RP9

• Aseptic technique


  Used to avoid contamination of the sample from outside substances such as microorganisms
• Aseptic technique


  • Important to get reliable and repeatable data
• Aseptic technique


  1. Wipe down surfaces with antibacterial cleaner before and after experiment

  2. Use a Bunsen burner in the work space so that convection currents draw microbes away from the culture

  3. Flame the wire hoop before using to transfer bacteria

  4. Flame the neck of any bottles before use to prevent any bacteria entering the vessel

  5. Keep all vessels containing bacteria open for the minimum amount of time

  6. Close windows and doors to limit air currents
• Equipment


  • Agar plate seeded with bacteria
  • Sample of garlic
  • Sample of mint
  • Mortar and pestle
  • Methylated spirit
  • Pipette
  • Paper discs
  • Petri dish
  • Forceps
  • Tape
• Method


  1. Carry out aseptic techniques detailed above

  2. Crush 3g of the garlic and mint (separately) with methylated spirit. Shake occasionally

  3. Use a sterile pipette to transfer plant extract to paper disc

  4. Leave paper discs to dry for 10 minutes

  5. Use sterile forceps to place the paper disc onto a petri dish

  6. Lightly tape a lid on, invert and incubate at 25°C for 24 hours

  7. Sterilise equipment used to handle bacteria and disinfect work surfaces

  8. Measure the diameter of the inhibition zone (clear circle) for each plant. DO NOT remove lid from agar plate

  9. Work out the area of the inhibition zone using the formula: pi * (d/2)^2 where d is the diameter
• Bacteria sample is incubated at 25°C as incubating at 37°C (human body temperature) could enable pathogens to grow that are harmful to humans
• Hazards


  • Disinfectant (flammable)
  • Biohazard (contamination, infection)
  • Naked flame (fire hazard, burns)
  • Methylated Spirit (flammable and toxic)
• Safety precautions


  • Keep disinfectant away from naked flame
  • Use disinfectant, wash hands with soap after dissection, do not incubate at human body temperature, do not open agar plate post incubation
  • Keep away from flammable materials, tie up long hair, keep away from edge of desk
  • Keep away from naked flame, do not ingest, wear gloves and goggles
• In emergency


  • Put out fire, seek assistance
  • Seek assistance
  • Put out fire, seek assistance, run burns under cold water immediately
  • Seek assistance
• Risk level


  • Low
  • Low/medium (depends on likeliness of bacteria sample used to cause infection)
  • Low
  • Medium
• Graph


  1. Plot a bar chart of the area of the inhibition zone against plant

  2. Include range bars to show the uncertainty from the ruler in measuring the diameter