Biology Bioenergetics SZABMU 2024
PMDC Verified Question 21 of 67
What is the efficiency of \( CO_2 \) fixation in plants with photorespiration?
A
20%
B
25%
C
45%
D
75%
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 75%
Concept:

Photorespiration is a wasteful process where RuBisCO accidentally binds to Oxygen instead of Carbon Dioxide, draining the plant's resources.

Solution:

  • In standard \( C_3 \) plants, when stomata close on hot days, \( O_2 \) builds up and outcompetes \( CO_2 \).
  • This oxygenase activity can undercut the plant's photosynthetic output by roughly 25%.
  • Consequently, the remaining operational efficiency of actual \( CO_2 \) fixation drops down to about 75%.


Why other options are incorrect:

  • 25% represents the amount of efficiency lost, not the amount retained.
  • 20% and 45% do not align with standard physiological metrics for photorespiratory drag.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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