Teaching Quantitative Skills using the Floating Disk Catalase Lab: Intro
I find it remarkable how deeply the biology education community has embraced the call to increase quantitative skills in biology. This is certainly not an easy change to incorporate into our curricula and it is one that the community will be working on, tweaking and improving over time as our own instructional quantitative strategies and skills mature. But even with this willing effort by the community where does one find the time to add “something else” to an already packed curriculum? The first part of the answer to that question is to first have confidence that it can be done; the second part of the answer has to do with strategic and efficient curriculum decisions; and the third part of that answer is to realize that, like our students, we are somewhere on learning progressions ourselves and that our skills and understandings will deepen the more we teach quantitative skills. No one has time to teach all the biology they would like to teach. Every year most of us make all sorts of decisions about what to include, what to emphasize, and what to leave out. The challenge of adding structured instruction in quantitative skills is daunting, particularly since most of us have not had time to develop our own math-based pedagogical tools and skills. With that in mind we often fall back on the type of math instruction that we likely encountered in our own educational background. If, like me, most of your math instruction was based on algorithms and focused on getting answers instead of learning how to do math, then likely if we model our quantitative skill instruction on the math instruction we experienced, we won’t be doing a very good job helping our students develop quantitative skills. Instead, perhaps we (the biology teaching community) should consider delivering quantitative skills instruction in a way that models effective and efficient math instruction informed by research. Here’s the good thing–it turns out that many of the strategies that work well for teaching science also work well for teaching math. We biology teachers just need a bit more experience trying to explicitly teach appropriate quantitative skills. We need to develop our own specialized pedagogical content knowledge. I thought I’d put out an example of how this might work in a classroom–certainly not as an exemplar but more as a starting point.
In this series of posts I’ll walk through the material we presented at NABT along with some discussion on the rationale of each example coupled with resources so that you should be able to design your own lab that structures quantitative skills. A caveat: I want to emphasize how rich this particular lab is for developing quantitative skills–in fact I’ll present more possible ideas than probably anyone will want to use in any particular class. So pick and choose what works for you and your class but consider the examples presented here as something to shoot for with your students. Let’s get started.
If you are not familiar with the lab it features a simple and student friendly method to measure/quantify enzyme action or kinetics using disks of filter paper soaked in a yeast solution as the enzyme source and a solution of hydrogen peroxide as the substrate. Here’s a write-up by Paula Donham on the technique: http://www.kabt.org/wp-content/uploads/2009/02/catalase-enzyme-lab.pdf Note that one of the educational goals that Paula used this lab for was to introduce the use of box plots as a way of presenting your data. (That’s a quantitative skill, btw.)
How does it work?
Dip the paper disk in the yeast solution. The yeast solution provides a set amount of catalase per disk. Drop the disk into a solution of hydrogen peroxide.
The catalase breaks down the hydrogen peroxide into water and oxygen. The oxygen bubbles catch in the paper fibers and eventually cause the disk to rise. You can see the disk staring to rise in the lower right hand corner of the cup.
I use the plastic cups to make a dilution series with the hydrogen peroxide and the 24 well plates for the testing. The well plates allow you to put one disk per well (which might lead to better precision).
Ready to collect data with eight data points per substrate dilution:
Here’s a short video of the procedure using the well plate:
Dip a disk in the yeast, drop it into the hydrogen peroxide and time how long it takes to rise.
Why use this lab for introducing quantitative skills?
The simplicity and precision of this lab technique allows the teacher and the class to more deeply explore concepts about enzymes but also to explore how different quantitative skills can provide a path to even deeper understanding. The key here is that the technique is so simple, the students can concentrate on thinking about what is going on with the enzyme, how to capture that quantitatively and how to support their conclusions with data. And, they can simply do it over if errors are made since it takes a small amount of time. There are some other aspects of this lab that allows you to introduce different approaches and deeper understanding as you build quantitative skills. In my classes, I had three main goals for this lab: 1. To begin an understanding of enzymes and enzyme action; 2. Introduce and practice a number of quantitative skills (including serial dilutions and graphing); and 3 Introduce and practice experimental design and scientific argumentation. In my classes, we would introduce the technique, let everyone in the class practice it, and then assign the actual data collection as homework. The students had to acquire their own materials at home, collect the data and report back to class. They could work collaboratively or with their families. The lab is safe, inexpensive and doable. By assigning the data collection as homework, this freed up class time to work on the quantitative skills. The students generated mini-posters to share their work with their peers. In the next post I’ll talk more about how you might present this lab to students and the types of quantitative skills you can build and practice.