Which statement about the citric acid cycle is true?

• A. It is aerobic and requires oxygen for full flux
• B. It occurs outside the mitochondria in anaerobic bacteria only
• C. It produces no NADH
• D. It does not require oxygen at all

Answer: (A)

The important idea here is how the citric acid cycle connects to oxygen via the electron transport chain. The cycle itself generates NADH and FADH2, which must be reoxidized to NAD+ and FAD to keep the cycle turning. That reoxidation happens in the electron transport chain, and oxygen serves as the final electron acceptor. So in the presence of oxygen, the cycle can run at full flux because NAD+ and FAD are continuously regenerated. Without oxygen, NADH builds up, NAD+ becomes scarce, and the cycle slows or stops, even though the cycle’s own steps don’t directly consume O2.

That’s why the statement describing the cycle as aerobic and requiring oxygen for full flux is true. It’s not confined to anaerobic bacteria or to outside the mitochondria, and the cycle does produce NADH, so those other options aren’t correct.