<prompt> Steriliation of culture media containing serum is by-AutoclavingMicropore filterGamma radiationCentrifugation  <response>: Ans. is b i.e., Micropore filter Sterilization of culture media The constituents of culture media must be carefully sterilized. Two methods are commonly used to sterilize culture media ? I Autoclaving - Constituents like water, salts and supplements like peptone, ttyptose etc., which are heat stable, are autoclaved. - Generally autoclaving is carried out at 121degC and at a pressure of 15 psi. - The time required for sterilization depends upon the volume of medium in the vessel? a For small volumes of liquids 100 ml or less, the time required for autoclaving is 15-20min. b For large quantities 2-4 liter 30-40 min is required. 2 Membrane filteration - Constituents like serum, trypsin, growth factors, proteins, amino acids, vitamins, hormones, carbohydrates and plant extracts are thermolabi le and may decompose during autoclaving. - These must be sterilized by filteration. - The porosity of the filter membrane should be no longer than 0.2 microns U m. - Empty glassware that is to hold media must be sterilized in an autoclave before filter sterilization. . These two autoclaving and membrane filteration are the most commonly used methods for sterilization of culture media. But when these are not available other methods can be used; e.g.? - For media containing sugar or gelatin, an exposure of 100degC for 20 minutes on three successive days may be used. This is known as Tyndallization. - Some media containing serum or egg fluid can be sterilized by heating to 80-85degC for 2-4 hours. 