Scientific Method

The first two steps in the scientific process involve studying and observing natural phenomena of interest. Therefore, in this exercise, we will observe the leaves and branches of individual plant species. As each species comes from a different environment, we will compare each branch to one another and record our observations about any qualitative similarities or differences between the species.

Then, we will use leaf clippers to cut the leaves from the branches and make some qualitative observations about leaves from each species. Now that we understand a little bit more about our different plant species, it's time to formulate a hypothesis. Think of some general questions that you might have after observing the different plant species.

Do the tree species have leaves with different surface areas? Is there a difference in leaf mass among the five species of plants? Do the tree species have leaves with different lengths?

Is there a relationship between the leaf surface area and leaf length? How can each of these questions be reformulated into a null or an experimental hypothesis? Now that we have a specific hypothesis that we would like to test, we can make more targeted observations and data collections.

Weigh and record the mass of each leaf, and measure and record the length of each leaf from the petiole to the tip in the table. Next, carefully trace each leaf outline onto a blank piece of computer paper. Then cut out and weigh and four by four centimeter square of the same paper, weigh the cutout tracing, and record these data in the table.

Now it's time to analyze the data we collected. First, let's calculate the leaf surface area. Divide the surface area of the four by four centimeter paper square by the mass of the paper square, and multiply the resulting number by the mass of the leaf tracing.

Next, create a bar graph with your five plant species listed on the x-axis, and the surface area in square centimeters indicated on the y-axis. Create a scatterplot graph with the leaf lengths on the x-axis and the leaf surface areas on the y-axis. Make sure to plot all five of the plant species.

Draw a trend line through the graph if a relationship is evident. Through the observation of qualitative and quantitative differences in leaf morphology between different tree species, you will have learned how to formulate questions into testable hypotheses. Further, collecting these data provides the necessary background for collecting and managing data for other experiments.

Lastly, analyzing and visualizing the leaf measurements through the generation of figures and graphs, you have gained experience in understanding the differences and similarities between experimental groups, helping you learn how to draw conclusions about the data you collected.