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Biogeochemical Cycle: Nitrogen and Carbon Cycle

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Biogeochemical Cycle: Nitrogen and Carbon Cycle

Biogeochemical Cycle: Nitrogen and Carbon Cycle

Biogeochemical Cycle:

The elements which are required for the proper growth and development of living organisms enter into the composition of living organisms circulate more or less in cyclic manner from abiotic environment to living organisms and again back to the non living environment is called biogeochemical cycle

The flow involves not only living organisms but also a series of chemical reactions in the abiotic environment these cycles are called biogeochemical cycle.

Nitrogen Cycle:

Nitrogen is essential constituent of many biologically significant molecules such as amino acids, proteins, enzymes chlorophylls, and nucleic acids etc. The main source of nitrogen is atmosphere where it is 78%.

Green plants contain nitrogen from soil solution in the form of ammonium, nitrate, and nitrite ions and the main source of all these nitrogen compounds is the atmospheric nitrogen. Nitrogen cycle consists of following steps:

nitrogen cycle

Nitrogen fixation:

Conservation of free atmospheric nitrogen into the biologically acceptable form or nitrogenous compounds is known as nitrogen fixation. It is of two types

Non-biological nitrogen fixation is the process in which lightning or electrical discharges in the clouds and produce different nitrogen oxides. These nitrogen oxides dissolve in rainwater and mix with earth surface.

Certain free-living bacteria in the soil and symbiotic bacteria present in the root nodules of leguminous carry out biological nitrogen fixation and cyanobacteria present in the soil.

The free-living bacteria present in the soil are like Coccus fix atmospheric nitrogen. The bacteria, which are found in the root nodules of leguminous plants, are called symbiotic bacteria they also fix atmospheric nitrogen and supply to the host plant. Different types of cayanobacteria like Nostoc, Anabaena, Spiriluna are also present in the soil which contain certain nitrogen fixing cells in the filament like heterocyst.

Nitrogen assimilation:

The fixed nitrogen is utilized by green plants and stored in the plants in the form of protein. When plants are eaten by animals the protein is transfer to animal. This is called nitrogen assimilation.


The dead bodies of plants and animals containing nitrogenous substances are acted upon a number of microorganisms like bacteria (Bacillus, Ramosus) and fungi. They utilize organic compounds and release ammonia in the soil. This process is called ammonification.


Some bacteria like Nitrosomonas converts ammonia into nitrites and the nitrites are converted into nitrates by Nitrobacter. These bacteria are called nitrifying bacteria and the conversion of ammonia into nitrate is called nitrification.


The process of conversion of nitrates into free nitrogen by certain bacteria like Bacillus denitrificans is known as denitrification. But sometime aminoacid is formed from ammonia and nitrates which is used by green plants.

Carbon Cycle:

The main source of carbon is atmospheric carbondioxide. In the atmosphere the carbondioxide is 0.03%.

carbon cycle

The atmospheric carbondioxide is fixed by green plants during photosynthesis. The plants in presence of water and carbondioxide manufacture food. The carbon is then stored in different form of carbohydrates in plant body.

When the plants are consumed by animals the food material is transferred to animals and they get carbon compounds and store in their body.

During respiration, both plants and animals release carbondioxide into the atmosphere. Respiration takes place to produce energy where oxygen is used to breakdown the food materials. Carbondioxide is the waste product produced during the process.

The CO2 is also produced in atmosphere from burning plants, animals and different other residues. It is mixed into the atmosphere during burning coal, firewood and fuel as well.

After death of animals and plants, the CO2 is produced and mixed into atmosphere during fermentation.

Fossilization takes place in dead plants and animals to form carbon compounds like coal and fuel as petrol or diesel.

Some amount of carbondioxide is also mixed during volcanic eruption and during mineralization of rocks.

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