Biconcave disc characteristic red color and transport oxygen from the lungs to the tissues. Mature red blood cells are round and biconcave because they lack a nucleus and unlike other cells, red cells require a small amount of oxygen for its metabolism and most oxygen is freed into the tissues. The absence of nucleus, ribosomes, and mitochondria partly contributes to the red blood cell’s disc-like structure which leaves room for hundreds of millions of hemoglobin molecules found within the cells. Hemoglobin is a red and iron-rich protein that merges with oxygen to carry oxygen from the lungs to the body tissues. Both
Red blood cell (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. Red blood cells in mammals "anucleate" when mature, meaning that they lack a cell nucleus. In comparison, the red blood cells of other vertebrates have nuclei; the only known exceptions are salamanders of the genus "Batrachoseps" and fish of the genus "Maurolicus". The elimination of the nucleus in vertebrate red blood cells has been offered as an explanation for the subsequent accumulation