What is the purpose of the oxygen we breathe in?

Oxygen serves a vital role in cellular respiration, especially during the electron transport chain, which is the final stage of aerobic respiration. The electron transport chain takes place in the inner mitochondrial membrane, where a series of protein complexes transfer electrons derived from NADH and FADH2, which are generated in earlier stages like glycolysis and the Krebs cycle.

As electrons are passed through these protein complexes, they lose energy, which is used to pump protons (H+ ions) across the mitochondrial membrane, creating a proton gradient. This gradient is crucial for the synthesis of ATP through chemiosmosis, facilitated by ATP synthase.

Once the electrons reach the end of the electron transport chain, they need a final acceptor to prevent a backup of the chain and to allow for the continued flow of electrons. Oxygen is that final electron acceptor. It binds with the electrons and protons to form water, a harmless byproduct. This process of oxygen accepting electrons is essential for maintaining the flow of electrons through the chain, enabling the continuous production of ATP.

In summary, the primary purpose of the oxygen we breathe is to act as the final electron acceptor in the electron transport chain, thereby facilitating the efficient production of ATP during aerobic respiration.