All animals get the nitrogen they need by eating plants or other animals. Nitrogen surrounds us, both in living things and in nonliving things like air, water and dirt.
The atmosphere contains about 78 percent nitrogen, which is an element. This nitrogen is in an unusable form for plants or animals, however. Instead, animals and humans eat plants or eat other animals that eat plants. The plants are rich in nitrogen that they acquire from either the soil or the water in which they grew. When plants or organisms die, they return the nitrogen they contain to the soil or water. Thus, the nitrogen is available to fuel the cycle again.