What happens to the electron transport chain (ETC) in the absence of oxygen, and how does this affect ATP production?

• A. The ETC accelerates, increasing ATP production.
• B. The ETC continues to function normally using sunlight instead of oxygen.
• C. The ETC uses lactic acid as a final electron acceptor instead of oxygen.
• D. The ETC shuts down, preventing oxidative phosphorylation and reducing ATP production significantly.

Answer: (D)