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If the light reactions of a chloroplast are stopped (for example, by darkness), the Calvin cycle

(a) soon stops, because ATP and NADPH run out Correct
(b) speeds up, because more CO₂ becomes available Your answer
(c) continues indefinitely Your answer
(d) reverses and releases O₂ Your answer

Your answer: Correct answer: (a)

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Explanation

Why (a) is correct

Without the light reactions, no new ATP and NADPH are made, so the Calvin cycle soon stops.

Why the other options are wrong

(b) · your answer More CO₂ cannot be fixed without ATP and NADPH.
(c) · your answer It cannot continue without ATP and NADPH.
(d) · your answer The Calvin cycle does not release O₂.

NCERT point: The dark reactions depend on the products of the light reactions.

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