22.6 Culturing Microorganisms in the Laboratory

Question 1

What is the culture of microorganisms?

Answer 1

growth of microorganisms

in the laboratory

Question 2

Why must health & safety regulations still be followed even when harmless bacteria are being cultured?

Answer 2

• MUTATION
  
  • mutation could cause harmless bacteria to become harmful
• CONTAMINATION
  
  • contamination of pathogenic bacteria could occur

Question 3

What are aseptic techniques?

Answer 3

techniques used to culture microorganisms in sterile conditions

so they are not contaminated

Question 4

What are the 2 types of inoculation?

Answer 4

1. INOCULATING BROTH - culturing of bacteria in a flask
2. INOCULATING AGAR - culturing of bacteria in agar

Question 5

How do you inoculate a broth?

Answer 5

(inoculating broth is the culturing of bacteria in a flask)

1. Make suspension of bacteria
2. Mix known volume of bacteria with sterile nutrient broth in flask
3. Stopper flask with cotton wool
   
   1. prevents contamination by microorganisms in air, but allows air flow to prevent anaerobic respiration.
4. Incubate at suitable temperature shaking regularly for aeration.

Question 6

How do you inoculate agar?

Answer 6

(inoculating agar is the culturing of bacteria in an agar plate)

1. Wire inoculating loop sterilised by holding over Bunsen flame until glows red hot, allow to cool.
2. Dip sterilised inoculating loop in bacteria suspension.
3. Remove lid of petri dish, make zig-zag streak across agar surface.
4. Tape lid to petri dish. Ensure air flow remains so bacteria do not respire anaerobically.

Question 7

What are the 4 stages of bacterial growth?

Answer 7

1. LAG
2. LOG
3. STATIONARY
4. DEATH

Question 8

Describe & explain the stages of bacterial growth:

Answer 8

1. LAG
   
   1. slow rate of growth
      
      1. bacteria adapting to new environment, synthesising enzymes etc
2. LOG
   
   1. very high rate of growth
      
      1. plentiful nutrients for bacteria to thrive & proliferate due to little/no competition
3. STATIONARY
   
   1. rate approx = 0
      
      1. nutrients become limiting, increases competition
4. DEATH
   
   1. rate = negative
      
      1. waste products build up, bacteria die out due to toxic environment

Question 9

What factors limit the rate of exponential growth of bacteria?

Answer 9

• NUTRIENT AVAILABILITY
  
  • initially plenty of nutrients to allow exponential growth
  • eventually cannot support further growth & reproduction (stationary phase)
• O₂ LEVELS
• TEMPERATURE
  
  • controls rate of enzyme-controlled reactions
  • limits rate of reproduction
• WASTE BUILDUP
  
  • toxic waste material inhibits bacterial growth
• CHANGE IN pH
  
  • CO₂ released from aerobic respiration decreases pH