a Order b Regulation

c Growth and development d Energy utilization

THE SCOPE OF LIFE The Properties of Life

e Response to the environment

f Reproduction

g Evolution

THE SCOPE OF LIFE The Properties of Life

– Biologists explore life at levels ranging from the biosphere to the molecules that make up cells.

Life at Its Many Levels

BiosphereEcosystems

Communities

Populations

Organisms

Organ Systemsand Organs

Tissues

Cells

OrganellesMolecules and Atoms

Atom

Nucleus

Life in Its Diverse Forms– Diversity is the hallmark of life.

• The diversity of known life includes 1.8 million species.• Estimates of the total diversity range from 10 million to over

100 million species.

Grouping Species– Biodiversity can be beautiful but overwhelming.– Taxonomy is the branch of biology that names and

classifies species.

The Three Domains of Life• The three domains of life are

– Bacteria

– Archaea

– Eukarya

Chemistry of Life– Matter is anything that occupies space and has mass.– Matter is found on the Earth in three physical states:

• Solid • Liquid• Gas

– Matter is composed of chemical elements.• Elements are substances that cannot be broken down

into other substances.

Chemistry of Life

Change the number of PROTONS in the nucleus and you change the ELEMENT

Atoms

Nucleus

Protons

Neutrons

Electrons

Nucleus

Cloud of negativecharge 2 electrons

2

2

2

– Each element consists of one kind of atom.• An atom is the smallest unit of matter that still retains the

properties of an element.

– Elements differ in the number of subatomic particles in their atoms.• The number of protons, the atomic number, determines which

element it is.• An atom’s mass number is the sum of the number of protons

and neutrons.• Mass is a measure of the amount of matter in an object.

Chemistry of Life

Periodic Table of the Elements

Atomic number = number of protons within the nucleus

Other nonmetals    Halogens    

Noble gases    

Other metals    

Rare earth metals    Transition metals    

Alkali earth metals    

Alkali metals    

Synthetic      

Gas     

Liquid     

Solid    

Legend

Chemistry of Life

Carbon C: 18.5%

Hydrogen H:9.5%

Nitrogen N:3.3%

Calcium Ca: 1.5%

Trace elements: less than 0.01%

Boron B Manganese Mn

Oxygen O:65.0%

Magnesium Mg: 0.1%

Phosphorus P: 1.0%

Potassium K: 0.4%

Sulfur S: 0.3%

Sodium Na: 0.2%

Chlorine Cl: 0.2%

Cobalt CoChromium Cr

Iron FeIodine IFluorine FCopper Cu Silicon Si

Zinc ZnVanadium VTin Sn

Molybdenum MoSelenium Se

– Twenty-five elements are essential to life.– Four elements make up about 96% of the weight of

the human body:• Oxygen• Carbon• Hydrogen• Nitrogen

First electron shellcan hold 2 electrons

Outer electron shellcan hold 8 electrons

Hydrogen HAtomic number = 1

Carbon CAtomic number = 6

Nitrogen NAtomic number = 7

Oxygen OAtomic number = 8

Electron

Chemical Properties of Atoms– Electrons determine how an atom behaves when it encounters

other atoms.

© 2010 Pearson Education, Inc.

Covalent Bonds– A covalent bond forms when two atoms share one or

more pairs of outer-shell electrons.– Atoms held together by covalent bonds form a

molecule.

Namemolecular formula

Hydrogen gas H2

Oxygen gas O2

Methane CH4

Electron configuration Structural formula Space-filling model Ball-and-stick model

Single bonda pair of shared electrons

Double bondtwo pairs of shared electrons

Ionic Bonds– When an atom loses or gains electrons, it becomes

electrically charged.• Charged atoms are called ions.• Ionic bonds are formed between oppositely charged ions.

Outer shellhas 1 electron

Outer shellhas 7 electrons

The outer electron is strippedfrom sodium and completesthe chlorine atom’s outer shell

NaSodium atom

ClChlorine atom

Completeouter shells

The attractionbetween theions—an ionicbond—holdsthem together

Na

Sodium ionCl

Chlorine ion

Sodium chloride (NaCl)

Hydrogen Bonds– Water is a compound in which the electrons in its

covalent bonds are shared unequally.• This causes water to be a polar molecule, one with opposite

charges on opposite ends.

H H

O

slightly slightly

slightly –

Hydrogen bonding• Weak bonds formed

between hydrogen and another atom – Surface tension of water

• Important as intramolecular bonds, giving shape to proteins and other biomolecules