What converts nitrogen into a useable form for plants and animals?

Nitrogen is converted into a usable form for plants and animals through a process called nitrogen fixation. Here are the steps:

1. Nitrogen Fixation: Nitrogen gas (N2) in the atmosphere is converted into ammonia (NH3) by certain bacteria and archaea. This process is called nitrogen fixation. These microorganisms, known as diazotrophs, include bacteria such as Rhizobium, which lives in the root nodules of legumes, and cyanobacteria.

2. Nitrification: The ammonia is then converted into nitrite ions (NO2-) by bacteria such as Nitrosomonas species. This process is called nitrification.

3. Further Nitrification: Nitrite ions are then converted into nitrate ions (NO3-) by bacteria such as Nitrobacter species.

4. Assimilation: Plants absorb the nitrate ions through their roots and convert them into proteins and other organic nitrogen compounds.

5. Ammonification: When the plants and animals die and decompose, the organic nitrogen is converted back into ammonia by bacteria and fungi. This process is called ammonification.

6. Denitrification: Some bacteria in the soil and in the bottom sediments of lakes, oceans, swamps, and rivers convert the ammonia and nitrate ions back into nitrogen gas, which is released back into the atmosphere. This process is called denitrification.

This cycle of nitrogen fixation, nitrification, assimilation, ammonification, and denitrification is known as the nitrogen cycle.