Culturing Microorganisms

• Method:

  1. Sterilise all equipment
  2. Transfer bacteria into culture using an inoculating loop
  3. Attach the lid of the petri dish using adhesive tape. This stops the lid from falling off and unwanted microorganisms from entering
  4. Place the agar plate upside down into an incubator. This stops moisture from dripping onto the bacteria and disrupting colonies
• Independent variable

  Disinfectant type
• Control variable

  • Agar
  • Size of discs
  • Type of bacteria
• Dependent variable

  Area of the zone of inhibition
• How do bacteria multiply?

  Bacteria multiply by simple cell division (binary fission).
• What conditions allow bacteria to carry out binary fission every twenty minutes?

  As long as they have enough nutrients and the temperature is suitable.
• How do you calculate the number of bacteria present after a certain time using binary fission?


  • Use the formula: $b =$$2^n$
  • Where $n$ is the number of rounds of division.
  • Calculate $n$ by dividing the total time in minutes by the time per division (20 minutes).
• Sterilisation is a process used to kill unwanted microorganisms
• Aseptic techniques that are used:

  Disinfect hands or work surfaces

  Pass inoculating loop through flame