CUlturing microorganisms

Question 1

Why when culturing microorganisms, safety procedures must be followed?

Answer 1

• risk of mutation, making the strain pathogenic
• may be contamination of pathogenic organisms from the environment

Question 2

What must be controlled when culturing microorganisms?

Answer 2

• need the right food/nutrient medium
• temp
• oxygen
• and pH

Question 3

What is the differnece between broth and agar?

Answer 3

• both are nutrient mediums
• broth is liquid
• agar is solid

Question 4

How is a nutrient medium enriched?

Answer 4

• balance needed for organism
• protein sources such as blood or meat
• allows rapid reproduction

Question 5

Wgat are aseptic techniques?

Answer 5

• anything to keep sterile conditions

Question 6

How is broth inoculated?

Answer 6

• make suspensiton of the bacteria to be grown
• mix known volume of sterile nutrient broth in the flask
• stopper the flask with cotton woll to prevent contamination of the air
• incubate at a suitable temperature, shake to aerate the broth providing oxygen for growing bacteria.

Question 7

How is agar inoculated?

Answer 7

• the wire inocculating loop must be sterilised by holding it in a Bunesen flame until it glows red hot
  
  • must not be allowed to touch any surface as it cools to avoid contamination
• dip the sterilised loop in the bacterial suspension
  
  • remove lid of Petri dish and make a zig-zag streak across the surface
  • avoid the loop digging into the agar by holding it horizontal
• replace lid
  
  • held with tape but not sealed completely so oxygen can enter
  • preventing growth of anaeobic bacteria
  • incubate at suitable temperature

Question 8

What is the lag phase in the growth curve?

Answer 8

• when bacteria are adapting to their new environment
• they are growing, synthesising the enzymes they need
• they are not yet reproducing at their maximum rate

Question 9

What is the log phase?

Answer 9

• or the exponential phase
• when the rate of bacterial reproduction is close to or at its theoretical maximum

Question 10

WHat is the stationary phase?

Answer 10

• occurs when total growth rate is zero
• the number of new cells formed by binary fission is cancelled out by the number of cells dyingh

Question 11

WHat is the death stage?

Answer 11

• or decline stage
• reproduction almost ceased and death rate is incrasing.

Question 12

What are the limiting factors that prevent exponential growth?

Answer 12

• nutrients
  
  • initially plenty, used up, eventually insufficient to support further growth and reproduction
• oxygen
  
  • as pop rises, demand for oxygen rises
• temp
  
  • enzyme controlled reaction - high increases rate but eventually denatures them
• waste
  
  • tociv material inhibit further growth and may even poison or kill the culture
• change in pH
  
  • carbon dioxide produced increases as respiration increase
  • pH falls where it affects enzyme activity