In cellular respiration, which molecule is the final electron acceptor?

In cellular respiration, which molecule is the final electron acceptor?

• A. Water
• B. Carbon dioxide
• C. Oxygen
• D. NAD+

Answer: (C)

The final electron acceptor in cellular respiration is oxygen. In the electron transport chain, electrons are passed along a series of protein complexes, and their energy pumps protons across the mitochondrial membrane to create a proton gradient. Oxygen sits at the end of that chain and combines with the electrons and with protons to form water. This step is essential because it keeps the chain flowing and allows ATP synthase to generate ATP from the proton gradient. If oxygen isn’t available, the chain backs up, NADH can’t be reoxidized to NAD+, and oxidative phosphorylation halts, forcing the cell to rely on less efficient pathways like fermentation. Water isn’t the acceptor itself; it’s the product formed when oxygen receives the electrons and protons. Carbon dioxide is produced earlier in metabolism (in the TCA cycle) and expelled as a waste gas. NAD+ is an electron carrier that accepts electrons earlier in metabolism to form NADH and must be regenerated back to NAD+; it is not the final recipient of electrons in the chain.

The final electron acceptor in cellular respiration is oxygen. In the electron transport chain, electrons are passed along a series of protein complexes, and their energy pumps protons across the mitochondrial membrane to create a proton gradient. Oxygen sits at the end of that chain and combines with the electrons and with protons to form water. This step is essential because it keeps the chain flowing and allows ATP synthase to generate ATP from the proton gradient. If oxygen isn’t available, the chain backs up, NADH can’t be reoxidized to NAD+, and oxidative phosphorylation halts, forcing the cell to rely on less efficient pathways like fermentation.

Water isn’t the acceptor itself; it’s the product formed when oxygen receives the electrons and protons. Carbon dioxide is produced earlier in metabolism (in the TCA cycle) and expelled as a waste gas. NAD+ is an electron carrier that accepts electrons earlier in metabolism to form NADH and must be regenerated back to NAD+; it is not the final recipient of electrons in the chain.