Which statement about NAD+/NADH is true?

• A. NADH donates electrons to the electron transport chain
• B. NAD+ is reduced to NADH in glycolysis
• C. NAD+ accepts electrons to become NADH, which donates electrons to the chain
• D. NAD+ is a cofactor for ATP synthase

Answer: (C)

NAD+/NADH act as redox carriers that shuttle reducing equivalents from metabolism to the electron transport chain. The true statement captures the whole cycle: NAD+ accepts electrons (and a proton) to become NADH, and that NADH then donates those electrons to the electron transport chain to drive ATP production. This describes the direction of electron flow and the roles of the two forms across glycolysis and respiration. NAD+ is not a cofactor for ATP synthase, and while glycolysis does generate NADH by reducing NAD+, the essential idea is the NAD+/NADH interconversion and its delivery of electrons to the chain.