A major constituent of Earth's atmosphere is nitrogen gas (N2), which makes up 79% of the air we breathe. Primary producers such as plants and algae cannot assimilate this form of nitrogen into biomolecules. Instead they rely on Bacteria and Archaea to convert N2 to ammonia (NH3). This important biological reaction is called:__________.

Nitrogen fixation refers to the process in which the gaseous form of nitrogen is reduced into ammonia. This process is performed by free-living bacteria and symbiotic bacteria, archaea, and cyanobacteria. The reduction of nitrogen to ammonia is catalyzed by the enzyme nitrogenase. It is an energy-requiring process. It makes the nitrogen available to the producers of an ecosystem as they can not use the N2 directly. The ammonia then can be incorporated into organic compounds by plants and algae.