Blackworm lesson: Using mystery to capture student interest
Introduction: Use the powerpoint presentation to introduce the idea of toxicology. There are many different tacks that you can take on this- with younger groups I would recommend not going over all the areas, but use a couple to lead into the mystery and experiment and revisit these throughout the lesson and in the wrap-up.
1)Dose Response
2)Routes of entry
3)Acute vs. Chronic
4)Etc…..(get the rest from the powerpoint presentation)
Once the students are introduced to the idea of toxicology, introduce the mystery.
Mystery:
Ahead of time, set up a table with at least 2 replicates of each of the dilutions used in the Blackworm lab (10%, 2.5%, 0.25% and 0% alcohol). Label each one of them with A, B, C, and D and place the dilutions in a random order- so that the students do not know which one is which. The table will be set up as follows:
ABCD
Give the students the following story:
Ask if they have ever heard of canaries being brought into mines with miners. Let them know that the miners brought the canaries in with them because the canaries were more sensitive to changes in the air quality than the miners were, and if the canary started to seem sick or even died, it was a signal to the miners that they needed to get out of the shaft where they were. Lots of different things are used as indicators- and in this scenario, we are using California blackworms as indicators- not of air, but of water quality.
You can give them some background on the blackworms- lots of interesting information is available at: (give website)
Give the scenario. “We have sampled water from a stream along the banks of a river where there is a suspected contamination. Water has been sampled from the points shown along this stream (show picture) and we are going to use the California blackworms to tell us something about the quality of the water from each site. While we might not necessarily want to drink water from a place that can sustain worms, we most definitely do not want to drink from a place that has a negative effect on these worms. What we want to do is take a look at what the natural behavior of the worms and then compare how the worms behave in each of the different samples.”
There is a great opportunity to talk about what a control is, as well as a qualitative measure versus a quantitative one. All you expect the students to do here is to make qualitative observations and inferences.
Now put the worms into each of the treatments, asking students to observe what happens and discuss while you continue to place the worms in each treatment.
Once the worms are all placed in the treatments, ask the students to guess which of the treatments might be considered control, low concentration toxin, medium concentration toxin, and high concentration toxin. Ask for a show of hands and record their responses on an overhead:
Control
Low
Medium
High
Discuss the responses and why it is that each was chosen. Perhaps make some observations and write them beneath each lettered column.
Then get an idea of what the students know about dilutions. Give them the following picture and have them tell you which they would consider the control, low concentration, medium concentration, and high concentration of toxin. Ask what the final volume is of each one as well. It is important that they realize that this is the reason it is easy to compare the concentrations.
ml H2O4003903000
ml Toxin010100400
Now introduce the experiment:
Experiment:
In the experiment, you will explore whether the inferences you made during the mystery are correct. Do the worms behave in the control, low, medium and high concentrations like you decided they did? Ask the students how you would test this. They should get the idea that they will try different concentrations of toxin and see how the worms behave in each one. They will make objective observations of how the worms behave normally, allow the worms to acclimate to their control environment (100% water), and then observe how the behavior changes in each treatment.
In this modification of the blackworms lab, you may provide the dilutions to the students- having multiple containers of each concentration makes this easier in large groups. The students receive the following:
a)50ml graduated cylinder
b)9 plastic weigh boats (2/treatment and one with original worms in water)
c)Pencil or grease pencil
d)4 spoons or 4 pipettes
e)Clock with a way to count seconds
f)Sheet with places for observations during experiment and for recovery
Each group will label their weigh boats in pairs- a water and a treatment for each (the students will place the worms from the provided weighboat into 4 different water filled boats, one per treatment). Then will fill the boats with appropriate solutions:
Treatment 1: one boat with water and one with control (also water)
Treatment 2: one boat with water and one with low concentration (0.25%)
Treatment 3: one boat with water and one with medium concentration (2.5%)
Treatment 4: one boat with water and one with high concentration (10%)
(**have students think about the order they want to transfer solutions so as not to contaminate each with the other…students can come up with the appropriate order on their own- and if they don’t do it correctly, just make sure they think about what sort of effect the incorrect order might have)
Students will transfer the worms from a provided weighboat into each of the water solutions. While allowing the worms to acclimate for 2-3 minutes the students will take notes as to the normal behavior of the worms. They may just observe, or see how the worms react to different perturbations (probing, swirling, etc.).
After 2-3 minutes, the students can take each and transfer it to the treatment boats. They will take initial observations at 0 minutes, and then again at 3, 6, and 10 minutes. For each timepoint they will take both notes and make an activity assessment. Activity runs from 0 (no movement), to 2 (normal movement) to 4 (hyperactive).
At the end of the experiment, have them transfer the worms to the original water controls for each of the treatments and watch how the worms recover. This part can either be extended to talk about what it means, or the lab can end here.
Have the students clean up their areas.
Wrap-up.
Bring the students up and ask them how their inferences in the mystery compared with their experimental results. Were they the same? If so, what in their prior experience allowed them to correctly identify each toxicity? Different? If so, what do they think made them think it was the other way around before?
Now the big wrap-up….Put the picture back up of the river. Split the students into two groups and have each group come up with where each sample was taken and where the contamination event might have occurred. Have a representative from each group report for each group- presenting their solution and the reasons why they chose that solution. Students (7th grade at least) seem to have an intuitive sense of the dilution effect that can happen downstream- so this might be a good thing to bring up.
You can also follow up with identifying all of the abstract concepts from the initial presentation with what would be an example of each in the mystery and experiment.