by Benjamin Freedman, Molecular and Cell Biology
Teaching Effectiveness Award Essay, 2006
When I first started leading a discussion for MCB130 (Cell Biology), I used simple chalkboard drawings to illustrate cellular processes. Such drawings have been used for many years as a way for scientists to conceptualize experiments and molecular events. However, I could see on my students’ faces that these cartoons were inadequate. Such cartoons might make sense to scientists, who are already familiar with the methods and data that those drawings represent. But my students, many of whom have never seen a cell under a microscope, had a hard time relating to them.
For me, the breakthrough came after the first exam. While grading, a fellow GSI asked me whether I had used fishing as a metaphor for mitosis, or cell division, during my discussions. “How did you know?” I asked. Apparently, many of my students had invoked the same metaphor in response to a particular exam question. During mitosis, cells must move replicated chromosomes from the center of the cell to two opposite sides. To do this, the cell sends out retractable, line-like proteins, called “microtubules,” from either side. The microtubules hook onto chromosomes at the center of the cell and are then retracted by the cell, pulling the attached chromosomes to either side. Effectively, the cell “fishes” for chromosomes, using microtubules as a retractable fishing line. I had mentioned this fishing metaphor only briefly during discussion, yet somehow it had captured the imagination of my students and stuck in their minds during the exam.
Why had the fishing metaphor been so successful? I theorized that it gave the students a way to personally relate to the microscopic events of cell division. In the next class, I decided to take this one step further. I brought the students out of the building and onto the green lawn — the weather was perfect — and told them to imagine that the lawn was a huge cell that was going into mitosis. I asked each student in the class to represent either a chromosome or a microtubule pulling protein. I lined the “chromosomes” up in pairs in the center of the imaginary cell, and, at my signal, the student “microtubules” pulled the pairs apart to either side. Next, we reenacted meiosis, a more complex process that requires two divisions in a row. It was easy to see how, at the end of both mitosis and meiosis, each daughter cell receives exactly one copy of each chromosome — i.e., one student from a pair. At the conclusion of the exercise, the class spontaneously applauded.
Throughout the rest of the semester, I used verbal metaphors, play-acting, and homemade props to help students conceptualize various cellular events. These generated a lot of student interest and participation, and were a great supplement to traditional chalkboard diagrams and handouts. In my GSI evaluations, fifteen students specifically mentioned the demonstrations. Comments included, “The homemade visuals rule! They definitely help explain the material,” and “Visuals in class . . . are fun and helpful. How can we forget after such activities?” Notably, students love to be creative themselves. Next time I teach, I’d like to break students into groups and challenge them to design their own metaphors or activities for specific cellular events, which they might then present to the class.