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Year 11
AQA
Foundation

The effect of antimicrobial substances on bacterial growth: practical

I can use aseptic techniques to investigate the effect of antimicrobial substances on bacterial growth.

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New
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Year 11
AQA
Foundation

The effect of antimicrobial substances on bacterial growth: practical

I can use aseptic techniques to investigate the effect of antimicrobial substances on bacterial growth.

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Lesson details

Key learning points

  1. Uncontaminated cultures of microorganisms are required to investigate the action of antimicrobials.
  2. Bacteria can be grown on an agar plate using aseptic techniques.
  3. Examples of aseptic techniques used in culturing bacteria.
  4. Discs soaked in antimicrobial substances can be used to investigate their effect on bacterial growth.

Keywords

  • Aseptic technique - Practical methods that help to prevent contamination with unwanted microorganisms.

  • Agar plate - Petri dish containing growth medium solidified with agar jelly.

  • Culture - Growing cells or tissue in growth medium in a laboratory, usually in an incubator.

  • Antimicrobial - Substance that slows down or stops the growth of microorganisms such as bacteria.

Common misconception

Pupils may think that all antimicrobial substances are equally effective against all microorganisms.

The effectiveness of different antimicrobial substances against bacteria can be tested.


To help you plan your year 11 biology lesson on: The effect of antimicrobial substances on bacterial growth: practical, download all teaching resources for free and adapt to suit your pupils' needs...

Make a big point of showing students how to label their agar plate. Students often label the lids which can move around so then they don't know which antimicrobial is which. Do not let students open their plates once they have been incubated - they must stay sealed.
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Teacher tip
equipment-required

Equipment

Agar plate, disinfectant surface cleaner, Bunsen burner, heat proof mat, wire inoculating loop, bacterial suspension, sticky tape, forceps, paper discs, antiseptic solutions, incubator.

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Content guidance

  • Risk assessment required - equipment
supervision-level

Supervision

Adult supervision required

copyright

Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
True or false? Bacteria are eukaryotic.
true
Correct answer: false
Q2.
How does penicillin directly impact bacteria?
It stops the DNA from replicating.
Correct answer: It stops the formation of the cell wall.
It stops the formation of the cell membrane.
It stops the cytoplasm from dividing during replication.
Q3.
We grow microorganisms on agar gel because...
An image in a quiz
Correct answer: it contain nutrients.
it is translucent.
Correct answer: it provides water.
it can be made in a container.
Q4.
Which statements are correct?
Antibiotics and antimicrobials are the same.
Correct answer: Antimicrobials kill or slow the spread of microorganisms.
Correct answer: Antibiotics kill or slow the spread of bacteria.
Antibiotics only kill viruses.
Antimicrobials kill viruses and antibiotics kill bacteria.
Q5.
When bacteria mutate and become less susceptible to the action of antibiotics they are said to have developed antibiotic .
Correct Answer: resistance, insensitivity
Q6.
Put the following steps in order to show how antibiotic resistance develops.
1 - A random mutation occurs in the DNA of a bacterium.
2 - The mutation gives the bacterium resistance to the antibiotic.
3 - The bacterium reproduces passing on the mutation to the next generation.
4 - Many bacteria are now resistant to the antibiotic.
5 - The antibiotic no longer works.

Exit quiz

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6 Questions

Q1.
You are investigating the effect of different antiseptic solutions on bacterial growth on an agar plate. Match the variables to their descriptors.
Correct Answer:independent variable,type of antiseptic
tick

type of antiseptic

Correct Answer:dependent variable,size of clear zone
tick

size of clear zone

Correct Answer:control variables,incubation temperature and time
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incubation temperature and time

Q2.
Starting with sterilising the inoculating loop, put these steps in the correct order to explain how you culture bacteria using aseptic technique.
An image in a quiz
1 - Put the wire inoculating loop into the Bunsen burner flame until it glows.
2 - Wait for the loop to cool before using it.
3 - Open the bottle of bacteria and pass the neck of the bottle through the flame.
4 - Dip the inoculating loop into the bottle of bacteria and then remove.
5 - Flame the neck of the bottle again and replace the lid.
6 - Lift the lid of the agar plate and use the loop to streak bacteria on the plate.
7 - Flame the inoculating loop again to sterilise it.
Q3.
Match the aseptic technique to its purpose.
Correct Answer:flaming the inoculating loop,sterilises the wire to avoid contaminating the bacteria bottle
tick

sterilises the wire to avoid contaminating the bacteria bottle

Correct Answer:flaming the neck of the bottle,prevents bacteria escaping and contaminating the air
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prevents bacteria escaping and contaminating the air

Correct Answer:working next to a lit Bunsen burner,reduces risk of microorganisms settling on surfaces and equipment
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reduces risk of microorganisms settling on surfaces and equipment

Correct Answer:using an autoclave,sterilises equipment by killing microorganisms using heat before use.
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sterilises equipment by killing microorganisms using heat before use.

Q4.
When using an agar plate with a live culture, what details should you write on the plate?
Correct answer: your initials
the type of agar
Correct answer: the date you prepared the plate
Correct answer: the type of bacteria used
the date you plan to collect your results.
Q5.
In a school, what temperature should you incubate bacterial samples at?
Correct answer: 25 °C
30 °C
35 °C
37 °C
40 °C
Q6.
The Oak pupils are discussing how to seal their agar plates before incubation. Who is correct?
Jun: We should not put any tape on the agar plate as this might prevent growth.
Jacob: We should put tape all the way around to make sure no bacteria escape.
Correct answer: Izzy: We should only use a few bits of tape to avoid anaerobic bacteria growing.
Sam: We should only use two bits of tape so the plate can be opened and checked.

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