128 Chapter 5
Test Your Knowledge
- The net gain of ATP per glucose molecule in lactic acid
fermentation is ; the net gain in aerobic respiration is
generally .
a. 2;4 c. 30;2
b. 2;30 d. 24;38 - In anaerobic metabolism, the oxidizing agent for NADH
(that is, the molecule that removes electrons from NADH) is
a. pyruvic acid. c. citric acid.
b. lactic acid. d. oxygen. - When skeletal muscles lack sufficient oxygen, there is an
increased blood concentration of
a. pyruvic acid. c. lactic acid.
b. glucose. d. ATP. - The conversion of lactic acid to pyruvic acid occurs
a. in anaerobic respiration.
b. in the heart, where lactic acid is aerobically respired.
c. in the liver, where lactic acid can be converted to glucose.
d. in both a and b.
e. in both b and c.- Which of these statements about the oxygen in the air we
breathe is true?
a. It functions as the final electron acceptor of the electron-
transport chain.
b. It combines with hydrogen to form water.
c. It combines with carbon to form CO 2.
d. Both a and b are true.
e. Both a and c are true. - In terms of the number of ATP molecules directly produced,
the major energy-yielding process in the cell is
a. glycolysis.
b. the citric acid cycle.
c. oxidative phosphorylation.
d. gluconeogenesis. - Ketone bodies are derived from
a. fatty acids. c. glucose.
b. glycerol. d. amino acids.- The conversion of glycogen to glucose 6-phosphate occurs
in
a. the liver.
b. skeletal muscles.
c. both a and b. - The conversion of glucose 6-phosphate to free glucose,
which can be secreted into the blood, occurs in
a. the liver.
b. skeletal muscles.
c. both a and b.
Review Activities
- The formation of glucose from pyruvic acid derived from
lactic acid, amino acids, or glycerol is called
a. glycogenesis. c. glycolysis.
b. glycogenolysis. d. gluconeogenesis. - Which of these organs has an almost absolute requirement
for blood glucose as its energy source?
a. liver c. skeletal muscles
b. brain d. heart - When amino acids are used as an energy source,
a. oxidative deamination occurs.
b. pyruvic acid or one of the Krebs cycle acids (keto acids)
is formed.
c. urea is produced.
d. all of these occur. - Intermediates formed during fatty acid metabolism can enter
the citric acid cycle as
a. keto acids. c. Krebs cycle acids.
b. acetyl CoA. d. pyruvic acid.
Test Your Understanding- State the advantages and disadvantages of the lactic acid
pathway. - What purpose is served by the formation of lactic acid
during anaerobic metabolism? How is this accomplished
during aerobic respiration? - Describe the effect of cyanide on oxidative phosphorylation
and on the citric acid cycle. Why is cyanide deadly? - Describe the metabolic pathway by which glucose can be
converted into fat. How can end-product inhibition by ATP
favor this pathway? - Describe the metabolic pathway by which fat can be used
as a source of energy and explain why the metabolism of
fatty acids can yield more ATP than the metabolism of
glucose. - Explain how energy is obtained from the metabolism
of amino acids. Why does a starving person have a high
concentration of urea in the blood? - Explain why the liver is the only organ able to secrete glucose
into the blood. What are the different molecular sources and
metabolic pathways that the liver uses to obtain glucose? - Why is the production of lactic acid termed a “fermentation”
pathway? - Explain the function of brown fat. What does its mechanism
imply about the effect of ATP concentrations on the rate of
cell respiration? - What three molecules serve as the major substrates for
gluconeogenesis? Describe the situations in which each one
would be involved in this process. Why can’t fatty acids be
used as a substrate for gluconeogenesis? ( Hint: Count the
carbons in acetyl CoA and pyruvic acid.)