The micro organism that helps in nitrogen fixation is ..........

 

Dear Student.

Ans. Option b) is correct: Nostoc
 
Reduction of nitrogen to ammonia by living organisms (bacteria) is called biological nitrogen fixation. Certain prokaryotes are able to fix nitrogen because the enzyme nitrogenase is present exclusively in them. They are called nitrogen fixers. For example bacteria such as Azotobacter, Rhizobium, Frankia, Rhodospirillum etc. These bacteria are able to convert atmospheric nitrogen into more usable forms such as nitrates and nitrites. Such nitrogen fixing bacteria are commonly found in the roots of legumes (plants of pulses) inside special structures called root nodules.

Nitrogen fixation is of following types:-  
1. Symbiotic nitrogen fixation:- In this type of fixation plant and microbe are in symbiotic association means plant provide the microbe with food source and microbe provide them nitrogen.  
2. Associative nitrogen fixation:- In this type of fixation microbe remain attached to the plant roots or leaves, plant provide microbe with food source whereas microbe provide them nitrogen when they die.  
3. Free living nitrogen fixation:- In this type of fixation microbes carry out fixation freely without any association. 

Regards.

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The correct answer is option (B) Nostoc
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Dear student

The correct answer is option B .Nostoc is a genus of filamentous nitrogen-fixing cyanobacteria that form macroscopic or microscopic colonies and is common in both terrestrial and aquatic environments (Potts, 2002). Nostoc spp. also occurs in symbiotic associations with liverworts, ferns, and the angiosperm Gunnera.
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Nostoc
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