RP culturing microorganisms

Question 1

list 6 ways to reduce contamination

Answer 1

1. petri dishes must be sterilised before use
2. inoculating loop must be sterilised first by passing it through a hot flame
3. lid of petri dish should be lightly taped on
4. petri dish stored upside down
5. lift lid of agar plate at and angle
6. spray area with disinfectant

Question 2

why does the equipment need to be sterilised?

Answer 2

to kill any bacteria present

Question 3

why does the lid of the petri dish need to be taped on?

Answer 3

to stop microorganisms from the air getting in

Question 4

why does the petri dish need to be stored upside down?

Answer 4

to stop drops of condensation falling onto the agar surface

Question 5

culture medium

Answer 5

a gel or liquid that contains the conditions bacteria need to grow

Question 6

what temperature do harmful pathogens grow above?

Answer 6

25°c

Question 7

method investigating effect of antibiotics

Answer 7

1. clean hands and work space with disinfectant
2. mark the bottom of the plate, split into 3 sections
3. put a different antiseptic on each filter paper disc
4. carefully lift the lid of the agar plate at an angle away from your face and use forceps to place each paper disc in each section, note which antiseptic is in which zone
5. secure the lid using two pieces of tape
6. incubate the plate at 25°C for 48 hours
7. measure the diameter of the clear zone around each disc, and take another measurement at 90° to the first one and calculate mean
8. calculate the area using πr²

Question 8

safety

Answer 8

1. wear goggles when handling disinfectant
2. wash hands before and after handling bacteria

Question 9

error

Answer 9

1. shape of clear zone may be irregular and width difficult to determine
2. contamination may occur

Question 10

why do you not completely seal the lid?

Answer 10

to allow oxygen to enter the agar plate, preventing the growth of harmful anaerobic bacteria

Question 11

variables antiseptic experiment

Answer 11

independent-antiseptic
dependent-zone of inhibition
control-size of paper, amount of antiseptic used

Question 12

larger zone meaning

Answer 12

larger the inhibition zone, more effective the antibiotic is against bacteria

Question 13

why are cultures incubated at 25°C in school?

Answer 13

harmful pathogens are less likely to grow at this temperature

Question 14

how would you measure the zone of inhibition?

Answer 14

use a ruler to measure from a point on one side to the other, measure again at 90° to first measurement and calculate mean

Question 15

why should you measure diameter twice?

Answer 15

clear zones aren’t always uniform, taking two measurements allows a mean diameter to be calculated

Question 16

method preparation of culture

Answer 16

1. sterilise equipment
2. pour sterile agar jelly into petri dish and set
3. sterilise inoculating loop by passing it through a bunsen burner
4. dip inoculating loop into solution of microorganisms and make streaks with loop on surface of agar
5. put the lid on petri dish and secure with tape
6. store upside down at 25°C

Question 17

state 2 ways in which bacteria can be grown?

Answer 17

nutrient broth solution
colonies on an agar jelly plate