The effect of antimicrobial substances on bacterial growth: analysis and conclusions | Biology

Starter quiz

What is this?

'Agar plate' ✓
What letter represents the radius of this circle?

A ✓

B

C
Using a value of 3.14 for 𝜋, calculate the area of this circle.

28.3 cm²

9.4 cm²

7.1 cm² ✓

4.7 cm²
Match the aseptic technique to its reason.

flaming the inoculating loop

⇔

sterilises the wire to avoid contaminating the bacteria bottle ✓

lift the plate lid to a 45° angle

⇔

prevents unwanted microorganisms from settling on the agar ✓

flaming the neck of the bottle

⇔

prevents bacteria contaminating the air ✓

spraying disinfectant

⇔

kills microorganisms on work surfaces ✓
The Oak pupils are discussing aseptic technique. Who is correct?

Lucas: You shouldn't use a Bunsen burner because you could burn yourself.

Sofia: You should use a Bunsen burner so microorganisms in the air won't settle. ✓

Laura: You should use a Bunsen burner to kill bacteria in your agar plate.

Jun: You shouldn't use a Bunsen burner as agar is flammable.
Which variables should be controlled in the investigation into the effect of antimicrobial substances on bacterial growth.

the size of the clear zone

the type of antiseptic

incubation time ✓

incubation temperature ✓

the size of the paper discs ✓

What are the clear areas around the paper discs?

areas with lots of bacterial growth

areas of antiseptic

areas where bacteria can not grow or have been killed ✓

areas where the agar can not grow

areas where the antiseptic has covered via active transport
Which antibiotic is the most effective?

a

b ✓

c

d
Put these steps in order to show how you would test which antibiotics should (and should not) be used to treat a patient's disease.

1

⇔

Take a sample of bacteria from the patient.

2

⇔

Grow the sample bacteria on an agar plate in culture.

3

⇔

Add antibiotic discs to the bacteria and culture the plate again.

4

⇔

Compare the sizes of any clear zones of inhibition around the discs.
The area of the zone of inhibition is ______ mm².

'200.96' ✓
Which antibiotic are bacteria resistant to?

a ✓

b
Which antimicrobial is the least effective?

'C' ✓

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The diameter of a clear zone of inhibition around an antimicrobial disc can be measured.
The areas of clear zones can be calculated using 𝜋r² and compared to investigate antimicrobial effectiveness.
The larger the clear zone of inhibition, the more effective the antimicrobial has been in killing the bacteria.
The importance of testing the effectiveness of antimicrobials in clinical settings.

Pupils often use the diameter instead of the radius when calculating the area of a clear zone of inhibition around a disc.

Remind pupils that we use 𝜋r² to calculate the area, so they need to find the radius first.

Antimicrobial - A substance that slows down or stops the growth of microorganisms, such as bacteria.
Agar plate - A Petri dish containing a growth medium solidified with agar jelly, used for culturing microorganisms.
Zone of inhibition - The clear area around an antimicrobial disc on an agar plate where bacterial growth has been stopped.
Aseptic technique - Practical methods used to prevent contamination by unwanted microorganisms.