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CO2 supply to an illuminated plant is suddenly cut off. Which change is expected in the chloroplast?

  • (a) 3-PGA rises and RuBP falls Your answer
  • (b) ATP falls sharply Your answer
  • (c) both rise Your answer
  • (d) RuBP rises and 3-PGA falls Correct
Your answer: Correct answer: (d)
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Explanation

Why (d) is correct

Without CO2, RuBP is not carboxylated, so it builds up, while 3-PGA keeps being reduced and falls.

Why the other options are wrong

  • (a) · your answer This is the effect of darkness, not of CO2 removal.
  • (b) · your answer Light reactions continue, so ATP does not fall sharply.
  • (c) · your answer 3-PGA falls, because no more is formed.
NCERT point: Carboxylation links CO2 supply to RuBP and PGA levels.
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