Allelopathy: Investigating the Detrimental Effects of Chemicals Released by One Plant on Another

This activity is designed for students to gain a practical knowledge of experimental design, use critical thinking and observation skills to develop their scientific reasoning abilities, and increase their ability to work as part of a team. The scientific method will be a core concept as students plan an individual experiment, research the methods, assemble the necessary apparatus, perform the experiment, and report their work both as a written report and orally for peer review. Additionally, this will be the first exposure for many students to the concept of plants influencing their environment to gain a competitive advantage via the production and use of chemicals. Furthermore, students will consider the significance to allelopathy to bioindustry and the potential benefits of this research to man and the environment.

Vocabulary:

-Allelochemistry

-Herbicide

-Germination

-Controlled experiment

-Independent variables

-Dependent variables

The essence of this activity is in the use of scientific methods and working effectively as a team. Therefore, it is ideal if students have already had some practice with each of these skill sets. Consequently, it may be best to perform the activity in the final quarter/semester of a high school biology class. The amount of time needed could vary considerable from group to group depending on the parameters the instructor provides. For example, if you limit the experiments to the effect on germination then it will be a rather short experiment, but if you allow for the full range of possible effects on plants at any point in their life cycle then if may be a much longer time frame to allow test plants to mature. The equipment needed is rather minimal as the plants they are testing must grow locally and a variety of plants and plant seeds are inexpensive and easily acquired by instructor or students. Suitable indoor or outdoor growing conditions would be necessary for more extensive experiments that examine growth and development of the plants.

This activity is easily adaptable and can be carried out as a simple guided discovery lab by simply providing all students with a set of procedures to follow. On the other hand, it can be even more involved by included more chemistry elements such as exploring various methods of plant chemical extraction and assessing the concentration of plant extract being used.

The students will begin by getting into their groups and engaging in the planning process. Using the definition of allelopathy provided, they will brainstorm a testable question, make their hypothesis, and come up with a rough idea of the procedure they will use to test their hypothesis. The draft will be submitted to me verbally by the group to ensure their methods will be realistic, based on the resources available. They may divide work among the group members as they see fit and then use a predetermined amount of time outside of class to make observations, consider what specie or species of plant they wish to test for allelopathic properties, and collect some samples to share with their group at the next meeting.

Groups will reconvene to discuss what they have observed, share ideas and samples of what they found, and then come to a consensus on what plant they will be testing as well as what part or parts of the plant. With this information they can then refine their drafted procedure and come up with a working plan for carrying out there experiment, focusing primarily on the materials and methods section, which will be submitted to me for review and to ensure the availability of needed materials.

Students will then simply follow their procedure, taking note of any additions or changes they make along the way. A limited amount of time may be allowed for the duration of the experiments for groups to collect data depending on experimental design. Once all the data has been gathered, groups will complete an analysis and write up a report based on a predetermined format provided by you, the instructor. At the end of the semester, the groups will present their findings at a symposium held in the classroom. Access to data from other classes will also be made available for a discussion of practical applications, new avenues of research, or further investigations into what has been discovered by the class via the scientific method.

The experiment that introduced me to allelopathy provided students with step by step instructions, with their only decision being what plant they would attempt to test for allelochemicals. I felt there was much more to be gained by making this an inquiry activity that challenged students to use and develop a broader range of skills. With the original cookbook approach there were few things to worry about as long as students followed the provided instructions. We did have some concerns about not being able to collect data over the weekend when groups considered the possibility that germination may have been delayed. With the student led approach to the activity I am proposing here, checking in with students frequently during the planning process is going to be the most critical element. The instructor will need to make sure what the lab teams are planning to do is reasonable in terms of time and resources.

Informal assessments include observation of group interactions and lab work, check-ins and conferences with each group, submitted experimental design ideas from each group, and a submitted draft of the material and methods prior to carrying out the experiment. Formal assessments include the group lab report and oral presentation.

I.B.1.1-The student will design and complete a scientific experiment using scientific methods
I.B.1.4-The student will identify possible sources of error and their effects on results.
IV.C.1.4-The student will predict and analyze how a change in an ecosystem can affect both the number of organisms in a population and the biodiversity of species in the ecosystem.