Variation means the differences that exist between individuals of the same species. A student investigated one example of variation in plants. Walking along...
Question 1 Report
Variation means the differences that exist between individuals of the same species. A student investigated one example of variation in plants. Walking along a single hedge, the student picked 100 leaves at random, choosing them from many different parts of the hedge, and measured the length of each leaf in millimetres. To display the results, the lengths were grouped into equal classes and the number of leaves in each class was counted. These numbers are plotted as the frequency diagram in Fig. 1.1, in which the leaf length in millimetres is shown along the horizontal axis and the number of leaves is shown up the vertical axis. Use the frequency diagram in Fig. 1.1 to answer the questions that follow.
(a) State the type of variation shown by leaf length. [1]
(b) Using Fig. 1.1, state the class of leaf length that occurs most often. [1]
(c) Calculate the number of leaves that were 60 mm or longer. [2]
(d) Describe the overall shape of the distribution shown in Fig. 1.1. [2]
Answer Details
(a) Leaf length can take any value within a range and is measured on a continuous scale, so it shows continuous variation. Continuous variation is controlled by many genes together, usually with an environmental influence, and gives a smooth range of values rather than a few distinct categories. [1]
(b) The most common class is the one with the tallest bar, which is 50-59 mm. [1]
(c) "60 mm or longer" means adding the three classes 60-69, 70-79 and 80-89. Reading their bar heights from Fig. 1.1 and adding them: \( 19 + 9 + 3 = \mathbf{31} \) leaves (1 mark for correct working, 1 for the answer 31). [2]
(d) The distribution is roughly symmetrical / bell shaped [1], with most leaves in the middle classes and only a few at the two extremes [1]. This bell shape is the typical pattern produced by continuous variation. [2]
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