How do worms smell? A visit with 7th grade science classes at McDevitt middle school

Introduction Visit to McDevitt Middle School Methods During each 55 minute session we began with a 10-minute slide presentation to introduce the students to the topic. We emphasized that roundworms are very common, that they come in a wide range of sizes and come from diverse habitats. We also described the habitat of C. elegans - rotting fruit and compost - as well as their bacterial food source. The introduction also included details about taste and smell in the worm and how these relate to the activity stations, which were also described briefly. Students were then divided into three groups, and were sent to one of the three stations. Students were given instructions as detailed below which they read briefly as a group before a verbal introduction by the scientist or teacher. 10 minutes was devoted to each station with a brief wrap-up time period so the students could fill in their respective worksheet. Results Station 1 Students generally found visualizing and counting of eggs to be difficult. Visualizing worms was much easier and students were asked to make qualitative observations about the behavior and appearance of worms around food. Mutant worms tended to be found off food somewhat more often, but this was variable in each session. Worms on the plates without food were difficult to locate, and many had crawled off of the agar and possibly died. With sealed plates this station allowed most students their first chance to see worms up close. Station 2 Opinions of students with the simulations varied. In lieu of chromebooks we used single laptops for this station. Most groups found the use of the simulation straightforward, some groups discovered the main purpose and conclusions in this section a little more vauge. The intention of this simulation was to introduce “rules” that the students could discover about strategies to maximize reproductive output. The optimal strategies involved limiting egg-laying and feeding rate when there was competition or food was sparse, but to maximize these when food was plentiful. Station 3 Students generally liked this station the most. Most were able to handle the pipetting with enough instruction and were eager to volunteer. After the first session we determined it would help more to have tubes with water with which the students could practice before pipetting worms for the experiments. Although there was considerable variability in the number of viable worms per assay, we were able to gather enough data over the 4 sessions to quantify the results. We found that mutant worms were less likely to find the food patch during 30 minute time points but that at later time points (1.5 hrs), even mutant worms accumulated on the food patches. This indicates that olfactory sensory input, and possibly other modalities affected by daf-19 mutations, is important in regulating the rate of accumulation at a food source. Other modalities might play a role in maintaining worms at the food source. Discussion The demonstration and visit were overall well-received by students and teachers. During the course of the demonstrations we found that allowing more time and giving more simple introductions helped the students to understand and perform the planned experiments. Station 1 could be redesigned to allow students to make a better connection between the behavior of the worms and egg-laying, although microscope optics and the time allowed during this station makes counting eggs difficult for middle-shcoolers. The students were engaged, especially in station 3 and apparently understood the important concepts. Some additional changes and planning could make these demonstrations more smooth in the future, but we considered the overall visit successful.