Oxygen serves as the final electron acceptor in the electron transport chain during the process of cellular respiration.

Cellular respiration is a metabolic pathway that cells utilize to extract energy from nutrients. This process primarily involves the breakdown of glucose and other molecules in the presence of oxygen to generate adenosine triphosphate (ATP), which acts as the main energy currency of the cell. Oxygen is essential in this process, especially in the final stage known as oxidative phosphorylation.

Oxidative phosphorylation occurs within the mitochondria, where electrons are transferred from electron carriers to oxygen via a series of protein complexes collectively referred to as the electron transport chain. This electron transfer leads to the movement of protons across the mitochondrial membrane, creating an electrochemical gradient. The energy stored in this gradient is subsequently harnessed to synthesize ATP from adenosine diphosphate (ADP) and inorganic phosphate ($P_i$).

The function of oxygen as the final electron acceptor is critical for the ongoing operation of this process. When oxygen accepts electrons, it also combines with protons from the surrounding environment to form water. This reaction is vital because it prevents the build-up of electrons and protons within the system, which would otherwise disrupt the electrochemical gradient and inhibit ATP production.

In the absence of oxygen, the electron transport chain cannot function, forcing the cell to rely on less efficient energy production methods such as anaerobic respiration or fermentation. While these processes do not require oxygen, they yield significantly lower amounts of ATP compared to aerobic respiration. Thus, the availability of oxygen significantly enhances a cell’s capacity to produce energy and perform its functions.

In conclusion, the role of oxygen in cellular respiration is to act as the final electron acceptor in the electron transport chain. This function is essential for maintaining the electrochemical gradient needed for ATP synthesis and for preventing the accumulation of electrons and protons in the system. Without oxygen, cells would be constrained to less efficient energy production pathways.