culturing microorganisms practical

Question 1

investigating effect of antiseptics

Answer 1

• place paper discs soaked in different
  antiseptics on an agar plate that has an
  even covering of bacteria, leaving space
  between the discs
• antiseptics should diffuse into the agar
  jelly. antiseptic-resistant bacteria will
  continue to grow, but non-resistant strains
  will die.
• a clear area will be left where the bacteria
  have died - this is the inhibition zone
• use a control - a paper disc soaked in
  sterile water. then you can be sure any
  difference in growth is due to the effect of
  the antiseptic
• leave the plate for 48 hours at 25’C

Question 2

why cant cultures of microorganisms be kept above 25’C

Answer 2

because harmful pathogens will grow

Question 3

why should we use uncontaminated cultures

Answer 3

contamination by unwanted microorganisms will affect your results and can result in the growth of pathogens

Question 4

how to avoid contamination

Answer 4

• sterilise petri dishes by heating it
• sterilise innoculating loop with a flame
• tape on lid of petri dish to stop
  microorganisms from the air getting in
• store petri dish upside down to stop drops
  of condensation falling onto the agar
  surface

Question 5

calculating inhibition zone

Answer 5

area = 𝝅r²