And this iron atom can bind oxygen via an oxidation reduction process. So the iron is capable of changing its oxidation state via a redux reaction and that can bind our oxygen. Now, one heme group can bind a single diatomic oxygen molecule. So that means because we have four heme groups, in a single hemoglobin, a maximum of four diatomic oxygen molecules can be carried by our hemoglobin. So we see that as oxygen diffuses across our respiratory membrane from the alveoli and into the capillaries in the lungs, our red blood cells pick up our oxygen. And inside the red blood cells, the hemoglobin then picks up the oxygen.