The Carbon Cycle

OCR A-level BiologyEcosystemsLesson 14 of 21

Carbon is found in all organic molecules: carbohydrates, lipids, proteins and nucleic acids. The carbon cycle describes how carbon moves between the atmosphere, oceans, living organisms and rocks. Atmospheric carbon dioxide is only about 0.04% of the air, but it is the source of all the carbon in living things.

Removing CO₂ from the atmosphere
• Photosynthesis by plants, algae and cyanobacteria fixes CO₂ into sugars. Carbon then passes along food chains when organisms are eaten.
• CO₂ dissolves in the oceans. Some is used by marine organisms to make calcium carbonate shells, which can form limestone rock when they die and settle.

More in Ecosystems

• Decomposers
• The Nitrogen Cycle
• Nitrogen-Fixing Bacteria
• Nitrification and Denitrification
• Succession
• Primary Succession
• Secondary Succession
• Deflected Succession

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