Red blood cells (erythrocytes, red) and a single white blood cell (leucocyte or leukocyte), coloured transmission electron micrograph (TEM). Erythrocytes contain the iron rich protein haemoglobin which binds oxygen. Erythrocytes transport oxygen from the lungs to the rest of the body and also remove carbon dioxide from the body by transporting it to the lungs where it is exhaled. Although only accounting for approximately 1% of blood, leukocytes are essential for good health and work to protect against illness and disease. They are made in the bone marrow and are stored in the blood and lymphatic system. When an area of the body comes under attack from bacteria, a virus or other foreign invaders that may be a threat to health, leukocytes will travel to the affected area to destroy the potential threat and prevent illness. Magnification: x4500 when printed at 10cm wide.