Final answer:
Nitrogen fixation is carried out by microorganisms that convert atmospheric nitrogen into ammonia using the enzyme nitrogenase. Rhizobia bacteria, which engage in symbiotic relationships with legumes, are key players in this process, vital for farming and ecosystems.
Step-by-step explanation:
Nitrogen fixation is a crucial biological process whereby microorganisms in the soil convert atmospheric nitrogen (N₂) into ammonia (NH₃), a form beneficial to plants. The enzyme responsible for this conversion is called nitrogenase, which is particularly sensitive to oxygen; thus, the process often occurs in oxygen-poor environments to prevent the inactivation of nitrogenase.
The most well-known microorganisms capable of nitrogen fixation are bacteria, specifically rhizobia, which enter into a symbiotic relationship with legumes. These bacteria colonize the root nodules of the plants, where they receive carbohydrates from the plant and in return provide the plant with fixed nitrogen. This relationship is vital for agricultural systems, especially in crops like soybeans and peanuts, which are significant sources of protein.
In aquatic environments, cyanobacteria lead in nitrogen fixation. In soil, the genera Clostridium and Azotobacter represent free-living, nitrogen-fixing bacteria quite important to the ecosystem. Both symbiotic and free-living nitrogen-fixing bacteria contribute significantly to the nitrogen available in the soil, with symbiotic relationships often being more efficient.