Why only prokaryotes have ability to fix atmospheric nitrogen? Why this ability is not found in eukaryotes ?

Explanation

Fixation of atmospheric nitrogen by prokaryotes is medicated by the activity of an enzyme system, the nitrogenase system, which has two components : Nitrogenase and Nitrogenase reductase. These components are exteremly sensitive to oxygen (i.e., get inactivated in presence of oxygen). Therefore, facultative anaerobes fix nitrogen only under anoxic conditions. Cyanobacteria fix nitrogen in heterocysts in absence of oxygen. Rhizobium bacteria fix nitrogen only in presence of leghaemoglobin. Moreover, these enzymes are synthesised by the activity of specific gene, called Nif gene. The Nif gene is located in the plasmids of prokaryotes. The plasmids are extrachromosomal DNA mostly found in prokaryotes and capable of replicating independently. Since the Nif genes (responsible for synthesis of nitrogenase) are located only in the plasmids of prokaryotes, the eukaryotes are unable to synthesize the enzyme nitrogenase and fail to fix atmospheric nitrogen.