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MBBS QUESTION #10342
Question 1
Sequential electron carriers of the respiratory chain are arranged in order of progressively more positive redox potential, culminating in molecular oxygen as the final electron acceptor. This arrangement reflects:
  • A thermodynamically favorable, ordered transfer of electrons from carriers of more negative (higher-energy) redox potential toward carriers of more positive (lower-energy) redox potential, releasing free energy used to pump protons across the inner mitochondrial membrane✔️
  • An essentially random, non-sequential process with no defined order
  • A physiological reversal of the normal direction of electron flow
  • No meaningful relationship between redox potential and the direction of electron flow
Correct Answer Explanation
Electrons flow spontaneously from carriers with more negative redox potential (better electron donors) to those with more positive redox potential (better electron acceptors), releasing free energy at each step; three of these transitions (at Complexes I, III, and IV) release enough energy to drive proton pumping, ultimately powering ATP synthase.