Nitrogen fixation is the process by which the atmospheric N2 is converted into usable nitrogen forms such as ammonia and nitrates by different nitrogen-fixing bacteria such as Rhizobium, Azotobacter, Anabaena, etc.
Nitrogen fixation is important for animals for biosynthesizing essential nitrogen-containing organic compounds, such as proteins, nucleic acids, nitrogenous bases, etc., from the fixed atmospheric N2.
Nitrogen fixation is essential as the atmospheric N2 cannot be directly utilized by animals, hence needs to be converted into usable forms.
Nitrogen fixed by bacteria is utilized by plants to synthesize important biomolecules which are in turn used by animals to derive their nitrogen requirements from plants.
Therefore, nitrogen fixation is essential for the synthesis of important biomolecules required to carry out life processes.