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In C4 plants, CO2 is fixed

  • (a) once only, by PEPcase in the mesophyll Your answer
  • (b) twice, both times by RuBisCO in the sheath Your answer
  • (c) once only, by RuBisCO in the mesophyll Your answer
  • (d) twice: by PEPcase, then by RuBisCO Correct
Your answer: Correct answer: (d)
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Explanation

Why (d) is correct

In C4 plants, CO2 is fixed twice: first by PEPcase in the mesophyll, and then by RuBisCO in the bundle sheath.

Why the other options are wrong

  • (a) · your answer The CO2 is fixed a second time by RuBisCO.
  • (b) · your answer The first fixation is by PEPcase, not RuBisCO.
  • (c) · your answer C4 mesophyll cells lack RuBisCO.
NCERT point: This is called double carboxylation.
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