Pre-Lab for “Wormbeat”
A Lab to Introduce the Scientific Method
Problem Solving
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, justproblem solving. Logical, step-wise thinking is also known as “the scientific method.”
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 so 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 also learn that earthworms are ectotherms. Ectotherms are considered “cold-blooded” animals, which means that they use the external environment to control their body temperature.We reflect on other ectotherms we have seen or touched such as snakes, lizards, or turtles. Eventually, we make our prediction. After we do that, we are ready to test it.
Good Experimental Design
In a well designed experiment, the researcher allows a single experimental factor or independent variable (IDV) (manipulated variable) to change. The independent variable in this lab is the temperature, which we will change by cooling the water around the worms. All other conditions/variables (for example, the worms’ diets, etc.) are controlled (i.e. held constant). The variable which we measure (in this lab, the pulse rate of the worm) is called the dependent variable (DV) (responding variable). We will measure the pulse rate of the worms in both groups (room temp. and 10C) So, think about your hypothesis . . . how will changing the temperature affect an earthworm’s pulse rate?
“Wormbeat”: A Lab to Introduce the Scientific Method
Our specific and focused research question: “How does a change in environmental temperature affect the circulation of blood in earthworms?”
MATERIALS & METHODS
Our experimental plan:
(a) Materials per lab team:
1. worm 5. thermometer
2. tray 6. ice
3. petri dish 7. timer
4. filter paper
(b) Procedure:
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.
Name ______Period ______Date ______
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.LIST 3 background facts that you learned about earthworms from the reading.
4.What is the Independent variable for this lab?______
5.What is the Dependent 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 Procedure.)
7.DRAWthe Lab set up for our wormbeat experiment. This in in the Materials and Methods part of the lab protocol. Now look at this diagram of the experimental set-up. Why is the worm in a petri dish?
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.After reading the pre-lab and lab procedure, what do you think will happento the earthworm’s blood circulation when we put it in cold water?
Hypothesis: (use “If……., then…….. because……” statement).
11. Define Independent variable.
12. Define Dependent variable.
13. LIST some control variables from the experiment (what things are we keeping the same?).
14. Define ECTOTHERMIC.