BIO250L Lab 4 Selective Media & Agar

1. What is the difference between chemically defined and chemically complex media? Give either a clinical or environmental research example for which each media type would be the most appropriate choice for culturing microorganisms. The key difference between chemically defined and chemically complex media are their compositions. Chemically defined media is made up of all known compositions. While, chemically complex media is made up of unknown compositions (which can vary from batch to batch). An example of chemically defined media would be glucose broth and an example of chemically complex media would be nutrient broth. 2. Why is differential media typically inoculated with isolated colonies that have been previously cultured on general growth media? Differential media is typically inoculated with isolated colonies that have been previously cultured on general growth media as it allows the growth of certain bacteria. These organisms tend to be visually differentiated from biochemical reactions from different species or groups. You want to have a pure, isolated colony that has been able to grow without a medium affecting it. Once you have your pure culture, you can use it to test against the known cultures on the selective and differential media.You can then compare your unknown reactions to those of the known cultures to try and determine which bacteria it is based on the known bacteria you've tested it against on the media.