Now, inside a single red blood cell, we have about 280,000,000 of these individual hemoglobin proteins. And because hemoglobin carries four oxygens, four multiplied by that gives us over 1 billion of these oxygen molecules, is carried in a single red blood cell. So red blood cells are very, very efficient at their job. They can carry a lot of these, many of these oxygen molecules. Now, another important point that I should make is because red blood cells don't actually have any mitochondria, that implies they don't actually use cellular respiration. So that means they do not use up the oxygen supply that is found within our cell.