what makes something the reducing agent or oxidizing agent?
 The oxygen (O2) is being reduced, so it is the oxidizing agent. The glucose (C6H12O6) is being oxidized, so it is the reducing agent. Every time a reducing agent loses electrons, it forms an oxidizing agent that could gain electrons if the reaction were reversed. Conversely, every time an oxidizing agent gains electrons, it forms a reducing agent that could lose electrons if the reaction went in the opposite direction. 