Answer:
Firstly, the partial pressure of nitrogen (78%) is crucial to breathing purposes. Without this pressure, the lungs will burst and animals cannot survive.
Secondly, nitrogen is required for the formation of amino acids (building blocks of proteins) and other organic compounds that are necessary for the survival of living organisms. Principally, in the atmosphere, nitrogen is present in the form of molecular nitrogen (N2). N2 is fixed by nitrogen-fixing bacteria that form nitrates and nitrites. These molecules are then used in biochemical processes to produce proteins (amino acids) and other organic compounds. In the absence of nitrogen, these processes could become seize of limited significantly thus affecting life overall.
Thirdly, nitrogen and its derivatives act as greenhouse gases that maintain the Earth's temperature within a range that supports life. Yes, the increased abundance of nitrous oxides is not good because of acid rain and other issues, however, still, the presence of nitrogen is important for life on this planet.
