Brett Couch and Angie O’Neill recently teamed up to create an activity to help students better understand and visualize scale and size of microscopic objects in their separate eukaryotic microbiology and neurobiology courses.
Below, they describe the activity they developed, the changes they’ve made based on the assessment and student feedback they received, and what they learned along the way.
What was your motivation for developing this activity?
The motivation was trying to get students to have a better understanding of scale when they’re looking at things under the microscope. We both have experienced that students often have misconceptions about the sizes of microscopic things they view in class based on what they see in textbooks. For example, textbook figures will have a figure of a cell and it’ll show the nucleus, mitochondria, chloroplasts, ribosomes, and proteins all within the same figure, which can lead students to think that they should be able to see all of this stuff when they look at a cell under the microscope. So we wanted to get them a better intuitive sense of scale. What are the things they’re likely to see? What are the things they’re likely not going to be able to see? How big are cells? Imagining things that are outside of our experience, for example, things that are really, really small or really, really large, is hard for people. We wanted to help students with this, so that was the initial motivation.
How did you do it?
We both saw a need for this type of activity in our courses, so we worked on this together as a first draft and then implemented different flavours of it in our specific course; Angie used a more neurobiology-focused version in her course and Brett used a more eukaryotic microbiology version in his course. But the activity was the same, and it was nice to work together on it as we had lots of informal discussions as we developed the activity, then we tried it out in our different courses and assessed it using a pre- and post-survey to determine what students were learning and how they were experiencing the activity. This assessment was helpful in determining what revisions to make for the second iteration.
What changes did you made to the activity in the second iteration?
In the first iteration of the activity we tried to do too much. We had a lot of calculations that students needed to complete, but this was confusing for students and it seemed to detract from the main purpose of the activity, so we revised the activity to simplify it and make sure it really focused on our specific learning outcomes of getting students to understand scale and recognize the things that they can and can’t see with a light microscope.
Another change was to include some ambiguity in the questions that we asked. In the first iteration we asked questions that had very black and white answers, like ‘yes’ or ‘no’. However, we found that this didn’t work well for examples that were on a borderline. For example, we asked if you could see an E. coli cell when you viewed it with 40X magnification, but the E. coli cell is sort of on this boundary where it could be seen at that magnification theoretically, but it’s sort of on the boundary of what can be seen. So, in the second iteration we added ‘maybe’ as another possible answer, which allowed us to get students to consider some additional factors that influence whether something can be seen or not, such as staining and contrast. For example, cells are generally pretty clear and increasing contrast between the cell and the background means that you can often see the cells better. We found that making this little change of adding ambiguity allowed us to incorporate discussion of other microscopy concepts.
What did you learn or find surprising?
We found that students were better at some of these things than we thought they would be, based on their answers in the pre-survey. They actually started off with a reasonable ability to estimate the size of things using the scale bar as a reference, using a field-of-view as a reference, and using other things of known size as a reference. So that was surprising.
Also, more of the students seemed to have had some experience with microscopes than we expected. We often have trouble getting students comfortable using their microscopes in the lab, so our impression has always been that they didn’t have a lot of experience. Students seem to have more experience than we think, but that experience may not exactly translate into being able to use the microscopes effectively in the lab, so we still need to train them. But they did better at that than what we originally thought.
What advice would you give someone who wanted to do something similar in their course?
Talk to us! We’re happy to share the activity with you. It is organism agnostic and could apply to any course that involves using microscopes or microscopic images. It can also be modified to meet the needs of your course context. For example, it could be adapted to be completed online, you could have students work through it in groups or individually, or you could use a shortened version of the activity (it takes about an hour to complete in its current form). You also don’t need physical microscopes to do the activity, so it could be done in a classroom or lab.