Carbon is just one element that moves through an ecosystem via a biogeochemical cycle. The element nitrogen also cycles through the environment. Nitrogen is also known as a building block of life because it is present in proteins. Click through the slides below to learn more about the nitrogen cycle.

Nitrogen Gas Almost 80% of the atmosphere is made of nitrogen gas. This makes the atmosphere the largest reservoir of nitrogen on the earth. Nitrogen Fixation Bacteria in the soil and in the roots of certain plants are able to take the nitrogen from the atmosphere and change it into a usable form. This process is called fixation. (For example, the bacteria take nitrogen atoms from the atmosphere and use them to make NH4+.) Nitrogen can also be "fixed" (converted to a usable form) by lightning strikes. Ammonification/Nitrification Ammonium (NH4+) is a substance that contains nitrogen. Waste from animals, as well as dead tissue, is turned into ammonium by bacteria, fungi, and other decomposers, as well as bacteria that are living in the soil. Ammonium is then converted to another nitrogen-containing compound called nitrate (NO3-). Again, bacteria in the soil complete this step of the nitrogen cycle.  Assimilation Plants take in nitrate or ammonium through their roots in a process called uptake or assimilation. Animals assimilate when they consume plants or plant parts. (Assimilate means "to become part of"; the nitrogen becomes part of plant and animal cells.) Denitrification Some bacteria convert nitrates back into nitrogen gas, which is then released into the atmosphere. Eutrophication Too much nitrogen in an ecosystem can be harmful. Eutrophication can occur when nitrogen (from the fertilizers used on lawns and crops) enters a body of water through runoff. Excess nitrogen can cause algae and other plants in the body of water to grow out of control, causing an upset in the balance of the ecosystem and death of the animals that rely on oxygen in the water.

How well do you understand the nitrogen cycle? Drag the vocabulary term to the blank that completes the sentence correctly.