Subjective And Short Questions For Nitrogen Metabolism


  1. Write note biological nitrogen fixation.
  2. Give mechanism of biological nitrogen fixation.
  3. Write note on symbiotic bacteria.


Define biological nitrogen fixation.

Ans: The synthesis of organic nitrogenous compounds from atmospheric nitrogen by certain microorganisms is called biological nitrogen fixation.

  1. Why do plant need fixation of atmospheric nitrogen?Ans:    Higher plants cannot directly utilize molecular nitrogen of the

    atmosphere. But certain micro-organisms can utilize atmospheric nitrogen. There are two types of nitrogen fixing micro­organisms: Asyinbiotic and symbiotic.

    1. What is role of lichens in biological nitrogen fixation? Ans: Nostoc and Scytonema develops symbiotic association with fungi. This association is called lichens. The algal components fix the molecular nitrogen in the form of organic compounds:
    2. What is the role of fungi in biological nitrogen fixation?

    Ans: Several species of Actinomycetes develop mycorrhizal association with the root of Casurina, Pinus and other plants. These mycorrhizae may be ectotropic and endotropic mycorrhizae. These fungi have ability to fix atmospheric nitrogen.



    1. What is leghaemoglobin?

    Ans: The nodule is pink in colour. The pink colour is due to the presence of pigment leghaemoglobin. This pigment is synthesized by the host cells in response to bacterial infection. It is similar to haemoglobin of red blood cells of mammals.

    1. Which intermediate compound is formed during biological nitrogen fixation?

    Ans: Diamide (NH = NH) and hydrazine (NE12—NFI2) and NH3 —NH3 are the intermediate compounds

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