Biology Now, 2e

Answers ■ A5

A2: “Herd immunity” means that fewer people contract the

disease, and therefore vulnerable people are less likely to be

exposed to a contagious person.

Q3: How does vaccination help an individual person? How does it

help that person’s community?

A3: An individual who is vaccinated is much less likely to become

ill and is therefore less likely to pass on a disease to others in the

community.

CHAPTER 3

END-OF-CHAPTER ANSWERS

1. a


2. d


3. ion: 3, matter: 6, solution: 9, element: 5, chemical compound:

8, molecule: 4, isotope: 7, polymer: 2, atom: 1

4. a


5. polymers, sugar, nucleotides, are not, carbon


6. a, c, e


7. Carbon can be the basis of more complex molecules than

can hydrogen or oxygen because carbon can form four bonds

(versus one for hydrogen and two for oxygen).

8. Six of the amino acids produced contained sulfur; these could

not have formed in the absence of a sulfur-containing reac-

tant.

9. b


10. b


11. (a) oven, (b) coffee maker, (c) neither, (d) oven, (e) coffee maker


12. The nonpolar end of the detergent will bond to the oil in the

salad dressing while the polar end bonds to the water mole-

cules, lifting the oil into the wash water. Vinegar is a polar

molecule, so it will dissolve in the wash water; you don’t need

detergent to remove vinegar.

ANSWERS TO FIGURE QUESTIONS

Figure 3.1

Q1: How many protons, electrons, and neutrons does the hydrogen

atom shown here have? What are the atomic number and the

atomic mass number of the hydrogen atom?

A1: 1 proton, 1 electron, 0 neutrons. The atomic number (number

of protons) and the atomic mass number (number of protons plus

neutrons) are both 1.

Q2: What are the atomic number and the atomic mass number of

the carbon isotope shown?

A2: The atomic number is 6 (6 protons); the atomic mass number,

12 (6 protons plus 6 neutrons).

Q3: Nitrogen-11 is an isotope of nitrogen that has 7 protons and 4

neutrons. What are the atomic number and atomic mass number

of nitrogen-11?

A3: The atomic number is 7 (7 protons); the atomic mass number,

11 (7 protons plus 4 neutrons).

Figure 3.2

Q1: Before the experiment was run, the apparatus was sterilized

and then carefully sealed. Why was this an important thing to do?

A1: Having a spotlessly clean apparatus was important to

ensure that any amino acids were produced by the experimental

conditions, not from contamination.

Q2: Why is inclusion of methane in the gas flasks an essential part

of the hypothesis that complex organic molecules were formed

in the early atmosphere of Earth? (Hint: What makes a molecule

organic?)

A2: Amino acids contain carbon, and methane (a simple organic

molecule) is the only chemical in the mixture that contains carbon.

Q3: Answer this question after reading about Miller’s “steam

injection” experiments: Where was the steam injected in the

experimental apparatus?

A3: The steam was injected straight into the gas chamber,

allowing the gases to interact with the water (and the other gases)

more directly.

Figure 3.4

Q1: Where are the covalent bonds in this figure?

A1: The covalent bonds are located at the electrons shared

between the oxygen atom and the two hydrogen atoms.

Q2: This figure shows a water molecule (H 2 O). A hydrogen

molecule (H 2 ) consists of two hydrogen nuclei that share two

electrons. Draw a simple diagram of a hydrogen molecule

indicating the positions of the two electrons.

A2: The electrons are equidistant from the two hydrogen nuclei

because there is no difference in the strength of their attraction to

electrons.

Figure 03.B

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Q3: When table salt (sodium chloride, NaCl) dissolves in water, it

separates into a sodium ion (Na+) and a chloride ion (Cl–). Which

portion of a water molecule would attract the sodium ion, and

which portion would attract the chloride ion?

A3: The Na+ ions are attracted to the partial negative charges on

the oxygen atoms, and the Cl– ions are attracted to the partial

positive charges on the hydrogen atoms.

Figure 3.5

Q1: Describe what will happen to the molecules of olive oil if you

shake the bottle and then leave it alone for an hour. What about

the molecules of vinegar?