Interactive Demonstrations: Examples from Biology Lectures; Demonstrate, from the Latin, Demonstrare: De-Completely; Monstrare-To Show

Article excerpt

Demonstrations have long been part of postsecondary science teaching. However, in today's constructivist classroom we know that to show completely, we must actively involve students in their learning. This need for active student involvement extends to all aspects of instruction, including learning from demonstrations. Given this viewpoint, we'd like to share a few of our most successful student-involved demonstrations.

Three interactive demonstrations

One of our favorite interactive demonstrations for general biology involves a Far Side comic (Larson 1985, p. 15). The panel depicts a resourceful shark in the water near shore, yelling, "Bear! Bear!" to frighten beachgoers into the water. We actively engage students by showing the comic and posing questions such as, "Predict what would happen to the allele frequency of the mutation (resulting in the behavior shown in the Far Side comic) in the aquatic species." Or, "Given this selective pressure, which shift(s) in gene frequency would you predict in the terrestrial species? Describe in terms of phenotype. Support your prediction."

Student responses to this simple activity are insightful and enthusiastic. They offer predictions such as, "Selection for deafness in the terrestrial species," "Elimination of shoreline populations, but no significant shift in gene frequency across species," and, "A mutation resulting in a trait that disgusts sharks (with associated warning coloration) would become fixed." Students also discuss the viability of each other's ideas, comparing, critiquing, and improving their responses. This active demonstration requires students to apply the evolutionary principles and population genetics to the problem, thereby facilitating deeper understanding of the concepts learned.

Another active demonstration involves the presentation of data in a table. For example, in physiology we use glucose tolerance test data (see Table 1). After lecturing on glucose transport across cell membranes and glucose metabolism inside the cell, students are presented with the data table and instructed to work with a classmate to analyze the data, and organize it in graphic form. Students are told that the objective of their analysis is to find a pattern in the numbers and are encouraged to arrange the data in ways that help them to see the pattern. After identifying the pattern, students are prompted to provide a causal explanation for the data. We then collect responses from students and review them as a class. This activity allows us to segue to a lecture on the purpose and function of a glucose tolerance test and the pathophysiology of diabetes.

This gives a context to subsequent lectures and develops the science process skills of analyzing and organizing data and developing causal explanations. We have noticed anecdotally that students seem to pay more attention during class sessions that include interactive demonstrations and that overall test scores are a bit higher in courses that include such demonstrations.

In our general biology class we present the following items on a table in front of the lecture hall: an igneous rock, a toy frog that croaks and blinks when you squeeze its belly, a burning candle, a pine cone, a real human humerus bone, a solar-powered calculator, and a live Madagascar hissing cockroach (Gromphadorhina portentosa). Students are challenged to categorize the objects as either living or nonliving and to justify each object's placement.

After much excitement and debate, we tell students to compare their lists with those of the students sitting closest to them. Students should then try to convince each other that their own list is right, while their neighbor's is wrong. They are free to revise their list if the arguments are convincing enough. After another round of lively discussion, students are then prompted to come up with one characteristic that can be easily used to separate the living from the nonliving. …