What is the fate of electrons carried by NADH and FADH2 in aerobic respiration?

• A. They are stored as heat energy.
• B. They are transferred to oxygen to form carbon dioxide.
• C. They are used to synthesize glucose directly.
• D. They are donated to the electron transport chain to drive ATP synthesis.

Answer: (D)

Electrons from NADH and FADH2 power ATP production by the electron transport chain. NADH donates electrons to Complex I and FADH2 to Complex II; as these electrons move through the chain, their energy pumps protons across the inner mitochondrial membrane, creating a proton gradient. Oxygen sits at the end of the chain as the final electron acceptor and combines with these electrons and protons to form water. The proton gradient then drives ATP synthase to convert ADP and Pi into ATP. So the key fate of these electrons is passage through the electron transport chain to oxygen, with the resulting energy used to synthesize ATP.