From the Desk of the Editor

Doreen Schroeder

When Life Gives You Lemons (Or A Bad UV Lamp)…

If you are lucky, you have a few truly serendipitous experiences during your life.  One of mine occurred last spring in the lab of my general biology course.   We conducted an experiment using yeast to test the efficacy of various products that claim to protect the wearer from harmful UV rays.  This is a good experiment to use with non-science majors to gain experience in experimental design and appropriate controls.

Doreen Schroeder
Mail# OWS390, University of St. Thomas
2115 Summit Ave.
St. Paul MN 55105

The protocol is a simple one.  Students spread a suspension of yeast cells in sterile water onto a petri plate.  When the liquid is absorbed into the agar, they cover the top of the petri plate with their treatment (sunscreens, sunglasses lenses, turtle wax, etc.) and place the plates in a hood equipped with a UV lamp.  Then the student plates, plus controls, are exposed to the UV lamp for 1-1.5 hours.  Controls consist of plates that are exposed to the UV lamp without protection and plates that are covered with a light impervious material such as cardboard.  After 5-7 days of growth on a bench top, the plates can be compared and analyzed. 

A similar experiment worked well during fall semester in another course and my trial runs in January.  However, by the end of the week in spring semester, it became clear to me that something had gone wrong.  All the controls exposed to the UV lamp were growing as well as the other plates!  I knew that the light was not burnt out, as I had checked it several times during the week.  There were several explanations for the results, but I could not test any of them in the short time period left to me.  Outside of canceling lab the next week, my only choice was to “make lemonade”.  In this case that meant letting the students analyze the experimental results and see how much they really understood about experimental design and proper controls.

After a bit of thought and consultation with other instructors in the course, I devised a worksheet to help the students think about the experiment.  In this worksheet, they were asked to re-write their hypothesis and to sketch results they would expect if their hypothesis was supported.  Only after that portion of the worksheet was completed were they allowed to obtain their plates and look at the controls.  The worksheet also asked them to sketch their actual results and draw some conclusions.  At that point, they were to provide two possible explanations, or hypotheses, for the results and describe how they would test those hypotheses.

Despite my trepidation, the lab went very well the next week.  I admit that I was surprised at the number of students that did not look at the controls at all before drawing their conclusions.  However, all the lab instructors reported that the exercise resulted in excellent questions and discussions about the results and controls in particular.  As the lab coordinator, I gained a new insight on how better integrate discussion of controls in other lab exercises.  In fact, I used this lab experience to write a short case study for another course.  It was an experience that will affect the way I think about laboratory exercises for a very long time.