The answer is to function as the final electron acceptor in the electron transport chain. It is the only place that O2 partakes in the cellular respiration is at the end of the electron transport chain as the final electron acceptor. Oxygen's high affinity for electrons safeguards its success in this role. Its assistances to driving electron transport, forming a proton gradient, and synthesizing ATP are all indirect effects of its role as the terminal electron acceptor.
