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RuBisCO has a higher affinity for CO2 than for O2. This holds when

  • (a) O2 and CO2 are present in nearly equal amounts Correct
  • (b) O2 is completely absent from the leaf Your answer
  • (c) CO2 is completely absent from the leaf Your answer
  • (d) the leaf temperature falls below 0°C Your answer
Your answer: Correct answer: (a)
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Explanation

Why (a) is correct

RuBisCO has a much greater affinity for CO2 than for O2. So, when the two gases are present in similar amounts, CO2 binds more readily. Only when O2 greatly exceeds CO2 does oxygenation increase.

Why the other options are wrong

  • (b) · your answer If O2 were absent, there would be nothing to compare; the statement is about competition between the two.
  • (c) · your answer If CO2 were absent, RuBisCO could not bind CO2 at all.
  • (d) · your answer Freezing temperatures do not define RuBisCO's preference.
NCERT point: Relative concentration of O2 and CO2 decides which one binds.
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