Final answer:
Nitrogen fixation is the conversion of atmospheric nitrogen into biologically useful chemicals by microorganisms. Denitrification is the process by which bacteria convert nitrates into nitrogen gas. These processes have different functions in the nitrogen cycle.
Step-by-step explanation:
Nitrogen fixation is the process where organisms convert atmospheric nitrogen into biologically useful chemicals. To date, the only known kind of biological organisms capable of nitrogen fixation are microorganisms. These organisms employ enzymes called nitrogenases, which contain iron and molybdenum. Many of these microorganisms live in a symbiotic relationship with plants, with the best-known example being the presence of rhizobia in the root nodules of legumes.
In contrast, denitrification is the process by which denitrifying bacteria convert nitrates (NO3) into nitrogen gas (N₂). Denitrifying bacteria utilize nitrate as an electron acceptor and break it down into nitrogen gas through an anaerobic respiration process. This process happens in anaerobic environments, like waterlogged soils or wetlands.