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CO2 is a major limiting factor for photosynthesis because

  • (a) it is absorbed by roots Your answer
  • (b) its concentration in air is very low Correct
  • (c) it is toxic to plants Your answer
  • (d) it is not used in the light reaction Your answer
Your answer: Correct answer: (b)
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Explanation

Why (b) is correct

CO2 is a major limiting factor because its concentration in the air is very low (0.03 to 0.04%).

Why the other options are wrong

  • (a) · your answer CO2 for photosynthesis enters through stomata, not roots.
  • (c) · your answer CO2 is not toxic at normal levels.
  • (d) · your answer Not being used in the light reaction does not make it limiting.
NCERT point: Raising CO2 to about 0.05% increases fixation.
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Practise Photosynthesis in Higher Plants
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