What substance is necessary for cellular respiration?

Oxygen is essential for cellular respiration, particularly in aerobic respiration, which is the process most cells undergo to produce energy. During this process, cells convert glucose and oxygen into adenosine triphosphate (ATP), the energy currency of the cell, while generating carbon dioxide and water as byproducts. Oxygen acts as the final electron acceptor in the electron transport chain, allowing for the efficient production of ATP.

In contrast, while water, carbon dioxide, and glucose are all important to metabolic processes, they do not fulfill the same critical role as oxygen. Water is a product as well as a medium for reactions, carbon dioxide is a waste product formed during cellular respiration, and glucose serves as the primary energy source but does not enable the respiration process itself without the presence of oxygen.