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What is Nitrogen Cycle?

Chemistry | 7-14 yrs | Learning Pod

Nitrogen (N) is a colorless, odorless, tasteless gas with atomic number of 7 and atomic weight of 14.007.

Why do we need Nitrogen?

  • It is used to produce chlorophyll in plants.
  • It is used in cell processes like DNA, amino acids and proteins (for muscles, bones etc).
  • It is used in fertilizers.

Where is it found?

78% of atmospheric air consists of nitrogen.

Process of the Nitrogen Cycle


  • Nitrogen in its pure gas form is unusable. It is converted through a process called Fixation where N2 + 3 H2 -> 2 NH3 (ammonia).
  • Fixation can happen in three ways.
  • Nitrogen disperses in the earth’s soil and bacteria transforms it to ammonium ions (NH4+) which is accessed by plants.
  • Lightning changes nitrogen to nitrate ((NO†3-) and ammonia which gets absorbed in the soil along with rain.
  • Nitrogen is chemically transformed to ammonia.


After the nitrogen is converted to ammonia, it is further converted with oxygen to nitrite and nitrate by aerobic bacteria. 2 NH3 + 3O2 – > 2 NO2 + 2 H+ + 2 H2O & NO2- + O2 -> 2 NO3-.


Plants can now use it and animals eat plants to get their share of nitrogen.

What happens after plants and animals have got the nitrogen they need?


After the plants die and animals shed their waste products; the decaying bacteria again transforms the nitrite and nitrate to ammonia and ammonia salts.


Anaerobic bacteria then change nitrate to its original nitrogen gas form – NO3- + CH2O + H+ -> _ N2O + CO2 + 1_ H2O

Unique use of Nitrogen

Nitrogen gas is used where an inert atmosphere is needed. Historical documents like USA’s Declaration of Independence are stored in a sealed container containing nitrogen gas; as then the paper and ink will not react with it and thus preserve the writing.

For more such interesting chemistry articles and videos, visit: https://mocomi.com/learn/science/chemistry/