DR GARY GAUGLER / SCIENCE PHOTO LIBRARY DR GARY GAUGLER / SCIENCE PHOTO LIBRARY
Red blood cells. Coloured scanning electron micrograph (SEM) of red blood cells (erythrocytes). These biconcave, disc-shaped cells carry oxygen in the blood. They also carry carbon dioxide produced by respiration to the lungs to be exhaled. Their red colour is due to haemoglobin, a protein that binds to oxygen and carbon dioxide. In humans they measure about 8 micrometres in diameter.
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