Carbon Cycle:

  • The carbon cycle is the biogeochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere and atmosphere of the earth.
  • Carbon is the fourth most abundant chemical element in the universe and forms the building blocks of the living world along with hydrogen and oxygen. In fact, its concentration in the biotic world (living world) is almost 100 times more than that in the abiotic (non-living) world.
  • Other than this, carbon is an important element that forms a blanket around the Earth. It traps the heat of the sun within the atmosphere and hence prevents the Earth from freezing.
  • There is a constant exchange of carbon between the biotic and the abiotic world, thus forming a cycle which is called the carbon cycle. This cycle plays an important role in maintaining proper levels of carbon in the earth.


Steps of the Carbon Cycle:

   Carbon is regularly being exchanged among the atmosphere, land, water, and the living beings. In fact, it is constantly on the move! Let us understand how the carbon cycle works.

  1. CO2 used by Plants for Photosynthesis – The primary producers (green plants), also known as photoautotrophs, are constantly removing carbon dioxide from the atmosphere through the process of photosynthesis (the process in which green plants make food for themselves in presence of sunlight). Certain bacteria, also referred to as chemoautotrophs, use carbon dioxide to synthesize the organic compounds they need.
  2. Consumption by Animals – The carbon present in the food made by green plants reaches animals through the food chain. Carnivorous animals receive this carbon when they eat other animals.
  3. Ocean Intake – Carbon dioxide is continuously being dissolved in the seas and oceans through the process of diffusion. Once dissolved, this carbon dioxide may remain as it is in the marine waters or may get converted into carbonates and bicarbonates. The carbon dioxide dissolved in water is used by marine plants for photosynthesis. The carbonates are converted into calcium carbonate by certain marine organisms. This calcium carbonate is used by corals and oysters to make their shells. When these organisms die, their shells deposit on the sea floor and finally turn into sedimentary rocks.
  4. Decay and Decomposition – When living organisms die, their bodies decay and decompose. This happens due to various natural reasons. The energy as well as the carbon dioxide present in their bodies is released by the chemical reactions taking place on the body.
  5. Formation of Fossil Fuels – As plants and animals die and get buried under the ground after millions of years, they change into fossil fuels due to high pressure and other physical and chemical changes.
  6. Use of Fuels for Industrial Purposes – Fossil fuels stored in the heart of the Earth are dug out and used by industries for purposes of energy production. It is also used as a raw material for other purposes.
  7. Carbon Emissions – The fuel used by the companies leads to the production of waste gases. These gases also contain a large amount of carbon dioxide.
  8. Respiration by Plants and Animals – Carbon dioxide is regularly being returned to the atmosphere by the process of respiration in plants and animals. Burning of wood and fossil fuels in industries and automobiles also releases carbondioxide.



Role of Microorganisms in Carbon Cycle:

  • In less acid and neutral condition, Bacteria degrade lignin, cellulose and hemicellulose. Many fungi and bacteria attack cellulose and release carbon in the soil e.g. Trichoderma, Aspergillus, and Penicillum. Marasmius, Ganoderma, Psalliotta attack lignin. Actinomycetes and some bacteria also attack lignin.
  • Some specific groups of bacteria are particularly efficient in reducing carbon compounds to form lactic, butyric, and acetic acid. Likewise methane, hydrogen gas, and ammonia are also produced.
  • Some bacteria utilize hydrogen and reduce carbon dioxide to produce methane.
  • An increase in the evolution of carbon dioxide as a result of the decomposition of plant and animal residues added to the soil, or the soil humus, leads to an increase in carbon dioxide content of the soil. This result in the rise of hydrogen ion concentration of the soil which further interact with phosphates and silicates making them available to the plants.
  • Carbon dioxide in soil also supplements carbon dioxide in the atmosphere and in plants.
  • If they (microorganisms) do not act on organic matter, the limited supply of carbon dioxide in the atmosphere will be exhausted and green plants would cease to manufacture carbohydrates.
  • If the microbes are more active, then all the organic matter will be reduced to carbon dioxide, resulting in unfit for plant growth.

Thus, the carbon cycle is largely maintained by balanced action of microorganisms in soil.


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