Growing and Investigating Bacteria Biology GCSE AQA

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  • Created by: Caitlinyx
  • Created on: 24-04-13 17:54
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  • Growing and Investigating Bacteria
    • Growing Micro-organisms in the lab
      • To culture micro-organisms you need to provide them with everything they need, so they are put in a liquid/gel which contains nutrients - a culture medium
        • This contains carbohydrates for an energy source along with other minerals and sometimes chemicals
        • You can provide the nutrients in agar jelly. Hot agar jelly is poured into a petri dish and left to cool before adding micro-organisms
      • You have to be careful when growing micro-organisms. You may want to grow harmless bacteria, but it can mutate into something more dangerous
      • You want to keep the strains of bacteria away from other pathogens
        • Contamination may come from your skin, the air, the soil or the water
        • Investigation needs uncontaminated cultures of micro-organisms
    • Growing Useful Organisms
      • Petri dishes on which you culture the micro organisms, and the agar jelly, needs to be sterilised before use, to kill all unwanted pathogens
        • Oven called autoclave sterilises by using high pressure steam
        • Petri dishes often bought ready sterilized
        • UV or Gamma radiation used to kill bacteria
        • Next step is to innoculate the sterile agar with the micro-organisms you want to grow
          • Sterilise innoculating loop by heating it until it is red hot in the bunsen burner and then beave it to cool
          • Dip the sterised loop in the bacteria and use it to make zig-zag streakes on the surface of the agar. Replace the lid quickly to avoid contamination
          • Seal the lid of the Petri dish with tape to prevent micro-organisms in the air from contaminating the petri dish, or micro-organisms from escaping. Do not seal all the way  so oxygen can get in and anaerobic bacteria does not grow
          • They need to be incubated for a few days so the micro-organisms can grow
            • Schools and colleges do not keep them over 25.C because it reduces the chance of harmful bacteria growing
            • In industrial conditions bacterial cultures are kept at higher temperatures so they can grow at higher rates

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