Investigating antibiotics & antiseptics (Edexcel GCSE Biology Combined Science): Revision Notes
📚 Revision Notes
Investigating antibiotics & antiseptics
Comparing the sizes of the inhibition zones compares the effectiveness of different antibiotics (or antiseptics or plant extracts)
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The effectiveness of the selected antibiotic or antiseptic can be quantified using the formula for the area of a circle, πr². Using the diagram below:
- For π, use the value 3.14. This value may vary slightly in specific questions.
- Measure the diameter of the zone of inhibition and divide it by 2 to obtain the radius (e.g., 10 ÷ 2 = 5 mm).
- Apply the equation: πr²
- For example: 3.14 × 5² = 3.14 × 25 = 78.5 square millimetres.
Calculate the sizes of the inhibition zones to compare results
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The larger the inhibition zone around the disc the more bacteria killed so the more effective the antibiotic is against the bacteria