How to handle a big fat lab?

Deshelled eggs in solutions

Early on in my anatomy and physiology class comes a chapter with some of the essential concepts of cell biology: the cell membrane, and its transport and signaling mechanisms. In my early days I (wrongly) assumed that students knew the basics of this from previous classes, and I would quickly move forward to the deeper topics related to body systems. With time I realized the importance of spending extra time with this chapter: otherwise students will struggle the rest of the course to understand nutrient transport, membrane potential, effect of drugs and hormones etc. The lab exercises that usually accompany this topic are diffusion labs: filling small dialysis bags with different solutions, measuring their weight and testing what crosses the membrane or not. I got excited around a year ago when I saw a protocol involving deshelled eggs. Eggs left overnight in acid (can be simple vinegar) lose their hard shell as it dissolves, leaving them slightly gross and spooky. However they are a great and very realistic tool to show what happens to cells when placed in a hypotonic or hypertonic solution (swell or shrink). I remember the first time actually testing deshelling eggs at home, as I was not sure about their consistency. 

The official lab (from the manual we use, Marieb's lab manual), includes several activities besides the dialysis bags and the eggs. Add a class of over 30 students (many of them not knowing what a beaker or measuring cylinder is), and you realize how complicated it gets. Over time I made short videos describing each procedure and specifically directed students to read the instructions, but as we all know, only few do that.

The first time I set up this experiment, it was crazy. I explained what it was about, divided them in groups, and let them go. For the next 2 hours, I had a restless and confused mass of students running around with dripping dialysis bags or eggs in their hands, looking for reagents and asking questions. However, when we collected the data I was elated: the numbers actually made sense. We had sets of weight data in function of time. With so many groups, we could do basic statistics. We could make graphs. The numbers just looked beautiful. Unfortunately, we did not have the time to process the data in depth. 

I ran the third iteration of this lab yesterday. As far as I know, I am the only one of my fellow instructors who teaches this lab, and I don't blame them. It is pretty intense. Luckily I have an angel in a lab tech who likes challenges and has been steadily improving his part of the equation (setup of materials, labeling). Yesterday I felt quite content with the results, and would like to share with you what we did.

Inquiry based: I did not lecture the cell transport part before the lab. I wanted them to figure out what happens and why, so I merely introduced the fact that we would be exploring some parameters that affect membrane transport in the cells. Of course some students had previous knowledge, so I heard them talking to others about what was going on.

Active-interactive learning: I experimented this group managing technique for the first time in the Critical Thinking workshops by Joel Levine, a charismatic Dean at Southwestern College. Once students are divided in groups, they choose "specialists" among them for different tasks. The tasks may be different aspects of the same topic, or in this case, different experiments. Then I have the "specialists" for each experiment come together, discuss, and check with me if they understand the procedure. When they return to the original group, they have the responsibility to explain the others and clarify any questions. This way they take responsibility for their learning process, reinforced by teaching the others. 

Data collection: I projected a big excel table and directed students to record their data as they collected them. As the numbers unfolded in real time, students were paying attention, comparing their numbers to others', questioning if their numbers were very different, and already comparing their results with their expectations. 

Processing and data analysis: after the lab we came together for actual lecture time. Now it was the time to talk about passive and active processes, diffusion, and osmosis. But instead of abstract examples, now I referred to what the students did and observed. Students deducted what happens when cells are placed in hypotonic versus hypertonic solutions. Then we went back to the numbers, and checked if the results corresponded to what they expected. Explanations for discrepancies were discussed. My hope was to include graphing/statistics, but we ran out of time. 

I have always loved playing with numbers- making huge tables of numbers understandable through graphs was one of my joys as a researcher. When I look at this simple bar graph, based on a group of students who did this procedure the first time in their lives (and indeed, for many this was the first wet lab of their lives), I feel really proud of them. And what really made my day (or evening) yesterday was the student who in the middle of the lab exclaimed, with a big smile: "This is fun!"