How do humans obtain the nitrogen they use in their bodies?

By consuming plants or other animals

by absorbing ammonia from bacteria growing in the roots of plants

by breathing the nitrogen present in the atmosphere

by absorbing nitrogen found in the soil

Animals get the nitrogen they need by eating plants or other animals that contain nitrogen. When organisms die, their bodies decompose bringing the nitrogen into soil on land or into ocean water. Bacteria alter the nitrogen into a form that plants are able to use.