My Fish Tank: An Active Learning Activity for Bacterial Nitrogen Metabolism

This active learning activity introduces students to the second part of the nitrogen cycle, nitrification. In terrestrial and aquatic environments, bacteria from the Nitrosomonas and Nitrobacter genera oxidize ammonia first to nitrite (via a hydroxylamine intermediate) and then to nitrate, which is less toxic to animals such as the fish in a fish tank. Nitrification has many practical implications, for example in waste water treatment, but also for those wanting to set up their own fish tank. The activity consists of a pre-class reading, a 50-minute class session, and a home assignment. The class session covers two exercises, each consisting of a group discussion, followed by student reporting, and a compilation of information by the instructor. Students will identify animal nitrogen waste products and fish skin bacteria that are involved in nitrification. Students will also identify the metabolic reactions of the nitrogen cycle, the oxidative state of nitrogen in four metabolic compounds, and the number of electrons transferred through each reaction. The third and final exercise is the take-home assignment, where students write about how they would set up their own fish tank and take care of their fish based on knowledge gained from the in-class exercise. Primary Image: Nitrification is one of three parts of the nitrogen cycle in both terrestrial and aquatic environments. Nitrification consists of two reactions that first convert ammonia to nitrite and then to nitrate. In the fish tank, this serves to detoxify the water that the fish live in.