Biology Bioenergetics NUMS 2022
PMDC Verified Question 42 of 67
During photosynthesis, \( CO_2 \) works as:
A
Proton donor
B
Electron donor
C
Proton accepter
D
Source of \( O_2 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Proton accepter
Concept:

During the Calvin cycle (light-independent reactions), carbon dioxide is reduced to form glyceraldehyde 3-phosphate (G3P).

Solution:

  • In the reduction phase of the Calvin cycle, \( CO_2 \) receives protons and electrons from \( NADPH \) (which is oxidized to \( NADP^+ \)).
  • Because it accepts protons during this reduction, \( CO_2 \) acts as a proton acceptor.


Why other options are incorrect:

  • \( CO_2 \) does not donate protons or electrons.
  • Water (\( H_2O \)), not \( CO_2 \), is the source of oxygen evolved during photosynthesis.

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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