The Nitrogen Cycle — Passage and Quiz

Nitrogen is a gas that makes up most of the air we breathe. It's also very important for all living things. The nitrogen cycle is how nitrogen moves through the air, soil, and living things.

Most plants and animals can't use the nitrogen in the air directly. It needs to be changed into a form they can use. This happens through a process called nitrogen fixation. Some special bacteria in the soil can do this. They turn nitrogen from the air into a form that plants can use.

Plants take in this usable nitrogen through their roots. When animals eat these plants, they get nitrogen too. When plants and animals die, decomposers break them down. This releases nitrogen back into the soil.

Some of this nitrogen turns back into a gas and goes into the air. This is called denitrification. The cycle then starts all over again.

Farmers sometimes add nitrogen to the soil to help plants grow better. This is called fertilizer. But too much fertilizer can be bad for the environment. It can pollute water and harm animals.

The nitrogen cycle is important because it makes sure living things have the nitrogen they need to grow and live. Without it, plants wouldn't be able to make food, and animals wouldn't have enough protein to build their bodies.