| 1. | Ecology. the circulation of carbon atoms in the biosphere as a result of photosynthetic conversion of carbon dioxide into complex organic compounds by plants, which are consumed by other organisms: the carbon returns to the atmosphere in the form of carbon dioxide as a result of respiration, decay by fungi, bacteria, etc., and combustion of fossil fuels. |
| 2. | Astrophysics. a cycle of nuclear transformations in the interiors of the stars by means of which hydrogen is gradually converted into helium with the release of nuclear energy. |
| carbon cycle n.
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| car·bon-ni·tro·gen cycle (kär'bən-nī'trə-jən) n. A chain of thermonuclear reactions in which nitrogen isotopes are formed in intermediate stages and carbon acts essentially as a catalyst to convert four hydrogen atoms into one helium atom with the emission of two positrons. The entire sequence is thought to generate significant amounts of energy in the sun and certain other stars. Also called carbon cycle, nitrogen cycle. |
In ecology, the movement of atoms of carbon through the biosphere. Molecules of carbon dioxide are taken in by plants, to be incorporated into their tissues, which may then be eaten by and incorporated into animals. Animals return the carbon to the air in the form of carbon dioxide, and the cycle starts again. (See photosynthesis and respiration.)
carbon cycle n.
The combined processes, including photosynthesis, decomposition, and respiration, by which carbon as a component of various compounds cycles between its major reservoirs—the atmosphere, oceans, and living organisms. Also called carbon dioxide cycle.
carbon cycle
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