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In CAM plants, CO2 taken in at night is fixed by

  • (a) RuBP carboxylase Your answer
  • (b) both RuBP carboxylase and PEP carboxylase Your answer
  • (c) PEP carboxylase Correct
  • (d) RuBP oxygenase Your answer
Your answer: Correct answer: (c)
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Explanation

Why (c) is correct

In CAM plants, stomata open at night and CO2 is fixed by PEP carboxylase into organic acids (malic acid), which are stored in the vacuole until daytime.

Why the other options are wrong

  • (a) · your answer RuBisCO works in the daytime, using CO2 released from the stored acids.
  • (b) · your answer At night only PEP carboxylase fixes CO2; RuBisCO works by day.
  • (d) · your answer RuBP oxygenase activity is photorespiration, which does not fix CO2.
NCERT point: C4 plants have two carboxylases: PEPcase in the mesophyll and RuBisCO in the bundle sheath.
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