Culturing microorganisms

• How do bacteria multiply


  binary fission
• How often do bacteria multiply?


  once every 20 minutes
• 2 ways bacteria can grow?


  .nutrient broth solution

  .colonies on an agar gel plate
• What nutrients make up a nutrient broth solution?

  nitrogen-protein synthesis

  carbohydrates-energy

  other minerals
• What are uncontaminated cultures of microorganisms needed for?


  Investigating disinfectant and antibiotic action
• Describe prep of an uncontaminated culture using aseptic technique?


  1. use pre-sterilised petri dish and agar gel before using with autoclave
  2. pour the sterile agar gel into the petri dish and allow time to set
  3. sterilise the inoculating loop by passing it through a bunsen burner flame
  4. dip the inoculating loop into the solution of microorganisms and make streaks with the loop on the surface of the agar
  5. put the lid on the petri dish and secure with tape. label it and turn and store upside down
  6. incubate the culture at 25 degrees in school lab
• Why must petri dishes and culture media be sterilised before use?


  to kill any bacteria already present
• Why must inoculating loop be sterilised by passing it through a flame?


  to kill any bacteria present on the inoculating loop
• Why must the petri dish lid be secured with tape and stored upside down?


  stops bacteria in the air contaminating the cultue

  lid not fully sealed to prevent lack of oxygen for culture

  upside down to prevent condensation from forming and dripping onto the colonies
• Why is bacteria incubated at 25 degrees in school labs?

  harmful pathogens are less likely to grow at this temperature
• Formula used to calc cross-sectional area of bacterial colony or clear area around a bacterial colony?


  $πr^2$
• How is the number of bacteria in a population after a certain time calc from the mean division time?


  1.calc the number of times bacteria will divide given time period

  2.use the following equation to calculate the number of bacteria:

  number of bacteria in population at the end of time period= number of bacteria at the beginning of the time period x 2 to the power of number of divisions in time period