Carbon is exchanged among Earth's atmosphere, ecosystem, oceans, and geosphere. All living organisms are built of carbon compounds. It is the fundamental building block of life and an important component of many chemical processes. The carbon cycle is tied to the availability of other elements and compounds. For example, the carbon cycle is tied to the availability of oxygen in the atmosphere. During photosynthesis, plants take carbon dioxide from the air and used it to make glucose (stored carbon), while releasing oxygen.
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