And that's why we call it oxidative phosphorylation because we actually use an oxygen on the electron transport chain. So, remember, the citric acid cycle doesn't actually require oxygen itself, but the electron transport chain does. And we need the citric acid cycle to generate the majority of the NADH molecules and these Fadh two molecules. So the electron transport chain is a series of proteins that receive these high energy electrons from NADH molecules and Fadh two molecules and they move these electrons along the inner membrane of the mitochondria. And the final acceptor of these electrons is oxygen. So we reduce oxygen to form the H 20 molecules.