Question

The final electron acceptor in ETS of cellular respiration is

• A. Hydrogen
• B. water
• C. molecular oxygen
• D. Cyt. a. a3

Hint:

Oxygen is essential for aerobic respiration because it acts as the final electron acceptor, forming water at the end of ETS.

Answer 1

The Correct Option is C

Concept:
The Electron Transport System (ETS) is the final stage of aerobic cellular respiration, occurring in the inner mitochondrial membrane. Electrons are transferred through a series of carriers and ultimately reduce a terminal electron acceptor.

Step 1: Understand the flow of electrons in ETS. Electrons from NADH and FADH$_2$ pass through various complexes (I, II, III, IV) and cytochromes. At the end of the chain, these electrons must be accepted by a final molecule to prevent blockage of the chain.

Step 2: Identify the final electron acceptor. Molecular oxygen (\(O_2\)) acts as the terminal electron acceptor. It combines with electrons and protons to form water: \[ O_2 + 4e^- + 4H^+ \rightarrow 2H_2O \]

Step 3: Analyze the given options.
• (A) Hydrogen → Not the final acceptor $\times$
• (B) Water → Product, not acceptor $\times$
• (C) Molecular oxygen → Final electron acceptor \checkmark
• (D) Cyt. a.a$_3$ → Carrier (cytochrome oxidase), not final acceptor $\times$

Step 4: Conclusion. Thus, the final electron acceptor in ETS is: \[ \text{Molecular oxygen} \]