Required Practical 6

Question 1

Explain why there is a clear zone around each paper disk

Answer 1

Bacteria killed

Question 2

The student researched information on the disinfectant prior to carrying out his investigation. On the basis of this research, the student used a maximum concentration of disinfectant of 40% use the diagram to explain why

Answer 2

Clear zone would be too large

Clear zones would merge

Question 3

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

Answer 3

Same size
Same material
In solution for the same period of time

Question 4

Name the process by which bacteria cells divide

Answer 4

Binary fission

Question 5

Describe two aseptic techniques used when transferring a sample of broth culture onto an agar plate
Explain why each was important (4)

Answer 5

Keep lid on petrified dish-to prevent unwanted bacteria contaminating the dish
Wear gloves/mask/wash hands-prevent contamination from bacteria on hands
Use sterile pipette or flame the loop or the neck of the container of the culture-to maintain a pure culture of bacteria

Question 6

Suggest how low temperatures slows the rate of entry into cell surface membrane

Answer 6

Less kinetic energy

Question 7

Explain the purpose of boiling the agar

Answer 7

So no contamination

Question 8

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

Answer 8

So same number of bacteria transferred to allow comparison

Question 9

The student concluded that the minimum concentration of propanol 2-ol needed to stop the growth of lactobacillus was 15units. This conclusion is incorrect. Describe how you could obtain a more accurate estimate of the minimum concentration of propane-2-ol needed to stop the growth of this species of bacterium

Answer 9

Several values between 10 and 15 units

Repetitions of each