What is the function of an impeller?

Correct answer: To mix the medium

Direct answer: Option A is correct. An impeller is a rotating device inside a fermenter or bioreactor that stirs the culture medium. Stirring helps distribute nutrients, cells, heat and dissolved gases more evenly, and it can improve the transfer of oxygen from the air into the liquid. The basic chain is: the impeller rotates; rotation moves the liquid; moving liquid becomes mixed; better mixing supports more uniform growth and processing conditions. Option A describes this central function. Option B, packing the product, happens during a later packaging stage and is not done by the impeller inside the fermenter. Option C, melting glass, is unrelated to fermentation equipment. Option D, filtering soil, is not the purpose of a rotating mixing blade and does not describe bioreactor operation. The exact impeller design may vary according to the organism, viscosity and process, but its school-level role remains agitation and mixing. A small caution: an impeller is not identical to an aeration system; it mainly mixes, though it can assist oxygen transfer. Memory trick: impeller means “impel” or push the liquid around.