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AQA GCSE · Question 03.7 · Infection and Response
The scientists wanted to be more certain about which antibiotic should be prescribed. Describe how the results in Figure 4 could be used to obtain a quantitative comparison of antibiotics A and B.
The scientists wanted to be more certain about which antibiotic should be prescribed. Describe how the results in Figure 4 could be used to obtain a quantitative comparison of antibiotics A and B.
How to approach this question
The word "quantitative" means getting a numerical result. How could you measure the clear zones for A and B to get numbers that you can compare? Think about the geometry of the zones.
Full Answer
Measure the diameter or radius of the zones of inhibition for A and B and calculate their areas (using πr²). The one with the larger area is more effective.
A visual comparison can be subjective. To get a quantitative (numerical) comparison, the scientists should measure the zones of inhibition. The most accurate method is to:
1. Use a ruler to measure the diameter of the clear zone for both antibiotic A and antibiotic B.
2. Calculate the radius (diameter / 2) for each.
3. Calculate the area of each circular zone using the formula: Area = πr².
The antibiotic that corresponds to the larger calculated area is the more effective one. Simply comparing diameters is also a valid quantitative comparison, but calculating the area is a more complete method.
Common mistakes
✗ Just saying "measure the zones" without specifying what to measure (diameter, radius, or area).
✗ Forgetting to mention calculating the area, as this is the best measure of the total effect.
Practice the full AQA GCSE Biology Higher Tier Paper 1
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