A student investigated the width of leaves on nettle plants growing in two areas next to a woodland - Edexcel - GCSE Biology - Question 10 - 2022 - Paper 1

The student likely measured a leaf from the fourth pair because it provides a consistent and comparable sample across different plants. This helps to minimize variations caused by factors such as leaf age or position on the plant. By focusing on a specific leaf position, the student can ensure that the measurements are more reliable and can provide valid comparisons between the plants grown in shaded and sunlit areas.