carbon cycle

Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Wikipedia.
Related to carbon cycle: nitrogen cycle, water cycle, Oxygen cycle

carbon cycle,

in biology, the exchange of carbon between living organisms and the nonliving environment. Inorganic carbon dioxide in the atmosphere is converted by plants into simple carbohydrates, which are then used to produce more complex substances. Animals eat the plants and are then eaten by other animals. When these life forms die, they decay, breaking down into, among many other things, carbon dioxide, which returns to the atmosphere. Plants and animals also release carbon dioxide during respirationrespiration,
process by which an organism exchanges gases with its environment. The term now refers to the overall process by which oxygen is abstracted from air and is transported to the cells for the oxidation of organic molecules while carbon dioxide (CO2
..... Click the link for more information.
. Animals and some microorganisms require the carbon-containing substances from plants in order to produce energy and as a source of materials for many of their own biochemical reactions; this cycle is vital to them. The process of incorporating carbon dioxide into the molecules of living matter is called fixation. Nearly all carbon dioxide fixation is accomplished by means of photosynthesisphotosynthesis
, process in which green plants, algae, and cyanobacteria utilize the energy of sunlight to manufacture carbohydrates from carbon dioxide and water in the presence of chlorophyll. Some of the plants that lack chlorophyll, e.g.
..... Click the link for more information.
, in which green plants form carbohydrates from carbon dioxide and water, using the energy of sunlight to drive the chemical reactions involved. Green plants use carbohydrates to build the other organic molecules that make up their cells, such as cellulose, fats, proteins, and nucleic acids. Some of these compounds require the incorporation of nitrogen (see nitrogen cyclenitrogen cycle,
the continuous flow of nitrogen through the biosphere by the processes of nitrogen fixation, ammonification (decay), nitrification, and denitrification. Nitrogen is vital to all living matter, both plant and animal; it is an essential constituent of amino acids,
..... Click the link for more information.
). When carbohydrates are oxidized in cells they release the energy stored in their chemical bonds, and some of that energy is also used by the cell to drive other reactions. In the process of oxidation, or respiration, oxygen from the atmosphere (or from water) is combined with portions of the carbohydrate molecule, producing carbon dioxide and water, the compounds from which the carbohydrates were originally formed. However, not all of the carbon atoms incorporated by the plant can be returned to the atmosphere by its own respiration; some remain fixed in the organic materials that make up its cells. When the plant dies, its tissues are consumed by bacteria and other microorganisms, a process called decay. These microorganisms break down the organic molecules of the plant and use them for their own cell-building and energy needs; by their respiration more of the carbon is returned to the atmosphere. The carbon-containing molecules that an animal derives from consuming other organisms are reorganized to build its own cells or oxidized for energy by respiration, releasing carbon dioxide and water. When the animal dies it too is decayed by microorganisms, resulting in the return of more carbon to the atmosphere. Carbon-containing molecules in wood (or other dry, slow-decaying organic materials) may be oxidized by burning, or combustion, also producing carbon dioxide and water. Under conditions prevailing on earth at certain times, green plants have decayed only partially and have been transformed into fossil fuels—coal, peat, and oil. These materials are made of organic compounds formed by the plants; when burned, they too restore carbon dioxide to the atmosphere.

carbon cycle

(Bethe–Weizsächer cycle) A chain of nuclear fusion reactions by which energy may be generated in stars. The overall effect of the cycle is the transformation of hydrogen nuclei into helium nuclei with emission of gamma-ray photons (γ), positrons (e+), and neutrinos (ν). The major sequence of reactions is as follows:
12C + 1H → 13N + γ
13N → 13C + e+ + ν
1H + 13C → 14N + γ
1H + 14N → 15O + γ
15O → 15N + e+ + ν
1H + 15N → 12C + 4He

The carbon nucleus, 12C, reappears at the end of the cycle and can be regarded as a catalyst for the reaction:

1H → 4He + 2e+ + 2ν + 3γ

Because nitrogen (N) and oxygen (O) intermediates are involved, the cycle is often termed the carbon-nitrogen-oxygen cycle or CNO cycle.

The carbon cycle is very strongly temperature dependent and becomes the dominant energy-producing mechanism at core temperatures exceeding about 20 million K. It is therefore thought to be the major source of energy in hot massive stars of spectral types O, B, and A. The carbon cycle was proposed by Hans Bethe and independently by Carl von Weizsächer in 1938. See also proton-proton chain reaction.

carbon cycle

[′kär·bən ‚sī·kəl]
The cycle of carbon in the biosphere, in which plants convert carbon dioxide to organic compounds that are consumed by plants and animals, and the carbon is returned to the biosphere in the form of inorganic compounds by processes of respiration and decay.
(nuclear physics)
References in periodicals archive ?
Plate tectonics is an important piece in the temperature-controlling carbon cycle, as the shifting and sinking plates that cover Earth's surface carry carbon into Earth's interior that later erupts from volcanoes.
I believe our industry has to help balance the carbon cycle by engaging and dialoguing with the brand owner.
The workshop was made possible through support from the Carbon Cycle Interagency Working Group, the U.
The diagram shows how an enormous carbon cycle moves carbon between these reservoirs in a number of sub-cycles.
Coral reefs cover less than one tenth of 1% of the world's oceans, but support more than a quarter of its marine species, while seagrass covers some 10% of all coastal ocean and plays an important part in the global carbon cycle, filtering sea water and supporting marine wildlife.
Speaking in December 2010 while launching Bamboo and Climate Change Mitigation - a report on bamboo's potential role in adaptation, mitigation and sustainable development - during the UN Climate Change Conference in Cancun, Mexico, in December, Hoogendoorn stated that although botanically bamboo is a woody grass and not a tree, "bamboo forests have comparable features to other types of forest regarding their role in the carbon cycle.
They cover challenges for a comprehensive strategy; escaping radioactivity from coal-fired power plants; potential changes in the design, operation, and regulation of coal fired power plants in a carbon constrained future; spatial impacts of tradable permits markets as illustrated by sulfur dioxide emissions; implications of the carbon cycle for climate change and congress; whether carbon dioxide emissions are rising more rapidly than expected; and how US government actions will greatly affect the viability of carbon capture and storage as a key option for mitigating climate change.
If you or your little ones have ever wondered why the sea moves and what might happen if it stops, why the wind blows, how earthquakes happen, and why the weather changes; if you've ever wanted to understand the carbon cycle, the greenhouse effect, and how to forecast the weather by understanding the meaning of different cloud formations, then the activities and amazing pop-ups in How the World Works will provide hours of shared enjoyment as they awaken your minds and hearts to the wonder and beauty of the planet we call home.
2] and the carbon cycle, another poorly understood process is the nitrogen cycle in the vineyard.
Scientists call this a short carbon cycle, maybe 30 to 100 years to grow the trees again.
2] as a waste product, ready to be pumped straight into storage or, better still, recycled using renewable energy (for instance in algae bioreactors back into biomass) which could be converted to bio-char to feed the DCFC in a closed carbon cycle.
She recently received her masters of science in environmental education and works at ESRL as a Logistics Coordinator for the Carbon Cycle Greenhouse Gases Group.