Three Stages of Calvin Cycle — NEET Biology
✅ Asked in NEET 2025NEET 2025: Identify the correct sequence of events in the Calvin cycle:
NEET 2025: Identify the correct sequence of events in the Calvin cycle:
Observe the given figure. Identify the different stages labelled with alphabets by selecting the correct option:
Answer & NCERT explanation
Correct answer: B — Carboxylation → Reduction → Regeneration
The Calvin cycle has three sequential phases: (1) Carboxylation - CO₂ fixation with RuBP to form 3-PGA, (2) Reduction - 3-PGA reduced to triose phosphate using ATP and NADPH, (3) Regeneration - RuBP is regenerated from triose phosphate using ATP.
Read more NCERT concept on the PYQ
For ease of understanding, the Calvin cycle can be described under three stages: carboxylation, reduction and regeneration.
The Calvin cycle has three distinct stages: carboxylation (CO₂ fixation via RuBisCO), reduction (using ATP and NADPH to form G3P), and regeneration (regenerating RuBP to restart the cycle). Students often confuse the order of stages or mix them with light reactions, leading to incorrect answers. They may also forget that carboxylation is the first committed step where CO₂ actually enters organic molecules. Remember: carboxylation fixes CO₂, reduction builds sugars using energy, regeneration maintains the cycle's continuity. This three-step framework is fundamental to understanding photosynthetic efficiency and is repeatedly tested in NEET because it directly connects light reactions to carbon fixation outcomes.
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