51. During photorespiration a. sugar synthesis is made more efficient b. rubisco

Question

51. During photorespiration a. sugar synthesis is made more efficient b. rubisco binds O instead of CO c. light reactions are uncoupled from the Calvin Cycle d. the Calvin Cycle is stopped e. loss of water, which only happens in succulents 52. Why are C4 plants able to photosynthesize with no apparent photorespiration a. They do not participate in the Calvin cycle b- They use PEP carboxylase to initially fix CO2. c. They conserve water more efficiently. d. They exclude oxygen from their tissues. e. The organization of the chloroplasts is less compacted CAM plants keep stomata closed in the daytime, thus reducing loss of water They can do this because they 53. a. fix CO2 into organic acids during the night b. use CO2 from PEP instead of RuBP at the start of the Calvin Cycle c. fix CO2 in the Calvin Cycle d. open their stomata at night e. all of the above Mitochondria and chloroplasts have similar structures. The current hypothesis suggests that this is because 54. a. both require lots of membrane area so evolved the same way b. each evolved from vesicles by involuting cell membranes c. both have evolved from once free-living prokaryotes d. both evolved from primitive eukaryotic cells e. they both have elements of extraterrestrial life forms 55. The likely force driving the evolution of C4 and CAM plants is a. adapting to hot, dry conditions b. adapting to periodic floods c. the increases in atmospheric CO2 and O2 d. the type of soil e. seasonal temperature changes

Explanation / Answer

51. Option B is correct.
During photorespiration, RuBisCO binds to oxygen and functions as an oxygenase.

52. Option B is correct.
C4 plants use PEP carboxylase as the primary carboxylase. They do not exhibit photorespiration as PEP carboxylase does not have oxygenase activity (unlike RuBisCO).

53. Option E is correct.
CAM plants exhibit C4 cycle at night times. They close stomata during daytime to reduce water loss. They also do not show photorespiration as PEP carboxylase is the primary CO2 fixing enzyme.

54. Option C is correct.
According to endosymbiotic theory, both mitochondria and chloroplasts have evolved from a free-living prokaryote which got ingested into another organism and resisted digestion.

55. Option A is correct.
Photorespiration is the major driving force for the evolution of C4 and CAM plants. Low CO2 concentrations during ancient times is a predominant factor for the evolution of these plants. These plants could also sustain hot, dry conditions which enabled them to spread rapidly.

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