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In C4 plants, CO2 first combines with

  • (a) phosphoglyceric acid Your answer
  • (b) phosphoenol pyruvate Correct
  • (c) phosphoglyceraldehyde Your answer
  • (d) ribulose diphosphate Your answer
Your answer: Correct answer: (b)
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Explanation

Why (b) is correct

In C4 plants, CO2 first combines with phosphoenol pyruvate (PEP) in the mesophyll cells to form oxaloacetic acid.

Why the other options are wrong

  • (a) · your answer PGA is a product of CO2 fixation by RuBisCO, not the first acceptor.
  • (c) · your answer Phosphoglyceraldehyde is formed in the reduction stage of the Calvin cycle.
  • (d) · your answer Ribulose diphosphate is the acceptor in C3 plants and in the bundle sheath of C4 plants, not the first one.
NCERT point: PEP (3C) + CO2 → OAA (4C), catalysed by PEP carboxylase.
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