chemically defined and complex media



Lab 4 Selective Media & Agar BIO250L”

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“Pre-Lab Questions”

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.

In chemically defined media, the ingredients that make up the chemical media are know

and can be identified and quantity known such a medium is use to determine the least

amount of nutrients that a microbe needs to survive In chemically complex media the

chemical composition is unknown.the ingredients in this media have an organic origin for

instance, blood, and animal or human tissue can be added to a culture to enable a

pathogen to grow. The reason these organic ingredients are added is because the

pathogen is already know to grow in an animal or a human being

2. Why is differential media typically inoculated with isolated colonies that have been previously

cultured on general growth media?

Differential media is used in previously isolated colonies to identify specific microbes on

basis of the characteristics of that mircorogranism. One example is how agar can

differentiate between hemolytic and non hemolytic bacteria-

3. Use a textbook or a reputable internet source (such as to research and describe a

scenario in a lab or clinical setting in which a selective and/or differential test would be


In the case where a microbe is resistant to an antibiotic, selective test can and have

been used on a culture that is already resistant to anti-biotic.this allows for the cells that

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