Nitrogen gas (N₂) is abundant in the atmosphere, but this form of nitrogen gas is not usable by most organisms.

Consumers obtain nitrogen by eating producers. Consumers use the compound to build protein.

Energy from lighting converts nitrogen gas, N₂ into nitrates, NO₃.

Denitrifying bacteria are free-living in the soil and can break down nitrates, NO₃, back into nitrogen gas, N₂.

Decomposers convert the organic nitrogen found in decaying plants and animals into ammonia, NH₄.

Animal waste contains ammonia, NH, and is found in the soil.

Plants can absorb nitrate, NO₃, through their roots and use the compound to build proteins.

Nitrifying bacteria, that in in the roots of some type of plants, convert nitrogen from the air into nitrates, NO₃.

Free-living nitrifying bacteria can convert ammonia back into nitrates, NO₃.