C3, C4 and CAM plants Transitional Reasoning Download PDF

Questions

1. 1.

   An agricultural scientist investigates the photosynthetic adaptations of two drought-tolerant crops grown under intense sunlight and high daytime temperatures. Crop X opens its stomata at night to assimilate carbon dioxide into organic acids stored within large central vacuoles, decarboxylating these acids during the day behind closed stomata. Crop Y keeps its stomata partially open during the day, initially fixing inorganic carbon in mesophyll cells into a four-carbon compound before transferring it to specialized bundle-sheath cells where the Calvin cycle operates. Based on these mechanisms, which statement correctly evaluates the carbon-fixation strategies of these two plants?

   • A) Crop X minimizes transpiration through temporal separation, whereas Crop Y relies on elevated photorespiration within mesophyll cells to release carbon dioxide.
   • B) Crop X directly fixes carbon dioxide into 3-phosphoglycerate using RuBisCO at night, while Crop Y bypasses the Calvin cycle entirely in bundle-sheath cells.
   • C) Crop X uses temporal separation of initial carboxylation and the Calvin cycle to conserve water, whereas Crop Y uses spatial separation between distinct cell types to suppress photorespiration.
   • D) Both Crop X and Crop Y avoid the use of phosphoenolpyruvate carboxylase, depending exclusively on RuBisCO to capture atmospheric carbon dioxide under arid conditions.