The Carbon Cycle

the carbon cycle

The Carbon Cycle

  • The primary biogeochemical cycle is the carbon cycle.
  • In biogeochemical cycles elements are oxidized and reduced by microorganisms to meet their metabolic needs.
  • All organisms, including plants, microbes, and animals, contain large amounts of carbon in the form of organic compounds such as cellulose, starches, fats, and proteins.
  • Autotrophs perform an essential role for all life on Earth by reducing carbon dioxide to form organic matter.

Some Reactions in Carbon and Carbon dioxide:

Burning coal or carbon:  carbon+oxygen→ carbon dioxide.

Respiration: glucose+oxygen→ carbon dioxide+water.

Photosynthesis: carbon dioxide+water→ glucose+oxygen.

The first step of the carbon cycle in which photoautotrophs such as cyanobacteria, green plants, algae, and green and purple sulfur bacteria fix (incorporate) carbon dioxide into organic matter using energy from sunlight.

In the next step of the cycle, chemoheterotrophs such as animals and protozoa cat autotrophs and may in turn be eaten by other animals.

Thus, as the organic compounds of the autotrophs arc digested and re-synthesized, the carbon atoms of carbon dioxide are transferred from organism to organism up the food chain.

Chemoheterotrophs, including animals, use some of the organic molecules to satisfy their energy requirements. When this energy is released through respiration, carbon dioxide immediately becomes available to start the cycle over again.

The carbon cycle

Much of the carbon remains within the organisms until they excrete it as wastes or die. When plants and animals die, these organic compounds are decomposed by bacteria and fungi.

During decomposition, the organic compounds are oxidized, and CO2 is returned to the cycle.

Carbon is stored in rocks, such as limestone (CaC03), and is dissolved as carbonate ions in oceans. Vast deposits of fossil organic matter exist in the form of fossil fuels, such as coal and petroleum.

Burning these fossil fuels releases CO2, increasing the amount of CO2 in the atmosphere.

Many scientists believe the increased atmospheric carbon dioxide may be causing a global warming of the Earth.

The Carbon Cycle


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