Culturing Microorganisms (Practical)

• What are the conditions needed for bacteria growth?

  1. Temperature - most bacteria grow fastest in warm environments.
  2. Nutrient availability - bacteria need a good supply of nutrients in order to grow rapidly.
  3. Moisture - most bacteria grow fastest in moist conditions.
  4. Oxygen - different types of bacteria either need the presence or absence of oxygen for growth.
• What are the two nutrients needed for the plant to grow?

  1. Nutrient broth - a liquid medium (like water)
  2. Agar - a gel medium (like firm jelly)
• What is one technique used to prevent contamination?

  Cleaning surfaces with disinfectant
• Why is it important to clean the work area before and after use?

  To eliminate potential contaminants
• What should you do before handling microorganisms?

  Wash hands with antiseptic soap
• What does sterilising instruments involve?

  Heating objects to destroy microorganisms
• What is a sterile field created by?

  A Bunsen burner flame updraft
• How does a sterile field help biologists?

  It minimizes exposure to contaminants
• What is the maximum temperature set for incubators when growing bacteria?

  25°C
• Why is 25°C used for incubating bacteria?

  It prevents growth of harmful pathogens
• How does the temperature of 25°C compare to the body temperature of pathogens?

  25°C is lower than the body temperature
• How is the inoculating loop sterilised before use?

  By placing it in a Bunsen burner flame
• Why is the inoculating loop allowed to cool in the sterile field area?

  To prevent killing the bacterial culture
• What is done after removing the lid from the bacterial culture bottle?

  The neck of the bottle is flamed
• What is the purpose of flaming the neck of the bacterial culture bottle?

  To move air out and prevent contamination
• What should be done after flaming the neck of the bottle?

  Dip the sterilised inoculating loop into the culture
• What is done after dipping the inoculating loop into the bacterial culture?

  The neck of the bottle is flamed again
• Why is the Petri dish lid lifted slightly?

  To make zig-zag streaks across the agar
• How are the zig-zag streaks made on the agar?

  Gently and carefully with the inoculating loop
• What is done after making the zig-zag streaks?

  The Petri dish lid is quickly replaced
• Why is the lid of the Petri dish secured?

  To prevent contamination
• How should the Petri dish be stored in the incubator?

  Upside down
• What is the maximum temperature in the incubator at schools and colleges?

  25°C
• Why is the maximum temperature set at 25°C in educational settings?

  To prevent the growth of harmful bacteria
• What is done after the Petri dish is stored?

  The inoculating loop is sterilised again
• Why are all work surfaces disinfected after the procedure?

  To eliminate any potential contaminants
• What is the zone of inhibition?

  • Bacteria that are not affected by the substance will grow - bacterial growth will be visible close to the paper discs.
  • Bacteria that are affected by the substance will die - leaving a clear area surrounding the paper discs.

  This clear area is called the inhibition zone, and it can be calculated using the equation:

  area = $\pi\ r^2$
• When bacteria are grown on agar plates, each visible 'group' of bacteria is referred to as a:

  Colony
• Why is the Petri dish lid only partially lifted?

  To prevent the entry of microorganisms from the air.
• Bacteria can be grown in a...

  Nutrient broth

  Agar plate
• The agar gel provides bacteria with the ______ they require to grow.

  nutrients
• What is the term for the procedures used to prevent contamination when culturing microorganisms?

  Aseptic techniques
• A student placed an antibiotic disc on an agar plate containing bacteria. There was no clear area around the antibiotic disc. 

  What does this observation tell you about the effectiveness of the antibiotic?

  The antibiotic is ineffective