Day Number of bacteria killed by the standard dose 1 980 2 910 3 640 4 320 5 90 Bacteria can reproduce very rapidly, and a large population may contain a fe...
Question 1 Report
| Day | Number of bacteria killed by the standard dose |
|---|---|
| 1 | 980 |
| 2 | 910 |
| 3 | 640 |
| 4 | 320 |
| 5 | 90 |
Bacteria can reproduce very rapidly, and a large population may contain a few individuals that differ from the rest because of random changes in their genes. When an antibiotic is used to treat an infection, these differences can affect whether a bacterium survives. A scientist grew a population of bacteria and treated it with the same dose of an antibiotic every day for five days, counting the number of bacteria killed by the standard dose each day. The results of this investigation are shown in Table 10.1.
(a) Using the data in Table 10.1, describe how the number of bacteria killed by the antibiotic changed over the five days. [2]
(b) State the name of the process, first described by Darwin, by which the resistant bacteria became more common in the population. [1]
(c) Explain, in terms of variation and survival, why the population of bacteria became resistant to the antibiotic. [4]
(d) Suggest one way in which the spread of antibiotic-resistant bacteria between human patients could be reduced. [2]
(e) State the source of the original variation that allowed a few bacteria to survive the antibiotic. [2]
Answer Details
This question tests natural selection using antibiotic-resistance data: variation exists, the antibiotic selects the resistant survivors, and they pass on the resistance.
(a) Using the data, the number of bacteria killed fell each day [1], from 980 on day 1 to 90 on day 5 (a large decrease) [1]. Fewer are killed because more of the survivors are resistant.
(b) The process, first described by Darwin, is natural selection [1].
(c) Why the population became resistant, in terms of variation and survival: there is variation among the bacteria [1]; a few have an allele that gives resistance to the antibiotic [1]; these resistant bacteria survive and reproduce while the non-resistant ones are killed [1]; and the resistance allele is passed on to the offspring, so resistant bacteria become more common in the population [1].
(d) One way to reduce the spread of resistant bacteria between patients (clear points, max 2): doctors prescribe antibiotics only when they are really needed; patients always finish the full course; or good hygiene and isolation of infected patients [2].
(e) The source of the original variation was mutation [1]: a random change in the genes / DNA of a bacterium [1].
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