Blood cells. Coloured scanning electron micrograph (SEM) of human blood showing a red and white cell ( lymphocyte). Red blood cells (erythrocytes) have a characteristic biconcave-disc shape and are numerous. These large cells contain haemoglobin, a red pigment by which oxygen is transported around the body. They are more numerous than white blood cells, one of which is visible in this sample (white). White blood cells (leucocytes) are rounded cells with microvilli projections from the cell surface. Leucocytes play an important role in the immune response of the body. Magnification: x8500 when printed at 10 centimetres wide.