What is produced when oxygen is reduced during cellular respiration?

During cellular respiration, the process of oxygen reduction leads to the formation of water. This occurs during the final stage of oxidative phosphorylation in the electron transport chain, where electrons are transferred through a series of proteins. As these electrons move, they ultimately reduce molecular oxygen, which combines with protons (hydrogen ions) to form water.

This reaction is critical for the continuation of the electron transport chain, as it allows for an efficient flow of electrons, which in turn drives the synthesis of ATP through chemiosmosis. While the other options—carbon dioxide, NADH, and ATP—are also products or intermediates in cellular respiration, they are not the direct products of the reduction of oxygen itself. Carbon dioxide is produced during the Krebs cycle, NADH is generated during glycolysis and the Krebs cycle, and ATP is generated as a result of the proton gradient created in the electron transport chain. Therefore, water is the specific product resulting from the reduction of oxygen during this metabolic process.