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Observe the figure. Identify the stages labelled A, B and C.

  • (a) A - Carboxylation, B - Regeneration, C - Reduction Your answer
  • (b) A - Reduction, B - Decarboxylation, C - Regeneration Your answer
  • (c) A - Carboxylation, B - Reduction, C - Regeneration Correct
  • (d) A - Reduction, B - Carboxylation, C - Regeneration Your answer
Your answer: Correct answer: (c)
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Explanation

Why (c) is correct

The figure shows the Calvin cycle. Stage A is carboxylation (RuBP + CO2 → 3-PGA, by RuBisCO), stage B is reduction (3-PGA → triose phosphate using ATP and NADPH), and stage C is regeneration of RuBP.

Why the other options are wrong

  • (a) · your answer This swaps stages B and C: reduction comes before regeneration.
  • (b) · your answer The Calvin cycle starts with carboxylation, and there is no decarboxylation step in it.
  • (d) · your answer Carboxylation (fixing CO2) is the first stage, not the second.
NCERT point: Calvin cycle: carboxylation → reduction → regeneration of RuBP.
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