A10fiffAnswers
A2: ATP and NADPH.
Q3: What are the two major products of photosynthesis?
A3: Glucose and oxygen.
Figure 5.8
Q1: Why is it important that enzymes are not permanently altered
when they bind with substrate molecules?
A1: The fact that they are not permanently altered means
that they can continue to perform their function without having
to be present in great numbers or needing to be continually
produced.
Q2: How would a higher temperature or higher salt concentration
make it more difficult for an enzyme to function effectively?
A2: Both would change the shape of the enzyme so that it would
not be able to bind to its specific molecules.
Q3: If a cell was unable to produce a particular enzyme necessary
for a metabolic pathway, describe how the absence of that enzyme
would affect the cell.
A3: The metabolic pathway would either proceed very slowly or,
possibly, come to a complete halt, so the cell would not be able to
function.
Figure 5.11
Q1: What are the products of cellular respiration?
A1: Carbon dioxide and water.
Q2: Considering the inputs and products of each process, why
is cellular respiration considered the reciprocal process to
photosynthesis?
A2: Photosynthesis uses carbon dioxide and produces oxygen,
whereas cellular respiration does the opposite, using oxygen and
producing carbon dioxide.
Q3: Which of the three stages of cellular respiration—glycolysis,
the Krebs cycle, or oxidative phosphorylation—could organisms
have used 4 billion years ago, before photosynthesis by
cyanobacteria released oxygen into the atmosphere?
A3: Glycolysis, because it does not depend on oxygen. As the text
says, “Glycolysis was probably the earliest means of producing ATP
from food molecules, and it is still the primary means of energy
production in many prokaryotes.”
Figure 5.12
Q1: Which product released by fermentation accounts for the
bubbles in beer?
A1: Carbon dioxide (CO 2 ).
Q2: Bakers of yeast breads also rely on fermentation, allowing
bread to “rise” before baking. Describe what is occurring with the
yeast as the bread rises.
A2: During bread rising, yeasts are performing metabolic
functions—and growing and reproducing—using energy created
through fermentation. The fermentation produces CO 2 as a
waste product, which is trapped within the bread dough and
causes it to rise.
Q3: Explain in your own words why lactic acid builds up in your
muscles during strenuous physical activity.A3: Something like this: “During strenuous exercise, my muscles
can’t get enough oxygen to produce all the needed ATP. So,
glycolysis produces ATP anaerobically, which generates lactic acid
as a by-product.”CHAPTER 6
END-OF-CHAPTER ANSWERS
- b
- a
- (a) 4, (b) 1, (c) 2, (d) 3
- Meiosis, binary fission, homologous chromosomes, sister chro-
matids - (a) 1, (b) 2, (c) 5, (d) 3, (e) 4
- a
- b
- b
- b
- S phase. Chromosomes replicate during S phase; at some
point during S phase, there will be the original DNA strands
and half of the newly synthesized DNA strands. In all other
phases, there is either the same amount of DNA as in the G 1
phase, or twice as much DNA as in G 1. - (a) 54, (b) 27, (c) 27
- c
- The G 1 checkpoint ensures that the cell is ready to divide—
for example, that it is large enough and has enough energy
to produce two normal daughter cells. The G 2 checkpoint
ensures that the cell’s DNA has been replicated and packed
into pairs of sister chromatids. Bypassing the G 1 checkpoint
could allow cells to divide before they’re ready; bypassing the
G 2 checkpoint could lead to the production of daughter cells
with defective chromosomes.
ANSWERS TO FIGURE QUESTIONS
Figure 6.2
Q1: When is DNA replicated during the cell cycle?A1: In interphase.Q2: When in the cell cycle does DNA separate into the two
genetically identical daughter cells?A2: Late in the mitotic phase of cell division.Q3: If a cell is not destined to separate into daughter cells, what
phase does it enter? Is this part of the cell cycle?A3: It enters the G 0 phase, which is not part of the cell cycle.