STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Lung tissue. Coloured scanning electron micrograph (SEM) of a section through a lung, showing numerous alveoli (spaces) and alveolar ducts. Alveoli are tiny airsacs that are the site of gas exchange, where oxygen from inhaled air is taken up by the blood, and carbon dioxide is released to be exhaled. Magnification: x20 when printed 10 centimetres wide.
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