A Petri dish (Petri plate) is a shallow cylindrical glass lidded dish that is typically used to culture microorganisms (agar plates). There are glass and plastic Petri dishes, and both can be sterilized (using an autoclave) and re-used. Before being used for culture purposes, it is important to ensure that the Petri dish is not only clean, but also sterile. This helps prevent the contamination of the new culture.Agar is a polymer made up of various sub-units of galactose and various species of red algae. Although it has other uses including culinary and dentistry, agar plays an important role in microbiology as culture media for a variety of microorganisms.As compared to some of the other alternatives like gelatin, agar has a number of advantages which include:Cannot be easily degraded by microorganism Stronger Firmer than gelatin
