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APPENDI X

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APPENDIX B

Answer Key

Answers to Collaborative Questions can be found on the website.

Chapter 1Concept ChecksFigure 1.4 It benefits humans in many different ways. Discoveries in biologyare important in the fields of medicine, research, agriculture, biotechnology,and many other disciplines. Most of the medicines we take were developed bybiologists.

Figure 1.6 It would be at the population level.

Figure 1.8 In monkeys, the tail has been modified to grasp onto things,

such as tree branches. In skunks, the tail is modified with a bright stripe; thetail can stick up and act as a warning signal to potential predators. In cattle,the tail has long hairs and is used to swat insects. Many more examples arepossible.

Figure 1.9 Natural selection is the process that causes evolution to happen.

Figure 1.11 A tree of life suggests that all living organisms evolved from asingle ancestor by vertical evolution with mutation. A web of life assumesthat both vertical evolution with mutation and horizontal gene transfer wereimportant mechanisms in the evolution of new species.

Figure 1.13 Taxonomy helps us to appreciate the unity and diversity of life.Organisms that are closely related evolutionarily are placed in smaller groups.

Figure 1.14 The genome stores the information to make an organismsproteins. In and of itself, the genome is merely DNA. The traits of cells andorganisms are largely determined by the structures and functions of the hun-dreds or thousands of different proteins they make.

Figure 1.17 Discovery-based science does not require a preconceived

hypothesis in order to carry out an experiment.

Figure 1.18 A researcher can compare the results in the experimental groupand control group to determine if a single variable is causing a particularoutcome in the experimental group.

Figure 1.19 After the CFgene was identified by discovery-based science,researchers realized that the CFgene was similar to other genes that encodedproteins that were already known to be transporters. This provided an impor-tant clue that the CFgene also encodes a transporter protein.

Feature Investigation Questions1. In discovery-based science, a researcher does not need to have a precon-

ceived hypothesis. Experimentation is conducted in the hope that it mayhave practical applications or may provide new information that willlead to a hypothesis. By comparison, hypothesis testing occurs when aresearcher forms a hypothesis that makes certain predictions. Experi-ments are conducted to see if those predictions are correct. In this way,

the hypothesis may be accepted or rejected.2. This strategy may be described as a five-stage process:

1. Observations are made regarding natural phenomena.

2. These observations lead to a hypothesis that tries to explain the phe-nomena. A useful hypothesis is one that is testable because it makesspecific predictions.

3. Experimentation is conducted to determine if the predictions arecorrect.

4. The data from the experiment are analyzed.

5. The hypothesis is accepted or rejected.

3. In an ideal experiment, the control and experimental groups differ byonly one factor. Biologists apply statistical analyses to their data to

determine if the control and experimental groups are likely to be dif-ferent from each other because of the single variable that is differentbetween the two groups. This provides an objective way to accept orreject a hypothesis.

Test Yourself1. d 2. a 3. c 4. c 5. d 6. b 7. d 8. d 9. a 10. b

Conceptual Questions1. Cells and organizationAll living organisms consist of cells; organism

maintain an internal order that is separated from the environment.

Energy use and metabolismAll living organisms acquire energyfrom the environment and use that energy to maintain their internaorder. An organisms chemical reactions are collectively known asmetabolism.Response to environmental changesLiving organisms respond toenvironmental changes. These responses are adaptations.Regulation and homeostasisLiving organisms maintain relativelystable internal conditions, homeostasis.Growth and developmentGrowth produces more or larger cells;development produces organisms with a defined set of characteristReproductionTo sustain life, organisms must produce others likethemselves; the genetic material maintains continuity over thegenerations.Biological evolutionPopulations of organisms change over thecourse of many generations.

2. The unity among different species occurs because modern species havevolved from a group of related ancestors. Some of the traits in thoseancestors are also found in modern species and thereby unites them.

The diversity is due to the variety of environments on the Earth. Eachspecies has evolved to occupy its own unique environment. For everyspecies, many traits are evolutionary adaptations to survival in a specenvironment. For this reason, evolution also promotes diversity.

3. Domains and kingdoms are very diverse, being composed of hundredof thousands or even millions of different species. The least-diversegroups are genera and species. A species is composed of just one typeorganism, and a genus is typically composed of several or several dozdifferent species, though some genera are quite large.

Chapter 2Concept ChecksFigure 2.4 An energy shell is a region outside the nucleus of an atom occpied by electrons of a given energy level. More than one orbital can be founwithin an electron shell. An orbital may be spherical or dumbbell-shaped a

contains up to two electrons.Figure 2.9 The octet rule states that atoms are stable when they have eigelectrons in their outermost shell. Oxygen has six electrons in its outer shelWhen two oxygen atoms share two pairs of electrons, each atom has eightelectrons in its outer shell, at least part of the time.

Figure 2.11 Strand separation requires energy, because the DNA strands aheld together by a large number of hydrogen bonds. Although each hydrogbond is weak, collectively the vast number of such bonds in a molecule ofDNA adds up to a considerable strength.

Figure 2.17 The oil would be in the center of the soap micelles.

Figure 2.19 Due to the colligative properties of water, the solutes in bloolower its freezing point. Human blood, for example, freezes at a temperaturthat is about half a degree Celsius lower than that of pure water.

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APPENDIX B A

oil. Thus, the phospholipids would form a layer at the interface between thwater and oil.

Figure 3.15 71; one less than the number of amino acids in the polypept

Figure 3.19 If the primary structure of Protein 1 were altered in some wathis would, in turn, most likely alter the secondary and tertiary structures oProtein 1. Therefore, it is possible that the precise fit between Proteins 1 anwould be lost and that the two proteins would lose the ability to interact.

Figure 3.24 Yes. The opposite strand must be the mirror image of the firs

strand, because pairs can form only between A and T, and G and C. Forinstance, if a portion of the first strand is AATGCA, the opposite strand alothat region would be TTACGT.

Feature Investigation Questions1. Many scientists assumed that protein folding was directed by some

cellular factor, meaning some other molecule in the cytoplasm, andtherefore, protein folding could not occur spontaneously. Othersassumed that protein folding was determined somehow by the ribosobecause this organelle is primarily responsible for synthesizing protei

2. Anfinsen was testing the hypothesis that the information necessary fodetermining the three-dimensional shape of a protein is contained witthe protein itself. In other words, the chemical characteristics of theamino acids that make up a protein will determine the three-dimensioshape.

3. The urea disrupts hydrogen bonds and ionic interactions that are nec

sary for protein folding. The mercaptoethanol disrupted the Si

S bonthat also form between certain amino acids of the same polypeptidechains. Both substances essentially allow the polypeptide chain tounfold, disrupting the three-dimensional shape. Anfinsen removed thurea and mercaptoethanol from the protein solution by size-exclusionchromatography. After removing the urea and mercaptoethanol, Anfinsen discovered that the protein refolded into its proper three-dimensioshape and became functional again. This was important because thesolution contained only the protein and lacked any other cellular matrial that could possibly assist in protein folding. This demonstrated ththe protein could refold into the functional conformation.

Test Yourself1. b 2. b 3. e 4. b 5. c 6. b 7. b 8. d 9. b 10. b

Conceptual Questions1. Isomers are two structures with an identical molecular formula but w

different structures and arrangements of atoms within the molecule.There are two major types of isomers: structural and stereoisomers.Because many chemical reactions in biology depend upon the actionsenzymes, which are often highly specific for the spatial arrangement atoms in a molecule, one isomer of a pair may have biological functioand the other may not.

2. a. Carbohydratesenergy storage and structural support

b. Lipidsenergy storage and components of cellular membranes

c. Proteinsmany functions, including enzymes, defense, transport,structure, contraction

d. Nucleic acidsinformation storage, gene expression

3. Saturated fatty acids are saturated with hydrogen and have only singl(CiC) bonds, whereas unsaturated fatty acids have one or more dou(CwC) bonds. The double bonds in unsaturated fatty acids alters theshape, resulting in a kink in the structure. Saturated fatty acids are

unkinked and are better able to stack tightly together. Fats containingsaturated fatty acids have a higher melting point than those containinmostly unsaturated fatty acids; consequently, saturated fats tend to bsolids at room temperatures, and unsaturated fatty acids are usuallyliquids at room temperature.

Chapter 4Concept ChecksFigure 4.1 You would use transmission electron microscopy. The othermethods do not have good enough resolution.

Figure 4.3 The primary advantage is that it gives an image of the 3-D surface of a material.

Figure 2.21 It is 106 M. Because [H][OH] always equals 1014 M, if [H] 108 M (i.e., pH 8.0), then [OH] must be 106 M.

Feature Investigation Questions1. Scientists were aware that atoms contained charged particles. Many

believed that the positive charges and mass were evenly distributedthroughout the atom.

2. Rutherford was testing the hypothesis that atoms are composed ofpositive charges evenly distributed throughout the atom. Based on thismodel of the structure of the atom, alpha particles, which are posi-tively charged nuclei of helium atoms, should be deflected as they passthrough the foil, due to the presence of positive charges spread through-out the gold foil.

3. Instead of detecting slight deflection of most alpha particles as theypassed through the gold foil, the majority, 98%, of the alpha par-ticles passed directly through the gold foil without deflection. A muchsmaller percentage either deflected or bounced back from the goldfoil. Rutherford suggested that since most of the alpha particles passedunimpeded through the gold foil, most of the volume of atoms is emptyspace. Rutherford also proposed that the bouncing back of some of thealpha particles indicated that most of the positively charged particleswere concentrated in a compact area. These results were counter to thehypothesized model.

Test Yourself

1. b 2. b 3. b 4. d 5. e 6. e 7. e 8. c 9. e 10. b

Conceptual Questions1. Covalent bonds are bonds in which atoms share electrons. A hydrogen

bond is a weak polar covalent bond that forms when a hydrogen atomfrom one polar molecule becomes electrically attracted to an electro-negative atom. A nonpolar covalent bond is one between two atomsof similar electronegativities, such as two carbon atoms. The van derWaal forces are temporary, weak bonds, resulting from random electricalforces generated by the changing distributions of electrons in the outershells of nearby atoms. The strong attraction between two oppositelycharged atoms forms an ionic bond.

2. Hydrophobic: Water-fearingmolecules that are not attracted to watermolecules. Hydrophilic: Water-lovinggenerally, ions and moleculesthat contain polar covalent bonds will dissolve in water and are said tobe hydrophilic.

3. Within limits, bonds within molecules can rotate and thereby change theshape of a molecule. This is important because it is the shape of amolecule that determines, in part, the ability of that molecule to interactwith other molecules. Also, when two molecules do interact through suchforces as hydrogen bonds, the shape of one or both molecules may changeas a consequence. The change in shape is often part of the mechanism bywhich signals are sent within and between cells.

Chapter 3Concept ChecksFigure 3.1 Due to the fact that he had earlier purified urea from urine andthen formed urea crystals, he already knew what urea crystals looked like.As seen in this figure, they are quite distinctive looking. Therefore, when hereacted ammonia and cyanic acid and got a compound that formed crystals,the distinctive look of the crystals made him realize that he had synthesizedurea.

Figure 3.6 One reason is that the binding of a molecule to an enzymedepends on the spatial arrangements of the atoms in that molecule. Enantiom-ers have different spatial relationships that are mirror images of each other.Therefore, one may bind very tightly to an enzyme while the other may notbe recognized at all.

Figure 3.7 Recall from Figure 3.5 that the reverse of a dehydration reaction iscalled a hydrolysis reaction, in which a molecule of water is added to themolecule being broken down, resulting in the formation of monomers.

Figure 3.11 Hydrogenation is adding hydrogens to double-bonded carbonatoms, changing them from unsaturated to saturated. This causes them to besolid at room temperature.

Figure 3.12 The phospholipids would be oriented such that their polarregions dissolved in the water layer and the nonpolar regions dissolved in the

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