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SAI International School
Subject- Biology, Class-VIII
Topic- Microorganisms: Friend and Foe
Subtopic- Nitrogen Fixation and Nitrogen Cycle
Module- 17
Lesson Notes
Nitrogen fixation and nitrogen cycle:Nitrogen is an important constituent of living
organisms because it is present in proteins, chlorophyll, nucleic acid(DNA and RNA),
vitamins, hormones and enzymes etc.
Our atmosphere contains 78% of Nitrogen in gaseous form but it cannot be used
directly by living organisms.
The cyclic movement of nitrogen from atmosphere to living organisms’ body and coming
back to atmosphere is called nitrogen cycle.
Nitrogen cycle is important because it ensures the survival of living organisms and
maintains the percentage of Nitrogen in atmosphere.
