The process that uses high energy electrons to convert ADP to ATP is known as oxidative phosphorylation. ATP, or adenosine triphosphate, is the molecule that provides the energy cells need to function.
ATP is created through the Krebs Cycle and glycolysis, both of which combine glucose and oxygen to form ATP and carbon dioxide. This process also creates NADH and FADH2, both of which store large amounts of glucose in high-energy electrons. These electrons are stored in pairs, which give up their energy as they are passed to oxygen molecules through the electron transport system during oxidative phosphorylation. The energy given off by these electrons is then used to convert ATP back to ADP.