Authors

Abstract

If you look at the leaves that fall off of the trees in autumn, you will notice that not all leaves of the same kind are alike. Some are larger than others, some are longer or wider, some have different stem lengths, and some may have slightly different shapes. This is not surprising if you consider that they may be from different trees. Just as two people have hands or feet of different sizes, so different trees may have leaves of different sizes. If you do further observations, however, separating out leaves found under one tree from leaves found under another tree, you find both sets are similar in having larger and smaller leaves. This suggests that leaf size is not simply a function of being from different trees, since it seems that leaves from the same tree differ in size. Consider what other factors may affect leaf size. One obvious factor is the amount of sunlight that leaves receive. Sunlight is required for photosynthesis, and photosynthesis produces the food that trees and leaves need to grow. In your lab book, write a hypothesis about the effect that different amounts of sunlight will have on the size of leaves. Now think about how this hypothesis might be tested. There are two questions. The first is how to obtain a set of leaves that have been exposed to more light than another set of leaves. One way to do this would be to pick leaves from a part of the tree that gets a lot of light (such as the outer branches) and compare them to leaves from a part of the tree that gets little light (such as near the trunk). How do you think the two sets of leaves would differ? The second question is how to assess the size of the leaves.