culturing microorganisms

• What technique is used to prepare uncontaminated bacterial cultures?

  Aseptic technique
• How do bacteria reproduce?

  By binary fission
• How often can bacteria double in number with enough nutrients?

  Every 20 minutes
• What is a nutrient broth solution used for?

  To grow and divide bacteria
• Why is the broth cloudy?

  It contains a large number of bacteria
• What is an agar gel plate?

  A petri dish with nutrient broth gel
• What chemical is used to solidify nutrient broth into agar?

  Agar
• What is the purpose of sterilizing petri dishes and nutrient broth?

  To kill unwanted microorganisms
• How is bacteria transferred into the culture?

  Using an inoculating loop
• How do you sterilize an inoculating loop?

  Pass it through a flame
• Why do we attach the lid of the agar plate with adhesive tape?

  To prevent contamination
• At what temperature do we normally incubate bacteria in schools?

  25 degrees Celsius
• Why do we incubate agar plates upside down?

  To prevent moisture from disrupting colonies
• What is the first step in investigating the effect of antibiotics?

  Clean the bench with disinfectant
• What does the flame do when opening a sterile agar plate?

  Kills bacteria in the air
• What do we place on the agar plate to test antibiotics?

  Sterile filter paper disks containing antibiotics
• What is the area where bacteria do not grow around the antibiotic disk called?

  Zone of inhibition
• How do we measure the effect of antibiotics on bacteria?

  By calculating the area of the zone of inhibition
• What is the formula to calculate the area of the zone of inhibition?

  Area = PI × R squared
• If the radius of the zone of inhibition is 12 mm, what is the area?

  452.45 mm²
• What is the value of PI used in calculations?

  3.14
• What are the steps to prepare an uncontaminated bacterial culture using aseptic technique?

  1. Sterilize petri dishes and nutrient broth
  2. Sterilize inoculating loop by passing through flame
  3. Transfer bacteria using the loop
  4. Attach lid with adhesive tape
  5. Incubate agar plate upside down at 25°C
• What are the steps to investigate the effect of antibiotics on bacterial growth?

  1. Clean bench with disinfectant
  2. Sterilize inoculating loop by passing through flame
  3. Open sterile agar plate near Bunsen burner flame
  4. Spread bacteria evenly over the plate
  5. Place sterile antibiotic disks on the plate
  6. Incubate at 25°C and observe results
• What factors affect bacterial growth in cultures?

  • Nutrient availability
  • Temperature
  • Oxygen levels
  • pH levels
  • Presence of antibiotics
• why must we use a control paper disc

  • soak disk in sterile water
  • can be sure that any difference between growth of bacteria around control disc and around one of the antibiotic discs is due to the effect of the antiobiotic alone
• how could the student improve the investigation

  repeat and calculate a mean