Petri dish medium

AGAR

This jelly-like substance derived from seaweed is commonly used in labs to grow bacteria or fungi. You might find it in a microbiologist’s kitchen—though it’s not for eating!

A Petri dish medium is the substance used in labs to grow bacteria or other microorganisms, and the most common one is agar. The clue is straightforward—no wordplay or tricks—just a direct reference to the jelly-like material made from seaweed. If you’ve ever seen a science experiment with cultures, agar is likely what’s in that dish. The answer fits neatly as a four-letter word starting with "A.