Group Work: The Nitrogen Cycle


These descriptions correspond to the numbers on the diagrams. Please fill in the blanks with the correct terms for each process or bacterial group described.

1. All fish ____________ nitrogen into the water as ammonia and organic nitrogen. These chemicals are byproducts of their metabolism and respiration.

What kind of nitrogen do fish eat? (circle correct answer)

Organic Nitrogen Ammonia Nitrate Nitrogen gas

2. All heterotrophic bacteria eat organic nitrogen and release ammonia as a byproduct. This process is called ______________ (there are two terms for this, either one is correct).

What is the difference between heterotrophic and autotrophic organisms?


Remember that the ammonia that is released into the water is chemically converted to ammonium, so the following statements use ammonium instead of ammonia.

3. There are other bacteria that use the ammonium in the water as a nitrogen source and take it up to make organic nitrogen and new bacteria. When they do this and hold the nitrogen inside bacterial cells, it is called _______________.

4. _________________ is when certain bacteria use ammonium as their energy source and convert it to nitrite or use nitrite and convert it to nitrate.

a. The bacteria that convert ammonium to nitrite are the ________- bacteria. An example is ______________________.

b. The bacteria that use nitrite and make nitrate are the ___________- bacteria; an example is _______________________.

5. ___________________ occurs when the ammonium in the water becomes a gas and enters the atmosphere.

6. In anaerobic (no oxygen) environments, like sediments, some bacteria use nitrate as their final electron acceptor (instead of oxygen). This process is called _______________ and produces nitrogen or nitrous oxide gas, which then leaves the water and enters the atmosphere.

7. A few groups of bacteria and algae are able to use the nitrogen gas in the atmosphere as their nitrogen source. During ___________________ they take up nitrogen gas and make new organic nitrogen in their cells.

8. When there are plants in your tanks to help clean the water, the plants use the ammonium and nitrate as nutrients to make new plant matter. It depends on which plants you are using as to which type of nitrogen they prefer. Can you find any examples of plants that prefer:

a. Ammonia?

b. Nitrate?

List the chemical symbols for the following nitrogen compounds:

Ammonia _____

Ammonium _____

Nitrite _____

Nitrate _____

Nitrogen gas _____

Nitrous oxide _____