Pre-Lab for “Wormbeat”
A Lab to Introduce the Scientific Method
We have a very human need to understand our world. Millions of years ago , we asked: “If I eat this plant, will it
hurt me? Where does the sun go each night? “ Today we ask: “why isn’t my car running well? Why do I get a side
ache when I run?” This is, of coarse, just problem solving. Logical, step-wise thinking is also known as “ the
Problem solving begins when we ask a question. We call the question our research problem. To solve a problem,
we must first find out what is already known about it; that is, we gather background information. We talk to
others, rely on past experiences, and consult reference books and journals. Perhaps another researcher has
already investigated the problem. If not, the references may at least shed some light on the types of
experiments we could conduct.
We collect background information until we feel confident enough to make a testable prediction. We make an
“educated guess,” or hypothesis, that can be tested. The next step is the testing of our hypothesis by carrying out
an experiment. Experiments allow us to observe things we might not be able to otherwise see! For a valid
experiment, we need to make careful observations, keep accurate records, and avoid jumping to conclusions. The
results of the experiment –the data – are recorded and analyzed. We may decide to group them in a table, display
them with a graph, or to show statistics on them.
Enter: The Earthworm
Let us assume that we are interested in the circulation of blood in animals. For starters, we elect to use a simple
animal – an earthworm. We state our research problem: “How does a change in environmental temperature affect
the circulation of blood in earthworms?”
Our first approach would be to gather background information. We learn from reading or talking to biologists that
an earthworm has a very large blood vessel running along the top (dorsal) side of its body, just beneath its skin.
The contraction of this blood vessel as it pumps blood causes this vessel to look alternately dark (fat), then light
(skinny); in other words, you can see the blood flow. We read a little about the effect of hot and cold on animals
like worms, which are ectotherms, or “cold-blooded” animals. We reflect on other ectotherms we have seen or
touched. Eventually, we make our prediction. After we do that, we are ready to test it.
Good Experimental Design
In our experimental set up, we’ll allow a single experimental factor or independent variable (IDV) (manipulated
variable) to change. The independent variable in the lab is the temperature, which we will change by heating or
cooling the water around the worms. In our control set up, all the conditions (for example, the worms’ diets, etc.)
are the same, except for the experimental factor. This will give us something to compare our experimental results
We will measure the pulse rate of the worms in both groups; pulse rate is the dependent variable (DV) (responding
variable) in this lab. So, think about your hypothesis . . . how will changing the temperature affect an earthworm’s
“Wormbeat”: A Lab to Introduce the Scientific Method
“How does a change in environmental temperature affect the circulation of
Our research question:
blood in earthworms?”
The background information (see pre-lab sheet):
Your testable prediction (hypothesis)
MATERIALS & METHODS
Materials per lab team:
Earthworm ice large pan petri dish thermometer filter paper stopwatch
1. Moisten some filter paper with water and press it into the bottom of a petri dish. (The wet filter paper makes it easier for the earthworm
to breathe, since it has no lungs and must breathe through its skin.)
2. Fill a pan with room temperature water. Take the temperature of the water (in ˚C) and record it in Table 1.
3. Obtain an earthworm and gently rinse any soil of the animal. Place the worm in the paper-lined petri dish. If your worm is too “wiggly,” lay a
small piece of moist paper towel over its head to quiet it down. Or, get a different worm.
4. Find the dorsal blood vessel along your worm’s back. Encourage each team member to find it.
5. Count the number of blood vessel contractions observed in 1 minute, and record in Table 1.
6. Repeat step #5 two more times, giving you three trials. Record the results of each trial in Table 1.
7. Take the average of your three trials (add them up and divide by three) and record in Table 1.
8. Now add ice to the pan until you lower the water temperature to 10˚C. Allow the earthworm to rest in its dish, on top of the ice water, 3-
5minutes before proceeding to step #9.
9. Again, count the number of blood vessel contractions observed in 1 minute, and record in Table 1. Do three trials at 10˚C.
>TIP: Make sure water temperature stays at 10˚C! Add ice if it started to warm up.
10. Return all lab supplies to their original locations. Gently return your worm to it container.
11. Report your data from both temperatures to the class, and copy down all other students’ data into data table #2. Calculate class averages.
your group's data table
class data table
graph of the class average
Use your best writing skills to compose your conclusion in which you:
Re-state the research question
Summarize the class results (you should include the average value and range of the values)
Restate your hypothesis
State if your data supported or refuted your hypothesis
In this lab, what was the independent variable? What was the dependent variable? (IF THE ANSWER TO THESE QUESTIONS
ARE NOT IN YOUR CONCLUSION, YOUR SCORE WILL BE VERY LOW! )
Why is the class average more accurate than your group’s average?
Point out some sources of potential inaccuracy (“experimental error”),
Suggest modifications to improve the experimental design (reduce errors or variables)
Your formal lab write up will follow the guidelines in “How to Write
a Science Lab Report” (see handout).
Name ___________________________________________ Period ______ Date _______ Seat# _________
Wormbeat Pre-Lab and Procedure Questions
1. List 3 ways you could gather background information on a lab topic. __________________________________________________
2. In which section of a Lab Report are tables and graphs recorded? ___________________________________________________
3. Write THREE facts about earthworms in the "background section" of your lab. _________________________________________
4. What is the manipulated variable for this lab? _________________________________________________________________
5. What is the responding variable for this lab? __________________________________________________________________
6. How will you measure the worm's pulse rate? (If you need to, look back at the background information and look ahead to the Lab
7. Read the Lab Procedure for Wormbeat. Now look at this diagram of the experimental set-up. Why is the worm in a petri dish?
Thermometer with WORM
water water PAN
8. Why do you do 3 trials for each experiment? __________________________________________________________________
9. Why do you need to allow the worm to rest in its dish for 3-5 minutes in step 8 of the Procedure? ___________________________
10. What is your research question? ___________________________________________________________________________
11. Write your Hypothesis (in a complete sentence). ________________________________________________________________