Banded snails live in woodland and in grassland. Their shells can be brown or yellow.
Song thrushes are birds that eat snails. They break the shells open on stones.
Scientists counted the living snails in each habitat. They also counted the broken shells left by thrushes near the stones.
The Table shows the results.
Table
| Habitat | Colour of the ground | Percentage of living snails with brown shells | Percentage of broken shells that were brown |
|---|---|---|---|
| woodland | dark brown leaf litter | 75 | 30 |
| grassland | green grass | 20 | 70 |
Calculate the percentage of living snails in grassland that have yellow shells.
Use the data to explain why snails with brown shells are more common in woodland.
There is usually a lot of genetic variation within a population of a species.
Give one cause of genetic variation.
A student says:
'Snails that live in woodland turn brown so that birds cannot see them.'
Explain why the student is wrong.
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.