Which molecule is the final electron acceptor in the electron transport chain?

The final electron acceptor in the electron transport chain is oxygen. During cellular respiration, particularly in the process of oxidative phosphorylation, electrons that have been passed down the chain ultimately combine with oxygen molecules and protons to form water. This reaction is crucial because it helps maintain the flow of electrons through the chain, which is essential for creating the proton gradient used to generate ATP. Without oxygen to accept the electrons, the entire process of aerobic respiration would halt, leading to a significant decrease in ATP production and cellular energy.

Other molecules listed, such as carbon dioxide, NADH, and FADH2, play important roles in cellular respiration but do not function as the final electron acceptor. Carbon dioxide is a byproduct released during the Krebs cycle, while NADH and FADH2 are electron carriers that donate electrons to the electron transport chain, rather than accepting them.