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. And a single hemoglobin can carry a maximum of four oxygen molecules one in each one of these four hein groups. Now, when our hemoglobin is fully saturated with oxygen, we call it oxymoglobin. But when the hemoglobin isn't actually carrying any oxygen, in that case, we call it deoxyhemogglobin.