Mitosis lab as the basis for a discussion of error

We were doing a lab in Biology the other day. AP Biology teachers will be familiar with it, but the basic idea is that students count the number of cells of each phase in the meristem of an onion root tip using a microscope. By using the count of each phase, they can estimate the percentage of time each phase takes. At 400x, there are typically about 250 or so cells in the field of view, and the phase of each cell is not always certain, so it is not a trivial task. With care and patience, however, results can be pretty good. My students were quite confident with their counts. And, in truth, their combined data provided values that were not at all bad.

But here’s the interesting part. I also gave them a sheet with a couple of these images (click to enlarge), and asked them to find and circle one example of each phase.

And, collectively,  They did really poorly. Few of the students could correctly identify three or more phases. And yes, these are photos of the same microscope slides they were using.

I am still coming to grips with the ramifications of this discrepancy, but some of the conclusions are:

  1. Students’ confidence in their ability is not always a good measure of their ability
  2. This mitosis activity is is fairly immune to error
  3. Sometimes, biology can be harder than it looks, and it is NOT about memorizing
  4. Real life doesn’t look like the picture in the textbook.
  5. This is an excellent exercise to highlight and discuss points 1-4 above with the students.

One added observation – while the students were not all able to identify the phases of mitosis, they did notice instantly that they did not have the same images as the person next to them. Hmmm.

3 thoughts on “Mitosis lab as the basis for a discussion of error

  1. Lucas Jones

    Great post! #3 especially. I teach freshman biology. I am finding that students can draw each phase with ease, but finding them in an activity such as the one you have posted, it seems they have real difficulty.

    1. ed Post author

      I had one student ask why he couldn’t be tested using pictures from the text rather than pictures from “real life”…


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