carbon dioxide of respiration is formed during
carbon dioxide. A colorless, odorless gas, CO 2, that is present in the atmosphere and is formed when any fuel containing carbon is burned. It is breathed out of an animal's lungs during respiration, produced by the decay of organic matter, and used by plants in photosynthesis. colorless, odorless, incombustible gas, CO 2, that is formed during respiration, combustion, and organic decomposition, is an essential component in photosynthesis, and is used in food refrigeration, carbonated beverages, inert atmospheres, fire extinguishers, and aerosols. Also called carbonic acid gas.