Nitrogen Cycle


Nitrogen Cycle introduces students to this important process that converts nitrogen into substances that are useful to living organisms. Students will discover why this process is so important to survival. They will also learn what each of the five steps are and be able to explain them to others.

In the “Options for Lesson” section, you will find several ideas for other activities you could incorporate into the lesson if you want to or have extra time. One idea is to have students create 3D models of the nitrogen cycle rather than posters for the activity.

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What our Nitrogen Cycle lesson plan includes

Lesson Objectives and Overview: Nitrogen Cycle teaches students about the importance of this process to life. Students will discover that it is essential to the survival of all living things. They will also learn and be able to explain what happens during each of the five steps of the cycle. This lesson is for students in 4th grade, 5th grade, and 6th grade.

Classroom Procedure

Every lesson plan provides you with a classroom procedure page that outlines a step-by-step guide to follow. You do not have to follow the guide exactly. The guide helps you organize the lesson and details when to hand out worksheets. It also lists information in the yellow box that you might find useful. You will find the lesson objectives, state standards, and number of class sessions the lesson should take to complete in this area. In addition, it describes the supplies you will need as well as what and how you need to prepare beforehand. For this lesson, you will need construction paper or other drawing paper, colored pencils or markers, and any other material you think students could use to create their posters for the activity.

Options for Lesson

The classroom procedure page contains an “Options for Lesson” section that lists a number of suggestions for additional activities or tasks to add to the lesson. A couple of these ideas relate specifically to the activity. Students could work in pairs or small groups rather than alone. They could create 3D models of the nitrogen cycle instead of flat posters, using the construction paper and other supplies. Another suggestion is to assign a different step to five groups of students. The students will then create a short skit that details that step. As another assignment, students could research other cycles that relate to this one. One more idea is to invite an environmentalist to speak with the class about related issues.

Teacher Notes

The teacher notes page provides a paragraph of extra information regarding the lesson. It suggests teaching this lesson at the same time as others that relate to ecosystems, the environment, and so on. The blank lines on this page are available for you to write out thoughts and ideas you have as you prepare the lesson.


Natural Cycles

The Nitrogen Cycle lesson plan contains three pages of content. One of the most basic cycles of the earth is the water cycle, which moves water all around the planet. There is no end or beginning to any of the earth’s cycles, including the water cycle. Water evaporates, turns into gas (water vapor), changes into clouds, and then comes back down as rain or other precipitation. Once the water reaches the surface of the earth, the cycle continues.

Another important cycle on Earth is the carbon cycle, which is closely tied to the water cycle. Carbon is the basis of life for all living things. It moves around constantly because many processes on the planet use and require carbon atoms. Some of the processes put carbon into the atmosphere and others remove it.

Yet another element that is necessary for all life on Earth is nitrogen. In fact, about 78% of the atmosphere is nitrogen. The element makes up about 3% of our body weight. However, most nitrogen in the air is not usable by plants and animals, so it must change into different states. The conversion of the nitrogen into something useful for animals and plants is the foundation of the nitrogen cycle.

Just as water moves between Earth and its atmosphere, nitrogen moves between plants, animals, bacteria, the air, and soil in the ground. It is the basis of the nitrogen cycle. Plants use nitrogen to help them to grow faster, but too much of it can cause acid rain.

Nitrogen Cycle

Neither plants nor animals can use the nitrogen in the air directly. Animals need nitrogen to make proteins, and plants need it to make chlorophyll. Chlorophyll is necessary during photosynthesis (the process plants use to make their own food). Animals receive nitrogen by eating plants or by eating other animals that have eaten plants. Nitrogen is actually essential to the growth and creation of DNA.

Students will learn that the cycle is continuous, so there is no real start or finish. For the sake of keeping track, the lesson marks the start as nitrogen in the atmosphere. It enters soil by either precipitation or by lightning. During the fixation step, the nitrogen bond breaks. Bacteria in the soil changes it into ammonium, a chemical derived from ammonia. Nitrogen at this step is still unsafe for plants so it must be combined with oxygen or hydrogen.

The next step is nitrification. The ammonium changes or converts first into nitrites and then into nitrates by a different bacterium. Plants can now absorb the nitrates and build up proteins. During assimilation, the plants absorb the nitrates from the soil into their roots. Then plants can use the nitrogen in amino acids, nucleic acids, and chlorophyll.

When animals eat the plants, they use it to build protein, too. As the animals either poop, pee, or die, decomposers break down waste. The nitrogen is then reintroduced into the soil in the form of ammonia during the step ammonification. Finally, the extra nitrogen in the soil can return to the air as gas with the help of special bacteria.

Problems with the Nitrogen Cycle

The cycle repeats itself once the nitrogen returns to the atmosphere. Without bacteria in the cycle, plants or animals could not convert the nitrogen for their use. All organisms rely on the nitrogen cycle to live and survive. However, if an organism receives too much or too little nitrogen, it causes negative effects.

As with each of the cycles of the earth, they can be affected by human behavior. The nitrogen cycle can be affected in three ways: nitrogen fertilizer, deforestation, and fossil fuel burning. The first, nitrogen fertilizer, is used on plants throughout the world. But it causes additional nitrogen to enter those ecosystems.

The trees and other plants in forests help retain the nitrogen in the atmosphere. When we clear our forests, the amounts of nitrogen in the air and in the wetlands increase. And when it comes to burning fossil fuels, the result is an increase in the amount of nitrogen in the atmosphere.

Since human behavior can cause problems with the nitrogen cycle, that means changing such behavior can diminish those problems. People can try to use natural fertilizer, such as is available through composting. We can also support environmental organizations and choose to walk or bike instead of using a car. The nitrogen cycle is vital for all living organisms today and in the future.


The Nitrogen Cycle lesson plan includes three worksheets: an activity worksheet, a practice worksheet, and a homework assignment. Each of these will help reinforce students’ grasp of the lesson concepts and help students demonstrate what they learned throughout the lesson. The guide on the classroom procedure page describes when to hand out each worksheet to the class.


For the activity, students will use the supplies you provide to create a poster that displays the steps of the nitrogen cycle. The posters should include images and labels for nitrogen, plants, animals, decomposers, nitrites, and so on. Students can use the content pages and other sources for help. They should use arrows to show the flow the steps and include text to help explain the steps clearly. In addition, they should include a title for their posters. The worksheet provides a space that students can use to sketch a rough draft before starting on the final poster.


The practice worksheet divides into two parts. For the first part, students will match information to the correct step of the nitrogen cycle. There are 12 statements or descriptions and five steps. Students will thus use each step more than once. The second part requires students to respond to nine questions or prompts based on what they learned in the lesson.


Similar to the practice worksheet, the homework assignment splits into sections. The first section requires students to fill in the blanks for 10 statements. There are 10 terms in the word bank at the top of the page for students to use to complete this section. For the second part, students will explain three concepts as they relate to the nitrogen cycle. Finally, students will respond to a prompt that requires them to name things they can do to prevent problems that relate to the cycle.

Worksheet Answer Keys

The last two pages of the lesson plan PDF are answer keys for the practice and homework worksheets. All the correct answers are in red to make it easy for you to compare them with students’ responses. For the most part, students’ work should match the answer keys. However, there will be some variation on the second part of the practice worksheet and the last part of the homework assignment given the nature of these sections. If you choose to administer the lesson pages to your students via PDF, you will need to save a new file that omits these pages. Otherwise, you can simply print out the applicable pages and keep these as reference for yourself when grading assignments.

Additional information


4th Grade, 5th Grade, 6th Grade



State Educational Standards


Lessons are aligned to meet the education objectives and goals of most states. For more information on your state objectives, contact your local Board of Education or Department of Education in your state.

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The Nitrogen Cycle

I absolute love it. It is so helpful and all the information you need to cover the Nitrogen Cycle. I will be ordering more topics!!

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Nitrogen Cycle

Just what I needed for my high school special ed students. The reading level was spot on for them.