In aerobic cellular respiration, which molecule serves as the terminal (final) electron acceptor in the electron transport chain?

Introduction / Context:
Respiratory chains transfer electrons from reduced carriers to a terminal acceptor, generating a proton motive force to drive ATP synthesis. The identity of the terminal acceptor distinguishes aerobic respiration from various forms of anaerobic respiration.

Given Data / Assumptions:

• The context is aerobic respiration.
• Standard mitochondrial or bacterial electron transport is implied.
• Common alternate acceptors (e.g., nitrate) are considered anaerobic.

Concept / Approach:
In aerobic respiration, oxygen (O2) is reduced to water at complex IV (cytochrome c oxidase). This high-potential acceptor allows maximal free energy capture, supporting efficient ATP production compared with most anaerobic acceptors.

Step-by-Step Solution:

Verification / Alternative check:
Inhibitors like cyanide block cytochrome c oxidase, preventing reduction of O2 and halting aerobic respiration, demonstrating O2’s role as terminal acceptor.

Why Other Options Are Wrong:
Nitrogen/Nitrate: Nitrate (NO3−) can be a terminal acceptor in anaerobic respiration (denitrification), not aerobic. Hydrogen: Is an electron donor in many pathways, not the terminal acceptor here.

Common Pitfalls:
Confusing “presence of oxygen” with oxidative phosphorylation generally; the key is that O2 is the final acceptor, forming water.

Final Answer:
oxygen