The Nitrogen Cycle

Nitrogen (N) is an element like carbon. All creatures need nitrogen to survive. There are huge amounts of nitrogen gas in the atmosphere, but most animals and plants have no way of using it. It needs to be fixed (put into a biologically useful compound). After it is fixed, it can then start to move through the cycles and organisms in an ecosystem. 

Where Can You Find It?

Let's start with the main sources of nitrogen. Nitrogen gas is the most abundant element in our atmosphere. The other main source of nitrogen is in the nitrates of soil. The nitrogen in the atmosphere cannot be used while the nitrates in the soil can be used by plants. Nitrogen can be converted into useful nitrate compounds by bacteria, algae, and even lightning. Once in the soil, the nitrogen becomes biologically accessible. 

Borrowing Nitrogen

Plants are the main users of nitrogen in the soil. They are able to take in the nitrates through their root system. Once inside the plant, the nitrates are used in organic compound that let the plant survive. Organic compounds have carbon atoms. Those compounds might be proteins, enzymes, or nucleic acids. 

Once the plants have converted the nitrogen, the element can be returned to the soil or taken up by animals. Herbivores eat plants and convert many of the amino acids into new proteins. Omnivores that eat both plants and animals are able to take in the nitrogen rich compounds as well. The nitrogen compounds are only borrowed. Nitrogen atoms are returned to the soil in poop and dead organisms. Once in the soil, the whole process can start again.