This nitrogen needs to be fixed first so that it can be used by plants and animals.In this short video, we learn that certain types of bacteria help to convert atmospheric nitrogen into usable forms such as nitrates and nitrites.These nitrogen fixing bacteria are commonly found in the roots of plants of pulses(legumes). These usable forms of nitrogen are absorbed by plants to produce amino acids, which in turn form proteins. When an animal eats these plants, nitrogen enters its body through the proteins present in plants.When plants and animals die, they start decomposing after some time. During this process, proteins containing nitrogen are converted into nitrates and nitrites by the action of decomposing bacteria ,which is present in the soil. Few other types of bacteria convert nitrates and nitrites into nitrogen gas.This way nitrogen cycle continues.