Agar medium is used in petri dishes primarily because it helps microorganisms grow. Agar is a gelatinous substance derived from seaweed that provides a stable and nutrient-rich environment for bacteria and other microorganisms to grow. It serves as a solid support for growing colonies while allowing the nutrients in the media to be accessible to the microbes.
The other options you listed do not accurately describe the primary purpose of agar in petri dishes. While agar can help create an environment that supports growth, it does not sterilize dishes, make bacteria appear larger, or make cells glow.
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