required practical: culturing microorganisms

• What technique is used to prepare uncontaminated bacterial cultures?

  Aseptic technique
• How do bacteria reproduce?

  By binary fission
• Under suitable conditions, how often can bacteria double in number?

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

  To grow and divide bacteria
• Why does the broth appear cloudy?

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

  A petri dish with nutrient broth gel
• 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 petri dish 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 do we use to spread bacteria on the agar plate?

  An inoculating loop
• What do we place on the agar plate to test antibiotics?

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

  Zone of inhibition
• How do you calculate the area of the zone of inhibition?

  Area = $\pi R^2$
• If the radius of the zone of inhibition is 12 mm, what is the area?

  Area = 452.45 mm²
• What are the steps to prepare an uncontaminated bacterial culture using aseptic technique?

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

  1. Clean the bench with disinfectant
  2. Sterilize inoculating loop
  3. Spread bacteria on agar plate
  4. Place antibiotic disks on the plate
  5. Incubate at 25°C and observe results
• What are the key components of a nutrient broth solution?

  • Water
  • Nutrients (carbohydrates, proteins, vitamins)
  • Minerals
• What factors affect bacterial growth in cultures?

  • Nutrient availability
  • Temperature
  • pH levels
  • Oxygen levels