Which statement correctly describes the relationship between cellular respiration and oxygen?

Which statement correctly describes the relationship between cellular respiration and oxygen?

• A. Cellular respiration never uses oxygen.
• B. Cellular respiration uses oxygen only during fermentation.
• C. Cellular respiration produces oxygen.
• D. Cellular respiration requires oxygen to produce ATP in mitochondria.

Answer: (D)

Oxygen serves as the final electron acceptor in the mitochondrial electron transport chain, which makes aerobic ATP production in mitochondria possible. During cellular respiration, nutrients are broken down to generate NADH and FADH2, which carry electrons to the chain. Oxygen accepts those electrons and, with protons, forms water, allowing the chain to keep functioning and ATP to be produced efficiently. Without oxygen, the chain stalls, NAD+ and FAD become scarce, and ATP yield from mitochondria drops dramatically, though some cells can sustain a small amount of ATP via glycolysis alone (fermentation) in the absence of oxygen. So, the correct idea is that cellular respiration requires oxygen to produce ATP in mitochondria. The other statements are inconsistent with how respiration uses oxygen: it does not avoid oxygen entirely, it is not limited to a role in fermentation, and it does not generate oxygen.

Oxygen serves as the final electron acceptor in the mitochondrial electron transport chain, which makes aerobic ATP production in mitochondria possible. During cellular respiration, nutrients are broken down to generate NADH and FADH2, which carry electrons to the chain. Oxygen accepts those electrons and, with protons, forms water, allowing the chain to keep functioning and ATP to be produced efficiently. Without oxygen, the chain stalls, NAD+ and FAD become scarce, and ATP yield from mitochondria drops dramatically, though some cells can sustain a small amount of ATP via glycolysis alone (fermentation) in the absence of oxygen.

So, the correct idea is that cellular respiration requires oxygen to produce ATP in mitochondria. The other statements are inconsistent with how respiration uses oxygen: it does not avoid oxygen entirely, it is not limited to a role in fermentation, and it does not generate oxygen.