What is the purpose of agar?

Agar is used to solidify microbiological media. Having a solid media allows microbiologists to see colonies of bacteria this eases the identification of a single microbe in a mixed population it also allows the selection of variants in a population, it perhaps allows identification from colonial morphology and enumeration of bacteria. Solid media in lawn cultures (spread plates) are used to calculate zones of diffusion/inhibition. Agar is used rather than other substances as reativly few microbes can manufacture the digestive enzymes required to break it down, so the solid media does not become liquid.

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It is a solidifying agent.