Which of the following is a product of the Citric Acid Cycle that enters the electron transport chain?

NADH is a key product of the Citric Acid Cycle that plays a crucial role in cellular respiration, specifically in the process of oxidative phosphorylation within the electron transport chain. During the cycle, NAD+ is reduced to NADH as it accepts electrons during the oxidation of various substrates. This reduction occurs at multiple points within the cycle, such as during the conversion of isocitrate to α-ketoglutarate and the conversion of malate to oxaloacetate.

Once formed, NADH carries high-energy electrons to the electron transport chain located in the inner mitochondrial membrane, where it donates these electrons to complex I. This donation initiates a series of redox reactions that ultimately contribute to the establishment of a proton gradient across the membrane, which is utilized to produce ATP through ATP synthase.

In contrast, fumarate, succinate, and GTP do not directly enter the electron transport chain. Fumarate and succinate are intermediates in the Citric Acid Cycle involved in the conversion processes within the cycle itself. GTP, while it can be converted to ATP and has energy-carrying capabilities, does not enter the electron transport chain directly. Thus, NADH is the correct answer as it is the key electron carrier