The Nitrogen Cycle Game

Students play the role of nitrogen atoms traveling through the nitrogen cycle to gain an understanding of the varied pathways through the cycle and the relevance of nitrogen to living things.

Learning Objectives

• Students understand that nitrogen cycles indefinitely through the Earth system
• Students understand the places that it is found on Earth
• Students understand that nitrogen is essential for life
• Students learn that the cycle is nonlinear traveling between living things and the physical environment.

Materials

• Pens or pencils
• Paper
• 11 dice
• 11 stamps
  • different rubber stamps and ink pads OR printed paper "stamps" (see below in materials to print) and glue

Materials to Print

Preparation

1. Print Reservoir Station Signs
2. Copy Passport Student Sheet for each student.
3. Set up stations around the classroom (or outside). Each station will need a reservoir sign, a die, plus either an ink pad and rubber stamp OR stamps and a glue stick.

Directions

1. Introduce nitrogen. Where is nitrogen found on Earth? Why is it important? Explain that nitrogen travels with the help of bacteria, water, lightning, plants, and animals.
2. Show the nitrogen reservoir signs around the room and explain that these are the places to which nitrogen can travel. These places are called reservoirs.
3. Tell students that for this activity they are each playing the role of a nitrogen atom. They will travel through the nitrogen cycle (i.e., to different stations around the room) based on dice rolls. Tell students that they will each carry a nitrogen passport with them and stamp it each time they get to a nitrogen reservoir station. They will then toss the die at the reservoir to determine their next destination. Remind students to note in the passport how they get from one place to another based on the roll of the die.
4. Spread students so that there are a few at each station and allow them to start traveling with their passports.

Discussion

After everyone has filled their passport student sheet, discuss as a class:

• How many stops can you make on your trip?
• Will your journey ever end?
• Was everyone’s journey the same? Why not?
• What would happen if a farmer used a lot of fertilizer? (In this game, that would mean that everyone starts from the fertilizer station at the same time.)
• What happen as we burn fossil fuels?
• Livestock farming creates a large amount of animal waste. How would this affect the nitrogen cycle?

Assessment

• Students write about their trip through the cycle, including (1) where they went and (2) how they got there.
• Show students a diagram of the nitrogen cycle. Ask them to create a diagram documenting only their journey.

Background

Nitrogen is an element that is found in both the living portion of our planet and the inorganic parts of the Earth system. The nitrogen cycle is one of the biogeochemical cycles and is very important for ecosystems. Nitrogen cycles slowly, stored in reservoirs such as the atmosphere, living organisms, soils, and oceans along its way.

Most of the nitrogen on Earth is in the atmosphere. Approximately 80% of the molecules in Earth’s atmosphere are made of two nitrogen atoms bonded together (N2). All plants and animals need nitrogen to make amino acids, proteins, and DNA, but the nitrogen in the atmosphere is not in a form that they can use. The molecules of nitrogen in the atmosphere can become usable for living things when they are broken apart during lightning strikes or fires, by certain types of bacteria, or by bacteria associated with legume plants. Other plants get the nitrogen they need from the soils or water in which they live, mostly in the form of inorganic nitrate (NO3- ). Nitrogen is a limiting factor for plant growth. Animals get the nitrogen they need by consuming plants or other animals that contain organic molecules composed partially of nitrogen. When organisms die, their bodies decompose, which brings the nitrogen into the soil on land or oceans. As dead plants and animals decompose, nitrogen is converted into inorganic forms such as ammonium salts (NH4+ ) by a process called mineralization. The ammonium salts are absorbed onto clay in the soil and then chemically altered by bacteria into nitrite (NO2- ) and then nitrate (NO3- ). Nitrate is the form commonly used by plants. It is easily dissolved in water and leached from the soil system. Dissolved nitrate can be returned to the atmosphere by certain bacteria in a process called denitrification.

Certain actions of humans are causing changes to the nitrogen cycle and the amount of nitrogen that is stored in reservoirs. The use of nitrogen-rich fertilizers can cause nutrient leaching in nearby waterways as nitrates from the fertilizer wash into streams and ponds. The increased nitrate levels cause plants to grow rapidly until they use up the nitrate supply and die. The number of herbivores will increase when the plant supply increases, and then the herbivores are left without a food source when the plants die. In this way, changes in nutrient supply will affect the entire food chain. Additionally, humans are altering the nitrogen cycle by burning fossil fuels and forests, which release various solid forms of nitrogen. Farming also affects the nitrogen cycle. The waste associated with livestock farming releases a large amount of nitrogen into soil and water. In the same way, sewage waste adds nitrogen to soils and water.

Extensions

This version of the Nitrogen Cycle Game was developed for students who have not yet learned chemistry. As such, the transformations that happen to nitrogen (mostly underground and as a result of bacterial activity) are deemphasized. You may wish to explore the chemistry of the nitrogen cycle to extend learning for students who have a chemistry background.

The game is a simple model, making it an opportunity to discuss how models are alike and unlike the real world. Students may compare nitrogen cycle diagrams with the game and discuss how to adapt the game to be more like the real cycle process.