Red Blood cells are without nucleus and any other organelle except Haemoglobin pigment which carries oxygen.

Red blood cells are formed in Red Bone marrow and there formation is known as erythropeoisis. RBC'S are about 5 million per cubic millimeter of blood in Males whiles as in Females this number is 4.5 million per cubic millimeter of blood. One RBC'S contain 128 million heamoglobin pigments and Each Hemoglobin pigment can carry 4 oxygen molecules. Therefore, one RBC can carry 128x4 oxygen molecules. The shape of RBC'S is biconcave in mammals and in birds,amphibians,reptiles they are biconvex and oval in shape and does contain nucleus. In camel and Llama (Mammals), RBC'S contain nucleus. The surface view of mammalian RBC'S is known as Raulaex (check spelling, apology for spelling mistakes). Structurally Hemoglobin is formed of Heme and globin protein. It is the heme which carry oxygen molecules.The structure of Heme contain Four pyrrole rings having Fe 2+ ion in the center linked to (Nitrogen) four pyrrole rings via coordinate bonds and two histidine molecules above and below this structure know as proximal histidine and distal histidine via coordinate bonds. When oxygen is delivered to the Heme, the heme changes its configuration during the loading of oxygen and binding capacity of Haemoglobin to oxygen molecules increases, a property known as Cooperative Binding.