Which two electron carriers donate electrons to the electron transport chain?

The correct answer is based on the roles that NADH and FADH2 play in cellular respiration, specifically in the process of oxidative phosphorylation. Both NADH and FADH2 are key electron carriers that are produced during the earlier stages of glucose metabolism, such as glycolysis and the Krebs cycle.

NADH is generated from reactions involving the oxidation of glucose and is capable of carrying high-energy electrons. Once formed, NADH transports these electrons to the electron transport chain, where they are passed through a series of protein complexes. This electron transfer is essential for the production of ATP as it contributes to the establishment of a proton gradient across the inner mitochondrial membrane.

Similarly, FADH2, which is formed during the Krebs cycle, also donates electrons to the electron transport chain. While FADH2 contributes electrons at a slightly later stage in the chain compared to NADH, both carriers ultimately facilitate the transfer of energy required for ATP synthesis.

In contrast, ATP is not primarily an electron carrier but is rather the main energy currency of the cell. NAD+ serves as an oxidized form of NADH and is involved in accepting electrons during metabolic reactions, but it does not donate them to the electron transport chain. Therefore, the pairing of