[Bacteriology Innovations | Innovation Home Page]

Timothy Paustian: "Seeing the forest for the trees: Getting students to think deeply about experiments using discussion groups"

About Bacteriology 304

The Introductory Microbiology course for Bacteriology majors, Bacteriology 304 has an enrollment of about 120 students a semester (40 students in 3 sections). The class teaches students how to handle microorganisms aseptically, isolation of microbes, testing and identification of bacterial species and introduces techniques for the biochemical and genetic manipulation of bacteria. Bacteriology 304 emphasizes experimentation as opposed to exercises and is modeled after a research lab. Students are encouraged to think.

The typical class day may contain an occasional lecture to introduce a new experiment and the performance of protocols as outlined in the lab manual. Students record their observations in a separate lab notebook. After all the data for an experiment is collected a discussion is written analyzing the results.

Outline of the Problem

When performing labs students would dutifully follow the protocol, get excellent results, and present them in their lab notebooks clearly. But when it came time to discuss the data, their analysis was superficial. A significant number of students were not understanding the point of performing the experiments, the basis of the techniques, or what the results really meant.

In the first experiment we have the students isolate bacteria from the environment using two different types of media. Nutrient broth + Glucose + YE (NGY) and Minimal medium + Nicotine (NEM). They isolate and observe microbes capable of growing on the media and save them for further experimentation. Here is an example of the kind of conclusions we were seeing for experiment one.

We were able to isolate bacteria from the two mediums we used. The NGY had more bacteria on it than the NEM. Restreaking onto new media helped to get the isolates pure. The NGY isolate was a gram positive rod, but not all of the rod stained purple. The NEM isolate was a gram positive cocci. Both were saved for further analysis on NA slants and grew just fine. This lab was fun and taught me useful techniques.

This is not a discussion of the data, but a repetition of the results with a small amount of analysis. The results this student reports are ripe with interesting questions to answer.

The question is... How can we encourage students to think more deeply about the experiments they are performing?

The Solution - Discussion Groups

The hope here is that if we get students to sit down together in class under instructor supervision and think about the experiment, it will help them write better conclusions

Format

At the end of each experiment students are organized into groups of three to five people and assigned questions that get them thinking about the experiment they just performed. For the first discussion group of the semester, students are presented with some simple rules to follow during their deliberations.

  1. Everyone should try to participate.
  2. Don't hog the conversation.
  3. One person of the group is chosen as speaker.
  4. Please be polite.

Each group is given one or two questions to think about. Here is an example.

Were the isolates from the NGY plate different than the ones on the NEM? Why or why not? If you want to get a maximum number of microbes and you had to choose one medium to use for this experiment, which would you choose?

The students are given about 10 minutes to answer the question. During that time the instructors will cycle through the room and listen to the conversations going on. The instructors goal is to keep them on track, but not give the students the answers.

After the discussion, the whole class will reconvene and the speaker for each group will present his/her groups answer to the class. The instructor serves as the M.C. for this presentation period. This is a difficult balancing act between making sure the speaker gives a thoughtful answer and not embarrassing a student if they are a little off the mark.

Results

Much better conclusions! Here is an excerpt from a discussion submitted for the Fall 1998 semester.

[....] The unknown sample came from a jar of moldy applesauce. This sample proved to grow quite a bit in the NGY broth, but not at all in the NEM broth. The reason that a lot of growth is usually seen on NGY is due to the fact that NGY is an all-purpose medium. It supports growth of many organisms because glucose is a rich carbon source. On the other hand, the carbon source of NEM is nicotine, which is a poor source of carbon. Less growth or no growth is generally seen on this media. The sugar in the applesauce contained dextrose (glucose) which probably selected for microbes that were able to metabolize [it]. There was no nicotine in the applesauce (At least I hope not). So finding microbes capable of degrading nicotine would be unlikely. [....]

The student compared the success of isolation on the two media and then related that to the source of inoculum. They even went beyond what we asked and started thinking about carbon sources available in the applesauce. The nice surprise here is that whetting their appetite for analysis inspired them to do more. If you run a lab, I encourage you to try discussion groups, they help students focus on analysis.

[Top ]

UW-Madison, October 1998