ventilation

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ventilation In biology, the process by which air or water is taken into and expelled from the body of an animal and passed over a surface across which gas exchange takes place. Ventilation mechanisms include breathing, by which air is drawn into the lungs for gas exchange across the wall of the alveoli, and the movements of the floor of a fish's mouth, coupled with those of its gill covers, which draw water across the gills. See also alveolus

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