Asked in ETEA MDCAT 2006 2006

Photorespiration accurs when:

Correct answer: D. Concentration of O2 inside leaf is high

  • A. Stomata are opened
  • B. Day is humid
  • C. Concentration of CO2 inside the leaf is high
  • D. Concentration of O2 inside leaf is high

Explanation

Photorespiration occurs when Rubisco, an enzyme involved in photosynthesis, binds with O2 instead of CO2. This process is more likely when the concentration of O2 inside the leaf is high, which happens when stomata are closed to prevent water loss in hot and dry climates. Consequently, CO2 levels drop, and O2 levels rise, increasing the likelihood of photorespiration. Thus, option D is correct. The other options are incorrect because open stomata (option A) and high CO2 levels (option C) favor photosynthesis, and humid conditions (option B) typically result in open stomata, reducing the chance of photorespiration.

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