Biogeochemical Carbon cycle in earth's environment

Carbon is the most important element of all living beings as well as in the earth's atmosphere. This article provides an insite of how its concentration is maintained and balanced through its biogeochemical cycle. This article also provides an account of how environment and living beings interact with each other to recycle carbon element in nature. Some frequently asked questions were also given along with this topic.


The way by which an element or compound moves between its various living and non-living components and locations in the biosphere is called the Biogeochemical cycle. Actually, carbon compounds are interchanged between the biosphere, pedosphere, hydrosphere, geosphere, and atmosphere of the earth.

All living beings in nature are mainly composed of organic compounds like carbohydrates, proteins, fats, and nucleic acids. The carbon element is the most important constituent of all these compounds. Carbon is the most important element of the living material protoplasm. Other than in living beings, carbon is present in various forms in the physical environment. CO2 is present in the earth's atmosphere, beneath the earth's crust, and in deeper depths of oceans.

The carbon cycle is a biogeochemical cycle in which through a series of chemical steps, the chemical element carbon is removed from CO2 from the atmosphere, used by living organisms in their body activities, and is finally returned to the atmosphere.

Sources of carbon

Carbon is present in different forms in our environment - as CO2 in the atmosphere, below the soil surface, and in water bodies like Seas, Oceans, rivers, lakes, ponds, etc. All these sources act as CO2 reservoirs.

The carbon is present in fossil fuels like petrol, coal, natural gas, etc. Carbon is present as carbonates in rocks in the earth's crust. When these stones containing carbonates are burnt, carbon content will be released into the atmosphere.

Carbon present in the atmosphere in the form of CO2 enters into the plant body as carbohydrate through photosynthesis and then passed on to herbivores and then into carnivores and decomposers. So all living beings also possess carbon content in their body and thus they are a part of the carbon biogeochemical cycle.

Various steps in Biogeochemical Carbon cycle

The following are the major steps in the Carbon cycle that help to maintain carbon elements in the earth's environment.

Carbon Cycle in nature
Carbon Cycle in nature (

  1. Photosynthesis

    The producers of food for all living beings, the green plants through a vital process of photosynthesis produce carbohydrate food. These carbohydrates can be transformed into proteins, sugars, fats, etc. through various chemical processes. A part of these food materials is utilized by plants for their life activities and the remains it donates to all living beings for their existence in nature. As plants prepare their own food by themselves through simple inorganic substances and through a chemical process are known as autotrophs. The other organisms that cannot prepare their own food but obtain either directly or indirectly from plants are known as heterotrophs. Interestingly, the carbon compound CO2 present in the atmosphere is only 0.03% by volume of air. But this little concentration of carbon source CO2 is enough for the plants to prepare tonnes and tonnes of food. Thus the green plants are more efficient in utilizing CO2 from the atmosphere through the process of photosynthesis. The carbon content that they prepared by the plants in the form of food is transferred to herbivores, carnivores, and decomposers through food chains.

  2. Food chains

    A group of organisms that form a chain in which food gets transferred from a lower to higher organism is known as the food chain. Through a food chain, the food containing carbon (carbohydrates and other products) are passed on from plants (producers) to animals (consumers). Carbon forms an important constituent element of all body tissues of plants and animals. Actually, carbon gets bioaccumulated into their bodies through these food transfers in all organisms. The animals that feed on plants and other animals digest the complex carbon compounds and reutilize the carbon element of these compounds to make still different carbon-containing materials.

  3. Respiration

    It is an energy-yielding activity of all living beings in which the carbohydrates are oxidized to give out the chemical energy, CO2, and water. The chemical energy will be utilized for the life activities of living organisms while CO2 released during respiration is added back to the atmosphere to maintain its concentration. All living organisms including plants respire and give out CO2 to replenish atmospheric CO2 concentration. Respiration is a reverse of photosynthesis, where the carbon compounds formed in photosynthesis are broken down to release CO2 and water along with chemical energy. Thus photosynthesis is an anabolic process while respiration is a catabolic process. So respiration is a biological process where CO2 from living beings get returned to the atmosphere.

  4. Decay of dead plants and animals

    The dead plants and animals or even their dead parts, when deposited on the earth's surface, are subjected to the activity of decomposers like bacteria and fungi. Thus carbon gets recycled in this process.

  5. Fossilization and burning of fossil fuels

    Sometimes the dead parts of plants and animals buried beneath the earth's crust as in forests and are subjected to high pressure and temperature that helps to form various kinds of fossil fuels. Under varied conditions in the past eras of geological times, the carbon present in animals and plants was preserved as peat, coal, oil, gas, and limestones in the form of rocks. For these fossil fuels to form it takes millions of years. So by using these resources continuously leads to their exhaustion in nature and cannot be renewed easily. Thus these fossil fuels are commonly known as non-renewable resources. These fossil fuels when they were burnt in their use evolve large quantities of CO2 and thus return to the atmosphere again.

  6. Similarly, the shells of molluscan organisms like snails, oysters, etc contain large quantities of CaCO3 in them. When these animals die, the shells of these animals were carried to the shores by tides and get deposited as limestone. To get lime, limestone will be burnt in Lime Kilns at high temperatures. During this process, CO2 gets released into the atmosphere. The burning of anything like fossil fuels or limestone to release CO2 into the atmosphere is known as combustion.

The carbon present in the atmosphere as CO2 is the basic source of carbon that will be fixed by green plants as carbohydrate food. This carbon content of plants is then passed on to herbivores and then successively into small carnivores and then into big carnivores. After the death of these plants and animals, decomposers breakdown and return CO2 from this process into the atmosphere. All living beings through the respiration process return CO2 to the atmosphere. The fossil fuels formed from dead plants and animals through the fossilization process, when burnt during their utility results in the addition of large quantities of CO2 into the atmosphere. Similarly, when limestone deposits are burnt in big kilns, a large quantity of CO2 is added to the atmosphere. This is simply how the carbon cycle works in nature.

Importance of Carbon cycle

  • Carbon cycle is important in the ecosystem because the life-sustaining carbon element will be recycled from the atmosphere, soil, and oceans into organisms and again return back into them.

  • Carbon cycle is responsible for the production of oxygen for all living beings to breathe.

  • The carbon cycle is responsible for the production of nutrients and energy in plants and that helps all the other organisms to survive.

  • From a biological point of view carbon element is a building block of life on earth.

  • Most frequently asked questions:-

    1. State the role of bacteria in Carbon cycle.
      Ans. Breaking down of organic compounds

    2. Name the process through which the majority of carbon moves from the lithosphere to the atmosphere.
      Ans. Fossil fuel burning

    3. Name the process through which living organisms return CO2 to the atmosphere in the carbon cycle.
      Ans. Respiration

    4. What gas will be taken up by producers in the carbon cycle?
      Ans. CO2

    5. Name the process in which carbon is transformed into stored chemical energy.
      Ans. Photosynthesis

    6. Name two non-renewable resources of energy.
      Ans. Coal and Petrol

    7. Name two reservoirs that hold the maximum amount of carbon in nature.
      Ans. Atmosphere and ocean

    8. Where does carbon cycle begins in nature?
      Ans. In the atmosphere


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