Blood cells. Comparison between a scanning election micrograph (SEM left) and transmission electron micrograph (TEM right) of human red blood cells (erythrocytes, red), white blood cells and platelets. The disc-shaped, biconcave erythrocytes transport oxygen to the body's cells and remove carbon dioxide to the lungs. Leukocytes are part of the immune system, defending the body against infection by ingesting pathogens by phagocytosis or by producing antibodies. Thrombocytes are involved with blood clotting. They gather at sites of injury and produce clotting factor. In the images top right to bottom are a basophil, neutrophil, lymphocyte, eosinophil and a monocyte. On the left a macrophage lies between two red blood cells with a small platelet below. The TEM image shows the ultastructure of the white blood cells or leukocytes. Magnification: x5000 when printed 10 centimetres high. For a series of comparisons between SEMs and TEMs see images C047/7006 to C047/7034.