GCSE Biology

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  1. what is the method to culturing microorganisms
    • 1) collect the equipment you need
    • 2) steralise the inoculating loop used to transfer microorganisms to the agar by heating it in a red hot bunsen flame , then leave it to cool
    • 3) dip the cool steralised loop into the suspension of bacteria you want to grow then use it to make zig zag streaks across the surface of the agar
    • 4) secure the lid of the petri dish with short pieces of tape
    • 5) label the petri dish clearly and place it in an incubator at no more than 25 °C
    • 6) after a few days . examine the surface of agar
  2. stage 3 involves dipping the cool steralised loop into the bacteria you want to use . We then use the innoculating loop to make zig zag streaks across the surface of the agar . Here we should :
    • tilt the lid of the petri dish to keep out unwanted microbes
    • we also have to close the lid as quickly as possible to avoid conatimiantion
  3. stage four involves securing the lif of the petri dish with a short piece of tape to
    stop microorganisms from the air contaminating your culture and to stop microbes from your culture from escaping into the air , however we musnt seal all the way around the edge
  4. what equipment do you need for culturing microorganisms
    • a sterile petri dish containing a layer of sterile nutrient agar jelly
    • culture of harmless bacteria
    • inoculating loop
    • bunsen burner
    • marker pen or label
    • sealing tape
  5. explain why agar is suitable as a culture medium for growing bacteria
    • we can steralise it without affecting it
    • microbes cannot digest agar so it is not used up as they grow
    • it supplies nutrients and moist conditions to the microbes to enable them to grow
  6. what temperature does agar melt and why is this an advantage
    it melts at 98°C so it can be poured into plates it then solidifies at 44°C
  7. what is meany by aseptic
    something that is clear of microorganisms
  8. give 3 ways in which microbiological equipment and media can be steralised
    • autoclave
    • ultraviolet
    • ionising radiation
  9. explain why the agar plates are cultured in the incubator at 25°C
    because it is at the lower end of the ideal conditions , this allows bacteria to grow , however harmful bacteria needs a higher temperature so will not grow at this temperature
  10. explain why the loop needs to be cooled before picking up the microbes
    the heat from the wire may kill the microbes
  11. suggest why the lid of the petri dish is not removed completly whne introducing the microorganisms
    so that other microbes cannot enter
Card Set
GCSE Biology
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