Biology Bioenergetics NUMS 2024
PMDC Verified Question 5 of 67
Which mechanism would be compromised in the absence of cytochrome complex during light reactions of photosynthesis?
A
Reduction of reaction center chlorophyll
B
Photolysis of water
C
Oxidation of primary electron receptor
D
Establishment of proton gradient across thylakoid membrane
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Establishment of proton gradient across thylakoid membrane
Concept:

The cytochrome complex sits between Photosystem II and Photosystem I and acts as a proton pump.

Solution:

  • As electrons move from PSII to PSI, they pass through the cytochrome \( b_6f \) complex.
  • This complex uses the energy of the electrons to actively pump protons (\( H^+ \)) from the stroma into the thylakoid lumen.
  • Without this complex, protons would not be pumped, heavily compromising the establishment of the proton gradient necessary for ATP synthesis.


Why other options are incorrect:

  • Photolysis of water is driven by PSII, upstream of the cytochrome complex.

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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