Environment and Ecology

The Earth’s Environment

What is the carbon cycle?

To survive, every organism must have access to carbon atoms, as carbon makes up about 49 percent of the dry weight of organisms. In general, the carbon cycle includes movement of carbon from the gaseous phase (carbon dioxide [CO2] in the atmosphere) to solid phase (carbon-containing compounds in living organisms) and then back to the atmosphere via decomposers. For example, the atmosphere is the largest reservoir of carbon, containing 32 percent CO2, and gets much of its “carbon cycling” from plants: The process of photosynthesis removes CO2 from the atmosphere, and cell respiration returns CO2 to the atmosphere.


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