Part 6: Culturing Microorganisms

Question 1

Why might scientists grow bacteria?

Answer 1

Bacteria can be used to investigate how effective disinfectants and antibiotics are.

Question 2

What is the use of disinfectant when growing bacteria?

Answer 2

Kills bacteria on the lid

Question 3

What is the use of a petri dish when growing bacteria?

Answer 3

Container with lid to grow bacteria

Question 4

What is the use of agar jelly when growing bacteria?

Answer 4

Food for the bacteria to grow on

Question 5

What is the use of a bunsen burner when growing bacteria?

Answer 5

• Used to sterilise equipment
• Creates an updraft to stop airborne contamination

Question 6

What is the use of an inoculation loop when growing bacteria?

Answer 6

Transfers bacteria from the culture to the agar jelly

Question 7

What is the use of a glass spreader when growing bacteria?

Answer 7

Spreads bacteria over the surface of the agar jelly

Question 8

What is the use of an incubator when growing bacteria?

Answer 8

Oven used to grow bacteria in at 25°C

Question 9

Explain the importance of keeping the conditions sterile.

Answer 9

1. It is important to sterilise solutions and equipment to kill bacteria already on them.
2. Otherwise, they would grow and contaminate the culture to be studied.

Question 10

Explain why microorganisms are not incubated above 25°C in schools.

Answer 10

There would be a high risk of growing some dangerous pathogens.

Question 11

Describe the different stages of growing bacteria and explain why you do this. (6)

Answer 11

1. Prepare by cleaning the desk with disinfectant and washing your hands with soap - you do this to kill unwanted microorganisms.
2. Sterilise the petri dishes on which you grow your microorganisms - this is so unwanted microorganisms are killed.
3. Inoculate by dipping a sterilised inoculating loop in a suspension of bacteria you want to grow - this is to investigate that specific bacteria.
4. Incubate: after the plates have been inoculated, the petri dishes have to be inoculated - this is do the microorganisms can grow.
5. Cleaning up
6. Disposal of the plate: once the experiment is finished, the agar plate is sterilised using a steam pressure cooker called an autoclave and can then be thrown away - this is to kill the bacteria before the petri dishes is thrown away so pathogens are not formed.

Question 12

Explain why you must never open a petri dish that has bacteria growing inside.

Answer 12

The growing bacteria can be exposed to mutations which can cause them to become pathogens.

Question 13

What does no zone of inhibition suggest?

Answer 13

No bacteria has been killed

Question 14

What does a zone of inhibition mean?

Answer 14

Bacteria has been killed or prevented from growing.

Question 15

Explain how you could calculate the area of the ‘zones of inhibition’.

Answer 15

Ω × r²