Calvin Pathway: Universal in All Plants — NEET Biology
📚 Practice ConceptCalvin and his co-workers then worked out the whole pathway and showed that the pathway operated in a cyclic manner; the RuBP was regenerated. Let us now see how the Calvin pathway operates and where the sugar is synthesised. Let us at the outset understand very clearly that the Calvin pathway occurs in all photosynthetic plants; it does not matter whether they have C₃ or C₄ (or any other) pathways.
Which of the following statements comparing the Calvin cycle in C3 and C4 plants are NOT correct? S1: The Calvin cycle is a universal pathway for carbon assimilation, present in both C3 and C4 plants. S2: In C4 plants, the C4 pathway operates in mesophyll cells, while the Calvin cycle takes place in the bundle sheath cells. S3: The enzyme PEPcase, which fixes CO2 in mesophyll cells of C4 plants, is absent in their bundle sheath cells. S4: The characteristic Kranz anatomy of C4 leaves ensures that mesophyll cells are rich in RuBisCO. S5: Photorespiration is completely absent in C4 plants because their Calvin cycle does not involve RuBisCO activity.
View solution & NCERT explanation
Correct answer: C — S4 and S5 only
Let's evaluate each statement regarding the Calvin cycle in C3 and C4 plants: S1: The Calvin pathway (C3 cycle) occurs in all photosynthetic plants, regardless of whether they have a C3 or C4 pathway. This statement is correct. S2: C4 plants have a spatially separated carbon fixation, where initial CO2 fixation into a C4 acid occurs in mesophyll cells, and then CO2 is released in bundle sheath cells to enter the Calvin cycle. This statement is correct. S3: Mesophyll cells of C4 plants contain PEPcase, which fixes CO2. Bundle sheath cells lack PEPcase but are rich in RuBisCO. This statement is correct. S4: Kranz anatomy in C4 plants is characterized by large bundle sheath cells around vascular bundles, which contain numerous chloroplasts and RuBisCO, while mesophyll cells lack RuBisCO. This statement is incorrect. S5: C4 plants have a mechanism that increases CO2 concentration at the RuBisCO site in bundle sheath cells, thereby minimizing photorespiration, but the Calvin cycle still uses RuBisCO. Photorespiration is minimized, not completely absent, and RuBisCO is very much involved. This statement is incorrect. Therefore, statements S4 and S5 are NOT correct.
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