The biological process involved in nitrogen fixation is the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) by certain microorganisms, such as bacteria and archaea. These organisms, including the well-known symbiotic bacteria in legume root nodules, utilize an enzyme called nitrogenase to facilitate this conversion. Nitrogen fixation is critical because it transforms inert atmospheric nitrogen into a form that can be used by plants for growth, ultimately entering the food web. This process supports the global nitrogen cycle and is fundamental for maintaining soil fertility and productivity in ecosystems.