What happens to the electrons carried by NADH and FADH2 in the citric acid cycle during cellular respiration?

A. They are used to convert glucose to pyruvate in glycolysis.

B. They are used to reduce molecular oxygen to water in the electron transport chain.

C. They are used to oxidize pyruvate to acetyl‑CoA.

D. They are used to drive the phosphorylation of ADP to ATP.

Answer : B. They are used to reduce molecular oxygen to water in the electron transport chain.

Explanation:

oxygen is the final electron acceptor in the electron transport chain (ETC) of cellular respiration.

If electrons were not accepted by oxygen, the concentration gradients which drives Co-enzymes NADH and FADH2 from the citric acid cycle to the matrix of mitochondrial for ETC will seize; proton pumps across the mitochondrial intramembranes will not exist.

Therefore no proton gradient for ATPase synthase to synthesise ATP from ADP. Thus no ETC

conclusively, oxygen must be reduced by the electron.

Note:

option D; is near to the correct option, but it is wrong because, it is the energy supplied by the proton gradient that drives the phosphorylation of ADP to ATP, not the electron. The electron only provided the potential energy for the pumping of the protons, but not for the direct phosphorylation