Nostoc can fix atmospheric nitrogen in specialised cell, called Heterocyst.

Heterocysts are specialized, thick-walled cells found in filamentous cyanobacteria like Nostoc and Anabaena.

These cells provide an anaerobic (oxygen-free) environment necessary for the enzyme nitrogenase to function and convert atmospheric nitrogen into ammonia.

They are distinct from vegetative cells, which perform photosynthesis.

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