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AQA GCSE · Question 03.5 · Infection and Response
What is the purpose of the paper disc with no antibiotic in Figure 4?
What is the purpose of the paper disc with no antibiotic in Figure 4?
How to approach this question
In a scientific experiment, what is the name for the setup that is kept under the same conditions but without the factor being tested? Its purpose is to provide a baseline for comparison.
Full Answer
It is a control.
The paper disc with no antibiotic is the control. Its purpose is to show that any zone of inhibition (the clear area where bacteria have not grown) around the other discs is due to the antibiotic itself and not due to the paper disc or the solvent used to dissolve the antibiotic. As you can see in the diagram, bacteria grow right up to the control disc, proving that the paper alone has no effect on their growth.
Common mistakes
✗ Saying "to see what happens" - this is too vague.
✗ Saying "to test if the bacteria grow" - we already expect them to grow. The purpose is for comparison.
Practice the full AQA GCSE Biology Higher Tier Paper 1
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