Nitrogen Cycle 2.2 Cycles of Matter 2.2.3 Nitrogen Cycle About 78 percent of the atmosphere is made up of nitrogen. Nitrogen from the atmosphere is transformed into compounds that can be used by living organisms. When organisms die, decomposers return nitrogen to the atmosphere to complete the cycle. The basic steps of the nitrogen cycle.
Bacteria use nitrogen from the air to make compounds.
These compounds can then be used by plants to make other compounds. These compounds can then be used by animals. When the animals die, bacteria break down the compounds and return the nitrogen to the soil or to the air, where the cycle begins again. The Nitrogen Cycle.