61

b. uses ATP and NADPH produced in the light reactions.

61. Photorespiration
a. results in CO2 fixation.
b. uses ATP and NADPH produced in the light reactions.
c. generates a proton gradient.
d. results in the synthesis of glucose.
e. All of the above

a. it cannot react with CO2.

62. When RuBP reacts with O2,
a. it cannot react with CO2.
b. carbohydrate production increases.
c. plant growth is stimulated.
d. net carbon fixation increases by 25 percent.
e. two carbon molecules combine to form the four-carbon phosphoglycolate.

b. O2

63. During photorespiration, rubisco uses _______ as a substrate.
a. CO2
b. O2
c. glyceraldehyde 3-phosphate
d. 3-phosphoglycerate
e. NADPH

b. 25

64. Photorespiration reduces the net carbon fixed by the Calvin cycle by _______ percent.
a. 70
b. 25
c. 2.1
d. 0.21
e. 0.02

e. As the ratio of CO2 to O2 falls in the leaf, the reaction of rubisco with O2 is favored, and photorespiration proceeds.

65. How does rubisco "decide" whether to act as an oxygenase or a carboxylase?
a. Rubisco has 10 times more affinity for O2 than CO2; therefore, it favors O2 fixation.
b. If O2 is relatively abundant, rubisco acts as a carboxylase.
c. If O2 predominates, rubisco fixes it and the Calvin-Benson cycle occurs.
d. Photorespiration is more likely at low temperatures.
e. As the ratio of CO2 to O2 falls in the leaf, the reaction of rubisco with O2 is favored, and photorespiration proceeds.

a. mitochondria, chloroplasts and peroxisomes

66. Photorespiration takes place in
a. mitochondria, chloroplasts and peroxisomes
b. chloroplasts and mitochondria
c. C4 plants only.
d. the microbodies.
e. the cytoplasm and peroxisomes

c. oxaloacetate.

67. In C4 plants, CO2 is first fixed into a compound called
a. pyruvate.
b. glucose.
c. oxaloacetate.
d. ribulose bisphosphate.
e. 3-phosphoglycerate.

c. carry CO2 to the bundle sheath cells.

68. In C4 plants, the function of the four-carbon compound that is synthesized in the mesophyll cells is to
a. reduce NADP+.
b. combine with CO2 to produce glucose.
c. carry CO2 to the bundle sheath cells.
d. drive the synthesis of ATP.
e. close the stomata.

e. bundle sheath cells.

69. In C4 plants, starch grains are found in the chloroplasts of
a. the thylakoids.
b. mesophyll cells.
c. the intracellular space.
d. the stroma.
e. bundle sheath cells.

a. can trap CO2 even at relatively low CO2 concentrations.

70. The enzyme PEP carboxylase
a. can trap CO2 even at relatively low CO2 concentrations.
b. catalyzes the synthesis of RuBP.
c. catalyzes the synthesis of 3PG.
d. is found in the chloroplasts of bundle sheath cells.
e. couples the synthesis of ATP to the diffusion of protons.