Question 18M.2.SL.TZ1.e
| Date | May 2018 | Marks available | [Maximum mark: 3] | Reference code | 18M.2.SL.TZ1.e |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Discuss | Question number | e | 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.
Discuss whether there is evidence in the data that colour plays a role in the survival of the snails.
[3]
Evidence that colour plays a role:
a. few yellow adults (relative to juveniles) means that yellow juveniles do not survive into adulthood
b. frequent brown adults (relative to juveniles) means brown juveniles survive well into adulthood
Evidence that colour does not play a role:
c. similar numbers of adult and juvenile pink individuals means pink colour does not play a role
d. all three colours show wide variation/considerable overlap therefore evidence is not strong
