RuBisCO and C3/C4 Plant Pathways—NEET Biology
✅ Asked in NEET 2026The enzyme required for carboxylation in the Calvin cycle is
The enzyme required for carboxylation in the Calvin cycle is
Answer & NCERT explanation
Correct answer: C — RuBP carboxylase - oxygenase
RuBisCO (RuBP carboxylase-oxygenase) catalyses the carboxylation of RuBP with CO2 in the Calvin cycle. PEP carboxylase fixes CO2 in the C4 pathway, not the Calvin cycle proper.
Read more NCERT concept on the PYQ
Thus, the basic pathway that results in the formation of the sugars, the Calvin pathway, is common to the C₃ and C₄ plants.
NTA focuses on how RuBisCO (Ribulose bisphosphate carboxylase-oxygenase) is present in both C₃ and C₄ plants because both use the Calvin pathway for sugar formation. The key trap is assuming C₄ plants lack RuBisCO or have a completely different enzyme for CO₂ fixation—they don't. C₄ plants use PEPcase for initial CO₂ fixation in mesophyll cells, but RuBisCO still catalyzes the Calvin cycle in bundle sheath cells. Remember: PEPcase vs. RuBisCO distinguishes C₃ and C₄ plants' *first* CO₂ fixation step, but the Calvin pathway with RuBisCO is universal to both. This distinction is crucial for photosynthesis pathway questions.
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