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Health, Disease and the Development of Medicines

Aseptic technique in culturing microorganisms

  • 3 things to know
  • Paper 1

Overview

Aseptic technique, sterilising growth medium and Petri dishes in an autoclave, flaming and cooling the inoculating loop, keeping cultures covered and taping lids, and why school cultures are incubated at 25 °C.

What you need to know

Answer each one before you reveal it.

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Key term

What is meant by aseptic technique?

Key term

What is an autoclave used for?

Key term

Explain why growth medium must be sterilised before it is used.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by aseptic technique?

    Model answer

    Working in a way that prevents unwanted microorganisms contaminating a culture or escaping into the surroundings.

  2. 2

    What is an autoclave used for?

    Model answer

    An autoclave uses steam at high temperature and pressure to sterilise growth medium and Petri dishes.

  3. 3

    Explain why growth medium must be sterilised before it is used.

    Model answer

    Any microorganisms already present would grow on the medium and make the results invalid.

  4. 4

    Describe how an inoculating loop is sterilised.

    Model answer

    It is held in a Bunsen flame until it glows red hot, then allowed to cool.

  5. 5

    Explain why an inoculating loop must be cooled before it touches a culture.

    Model answer

    A hot loop would kill the microorganisms it is meant to transfer.

  6. 6

    Explain why Petri dishes and culture vials are kept covered.

    Model answer

    The lid stops microorganisms in the air landing on the medium, and stops the cultured microorganisms escaping.

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