what does agar do
From Wikipedia, the free encyclopedia. An agar plate is a Petri dish that contains a growth medium (typically agar plus nutrients) used to culture microorganisms or small plants like the moss Physcomitrella patens. Selective growth compounds may also be added to the media, such as antibiotics.gar plates may also be indicator plates, in which the organisms are not selected on the basis of growth, but are instead distinguished by a color change in some colonies, typically caused by the action of an enzyme on some compound added to the medium.