Warfarin is a poison used to kill rats. It was first used in one town in 1955.
Scientists tested rats from the town to find the percentage that were resistant to warfarin.
The Table shows the results.
Table
| Year | Percentage of rats resistant to warfarin |
|---|---|
| 1955 | 1 |
| 1960 | 6 |
| 1965 | 30 |
| 1970 | 62 |
| 1975 | 81 |
Describe the trend shown in the Table.
Calculate the mean increase in the percentage of resistant rats per year between 1955 and 1975.
A farmer says:
'Warfarin made the rats change their genes so that they could survive the poison.'
Explain why the farmer is wrong.
Bacteria can become resistant to an antibiotic in a few years.
Suggest why it took about 20 years for most of the rats in the town to become resistant to warfarin.
122 exam-style questions on OCR GCSE Biology 5.2 Natural selection and evolution, covering 5.2.1 Genetic variation within a population, 5.2.2 Developments in classification systems, 5.2.3 How evolution occurs through natural selection, 5.2.4 Evolution as change over time, 5.2.5 Evidence for evolution, and 5.2.6 Darwin and Wallace. Each one has a worked solution and a mark scheme showing where the marks go.