C3, C4 and CAM plants Transitional Reasoning Practice

Questions

1. 1.

   An agricultural researcher placed three different crop species under high-temperature, low-humidity daytime conditions with intense sunlight to monitor their photosynthetic performance. Plant 1 exhibited high rates of photorespiration and significantly reduced net carbon fixation due to partial stomatal closure. Plant 2 maintained a high rate of carbon fixation without significant photorespiration by utilizing PEP carboxylase in its mesophyll cells and concentrating $CO_2$ around RuBisCO in bundle-sheath cells. Plant 3 completely closed its stomata during the daytime yet continued the Calvin cycle using carbon stored overnight as malate in vacuoles. Based on these physiological responses, which comparison correctly characterizes these plants?

   • A) Plant 1 minimizes photorespiration through temporal separation of carbon fixation, whereas Plant 3 uses spatial separation between mesophyll and bundle-sheath cells.
   • B) Plant 2 exhibits temporal separation of carbon fixation, accumulating organic acids at night to avoid daytime transpirational water loss.
   • C) Plant 2 relies on spatial separation of initial carbon fixation and the Calvin cycle, whereas Plant 3 relies on temporal separation of these two processes.
   • D) Plant 3 directly fixes atmospheric carbon dioxide with RuBisCO during the daytime, while Plant 1 fixes carbon dioxide exclusively into four-carbon oxaloacetate.

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