BIOL 105: Tues. 3:00PM – 4:50PM
A Comparative Analysis of the Sun and Shade Leaves of Burr Oak (Quercus macrocarpa) Abstract
This study was conducted to determine whether the leaf size of the burr oak (Quercus macrocarpa) is affected by the amount of solar radiation that the leaves receive. The outcome of the study indicated that the amount of solar radiation leaves obtain, does affect the size of the leaves. Results of the study verify that sun leaves are more likely to be larger in size than those leaves that are constantly in the shade. Introduction
Many factors influence plant characteristics, one major factor is the intensity of solar radiation that a plant receives. Solar radiation can be observed by looking at the plant as a whole or by observing specific parts of the plant. The study conducted observed the changes in leaf size with some leaves receiving more solar radiation and other leaves receiving less solar radiation. “Leaf display and light capture depend on… responses to light, and the size of the leaves” (Falster and Westoby 2003; Pearcy et al. 2004,2005). Many studies have shown that sun leaves typically are much larger than shade leaves. Analysis of the position of leaves scattered about trees have shown that most trees show similar results.
“Plant leaves that develop in full sunlight often are quite different from those that grow in shade” (McCain et al. 1988). The purpose of the experiment was to better understand that leaves found on areas of the tree that constantly receive more solar radiation, are typically larger than those that are found in the shade. “Anatomical differences between sun and shade leaves have been known for many years” (Osborn and Taylor 1990). Having this knowledge prior to the experiment the following was the null hypothesis for the experiment: Sun and shade leaves of the Burr Oak (Quercus macrocarpa) are the same size.
The null hypothesis being the basis of the experiment, the group came up with their own alternative hypothesis. Shade leaves of the burr oak (Q. macrocarpa) are generally larger than the sun leaves. By composing an alternative hypothesis, the group had reason to proceed with the experiment. Methods
The experiment began with the group’s observation of the sun and shade leaves of the burr oak (Q. macrocarpa). The observation consisted of describing four differences in the photocopied leaves the group had received. The first difference the group noticed was how much larger the shade leaves were compared to the sun leaves. Another major difference between the two types of leaves was the visibility of veins throughout the plant organs. Shade leaves tended to have thicker and more visible veins throughout the leaf as opposed to the sun leaves, which had less distinct veins. Shade leaves of the tree also proved to be more protected and had less damage done to the leaf. One last surprising difference between the sun and shade leaves was the thickness of the leaves. The shade leaves seemed to be much thicker than the sun leaves, which receive less solar radiation than its competitor.
The second step of the experiment was to form a hypothesis based on the observations the group had recorded. The group’s hypothesis was that the shade leaves of the burr oak (Q. macrocarpa) are larger than its sun leaves. The group then tested their hypothesis.
The testing of the hypothesis consisted of cutting out the photocopied leaves and labeling each leaf with a name, sun or shade, and a number, one through four. The group was to weigh their leaves using the digital scale provided, and to record their values in a table. Since the weight of the photocopied leaves were not a measurement that could be used for the data, the group had to convert the weight of each photocopied leaf to the area of the leaves. To calculate this, the group had to convert the leaf weights (g) to area (cm2), in other words leaf size. The equation to do so is listed below: Leaf...
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