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Carbon Cycle


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Carbon Cycle



The Carbon Cycle


An illustration of the carbon cycle


Why is recycling carbon important? Recall that carbon is the cornerstone of organic compounds, the compounds necessary for life. But do organisms make their own carbon? Do they have the genes that encode proteins necessary to make carbon? No. In fact, there are no such genes. Carbon must be recycled from other living organisms, from carbon in the atmosphere, and from carbon in other parts of the biosphere.

Carbon in the Atmosphere

Though carbon can be found in ocean water, rocks and sediment and other parts of the biosphere, the atmosphere may be the most recognizable reservoir of carbon. Carbon occurs in various forms in different parts of the carbon cycle. Some of the different forms in which carbon appears are described in Table below. KEY: C = Carbon, O = Oxygen, H = Hydrogen

Form of Carbon Chemical Formula State Main Reservoir
Carbon Dioxide CO2 Gas Atmosphere
Carbonic Acid H2CO3 Liquid Ocean
Bicarbonate Ion HCO3 Liquid(dissolved ion) Ocean
Organic Compounds Examples: C6H12O6 (Glucose), CH4 (Methane) Solid Gas Biosphere Organic Sediments (Fossil Fuels)
Other Carbon Compounds Examples: CaCO3 (Calcium Carbonate), CaMg(CO3)2 (Calcium Magnesium Carbonate) Solid Solid Sedimentary Rock, Shells, Sedimentary Rock

Carbon in Carbon Dioxide

Carbon cycles quickly between organisms and the atmosphere. In the atmosphere, carbon exists primarily as carbon dioxide (CO2). Carbon dioxide cycles through the atmosphere by several different processes, including those listed below.




  • Carbon cycles quickly between organisms and the atmosphere.


  1. What is the role of the carbon cycle?
  2. Why is cycling carbon important?
  3. Describe a major method that carbon is cycled.
  4. How have human activities increased atmospheric carbon dioxide levels?

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    carbon cycle Interconnected pathways through which carbon is recycled through the biotic and abiotic components of the biosphere.
    photosynthesis Process of using the energy in sunlight to make food (glucose).

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