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noun
1.
the act of respiring; inhalation and exhalation of air; breathing.
2.
Biology.

the sum total of the physical and chemical processes in an organism by which oxygen is conveyed to tissues and cells, and the oxidation products, carbon dioxide and water, are given off.
an analogous chemical process, as in muscle cells or in anaerobic bacteria, occurring in the absence of oxygen.

noun
1.
the process in living organisms of taking in oxygen from the surroundings and giving out carbon dioxide (external respiration). In terrestrial animals this is effected by breathing air
2.
the chemical breakdown of complex organic substances, such as carbohydrates and fats, that takes place in the cells and tissues of animals and plants, during which energy is released and carbon dioxide produced (internal respiration)

respiration res·pi·ra·tion (rěs’pə-rā’shən)
n.
Abbr. R

The act or process of inhaling and exhaling; breathing. Also called ventilation.

The act or process by which an organism without lungs, such as a fish or plant, exchanges gases with its environment.

The oxidative process occurring within living cells by which the chemical energy of organic molecules is released in a series of metabolic steps involving the consumption of oxygen and the liberation of carbon dioxide and water.

Any of various analogous metabolic processes by which organisms, such as fungi, obtain energy from organic molecules.

respiration
(rěs’pə-rā’shən)

The process by which organisms exchange gases, especially oxygen and carbon dioxide, with the environment. In air-breathing vertebrates, respiration takes place in the lungs. In fish and many invertebrates, respiration takes place through the gills. Respiration in green plants occurs during photosynthesis.

See cellular respiration.

respiration definition

The conversion of oxygen by living things into the energy by which they continue life. Respiration is part of metabolism.

Note: Carbon dioxide is a waste product of respiration.