Answers to Review Questions - Chapter 7
1. What is the specific role of oxygen in most cells?
Oxygen becomes reduced in aerobic respiration in the electron transport chain; it
is the final electron acceptor. Each of the 2 atoms of diatomic oxygen accepts 2
electrons, joining with 2 hydrogen ions in the surrounding medium to produce
water.
2. How much ATP is made available to the cell from a single glucose molecule by
the operation of a) glycolysis, b) the formation of acetyl CoA, c) the citric acid
cycle, and d) the electron transport chain and chemiosmosis? Please note whether
the ATPs (if any) produced are made via substrate-level phosphorylation or
oxidative phosphorylation.
a)
b)
c)
d)
glycolysis – 2 ATP – substrate-level phosphorylation
formation of acetyl-CoA – no ATP
citric acid cycle – 2 ATP – substrate-level phosphorylation
ETC/chemiosmosis – 32-34 ATP – oxidative phosphorylation
3. Why is each of the following essential to chemiosmotic ATP synthesis?
a) electron transport chain - these protein complexes pump protons into the
intermembrane space while passing electrons between them
b) proton gradient - so that hydrogen ions will diffuse through the ATP
synthase channels down their concentration gradient
c) c) ATP synthase complex – as hydrogen ions pass through the synthases,
the production of ATP from ADP and Pi is catalyzed, and oxygen is
reduced, forming water
4. What are the roles of NAD+ and FAD in aerobic respiration?
NAD+ and FAD receive electrons at varying steps during glycolysis (NAD+ only)
and the citric acid cycle (both NAD+ and FAD), to form NADH and FADH2,
which then carry these electrons to the electron transport chain. Oxygen acts at
the end of this chain, receives the electrons, joining with hydrogen ions to
produce water.
5. How can a person obtain energy from a low-carbohydrate diet?
Other carbohydrate molecules, fatty acids, and amino acids may be modified and
shuttled into the steps of aerobic respiration prior to the electron transport and
chemiosmosis phase.
6. What is the fate of the electrons/hydrogen atoms removed from glucose during
glycolysis when oxygen is present in muscle cells? How does this compare to the
fate of electrons/hydrogen atoms removed from glucose when the amount of
available oxygen is insufficient to support aerobic respiration?
When oxygen is present, it will act as the final electron acceptor during ATP
production in muscle cells. If oxygen is insufficient in muscle cells, an organic
molecule acts as the final electron acceptor, causing the formation of lactic acid.