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Nitrogen Cycle – Definition and Stages

Last Updated : 10 Jul, 2022
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Normal assets can be characterized as the assets that exist in a world free of human activities. Normal assets are normally happening materials that are helpful to man or could be valuable under possible innovative, financial, or social conditions or supplies drawn from the earth, supplies like food, building and attire materials, composts, metals, water, and geothermal power. These are the assets that are tracked down in the climate and are created without the mediation of people. Normal instances of regular assets incorporate air, daylight, water, soil, stone, plants, creatures, and non-renewable energy sources.

The Nitrogen Cycle 

Nitrogen Cycle


  • The nitrogen cycle is a cyclic cycle where the nitrogen goes from an inorganic structure in the environment to the natural way in the residing living beings.
  • This cycle is fundamental in keeping a legitimate environmental equilibrium and is available in both marine and earthly biological systems.
  • The nitrogen cycle contains a few stages, like nitrogen obsession, osmosis, ammonification, nitrification, and denitrification.
  • Living creatures require nitrogen for the blend of nucleic corrosive and proteins. The climate contains practically 78% of nitrogen present in a dormant structure (N2).
  • This nitrogen can’t be utilized by living creatures except if it is changed over completely to alkali, nitrates, and other usable mixtures of nitrogen.
  • It is one of the essential supplements and part of biomolecules like protein, amino acids and nucleic acids (DNA and RNA), and a few nutrients.
  • Just when utilized in alkali, it tends to be utilized by essential makers like plants. Despite the fact that it is broadly accessible, it goes about as a scant asset.


The marine biological system likewise has a comparable way to the nitrogen cycle. The nitrogen from the environment gets consumed in the water, and nitrogen-containing intensifies dregs as rocks on the sea depths. Numerous species can’t break major areas of strength between the nitrogen. Be that as it may, scarcely any microbes can oxidize the nitrogen particle and convert it into smelling salts. The phytoplankton plants can assimilate alkali. A few microbes can consume smelling salts and deliver nitrites. The nitrites are then changed over completely to nitrates that can later be involved by one more microorganism in the marine biological system. This course of changing over smelling salts into nitrates is called nitrification. Bigger life forms like the whale, fish, and so on get their stockpile of nitrogen by consuming phytoplankton. At the point when the fish pass on in the long run, they silt to the sea floor. They are disintegrated by the microscopic organisms present and deliver alkali which is again changed over completely to nitrates by nitrification, and the cycle proceeds.

Stages/ Process of nitrogen Cycle

Interaction of the Nitrogen Cycle comprises of the accompanying advances – Nitrogen obsession, Nitrification, Assimilation, Ammonification and Denitrification. These cycles happen in a few phases and are made sense of underneath:

Stage-1 (Nitrogen Fixation Process)

It is the underlying step of the nitrogen cycle. Here, Atmospheric nitrogen (N2) which is basically accessible in an idle structure, is changed over into the usable structure – smelling salts (NH3). During the course of Nitrogen obsession, the dormant type of nitrogen gas is kept into soils from the air and surface waters, for the most part through precipitation. The whole course of Nitrogen obsession is finished by advantageous microbes, which are known as Diazotrophs. Azotobacter and Rhizobium likewise play a significant part in this cycle. These microscopic organisms comprise a nitrogenase protein, which has the capacity to join vaporous nitrogen with hydrogen to frame smelling salts. There are three different ways nitrogen obsession can happen. They are ;

  1. Air Nitrogen Fixation – The dormant nitrogen present in the climate is changed over completely to nitrous oxide with the assistance of lightning because of the great – temperature present during lightning. The nitrogen is separated into nitrogen which responds with oxygen to frame nitrous oxide, nitrogen peroxide, and nitric oxide.
  2. Modern Nitrogen Fixation – It is a human-made elective where the air nitrogen is changed over into smelling salts by the Haber process and later into nitrates in different manures.
  3. Organic Nitrogen Fixation – There exist nitrogen-fixing microbes and blue-green growth that convert nitrogen present in the climate into nitrates.

Stage-2 (Nitrogen assimilation)

  • Inorganic nitrogen compounds present in soil after nitrogen obsession are consumed by plants as supplements and used for the biosynthesis of amino acids, proteins, nucleic acids and so on the cycle is known as Nitrogen osmosis.
  • These are the Primary maker’s plants that take in the nitrogen compounds from the dirt with the assistance of their underlying foundations, which are accessible as alkali, nitrite particles, nitrate particles, or ammonium particles and are utilized in the development of the plant and creature proteins.
  • Along these lines, it enters the food web when the essential shoppers eat the plants.
  • Likewise, a portion of the nitrogen compound goes through mineralization and gets kept in the dirt as ammonium salts.
  • At the point when creature benefits from plants, nitrogen is stored as protein as well as changed over into other structures like urea, and uric acids and discharged as dung and pee.

Stage-3 (Nitrogen Nitrification) 

Nitrification is the cycle, the smelling salts are changed over into nitrate by the presence of microbes in the dirt. Nitrites are shaped by the oxidation of smelling salts with the assistance of Nitroso-monas microbes species. Afterward, the created nitrites are changed over into nitrates by Nitrobacter. This change is vital as smelling salts gas is harmful for plants.

This cycle happens in two stages: they are

  • Transformation of Ammonia into Nitrites: This happens by the activity of Nitroso-monas microorganisms. They oxidize the smelling salts present in the dirt and convert them to nitrites. The compound condition to address the response is referenced below.

2NH4+ + 3O2 → 2NO2+ 4H+ + 2H2O

  • Transformation of Nitrites to Nitrates: This happens by the activity of Nitro bacteria species, which convert the nitrates in the dirt into nitrates. The synthetic condition of the response is referenced below.

2NO2¯+ O2 →  2NO3

Stage-4 (Ammonification )

  • At the point when plants or creatures bite the dust natural nitrogen is again delivered once more into the dirt which is changed over once more into ammonium by microorganisms or growths present in the dirt. This cycle is likewise called as mineralisation.
  • Dead remaining parts of plants and creatures are deteriorated by microorganisms (microbes and Fungi) present in soil and convert the natural nitrogen compound into smelling salts.
  • A few Bacteria (Pseudo-monas, Bacillus, clostridium, Serratia), parasites (Alternaria, Aspergillus, Mucor, Penicillium), and Actinomycetes can change over natural nitrogen compounds into smelling salts.

Stage-5 (Denitrification )

  • Denitrification is the cycle where the nitrogen intensifies advance once more into the air by changing over nitrate (NO 3-) into vaporous nitrogen (N).
  • This course of the nitrogen cycle is the last stage and happens without a trace of oxygen.
  • Denitrification is completed by the denitrifying bacterial species-Clostridium and Pseudo-monas, which will handle nitrate to acquire oxygen and gives out free nitrogen gas as a side-effect.

Conceptual Question 

Question 1: Explain the nitrogen Cycle’s importance? 


  • Assists plants with orchestrating chlorophyll from the nitrogen compounds.
  • Assists in changing over idol nitrogen with gassing into a usable structure for the plants through the biochemical cycle.
  • During the time spent, the microbes assist in deteriorating the creature and plant by making a difference, which is a roundabout way assists with tidying up the climate.

Question 2: Explain the stage of assimilation? 


It enters the food cycle when essential makers take in this gas from the dirt with the assistance of their underlying foundations as amino acids, nitrite particles, nitrate particles or ammonium particles. Then, at that point, the buyers eat the plants.

Question 3: Explain biological nitrogen fixation? 


Certain microorganisms or prokaryotes are equipped for switching environmental nitrogen over completely to alkali. This interaction is called natural nitrogen obsession. The compound nitrogenase changes over dinitrogen to smelling salts. Nitrogen-fixing microbes might be free-living or cooperative 

Question 4: Explain the fixation of nitrogen into compounds ? 


  • Certain blue green growth and microorganisms can fix climatic nitrogen.
  • Nitrogen fixing microorganisms found in the knobs of underlying foundations of vegetables like gram, bean, beats, and so forth, fix baro-metrical nitrogen into containing compounds.
  • Easing up likewise helps in the development of nitrogen containing compounds.

Question 5: What is meant by nitrogen Cycle and mention it’s stages  ? 


Nitrogen Cycle is a biogeochemical cycle which changes the latent nitrogen present in the environment to a more usable structure for living organic entities.” Nitrogen Cycle stages are 5 sorts, they are ;

  1. Nitrogen Fixation
  2. Absorption
  3. Ammonification
  4. Nitrification
  5. Denitrification

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