Fig. 7.1 shows the results of a study into the effectiveness of two antibiotics, A and B, against a type of bacteria. Antibiotics are drugs used to treat ba...
Question 1 Report
Fig. 7.1 shows the results of a study into the effectiveness of two antibiotics, A and B, against a type of bacteria. Antibiotics are drugs used to treat bacterial infections, but bacteria can become resistant to them. Scientists grew the bacteria on agar plates and measured the diameter of the clear zone where the bacteria had been killed around a disc of each antibiotic. A larger clear zone means the antibiotic is more effective. The results are shown in the table below.
| Antibiotic | Diameter of clear zone / mm |
|---|---|
| A | 28 |
| B | 9 |
(a) Using the data, state which antibiotic is more effective against these bacteria. Explain your answer. [2]
(b) Explain how the clear zone is produced around the antibiotic disc. [2]
(c) Suggest why some bacteria may still grow close to antibiotic B. [2]
Answer Details
(a) Antibiotic A is more effective [1], because it produced the larger clear zone (28 mm compared with 9 mm), showing that it killed the bacteria over a wider area [1].
(b) The clear zone is produced because the antibiotic diffuses out of the disc into the surrounding agar [1] and kills or stops the growth of the bacteria around the disc, leaving a clear area with no bacterial growth [1].
(c) Some bacteria still grow close to antibiotic B because some of those bacteria are resistant to antibiotic B [1], so they survive and continue to grow even where the antibiotic is present [1].
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