Now, when our electrons are transferred from Ubiquinon to cytochrome, cytochrome C then travels and attaches to protein complex number four, also known as cytochrome C oxidase. And the main function of protein complex number four is to basically use the electrons that is carried by cytochrome C to reduce our oxygen and form our water. Now, where exactly do we obtain the oxygen? Well, by breathing in. So when we breathe in, when we inhale, we take an oxygen, and that's the same oxygen that is used by protein complex number four. Now, once we reduce our oxygen, this protein complex number four also transports four H plus ions from the mitochondrial matrix to the intermembrane space.