The process of converting Nitrogen in the air to Nitrogen compounds which can be used by plants is called Nitrogen Fixation.

Nitrogen compounds are used by the plants for synthesis of plant proteins


The nitrogen can be fixed by

  • Nitrogen fixing bacteria in the soil
  • Rhizobium bacteria - which live in root nodules of leguminous plants such as beans and peas
  • By blue green algae
  • By Lightning

But, if we use the Nitrogen in the air to make compounds, then shouldn’t the Nitrogen in the air be reduced?

But Nitrogen in the air is constant. It is constant due to Nitrogen Cycle



NCERT Question 1(b) - Fill in the blanks:

Blue green algae fix __________ directly from air to enhance fertility of soil.

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NCERT Question 3 - Match the organisms in Column I with their action in Column II

Column I

Column II

(i) Bacteria

(a) Fixing Nitrogen

(ii) Rhizobium

(b) Setting of curd

(iii) Lactobacillus

(c) Baking of bread

(iv) Yeast

(d) Causing Malaria

(v) A protozoan

(e) Causing Cholera

(vi) A Virus

(f) Causing AIDS


(g) Producing antibodies

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NCERT Question 6 - Name the microorganisms which can fix atmospheric nitrogen in the soil.

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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo