Which complex of the electron transport chain directly reduces molecular oxygen to water?
- A Complex I (NADH dehydrogenase)
- B Complex IV (cytochrome c oxidase) ✓
- C Complex III (cytochrome bc1 complex)
- D Complex II (succinate dehydrogenase)
Correct answer: B. Complex IV (cytochrome c oxidase)
Explanation
Complex IV (cytochrome c oxidase) transfers electrons from cytochrome c to molecular oxygen, reducing it to water (O2 + 4H+ + 4e- → 2H2O). It also pumps protons across the inner membrane. Distractor A is wrong because Complex I passes electrons to ubiquinone. Distractor C is wrong because Complex III passes electrons to cytochrome c. Distractor D is wrong because Complex II passes electrons to ubiquinone.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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