Page "Red blood cell" Paragraph 34

The blood's red color is due to the spectral properties of the hemic iron ions in hemoglobin.

Each human red blood cell contains approximately 270 million of these hemoglobin biomolecules, each carrying four heme groups ; hemoglobin comprises about a third of the total cell volume.

This protein is responsible for the transport of more than 98 % of the oxygen ( the remaining oxygen is carried dissolved in the blood plasma ).

The red blood cells of an average adult human male store collectively about 2. 5 grams of iron, representing about 65 % of the total iron contained in the body.

( See Human iron metabolism.