What is the role of oxygen in metabolism?

Oxygen is an election acceptor in the reduction-oxidation reaction going on inside almost every living cell. Think of cellular metabolism in your body as a motor, in order to make things go there needs to be electron flow (in an electric motor there are positive and negative wires to conduct flow). At the molecular Biology level the elections move between atoms, with the cell as the circuit. The 'force' driving the elections through the metabolic process from one 'reduced' atom (usually organic carbon from the food you eat) to one 'oxidized' atom ( an oxygen in O2) is oxygen's 'election affinity' (like magnetism for electrons), remember chemistry 101? The completed circuit usually produces carbon dioxide, wherein the carbon has lost electrons and oxygen has gained them.