What is Nutrient Cycle? Explain Carbon Cycle and Nitrogen Cycle.

Nutrients are the chemical elements and compounds needed for organisms to grow and function. The important nutrients are carbon, oxygen, nitrogen, hydrogen, iron, calcium and back to the non-living component again in a more or less cyclic manner. This is known as biogeochemical cycle or inorganic, organic cycle. The flow of these elements through the ecosystem must be cyclic with mater being consistently recycled.


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There are three types of biogeochemical cycle;-

  • Hydrological cycle / water cycle.
  • Gaseous cycles.
  • Sedimentary cycle.

Carbon Cycle:

Carbon is a basic constituent of all organic compounds. Since energy transfer move to the ecosystem with flow of carbohydrates and fats, carbon moves to the ecosystem with flow of energy. The source of nearly all carbon found will living organisms is carbon dioxide which is found in the free state of atmosphere and in dissolved state with water on the earth green plants use carbon dioxide through photosynthesis and from carbohydrate. Later on complex fats and polysaccharides are formed in plants which are utilized by animals. Flash eating animals feed on herbivores and the carbon compounds are again digested and converted into the other forms. Carbon is released to the atmosphere directly as carbon dioxide in respiration of both plants and animals. Bacteria and fungi attack the dead remains of plants and animals. They degrade the complex organic compounds into simpler organic compounds into simpler substances, which are then available for other cycles.

Nitrogen Cycle:

Of all other elements which absorb from the soil nitrogen is most important for plant growth. The atmospheric nitrogen is not directly available to the organisms except for a few nitrogen cycles consists of the following steps:


1. Nitrogen fixation

2. Nitrogen assimilation,

3. Amonification


4. Nitrofication

5. Dentrification

6. Sedimentation.

1. Nitrogen fixation:

Conversion of free nitrogen of atmosphere into the biologically acceptance from or nitrogenous compounds is referred to as nitrogen fixation. Thus process is of two types:-

  • Physio-co-chemical or non-biological nitrogen fixation.
  • Biological nitrogen fixation.
  • In physio-chemical process of nitrogen fixation atmospheric nitrogen combine with oxygen during lightening and produce different nitrogen oxides


N2 + 2(O) Electrical 2NO

2NO + 2(O) 2NO2

2NO2 + (O) N2O3

Biological nitrogen fixation is carried out by certain prokaryotes. Symbiotic bacteria inhabiting the root nodules of legumes fix atmospheric nitrogen. These organisms combine the atmospheric nitrogen with hydrogen obtained from respiratory path way from ammonia which then reacts with organic acids to form amino acids.

2. Nitrogen assimilation:

In organic nitrogen in the form of nitrates, nitrates and ammonia is absorbed by the green plants and converted into nitrogenous organic converted into nitrogenous organic compounds. Animals derive their requirement from the plant proteins.

3. Ammonification:

The dead organic remains of plants and animals and excreta of animals are acted upon by a number of microbes. These organisms utilize organic compounds in their metabolisms and release ammonia.

4. Nitrification:

Certain bacteria convert ammonia into nitrites and then into nitrates. These bacteria primarily use the energy of dead organic material their metabolism.

2NH3 + 2O2 N2 + 2H2O + Energy

2NO2 + O2 NO3 + Energy

5. Denitrification:

Ammonia and nitrites are converted into free nitrogen by certai microbes. This process referred to as dentrification.

2NO3 + 2NO2 2NO N2O N2

6. Sedimentation:

Nitrates of the soil are washed away to the sea or leeched deep into the earth along with percolating water. Nitrates thus lost from the soil surface are locked up with rocks. This is sedimentation of nitrogen.

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