is a concern to an increasing numberof California school districts. Provision of glos-saries and summaries of key concepts for studentswhose knowledge of English is limited should begiven extra weight in the local adoption process.

Section i 'COtIolusioPuttingCriteria-info Oractice

WE conclude with some examples of what is and isnot to be desired in science writing.

The first example is the type that might come froma passage that could appear at the end of a section onthe "four main groups of reptiles." Crocodiles, turtles,lizards, and snakes would be presented, even thoughsnakes are, in a phylogenetic sense, merely special-ized lizards. No indication of the relationships of

Chapter 8Instructional Materials Criteria 211

these reptile groups is given, and another livinggroup, the sphenodontids, is omitted:

Most life scientists believe that many reptilegroups existed long ago. Their fossil remainsindicate that these large dinosaurs that onceexisted were reptiles.'Other reptile groups couldhave included species that dwelt in the ocea is ornevi. science has still left undetermined whythese organisms became extinct.

Of course, there is no reasonable doubt amongscientists that "many reptile groups existed long ago,"and fossil remains do more than "indicate" thatdinosaurs were reptiles. Nor is it merely that otherreptiles "could have" lived in the oceans or flownthrough the air. Yet, weasel-wording aside, the steriletext above has just managed to maul one of thescientific topics that excites children most: dinosaursand other fossil reptiles. That passage could begreatly improved in many ways, including this one:

The living groups of reptiles arc only a shadowof the many groups of reptiles that have lived onthe earth. Most of these am now extinct, butthey reached the climax of their evolutionaryhistory during the Age of Dinosaurs, whichbegan over 200 million years ago. But fossilreptiles also include many swimming and flyingspecies that were not dinosaurs. In fact, theearliest members of the living groups of reptilesarose at about the same time that the firstdinosaurs appeared. What does that suggest toyou about the extinction of the dinosaurs?

If the last two sentences arc omitted, the length ofthe text is as long as the original passage. But theadditional sentences could easily have fit on theoriginal page in question. The new text was written,incorporating some of the ideas in criteria 2, 3, 4, 5,7, and 8 discused in this chapter.

A second example might appear in a junior highgeneral science textbook:

Fault zones can also be at a distance from theends of crustal plates. Most geologists believethat the fault formation is related to platemotion. Movement of plates places stress on therocks of the plate. When the stress has enoughforce, the rock breaks at the weakest spots.These cracks are considered faults.

212 Part HIAchieving the Desired Curriculum

This example, apart from the objectionable phrase,"Most geologists believe," is mainly deficient byvirtue of its choppy sentence construction. Considerthe following possible text:

Not all faults are found at the edges of crustalplates. But maybe this should not be surprising.If you put a frozen chocolate bar in a vise andsqueezed it, the chocolate might snap at manyplaces along its length. Crustal plates are a bitlike that chocolate bar: they receive stress ontheir edges, but they often release the energy ofthat stress in faults well away from their edges.

This rewritten version attempts to incorporate someof the ideas given in criteria 6, 7, and 10.

The third example describes the simultaneousdiscovery by Darwin and Wallace of the theory ofnatural selection (often erroneously equated with thetheory of evolution). Here is how one text samplemight explain the process of science:

Alfred Wallace, a British biologist, was doingresearch in Malaya in 1858. He sent CharlesDarwin a scientific article he was planning topublish. Darwin was astonished to see his ideasrepresented in Wallace's article. Wallace arrivedat the identical conclusions as Darwin did. Thisoccurs in science quite often where two scien-tists, working alone, make similar conclusionsor discoveries.

Both scientists reached the conclusion thatdifferent species of plants and animals wererelated. They found new species appearing andother species disappearing. New species camefrom old. However, new species exhibiteddifferent characteristics.

Wallace and Darwin decided to present theirfindings to the world. Neither man had to havemajor credit. Both wanted to make their findingsknown everywhere. Their theory is referred toas the theory of evolution by natural selection.The theory demonstrates how slow, gradualchanges in organisms occur over a period ofyears. Changes result from selection of thoseorganisms best adapted to their surmundings.

The following rewrite avoids some of the misrepre-sentation of the case, as well as preserves the narra-tive style of the original text:

(' '1 0r t.>

In 1858, Alfred Wallace, a British biologist, wasstudying the tropical fauna and flora of Malaya.Sick in his tent from malaria, Wallace thoughtabout the amazing diversity of plants andanimals he had seen. What processes could leadto such a range of different forms and adapta-tions? Wallace knew from his observations oftropical life that there was great variation innatural populations of plants and animals. Healso knew that many more organisms are bornthan can survive to give birth to the next genera-tion. The ones that survive, he concluded, mustdo so because they ait better adapted to theirenvironments. Only they will live to pass ontheir characteristics to the next generation.

Wallace wrote to Darwin about his discoverybecause he learned from a mutual friend thatDarwin was exploring the same ideas. Darwinlater reported in his autobiography how shockedhe was at seeing his own ideas, on which he hadbeen woridng for decades, presented to him byWallace's distant hand. Darwin had beendeliberately waiting to bring his ideas to thepublic until he could accumulate what he feltwould be an undeniable mountain of evidence infavor of them. But now, he decided that he mustpublish his ideas immediately, and that thefairest thing to do would be to publish themtogether with Wallace. He did so, and theirtheory came to be known as natural Lelection.

The rewrite is a little longer, but it contains ap-proximately twice as much information and pitsentsevents as we now understand them to have happened.There ait also some differences corrected withrespect to the facts of the case and the theory that wasactually developed. It was written attempting to

231

incolporate some of the ideas described above incriteria 2, 3, 4, 5, 6, 7, and 8.

These examples should not be considered in anyway exceptional. The rewrites should in no way beregarded as definitive. They merely point out howmuch room them is for improvement on any typicalpage of any typical science textbook. Whetheradoption agencies encourage publishers to make suchimprovements is a matter of futuit history, butwithout such improvements science education can beconsigned to the oblivion of lists of trivia, memoriza-tion, and disjointed facts with no common thread.

In summary, the most important points made in thissection ait:

1. The desirability of thematic orientation in sciencecurricula

2. The motivation and learning that can be gener-ated by hands-on, experience-oriented activitiesand curricula

3. The importance of considerate prose and theelimination of readability formulas as determinersof grade-level appropriateness of curricularmaterials

4. The fundamental respect for scientific methods ofinquiry and for the language and philosophy ofscience that is absolutely necessary to anyadequate science program

Improvement in instructional materials, support formolt in-service training for teachers, and the reevalu-ation znd change in criwria commonly used in theadoption and selection of instructional materials arethe principal meais by wh:ch the current system ofdeveloping, adoptingkand using instructional materi-als can meet the challenges of educating studentsabout what science really is and how it can matter totheir lives.

Chapter 8. Instructional Materials Criteria 213

Appendix A

Significant Court Decisions RegardingEvolution/Creation Issues

1. Edwards v. Aguillad (1987) 482 U.S. 578, 55U.S. Law Week 4860, 107 S. Ct. 2573, 96 L. Ed2d 510. The U.S. Supreme Court invalidated asunconstitutional Louisiana's "Creationism Act,"which prohibited the teaching of the theory ofevolution in a public school unless accompaniedby instruction in the theory of "creation sci-ence." The Court found that the Act impermissi-bly endorses religion by advancing the religiousbelief that a supernatural being created human-kind. The term creation science embraces thisreligious teaching. Forbidding the teaching ofevolution when creation science is not alsotaught undermines the provision of a compre-hensive scientific education.

2. Epperson v. Arkansas (1968) 393 U.S. 97, 37U.S. Law Week 4017, 89 S. Ct. 266, 21 L. Ed228. The U.S. Supreme Court invalidated asunconstitutional an Arkansas statute that prohib-ited the teaching of evolution. The First Amend-ment to the.U.S. Constitution does not pennit astate to require that teaching and learning mustbe tailored to the principles or prohibitions ofany religious sect or dogma.

3. McLean v. Arkansas Board of Education (1982)529 F. Supp. 1255, 50 U.S. Law Week 2412. Inthis case the federal court held a balancedtreatment statute to be in violation of the Estab-lishment Clause of the U.S. Constitution. TheArkansas statute required public schools to givebalanced treatment to creation-science and toevolution-science. The court found that the

214 Science Framework

statute aid not have a secular purpose. The courtalso found that the emphasis on origins of life asan aspect of the theory of evolution is peculiarto creationist literature. Although the subject oforigins of life is within the province of biology,the scientific community does not considerorigins of life part of evolutionary theory. Thetheory of evolution assumes the existence of lifeand is directed to an explanation of how lifeevolved. Evolution does not presuppose theabsence of a creator or God.

4. Segraves v. State of California (1981) Sacra-mento Superior Court #278978. In this case Mr.Segraves contended that the California StateBoard of Education's Science Framework wasdogmatic in its discussion of evolution and thusprohibited the free exercise of religion byhimself and his children. The court found thatthe Science Framework, as written and as quali-fied by the antidogmatism policy of the StateBoard of Education, provided sufficient accom-modation for the religious views of Mr.Segraves. That pc:11'3...y provided that, in a discus-sion of origins in science texts and classes,dogmatism be changed to conditional statementswhere speculation is offered as explanation fororigins and that science emphasizes "how" andnot "ultimate cause" for origins. The coundirected the Board to make a widespreaddissemination of the policy. In 1989 the policywas expanded to include all areas of science, notjusi those addressing issues of origins.

Appendix B

Education Code Sections of Special Relevanceto Science Educators

Education Code sections that are of special signifi-cance to science educators appear below. Included areregulations pertaining to devices designed to protectthe eyes, instruction in personal health and publicsafety, treatment of animals, requirements for gradu-ation, and sex education courses.

32030. Duties Regarding Eye ProtectiveDevices

It shall be the duty of the governing board of everyschool district, and of every county superintendent ofschools, and of every person, firm, or organizationmaintaining any private school, in this state, to equipschools with eye protective devices as defined inSection 32032, for the use of all students, teachers,and visitors when participating in the courses whichare included in Section 32031. It shall be the duty ofthe superintendents, principals, teachers or instructorscharged with the supervision of any class in whichany such course is conducted, to require such eyeprotective devices to be worn by students, teachers, orinstructors and visitors under the circumstancesprescribed in Section 32031.

32031. Courses in Which Devices to Be Used;Substances and Activities Dangerous toEyes

The eye protective devices shall be worn in coursesincluding, but not limited to, vocational or industrialarts shops or laboratories, and chemistry, physics orcombined chemistry-physics laboratories, at any timcat which the individual is engaged in, or observing,an activity or the use of hazardous substances likelyto cause injury to the eyes.

Hazardous substanms likely to cause physicalinjury to the eyes include materials which are flam-mable, toxic, corrosive to living tissues, irritating,strongly sensitizing, radioactive, or which generatepressure through heat, decomposition or other meansas defined in the California Hazardous SubstancesLabeling Act'

Activity or the use of hazardous substances likelyto cause injury to the eyes includes, but is not neces-sarily limited to, the following:

1. Working with hot molten metal.2. Milling, sawing, turning, shaping, cutting,

grinding, and stamping of any solid materials.3. Heat treating, tempering, or kiln firing of any

metal or other materials.4. Gas or electric arc welding.5. Repairing or servicing of any vehicles, or other

machinery or equipment6. Working with hot liquids or solids or with

chemicals which are flammable, toxic, corrosiveto living tissues, irritating, strongly sensitizing,radioactive, or which generate pressure throughheat, decomposition, or other means.

32032. Standards for Devices

For purposes of this article the eye protectivedevices utilized shall be industrial quality eye protec-tive devices which meet the standards of the Ameri-can National Standards Institute for "Practice forOccupational and Educational Eye and Face ProtecLion" (Z87.1-1968), and subsequent standards thatarc adopted by the American National Standards

' Health and SafetyCode sections 28740 ct seq.

Appendix B 215

Institute for "Practice for Occupational and Educa-tional Eye and Face Protection."

32033. Sale of Devices at Cost to Pupils andTeachers

The eye protective devices may be sold to thepupils and teachers or instructors at a price whichshall not exceed the actual cost of the eye protectivedevices to the school or governing board.

32255.1. Pupil with Moral Objection to Dissec-tion or Otherwise Harming or Destroy-ing Animals; Notice; Alternative Educa-tional Project

(a) Except as otherwise provided in Section32255.6, any pupil with a moral objection todissectin2 or otherwise harming or destroyinganimals, or any parts thereof, shall notify his orher teacher regarding this objection, uponnotification by the school of his or her rights.If the pupil chooses to refrain from participa-tion in an education project involving theharmful or destructive use of animals, and ifthe teacher believes that an adequate alterna-tive education project is possible, then theteacher may work with the pupil to developand agree upon an alternate education projectfor the purpose of providing the pupil analternate avenue for obtaining the knowledge,information, or experience mquired by thecourse of study in question.

(c) The alternative education project shall mquirea comparable time and effort investment by thepupiL It shall not, as a means of penalizing thepupil be mom arduous than the originaleducation project.

(d) The pupil shall not be discriminated againstbased upon his or her decision to exercise hisor her rights pursuant to this chapter.

(e) Pupils choosing an alternative educationalproject shall pass all examinations of therespective course of study in order to mceivecredit for that course of study. However, iftests require the harmful or destructive use ofanimals, a pupil may, similarly, seek alterna-tive tests pursuant to this chapter.

(f) A pupil's objection to participating in aneducational project pursuant to this sectionshall be substantiated by a note from his or herparent or guardian. (Enacted 1988.)

(b)

51202. Instruction in Personal and PublicHealth and Safety

The adopted course of study shall provide instruc-tion at the appropriate elementary and secondarygrade levels and subject areas in personal and publicsafety and accident pievention, including emergencyfirst-aid instruction, instruction in hemorrhagecontrol, treatment for poisoning, resuscitation tech-niques, and cardiopulmonary resuscitation whenappropriate equipment is available; fire prevention;the protection and conservation of resources, includ-ing the necessity for the protection of our environ-ment; and health, including venereal disease and theeffects of alcohol, narcotics, drugs, and tobacco uponthe human body.

51540. Treatment of Animals

In the public elementary and high schools or inpublic elementary and high school school-sponsoitdactivities and classes held elsewhem than on schoolpiemises, live vertebrate animals shall not, as part ofa scientific experiment or any purpose whatever:

(a) Be experimentally medicated or drugged in amanner to cause painful reactions or inducepainful or 'lethal pathological conditions.Be injured through any other treatments, in-cluding, but not limited to, anesthetization orelectric shock.Live animals on the premises of a public ele-mentary or high school shall be housed andcared for in a humane and safe manner.The provisionl of this section are not intendedto prohibit or constrain vocational instructionin the normal practices of animal husbandry.

51225.3. Requirements for Graduation Com-mencing with the 1986-87 School Year

(a) Commencing with the 1986-87 school year, nopupil shall mceive a diploma of graduationfrom high school who, while in grades 9through 12, has not completed:

(1) At least the following numbers of coursesin the subjects specified, each coursehaving a duration of one year.(A) Thive courses in English.(B) Two courses in mathematics.(C) Two courses in science, including

biological and physical sciences.

(b)

216 Science Framework

,b 4

(D) Three courses in social studies,including United States history andgeography; world history, culture, andgeography; and American government,civics, and economics.

(E) One course in fine arts or foreignlanguage.

(F) Two courses in physical educationunless the pupil has been exemptedpursuant to the, provisions of this code.

(2) Such other coursework as the governingboard of the school district may by rulespecify.

(b) The governing board, with the active involve-ment of parents, administrators, teachers, andpupils, shall adopt alternative means forstudents to complete the prescribed course ofstudy which may include practical demonstra-tion of skills and competencies, supervisedwork experience or other outside schoolexperience, interdisciplinary study, independ-ent study, and credit earned at a postsecondaryinstitution. Requirements for graduation andspecified alternative modes for completing theprescribed course of study shall be madeavailable to pupils, parents, and the public.

51550. Sex Education Courses'No governing board of a public elementary or

secondary school may require pupils to attend anyclass in which human reproductive organs and theirfunctions and processes are described, illustrated ordiscussed, whether such class be part of a coursedesignated "sex education" or "family life education"or by some similar term, or part of any other coursewhich pupils are required to attend.

If classes are offered in public elementary andsecondary schools in which human reproductiveorgans and their ftInctions and processes are de-scribed, illustrated or discussed, the parent or guard-ian of each pupil enrolled in such class shall first benotified in writing of the class. Sending the required

' References to related sections from the Education Code appear in theHealth Instruction Framework for Ca-Immo Public Schools. Sacramento.California Department of Education, 1978, p. 68.

notice through the regular United States mail, or anyother method which such local school district com-monly uses to communicate individually in writing toall parents, meets the notification requirements of thisparagraph.

Opportunity shall be provided to each parent orguardian to request in writing that his child not attendthe class. Such requests shall be valid for the schoolyear in which they are submitted but may be with-drawn by the parent or guardian at any time. No childmay attend a class if a request that he not attend theclass has been received by the school.

Any written or audiovisual material to be used in aclass in which human reproductive organs and theirfunctions and processes are described, illustrated, ordiscussed shall be available for inspection by theparent or guardian at reasonable times and placesprior to the holding of a course which includes suchclasses. The parent or guardian shall be notified inwriting of his opportunity to inspect and review suchmaterials.

This section shall not apply to description orillustration of human reproductive organs which mayappear in a textbook, adopted pursuant to law, onphysiology, biology, zoology, general science,personal hygiene, or health.

Nothing in this section shall be construed asencouraging the description, illustration, or discus-sion of human reproductive organs and their func-tions and processes in the public elementary andsecondary schools.

The certification document of any person chargedwith the responsibility of making any instructionalmaterial available for inspection under this section orwho is charged with the responsibility of notifying aparent or guardian of any class conducted within thepurview of this section, and who knowingly andwillfully fails to make such instructional materialavailable for inspection or to notify such parent orguardian, may be 'evoked or suspended because ofsuch act. The certification document of any personwho knowingly and willfully requires a pupil toattend a class within the purview of this section whena request that the pupil not attend has been receivedfrom the parent or guardian may be revoked orsuspended because of such act.

235Appendix B 217

Appendix C

Seiected References

Aldridge, Bill G. "Essential Changes in SecondaryScience: Scope, Sequence, and Coordination,"NSTA Reports! (January, 1989) 66-74.

Burke, James. Connections. Boston: Little, Brown &Co., 1980.

Caught in the Middle: Educational Reform for YoungAdolescents in California Public Schools. Sacra-mento: California Department of Education, 1987.

EnglishLanguage Arts Framework for CaliforniaPublic Schools. Sacramento: California Depart-ment of Education, 1987.

Enrichment Opportunities Guide: A Resource forTeachers of Students in Math and Science. Sacra-mento: California Departrnmt of Education, 1988.

Feynman, Richard P. Surely You' re Joking, Mr.Feynman! New York: Bantam Books, 1986.

Feynman, Richard P., and Ralph Leighton. What DoYou Care What Other People Think? FurtherAdventures of a Curious Character. New York:W.W. Norton, 1988.

Foreign Language Framework for California PublicSchools. Sacramento: California Department ofEducation, 1989.

Gould, Stephen Jay. The Panda' s Thumb: MoreReflections in Natural History,. New York: W.W.Norton, 1980.

HammondRarnhart Dictionary of Science. Edited byRobert K. Barnhart. Maplewood, N.J.: Hammond,Inc., 1986.

Health Instruction Framework for Cahfornia PublecSchools. Sacramento: California Department ofEducation, 1978.

218 Science Framework

HistorySocial Science Framework for CaliforniaPublic Schools. Sacramento: California Depart-ment of Education, 1988.

Instructional Materials and Framework Adoption:Policies and Procedures. Sacramento: CaliforniaDepartment of Education, Office of CurriculumFramework and Textbook Development, 1988.

Kobrin, Beverly. Eyeopeners! How to Choose andUse Children's Books About Real People, Places,and Things. New York: Penguin Books, 1988.

Mathematics Framework for California PublicSchools. Sacramento: California Department ofEducation, 1985.

Miller, Jon D. "Who Is Scientifically Literate?" Paperpresented to the 1990 Science Education Forum,American Association for the Advancement ofScience.

Model Curriculum Standards, Grades Nine ThroughTwelve Sacramento: California Department ofEducation, 1985.

Moral and Civic Education and Teaching AboutReligion. Sacramento: California State Board ofEducation, 1988.

A Nation at Risk: The Imperative for EducationalReform, Washington, D.C.: U.S. GovernmentPrinting Office, 1983.

Quality Criteria for Elementary Schools. Planning,Implementing, Self-Study, and Program QualityReview. Sacramento: California Department ofEducation, 1990.

"".4 6

Quality Criteria for Middle Grades: Planning,Implementing, Self-Study, and Program QualityReview. Sacramento: California Department ofEducation, 1990.

Quality Criteria for High Schools: Planning, Imple-menting, Self-Study, and Program Quality Review.Sacramento: California Department of Education,1990.

Resnick, Lauren. Education and Learning to Think.Washington, D.C.: National Academy Press, 1987monograph.

Science Education for the 1980s. Sacramento:California Department of Education, 1985.

Science for All Americans. Washington, D.C.: Ameri-can Association for the Advancement of Science,Inc., 1989..

Science for Children, Resources for Teaching.Washington, D.C.: National Academy Press, 1988.

Science Model Curricqum Guide, K-8. Sacramento.California Department of Education, 1988.

The Science Report Card. National Assessment ofEducational Progress. Princeton: EducationalTesting Service, 1988.

Science Safety Handbook for California HighSchools. Sacramento: California Department ofEducation, 1987.

Statement on Preparation in Natural Science Ex-pected of Entering Freshmen. Sacramento: TheAcademic Senates of the California CommunityColleges, The California State University, and theUniversity of California, 1986.

Technology in the Curriculum: Science ResourceGuide (included in full package of six subjectareas, diskettes, and updates). Sacramento: Califor-nia Department of Education, 1986, 1987, 1988.

Temple, Robert. The Genius of China: 3,000 Years ofScience, Discovery and Invention. New York:Simon & Schuster, 1986.

Visual and Performing Arts Framework for Califor-nia Public Schools. Sacramento. California De-partment of Education, 1989.

2.17 Appendix C 219

Publications; Available from the Department of Education

This publication is one of over 650 that arc available from the California Department of Education. Some ofthe more recent publications or those most widely used are the following:

ISBN Title (Date of publication) Price

0-8011-0890-x Bilingual Education Handbook: A Handbook for Designing Instruction for LEP Students (1990) $4.250-8011-08624 California Education Summit: Background and Final Report (a set) (1990) 5.000-8011-0889-6 Calibmia Private School Directory, 1990 14.000-8011-0853-5 California Public School Directory, 1990 14.000-8011-0874-8 The Changing History-Social Science Curriculum: A Booklet for Parents (1990)* 51)01100-8011-0867-5 The Changing Language Arts Curriculum: A Booklet for Parents (1990)* 5.00/100-8011-0777-6 The Changing Mathematics Curriculum: A Booklet for Parents (1989)* 5.00/100-8011-0856-x English as a Second Language Handbook for Adult Education Instructors (1990) 4.500-8011-0041-0 English-Language Arts Framework for California Public Schools (1987) 3.000-8011-0849-7 Food Sanitation and Safety Self-Assessment Instrument for Child Care Centers (1990) 3.750-8011-0850-0 Food Sanitation and Safety Self-Assessment Instilment for Famili Day Care Homes (1990) 3.750-8011-0851-9 Food Sanitation and Safety Self-Assessment Instrument for School Nutrition Programs (1990) 3.750-8011-0804-7 Foreign Language Framework for California Public Schools (1989) 5.500-8011-0824-I Handbook for Teaching Cantonese-Speaking Students (1989)t 4.500-8011-0250-2 Handbook on California Education for Language Minority Parents-Chinese/English Edition (1986)** 3.250-8011-0712-1 History-Social Science Framework for California Public Schools (1988) 6.000-8011-0782-2 Images: A Workbook for Enhancing Self-esteem and Promoting Career Prcparation, Especially for

Black Girls (1988) 6.000-8011-0358-4 Mathematics Framework for California Public Schools (1985) 3.000-8011-0840-3 Price List and Order Form for Science Instructional Materials, 1990-1992 (1990) 2.500-8011-0368-1 Program Duscriptions for Science Instructional Materials (1986) 2.500-8011-0886-1 Program Guidelines for Individuals Who An Dcaf-Blind (1990) 6.000-8011-0817-9 Program Guidelines for Language. Speech, and Hearing Specialists Providing Designated Instruction and

Services (1989) 6.000-8011.0899-3 Quality Criteria for Elementary Schools: Planning, Implementing, Self-Study, and Program Quality

Review (1990) 4.500-8011-0906 x Quality Criteria for High Schools. Planning, Implementing Self-Study, and Program Quality Review (1990) 4.5f,0 8011-0905-1 Quality Critcria for Middle Grades. Planning, Implementing Sc If-Study, and Program Quality Review (1990) 4.300.801143858-6 Readings for Teachers of United Statcs History and Government (1990) 3.250-8011-0831-4 Recommended Literature, Grades 9-12 (1990) 4.500-8011-0863-2 Recommended Readings in Literature: Kindergarten Through Grade Eight, Addendum (1990) 2.250-8011-0745-8 Recommended Readings in Literature, Kindergarten Through Grade Eight, Annotaied Editiur. (1988)t t 4.500-8011-0870-5 Science Framework for California Public Schools (1990) 6.500-8011-0669-9 Science Safety Handbook for California High Schools (1987) (without binder) 5.750-8011-0668-0 Science Safety Handbook for California High Schools (1987) (with binder) 8.750-8011-0665-6 Science Model Curriculum Guide, K-8 (1988) 3.250-8011-0855-1 Strengthening the Arts in California Schools: A Design for the Future (1990) 4.750-8011-0846-2 Toward a Statc of Esteem: The Final Report of the California Task Force to Promote Self-Esieern and .

Personal and Social Responsibility (1990) 4.000-8011-0854-3 Toward a Statc of Esteem, Appendixes to (1990) 4.000-8011-0805-5 Visual and Performing Ms Framework for California Public Schools (1989) 6.00

Orders should be directed to:

California Department of EducationP.O. Box 271Sacramento, CA 95802-0271

Please include the International Standard Book Number (ISBN) for each title ordered.Remittance or purchase order must accompany order. Purchase orders withont diet..ks arc a.t..cptcd only from govern-

mental agencies. Sales tax should be added to all orders from California purchasers.A complete list of publications available from ihe Department, i:_luding apprcntit..cship instrut.tional rmiterial.), may be

obtained by writing to the address listed above or by calling (916) 445-1260.

*The price for 100 booklets is $30.00; the price for 1,030 booklets is S230.00.tAlso available at the same price, for students who speak Japanese, Pilipino, and Portuguese."The following editions are also available, at the same price. Armenian/English, Cambodiaranghsh, Ilmonanglash, Japanesangloh,

Korean/English, Laotizn/English, Pilipino/English, Spanish/English, and Vietnamese/English.tfincludes complimentary copy of Addendwn, (ISBN 0-8011-0863-2).

220 88 78089 87174 (034326) 78089 300 8.90

Appendix 16

:END

U.S. Dept. of Education

Office of EducationResearch and

Improvement (OERI).

ERIC

Date Filmed.

March 29, 1991