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If NADPH supply to the Calvin cycle stops while ATP and CO₂ are still available, which compound will accumulate first?

(a) RuBP Your answer
(b) oxaloacetic acid Your answer
(c) triose phosphate Your answer
(d) 3-PGA Correct

Your answer: Correct answer: (d)

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Explanation

Why (d) is correct

Without NADPH, 3-PGA cannot be reduced to triose phosphate, so 3-PGA accumulates first.

Why the other options are wrong

(a) · your answer RuBP is used up by carboxylation and is not regenerated, so it falls.
(b) · your answer OAA is not part of the Calvin cycle.
(c) · your answer Triose phosphate cannot form without NADPH, so it falls.

NCERT point: Reduction needs both ATP and NADPH.

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