What is the main function of oxygen in oxidative phosphorylation?

The main function of oxygen in oxidative phosphorylation is to serve as the final electron acceptor in the electron transport chain (ETC). As electrons are passed along the chain, they lose energy, which is used to pump protons across the inner mitochondrial membrane, creating a proton gradient. At the end of this chain, oxygen combines with these electrons and protons to form water. This reaction is crucial because it prevents the backup of electrons in the chain, which would halt the process of oxidative phosphorylation entirely. Without oxygen to accept the electrons, the entire electron transport chain would cease to function, leading to a cessation of ATP production via this pathway.

The other options pertain to different aspects of cellular respiration or are unrelated to the primary role of oxygen. Oxygen is not a substrate for the Krebs cycle, nor does it provide energy directly for ATP synthesis; instead, it plays a vital role in facilitating the overall process that leads to ATP production. Additionally, while various metabolic processes can influence pH, the primary function of oxygen in this context does not involve increasing the cellular pH.