RP6 - aseptic techniques

Question 1

explain why there is a clear zone around each paper disc

Answer 1

bacteria killed

Question 2

the student used only 40% concentration of disinfectant. explain why

Answer 2

clear zones would be too large and overlap

Question 3

suggest two variables the student should control in using filter paper discs in this investigation

Answer 3

any 2 from
- same size
- same material
- left in solution for same amount of time

Question 4

name the process in which bacterial cells divide

Answer 4

binary fission

Question 5

describe 2 aseptic techniques that should be used when transferring a sample of broth culture onto an agar plate. explain why each is important

Answer 5

• keep lid on petri dish
• to prevent unwanted bacteria contaminating the dish
  OR
• wear gloves
• to prevent contamination of bacteria on hands
  OR
• use sterile pipette
• to maintain pure culture of bacteria

Question 6

explain purpose of boiling the agar

Answer 6

so no contamination of other bacteria

Question 7

explain purpose of transferring the same volume of liquid culture onto each agar plate

Answer 7

so same number of bacteria transferred to allow comparison

Question 8

a student concluded that minimum concentration of propan-2-ol needed to stop growth of bacterium was 15 units. this conclusion was incorrect.
describe how you could obtain a more accurate estimate of the minimum concentration of propan-2-ol needed to stop the growth of this species of bacterium.

Answer 8

repeat several values in between 10 and 15