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Why do C4 plants not need to "waste" energy on photorespiration even though they use more ATP per glucose?

  • (a) They have no RuBisCO in any of their cells. Your answer
  • (b) They do not carry out the Calvin cycle at all. Your answer
  • (c) They fix CO2 only at night, when it is cool. Your answer
  • (d) Their extra ATP concentrates CO2 and saves fixed carbon. Correct
Your answer: Correct answer: (d)
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Explanation

Why (d) is correct

C4 plants spend extra ATP to regenerate PEP, but this concentrates CO2 around RuBisCO, so they lose no fixed carbon to photorespiration. The extra ATP buys higher net fixation.

Why the other options are wrong

  • (a) · your answer C4 plants do have RuBisCO, in the bundle sheath.
  • (b) · your answer They carry out the Calvin cycle in the bundle sheath.
  • (c) · your answer C4 plants fix CO2 in the day; night fixation is a CAM feature.
NCERT point: C4 plants increase the CO2 concentration at the site of RuBisCO, so photorespiration does not occur and productivity is higher.
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