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How many molecules of ATP and NADPH are required for every molecule of CO₂ fixed in the Calvin cycle?

(a) 2 ATP and 3 NADPH Your answer
(b) 2 ATP and 2 NADPH Your answer
(c) 3 ATP and 3 NADPH Your answer
(d) 3 ATP and 2 NADPH Correct

Your answer: Correct answer: (d)

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Explanation

Why (d) is correct

To fix one molecule of CO₂, the Calvin cycle uses 3 ATP and 2 NADPH: 2 ATP and 2 NADPH for reduction of PGA, and 1 more ATP for regenerating RuBP.

Why the other options are wrong

(a) · your answer The cycle needs more ATP (3) than NADPH (2), not the other way round.
(b) · your answer Regeneration of RuBP needs one more ATP, so it is 3 ATP, not 2.
(c) · your answer Only 2 NADPH are used per CO₂, in the reduction step.

NCERT point: Per glucose (6 CO₂): 18 ATP and 12 NADPH.

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