Concepts of Biology (BIOL115) - Dr. S.G. Saupe (ssaupe@csbsju.edu); Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

Willow Experiment - Scientific Analysis

Consider the following experiment.  Obtain four cuttings, each 10 inches long from a single willow bush behind PENGL Science Center.  Dip the ends of two cuttings in a powder containing auxin (a root-inducing hormone).  Plant each of the four cuttings in 1 cup of vermiculite that was moistened with 100 mL of water, covered with plastic wrap, and placed side‑by‑side in the light.  After several days, there was no visible change in the plants that had been dipped in the rooting powder.  The other two cuttings each had 7 roots that were 5 cm long.

1. Write a question that this experiment addressed:

2. Restate the question as a null hypothesis (H₀):

3. Identify one testable prediction of this hypothesis: (if�.then�)

4. What type of logic did you use to generate the predictions from the hypothesis?  inductive or deductive?  Explain.

5. State at least one alternative hypothesis (H₁):

6. Identify five variables that could affect this experiment:

7. Identify the experimental variable:

8. Identify the control group:

9. What do you conclude about the validity of the hypothesis?  Explain.

10. Although this is a pretty good experiment, it was not properly controlled.  What variable did we forget?  How could this experiment have been improved?  Explain.