Cambridge O Level Biology · Syllabus 5090 · Biotechnology and Genetic Modification
Impeller
What is Impeller?
A motor-driven stirrer inside an industrial fermenter. Turning the impeller distributes the microorganisms, the nutrients, the dissolved oxygen where air is supplied, and the heat produced by respiration, so that conditions are the same throughout the vessel rather than varying from place to place. Without stirring, cells settle out at the bottom, warm liquid collects at the top, nutrients are used up locally and oxygen reaches only the region above the sparger, so parts of the culture are starved while others overheat. Stirring distributes what is already present; it does not create nutrients or oxygen.
This definition is part of the Biotechnology and Genetic Modification chapter in Cambridge O Level Biology.
Common mistakes with Impeller
- “Stirring gives the bacteria more oxygen.” Why wrong Stirring cannot create oxygen. The oxygen came from the sparger; the impeller only moves it about. Say instead Stirring distributes the oxygen, nutrients, microorganisms and heat evenly through the culture.