Alligators and Crocodiles
Each semester of Bio 100, I start with a unit on stem cells. It is a timely and relevant topic and I use it as a jumping off place to get at the concepts of cells, cell identity, differentiation and regulated gene expression. I was two lectures deep into the topic discussing cell signaling required for determination and differentiation. I was using an example of embryonic stem cell treatment of disease, hoping to have students wrestle with the idea that some external signal, after binding to a receptor, would alter cell fate and induce the cell to differentiate into a particular cell type. Here is the question I asked:
Therapeutic cloning is used to produce embryonic stem cells (ESC) from a patient with diabetes. These cells are implanted into the pancreas of a diabetic patient in an attempt to replace the lost islet cells that produce insulin. However, the ESCs form a complex mass of tissues that include liver, pancreas, blood and intestinal cells. Which of the following represent the most likely cause of this problem?
1. The ESCs released signals that caused the pancreas cells to change and develop into a variety of tissues. 2. The ESCs received signals that induce them to develop into a variety of tissues. 3. The ESCs signaled each other, and activated complex developmental sequences independent of the environment (the pancreas) they were in. 4. all of the above 5. two of the above
After the question, I asked for comments and questions. A sea of hands went up. I was thrilled. It was early in the semester and this was the first time that my pushing for participation had really worked. The first students I called on asked about islet cells, unsure of what they were. I answered, and emphasized that when you don’t know some term, you should ask. The second student liked answer 5, arguing that both answers 2 and 3 could be correct. I was happy and reinforced the thinking, but did so briefly and went on with to explore the ideas from the other students with hands up. I suspected there were some points of confusion out there that hadn't been voiced. I called on a student in front row who had raised her hand at the start of discussion. With a dead serious voice she asked, “If an alligator and a crocodile were to mate, could they have babies?” I blinked. Twice. So did the other 400 students in the room. I didn’t want to react negatively. The whole idea of asking for question from the class is to provide a forum for students to discuss their ideas. This discussion allows me to figure out what they do get, and what they don’t. With their responses I can clarify misconceptions and emphasize key concepts and strategies for problem solving. If I nailed her for asking a lame off topic question this early in the semester, I may well poison the atmosphere and never get a sea of hands again. I answered the question as best I could suggesting that there are several species of both alligators and crocodiles, and the biological species concept defines different species as organisms that can not produce viable and fertile hybrids. I also qualified the answer. I’m not a herpetologist, and don’t know the specifics. For all I know there may be sterile crocigators? Then I took a breath, smiled, and confessed that it wasn’t clear to me how this helped get at the issues at hand, rather anxiously trying to turn the discussion back to stem cells in the pancreas. She explained, “Isn’t putting embryonic cells into a pancreas of an adult like putting alligator cells into a crocodile? Isn’t there something in the crocodile that might make the alligator cells not work right.” Bless her heart.
I didn’t take any more questions. I proceeded with my lecture. Here is the outline of ideas and key points I wanted to cover as we discussed this question:
1. Embryonic stem cells are initially undifferentiated and undetermined. 2. Embryonic stem cells can differentiate into a variety of mature cell types. 3. Cell determination restricts the range of cell types that an embryonic stem cell can differentiate into. 4. Embryonic stem cell differentiation occurs in response to specific extracellular signaling. 5. Signals can come from other cells either that are mature cells, or other embryonic cells. 6. Signals for proper determination and differentiation may only be present temporarily during development. Mature organs may no longer produce the array of signals present during early developmental stages. 7. Mature cells rarely change into other cell types.
I used the alligator / crocodile terminology to help get to several of these points.
This example gets to the crux of several of the classroom management issues that arise when pedagogical style shifts from straight lecture to an alternating lecture/question format. More to the point, this example identifies key teaching and learning challenges and opportunities that only arise when students are encouraged to voice their ideas, good or bad. The ideas students voice and questions they ask depend on the design and complexity of the question they are working on. Questions that require students to understand key concepts and apply those concepts to resolve a problem seem to bring out quality discussion.
Participating in these kind of activity in a large lecture hall asks a lot from students, who are quite happy quietly sitting and listening (or not) to lecture, and doing little else. When using clickers, students have to wake up, read something, think about it, talk to their classmates, work some handheld gizmo to submit their answer, see how they did, respond to the instructors inquiries about the question, listen to other students who also respond, fit the instructors comments back to the problem or question they tried to answer and figure out what about that experience is likely to actually be on the test. It's a lot of work.
To get students to play along requires significant cooperation on their part. Earning an adequate level of student cooperation is a challenge, but it is critically important. Traditionally instructors award points, or take away points, or threaten with quizzes or tough exams, or even lavish praise for the students who do best in order to get students to do what we think is important. Students may respond to these inducements by turning in homework or showing up for an exam, but they are especially unlikely to genuinely share their ideas about a challenging and complicated topic out loud, in front of hundreds of peers unless the environment is especially encouraging, nonjudgemental and safe.
Instructors need four basic qualities if they hope to create a classroom where students are consistently willing to take risks and share ideas: patience, fairness, respect and commitment.
1. Patience
Instructors need to realize that students are frequently not well spoken. They are uneasy with the vocabulary, and are likely to have a partial understanding of key concepts. They are likely to make mistakes of several types when they speak. Some students will get things just plain wrong. More often though, they have a kernel of a good idea, but struggle to get it out. With patience, an instructor can do some appropriation, taking the useful parts of the student comments, and mapping it back to the concept under discussion using the correct vocabulary and syntax. In this way, a student can be have their question answered or idea explored, even if that idea is quite fully baked or clearly stated. If an instructor displays a lack of patience with ideas that are not fully formed and stated with the accuracy of a mature scientist, they are likely to quickly run out of volunteers to share their comments.
Instructors patience is also critical for crowd control. Students can get pretty noisy in the question/answer environment, especially one in which they are encouraged to talk over answers with their classmates. At the same time, students need to be quiet when the instructor brings the class back together for whole class discussion. Most large lecture instructors are used to an environment where students are quiet and the only voice in the room is from the lecturer. If students a having private conversations in the back of the lecture hall it is rude, and a distraction for other students and the instructor alike. This set of manners still applies in the question/answer lecture hall, just not all the time. When questions are presented, students are supposed to talk. An important part of the active learning classroom is to have student discuss issues with each other. However, after that discussion, when the instructor is summarizing or emphasizing key points or setting up a question with lecture, the students need to be quiet. The problem is that students forget. They need to be reminded of the manners expected in the lecture hall. Frequently. Exactly because these reminders occur with some regularity, they need to be done with patience. There is no need to tolerate poor behavior from students. There is a need to appreciate the challenge for students of alternating between talking and quiet.