Red blood cell. Colored scanning electron micrograph (SEM) of a red blood cell. This disc-shaped cell, also known as an erythrocyte, transports oxygen from the lungs to the tissues during respiration. It contains large amounts of hemoglobin, a pigmented protein which binds oxygen. It is one of several types of blood cell, all of which develop from stem cells in the bone marrow. The formation of a red blood cell is known as erythropoiesis and takes about five days. Magnification: 11,200 at 6x7cm size.