An important part of microbiology labwork centers on isolating one microbe from all the other contaminants in the environment. It is common to use chemical additives to control bacterial growth on media so that growth of desired microbes is encouraged and growth of contaminants is suppressed. These media are called selective media, and the chemicals that stop growth of unwanted microbes are called inhibitors. Expect to encounter selective media in the microbiology lab.
Another strategy to control growth does just the opposite. Some media are made selective by forcing bacteria to use a single source of carbon or nitrogen. Those species of bacteria that can grow under these conditions do so, but those that cannot use the substance don't grow. We will see media that use this strategy when working in a micro lab.
There are also biochemical tests that give hints to metabolic activities of cells that we take advantage of to control growth. For instance, the nitrate reduction/nitrite reduction test looks at the use of those chemicals as final electron acceptors for some bacteria growing in the absence of oxygen. In such a test, it is possible to see from a microbiological perspective why the addition of the chemicals is a common practice in preparing processed meats in sealed plastic packaging.
For some examples of specialized media such as those described above, use VUMIEtm 2012 and complete MDM Exercise 6 "Controlling Microbial Growth".
Your instructor will inform you of what documentation to turn in: Virtual Lab Report, MDM Exercise 6, or other. When done, you may be asked to take a quiz over the material.