A term for the processes by which oxygen reaches body cells and is utilized by them, and by which carbon dioxide is eliminated. Air, containing oxygen, is breathed into the lungs and enters the alveoli. Oxygen diffuses into the blood, which carries it to cells in the body, where it is used to metabolize glucose to provide energy. Carbon dioxide is produced as a waste product and passes into the blood from the body cells. It is transported to the lungs to be breathed out (see respiratory system).


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