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Biogeochemical Cycles

Biogeochemical Cycles Synopsis


Biogeochemical Cycles

  • The term biogeochemical is derived from “bio” meaning biosphere, “geo” meaning the geological components and “chemical” meaning the elements that move through a cycle.
  • Biogeochemical cycles mainly refer to the movement of nutrients and other elements between biotic and abiotic factors.
  • Biotic and abiotic components interact with each other to form a stable system.
  • Living organisms require various nutrients for their growth and metabolism which are derived from the lithosphere. These nutrients are called biogeochemicals.
  • The biogeochemicals are constantly recycled between biotic and abiotic components. This circulation of biogeochemicals in the biosphere is called a biogeochemical cycle.

Types of Biogeochemical Cycles



Significance of Biogeochemical Cycles

Water Cycle

  • There is constant exchange of water between the air, land and sea.
  • The exchange of water also occurs between living organisms and their environment.


1. Global Water Cycle

  • Due to the sun’s heat, water evaporates from water bodies.
  • Water vapours along with air rise and condense when the temperature is low.
  • As condensation occurs, a large amount of water vapours condense and form clouds.
  • Winds carry clouds over land where they precipitate in the form of rain, snow, hail or sleet.
  • After precipitation, some water seeps into the ground and is stored as groundwater, while some water flows and meets the water bodies again.
  • Oceans are the largest global reservoirs, and the atmosphere is the smallest water reservoir.

2. Biological Water Cycle

  • Organisms obtain water from the atmosphere and return it to the global water cycle.
  • Plants give out excess water in the form of water vapour. This is called transpiration.
  • Animals drink water, and their food also has a certain amount of water. When animals respire, they return some amount of water vapours to the atmosphere.
  • Water is also given out at the time of excretion.

Nitrogen Cycle

  • Nitrogen is an important nutrient present in proteins, amino acids and nucleic acids.
  • Nitrogen present in the air is in its molecular form.
  • Although nitrogen is required by living organisms, it cannot be used when available in its free state.
  • Nitrogen is converted into a usable form by the process of nitrogen fixation.
  • Below are the stages of nitrogen cycle:



1. Nitrogen Fixation

  • Atmospheric nitrogen (N2) which is primarily available in an inert form, is converted into the usable form – ammonia (NH3).

 2. Nitrification

  • In this process, the ammonia is converted into nitrate by the presence of bacteria in the soil. Nitrites are formed by the oxidation of ammonia with the help of Nitrosomonas bacterium species.
  • Later, the produced nitrites are converted into nitrates by Nitrobacter. This conversion is very important as ammonia gas is toxic for plants.


  • Plants take in the nitrogen compounds from the soil with the help of their roots, which are available in the form of ammonia, nitrite ions, nitrate ions or ammonium ions.
  • They are used in the formation of the plant and animal proteins. This way, nitrogen enters the food web when the primary consumers eat the plants.

4. Ammonification

  • When plants or animals die, the nitrogen present in the organic matter is released back into the soil. 
  • The decomposers, bacteria or fungi present in the soil, convert the organic matter back into ammonium. This process produces ammonia, which is further used for other biological processes.

5. Denitrification

  • Denitrification is the process in which the nitrogen compounds makes their way back into the atmosphere by converting nitrate (NO3-) into gaseous nitrogen (N).
  • Denitrification is carried out by the denitrifying bacterial species- Clostridium and Pseudomonas, which will process nitrate to gain oxygen and gives out free nitrogen gas as a byproduct.

 Carbon Cycle

  • Carbon is an important constituent found in all living organisms in the form of carbohydrates, proteins, fats and nucleic acids.