As glucose is oxidized during cellular respiration, the coenzyme NAD\(^+\) accepts two electrons and is:

• A. converted to FADH\(_2\)
• B. hydrolyzed to ADP
• C. oxidized to NADH\(_2\)
• D. reduced to NADH

Answer: (D)

Verified step by step guidance

1. Understand the role of NAD\(^+\) in cellular respiration: NAD\(^+\) is a coenzyme that acts as an electron carrier during the process of cellular respiration. It plays a critical role in transferring electrons from one molecule to another.
2. Recall the concept of oxidation and reduction: Oxidation involves the loss of electrons, while reduction involves the gain of electrons. In this case, NAD\(^+\) gains electrons during cellular respiration.
3. Examine the chemical change: NAD\(^+\) accepts two electrons and one proton (H\(^+\)), which reduces it to NADH. This is a reduction reaction because NAD\(^+\) gains electrons.
4. Compare NADH with other molecules mentioned in the options: FADH\(_2\) is another electron carrier, but it is not formed directly from NAD\(^+\). ADP is a product of ATP hydrolysis, unrelated to NAD\(^+\). NADH\(_2\) is not a correct term; NADH is the proper reduced form of NAD\(^+\).
5. Conclude that NAD\(^+\) is reduced to NADH during cellular respiration, as it gains electrons and a proton in the process.