The Nitrogen Cycle
Adapted from â€œTraveling Nitrogenâ€ by the Windows to the Universe
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 Earthâ€™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 bringing the nitrogen into soil on land or into the 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 loading 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 releases 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.
The Nitrogen Cycle Activity
Student Learning Outcomes:
- 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 physical environment
In this activity you are playing the role of a nitrogen atom. You will â€œtravel throughâ€ the nitrogen cycle (i.e., to different stations) based on dice rolls.
On the first slide (after the title slide) in the Powerpoint below, you will select a location in the Nitrogen Cycle in which to start – you can select any place you like to start. Click on the reservoir name where you would like to begin. (You will need to hold down the â€œCtrlâ€ key while clicking on the Hyperlinked Text to get you to the next reservoir, if you are not viewing the Powerpoint as a slideshow.) Write this down on your worksheet.
You will then roll a die at each reservoir â€œstopâ€ to determine your next destination. Remember to note on your worksheet the next reservoir you â€œvisitâ€ and how you got from one place to another based the roll of the die. (If you do not have dice, you can use the dice roll simulator at https://www.random.org/dice/?num=1 or download a dice roll simulator as an app for your phone.)
Continue traveling through the nitrogen cycle until you make 12 stops on your trip and fill up your worksheet.
After your trip is complete, draw a diagram of your Nitrogen cycle based on the stops you made at each reservoir. See a picture of the nitrogen cycle in your textbook to get an idea about how you should draw this.