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Given below are two statements.
Statement I: In C3 plants, some O2 binds to RuBisCO, and hence CO2 fixation is decreased.
Statement II: In C4 plants, mesophyll cells show very little photorespiration, while bundle sheath cells do not show photorespiration.
In the light of the above statements, choose the correct answer.

  • (a) Both Statement I and Statement II are true. Your answer
  • (b) Both Statement I and Statement II are false. Your answer
  • (c) Statement I is true but Statement II is false. Correct
  • (d) Statement I is false but Statement II is true. Your answer
Your answer: Correct answer: (c)
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Explanation

Why (c) is correct

Statement I is true: in C3 plants some O2 binds to RuBisCO, so less CO2 is fixed. Statement II is false: C4 mesophyll cells have no RuBisCO, so they cannot photorespire at all, and NCERT says photorespiration does not occur in C4 plants.

Why the other options are wrong

  • (a) · your answer Statement II is not true: the mesophyll of C4 plants lacks RuBisCO, so it shows no photorespiration.
  • (b) · your answer Statement I is true: O2 competes with CO2 for RuBisCO in C3 plants.
  • (d) · your answer Statement I is true, so this option cannot be correct.
NCERT point: C4 plants: PEPcase in the mesophyll (no RuBisCO); RuBisCO in the bundle sheath, where the CO2 concentration is kept high.
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