Living organisms can incorporate into their metabolism.
ammonia
nitrates
nitrogen gas
nitrites
Living organisms can incorporate various forms of nitrogen into their metabolism. The dominant forms that are commonly assimilated by organisms include:
1. **Ammonia (NH3):** Many microorganisms and plants can directly use ammonia as a source of nitrogen. In plants, ammonia is often assimilated into amino acids through the glutamine synthetase/glutamate synthase pathway.
2. **Nitrates (NO3-):** Nitrates are a primary form of nitrogen that plants absorb from the soil. Plants possess nitrate reductase enzymes that convert nitrates into nitrites and then into ammonia, which can then be incorporated into organic compounds.
3. **Nitrites (NO2-):** Nitrites, produced from nitrates by the action of nitrate reductase, are usually rapidly converted into ammonia in plants and some bacteria because nitrites can be toxic at high levels.
4. **Nitrogen gas (N2):** Some microorganisms, particularly certain bacteria and archaea, can fix atmospheric nitrogen gas through the process of nitrogen fixation. They convert the inert N2 into biologically useful forms like ammonia, which can then be used by plants or further processed into other nitrogen compounds.
Most animals cannot directly use atmospheric nitrogen gas, nitrites, or nitrogen gas, and instead rely on consuming plants or other organisms to obtain organic nitrogen compounds, such as amino acids and proteins.