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The Nitrogen Cycle

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Format: Interactive (Online), Printable (PDF)
Grades: 45
Subjects: elareadingscience
Standards: RI.4.4RI.4.2
Languages: English, Spanish

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About this reader

The nitrogen cycle describes how nitrogen moves through the air, soil, and living organisms. It involves processes like nitrogen fixation and denitrification, ensuring nitrogen is available for plants and animals to grow and live. Understanding the nitrogen cycle highlights its role in agriculture and the environment.

Written by Neha Goel TripathiPublished by Workybooks

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nitrogen cycle, nitrogen fixation, denitrification, fertilizer

The Nitrogen Cycle: Nature’s Recycling Program

Nitrogen is a very important element for all living things. It helps build strong proteins and DNA, which are like instructions for life. In fact, about 78% of the air we breathe is made of nitrogen gas. But most plants and animals can’t use nitrogen directly from the air. It has to be changed into a form they can use, and that’s where the nitrogen cycle comes in.

Step 1: Nitrogen Fixation

The first step is called nitrogen fixation. Special bacteria in the soil and in little bumps called nodules on the roots of bean and pea plants can change nitrogen gas into ammonia, a form plants can use. Sometimes, lightning can also help by breaking apart nitrogen gas and turning it into useful compounds for plants.

Step 2: Plant Absorption

Once nitrogen is fixed, plants absorb these nitrogen compounds through their roots. Plants use nitrogen to grow and make their own food. Without enough nitrogen, plants can’t grow strong and healthy.

Step 3: Animal Consumption

Animals get nitrogen by eating plants. They use it to build their own proteins and muscles. When you eat beans, peas, or other plants, you are getting the nitrogen your body needs!

Step 4: Decomposition

When plants and animals die or produce waste, decomposers like bacteria and fungi break down the material. This process releases nitrogen back into the soil, so the cycle can continue.

Step 5: Denitrification

Some bacteria can change nitrogen in the soil back into nitrogen gas. This process is called denitrification. The nitrogen returns to the air, and the cycle starts again.

Why the Nitrogen Cycle Matters

The nitrogen cycle helps keep soil healthy and lets plants and animals grow. Farmers sometimes add fertilizer to soil to give plants extra nitrogen. But too much fertilizer can pollute rivers and lakes. That’s why some farmers plant beans and peas to naturally add nitrogen to soil instead of using chemicals.

The nitrogen cycle is like a recycling program for an essential vitamin—nitrogen travels from air to bacteria to plants to animals and back to air in an endless loop!

Interesting Fact: Some plants, like beans and peas, are called nitrogen-fixing plants because they help add nitrogen to the soil all by themselves.

What is nitrogen used for?

Building proteins and DNAMaking rocksCreating sunlightMaking water

Where is most nitrogen found?

In the atmosphereIn oceansIn treesIn animals

What do decomposers do?

Break down dead thingsMake sunlightFly in the skyAbsorb water

Why do farmers use fertilizer?

To add nitrogen to soilMake soil dryAttract animalsGrow more rocks

What happens if too much fertilizer is used?

Water pollutionMore rainFewer plantsColder soil

How do animals get nitrogen?

By eating plantsBy photosynthesisBy breathing airFrom the sun