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A C₄ plant is given ¹⁴CO₂ for a very short time. The label will first appear in

(a) RuBP in mesophyll cells Your answer
(b) glucose in bundle sheath cells Your answer
(c) oxaloacetic acid in mesophyll cells Correct
(d) 3-PGA in bundle sheath cells Your answer

Your answer: Correct answer: (c)

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Explanation

Why (c) is correct

In a C₄ plant, CO₂ is first fixed by PEPcase in the mesophyll, so the label first appears in oxaloacetic acid there.

Why the other options are wrong

(a) · your answer C₄ mesophyll cells have no RuBisCO, so RuBP is not the first labelled compound.
(b) · your answer Glucose is labelled much later.
(d) · your answer 3-PGA in the bundle sheath is labelled later.

NCERT point: This is how Hatch and Slack found the C₄ pathway.

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