Q.31 The terminal electron acceptor during mitochondrial respiration is
(A) O2 (B) FAD+
(C) NAD+
(D) ATP
Mitochondrial Terminal Electron Acceptor: O2 MCQ Solution
Oxygen (O₂) serves as the terminal electron acceptor in the mitochondrial electron transport chain during aerobic respiration. This makes option (A) correct.
Electron Transport Chain Overview
The mitochondrial ETC consists of four complexes (I-IV) in the inner membrane, transferring electrons from NADH/FADH₂ to O₂.
Electrons flow: Complex I/II → Q → Complex III → cyt c → Complex IV → O₂ (reduced to H₂O), pumping protons to drive ATP synthesis.
O₂’s high reduction potential ensures irreversible flow, preventing electron backup.
Correct Answer: O₂ Role
Option (A) O₂ receives electrons at Complex IV (cytochrome c oxidase), forming water: 4e−+4H++O2→2H2O.
Without O₂, the chain halts, causing hypoxia and ROS buildup in anaerobic conditions.
This defines aerobic respiration, yielding ~30-32 ATP per glucose.
Options Analysis Table
| Option | Molecule | Role in ETC | Why Incorrect |
|---|---|---|---|
| (A) O₂ | Oxygen | Terminal acceptor at Complex IV | Correct |
| (B) FAD⁺ | Flavin adenine dinucleotide | Accepts electrons at Complex II (succinate dehydrogenase); intermediate carrier | Not terminal |
| (C) NAD⁺ | Nicotinamide adenine dinucleotide | Accepts electrons via Complex I; cycles back from TCA cycle | Upstream donor |
| (D) ATP | Adenosine triphosphate | Energy product of oxidative phosphorylation; not an electron carrier | No electron role |
FAD⁺/NAD⁺ regenerate via earlier complexes, while ATP forms via ATP synthase.
Exam Significance
This fundamental concept appears in NEET/CSIR bioenergetics sections, distinguishing aerobic vs. anaerobic respiration.
Cyanide poisoning blocks Complex IV, highlighting O₂’s essential endpoint.
