In this portion of the lab you will be working with terrestrial isopods commonly known as
pillbugs, sowbugs, or roly-polys to learn about experimental methods. These organisms are
members of the Phylum Arthropoda, Class Crustacea, which also includes shrimp and crabs.
Most members of this group respire through gills.
Problem - Assume that you have been assigned to collect some pillbugs. Based on your
previous knowledge and experiences, where should look? What environmental factors determine
where pillbugs live? (see informational handout if you are unsure)
Your task is to design an experiment to test the environmental factors you believe may
determine where pillbugs live. You will use a choice chamber in your experiment.
1. General Idea
Example: I think that the amount of fertilizer has an effect on the growth rate of plants
2. Hypothesis Development
a. Factors that you think have a relationship: Example: fertilizer & growth rate of plants
b. Describe the type of relationship (positive, negative, neutral): Example: I think fertilizer will
increase plant growth, so “positive” __________________
c. Prediction of how a change in one factor affects the change in the other.
Example: more fertilizer will increase the growth rate of plants
d. If that relationship is accurate, then predict the actual changes that you will be able to
measure during the experiment. Example: When I increase the amount of fertilizer given to my
bean plants then my bean plants will grow taller.
e. Restate as a hypothesis: specific, includes a prediction & is testable (try to put it in an
“If…, then…” format): Example: If there is a positive relationship between fertilizer and plant
growth, then when I increase the amount of fertilizer applied to my bean plants, my bean plants
will grow taller.
3. Experimental Design
a. Which is your measured (dependent) variable? _______________________________
Example: height of plants (because I didn’t know how that was going to change
therefore I had to measure how its change was dependent on the amount of fertilizer).
b. Which is your manipulated (independent) variable? _____________________________
Example: amount of fertilizer (because I manipulated how much fertilizer was given; it
changed only how I chose it to change and was not dependent on any other factor in the
c. List three confounding variables that you would have to control to isolate your tested
variable. (Confounding means confusing, so confounding variables would be other factors that
could affect the results and therefore confuse your interpretation of the results)
Example: amount of water, type of soil, temperature, amount of light, age of plants…
d. Describe the experimental groups for your experiment.
Example: each group of 10 plants is treated with a different amount of fertilizer: 0
tsp/gallon, ¼ tsp/gall, ½ tsp/gall, 1 tsp/gall, 2 tsp/gall, 4 tsp/gall
e. Describe the control group(s) for your experiment.
Example: the group receiving only water (“standard” or no treatment condition)
f. Suggest a sample size for your test groups in this experiment. ____________________
Example: just NOT one plant; consider at least 10 or more per group
g. What result would cause you to conclude that your hypothesis is supported?
Example: the plants that are given more fertilizer grow taller than the ones given less.
h. What result would cause you to reject your hypothesis? Example: the plants that are given
more fertilizer do NOT grow taller than the ones given less
Use the information gathered from the pillbug experiment to write a lab report. You may
discussion options with your lab partners, but each person must write and submit their own
report. Using the criterion 6- to help in writing.
Score, from 1-5
(Scoring rubric: 1= element is missing; 2= minimally satisfies;
3=partially satisfies; 4=mostly satisfies; 5= fully satisfies)
Is the research question plausible? Does it make an inquiry that can be tested by
a classroom experiment?
Is the hypothesis worded as a statement and is a reasonable and educated guess
that pertains to the research question?
3. Are the independent and dependent variables correctly named?
4. Are at least two factors that must remain constant correctly identified?
5. Is the materials list comprehensive of the materials used in the experiment?
Does the introduction/purpose include a brief discussion of the topic and purpose
of the experiment?
7. Is the procedure written in paragraph form?
Does the procedure clearly explain the protocol (could another conduct the
experiment based on the description)?
Does the procedure seem scientifically plausible – will it accurately test one
variable while minimizing confounding variables?
10. Analysis includes a brief summary of the results?
11. Is all the experimental data collected included in the report and organized?
12. Is data included for control as well as experimental groups?
Is data included from multiple trials of the experiment conducted according to an
14. Are charts, graphs, or other visual aids used to visually present analyzed results?
15. Are charts, graphs, or tables numbered and have a descriptive titles?
16. Is the conclusion written clearly in narrative form?
Does the conclusion clearly indicate how the results do or do not support the
Does the conclusion address experimental error or other errors that may have
occurred, and make suggestions for future research?
Total (maximum: )_______