Question 18M.2.SL.TZ1.f
| Date | May 2018 | Marks available | [Maximum mark: 3] | Reference code | 18M.2.SL.TZ1.f |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | f | Adapted from | N/A |
The land snail Cepaea nemoralis is very common in North America and in Europe.
The base colour of its shell varies between brown, pink and yellow, and also in its intensity. Some shells are unbanded, but most show one to five bands of different width on top of the shell base colour.
The population of C. nemoralis has been studied for many years in open fields in a similar area. In the graph, each data point represents the percentage of adults of a given base colour plotted against the percentage of juveniles of the same base colour collected each year.
Using the theory of natural selection, explain the differences shown in the graph between the three colours of snail.
[3]
a. natural selection requires that snails become adults/live to reproduce their variations/undergo differential predation OWTTE
b. higher adult frequency of brown shows selection
c. but results for pink do not show selection
d. more brown juveniles survive into adulthood showing that brown is selected for/vice versa against yellow
e. not enough alone to support theory of natural selection but may be added evidence to similar observations in other organisms OWTTE
