Agar and agarose are two forms of solid growth media that are used for the culture of microorganisms, particularly bacteria. Both agar and agarose act to solidify the nutrients that would otherwise remain in solution. Both agar and agarose are able to liquefy when heated sufficiently, and both return to a gel state upon cooling.

Solid media is prepared by heating up the agar and nutrient components so that a solution results. The solution is then sterilized, typically in steam-heat apparatus known as an autoclave. The sterile medium is then poured into one half of sterile Petri plates and the lid is placed over the still hot solution. As the solution cools, the agar or agarose becomes gel-like, rendering the medium in a semi-solid. When bacteria contact the surface of the medium, they are able to extract the nutrients from the medium and grow...