2018年5月IB生物SL真题下载-Paper2
1. 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.
In the early 1950s, scientists studied the proportion of colours and banding of C. nemoralis in woods and fields near Oxford, UK, which differed in the type of plants and background colour. Each data point on the graph represents the percentage of yellow base colour shells and unbanded shells in a sample from either one type of wood or field, although other snail colours were present.
In the early 1950s, scientists studied the proportion of colours and banding of C. nemoralis in woods and fields near Oxford, UK, which differed in the type of plants and background colour. Each data point on the graph represents the percentage of yellow base colour shells and unbanded shells in a sample from either one type of wood or field, although other snail colours were present.
(a) Determine the maximum percentage of yellow base colour shells found in woods.
(b) Suggest either one possible advantage or one disadvantage of having a banded shell, stating whether it is an advantage or disadvantage.
(c) Using the data in the graph, distinguish between the distribution of C. nemoralis shells in woods and fields.
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.
(d) Deduce from the data in the graph which shell base colours are on average most and least frequent among adult snails.
Most frequent:
Least frequent：
(e) Discuss whether there is evidence in the data that colour plays a role in the survival of the snails.
(f) Using the theory of natural selection, explain the differences shown in the graph between the three colours of snail.
2018年5月IB生物SL真题余下省略！
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