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Which of the following is the correct sequence in the C₄ pathway?

(a) malate + CO₂ → OAA → PEP → RuBP (sheath) → Calvin cycle Your answer
(b) PEP + CO₂ → OAA → malate → CO₂ (sheath) → Calvin cycle Correct
(c) OAA + CO₂ → PEP → malate → pyruvate (sheath) → Calvin cycle Your answer
(d) RuBP + CO₂ → 3-PGA → OAA → malate → PEP → Calvin cycle Your answer

Your answer: Correct answer: (b)

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Explanation

Why (b) is correct

PEP + CO₂ → OAA (mesophyll) → malate → CO₂ released in the bundle sheath → Calvin cycle.

Why the other options are wrong

(a) · your answer The cycle starts with PEP, not malate.
(c) · your answer OAA is a product, not the acceptor.
(d) · your answer This starts with the C₃ step and mixes up the sequence.

NCERT point: The 3-carbon remainder returns to the mesophyll to regenerate PEP.

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