DO NOT WRITE ON THIS SHEET! Complete in your Lab Notebook
Skills:
- organizing and analyzing data
Objectives:
- Describe how an earthworm responds to stimuli
-Infer how physical and behavioral characteristics of the earthworm reflect adaptations to its
environment
Purpose:
In this lab, you will look at live earthworms, observe their external structures, and test their
responses to environmental stimuli.
Background:
Earthworms are animals that are classified as annelids, or segmented worms. They have digestive,
circulatory, and nervous systems. Gas exchange is through the skin. They live in rich soil, which they eat,
digesting the organic matter in it and passing the inorganic dirt particles out of the body. Earthworms are
not very mobile animals. They spend their lives in one small area and as a result do not encounter many other
earthworms. Their reproductive strategy is well suited to this type of life. Each earthworm is a
Anterior
hermaphrodite, that is, it has both male and female sex organs. Thus, any individual earthworm can
cross fertilize with any other earthworm it encounters.
Procedure:
1. Moisten a paper towel, and place it in a clean dissecting pan. Place the worm on the paper
towel. You are working with a live animal. Handle it gently, and follow all lab instructions carefully.
Watch the worm move, and notice which end leads. The worm’s leading end is its anterior end. Identify
the worm’s posterior end, that is, the end away from the leading end.
2. Notice how the body of the earthworm is divided into segments. Starting at
about segment number 32 there is a thickening in the body, called the clitellum,
as shown in the diagram below. The clitellum produces a mucus sac in which the earthworm
deposits its eggs. Why do all earthworms have a clitellum?
3. To determine whether an earthworm prefers a moist or dry environment, place a dry paper
towel next to the wet one. Place your worm across the two towels, so that the anterior is on the wet
towel and the posterior is on the dry. Record which direction your worm moved. Repeat step 3 for a
total of 3 trials.
Wet towel
Posterior
Dry towel
4. Now place the worm so that the posterior is on the wet towel and the anterior is on the dry. Record
which direction your worm moved. Repeat step 4 for a total of 3 trials.
5. Return your earthworm to the container in the front. Throw paper towels in the garbage cans.
Rinse dissecting tray and return it to the front of the room.
Answer all questions and record your investigations in your Lab Notebook
Title: Put a title at the top of the page in your lab notebook.
Problem: Write the following. “How do worms respond to the stimulus of a wet environment vs. a dry
environment?”
Background/Research:
In your lab notebook write a 3-5 sentence summary of the lab and what you have learned about
Earthworms before beginning the lab. This should be written so that you can go back and read it in a
month and remember what you did and what information was important.
Hypothesis: Write a hypothesis for your experiment. Remember this should look something like the
following. If__________ then ___________ because____________.
Write your independent variable (IV) and your dependent variable (DV).
Data
Make a data table below to record your results. Remember to include both the independent and
dependent variables in your table. Clearly label all of your data and trials with units.
*Have Ms. Henriksen approve your data table before you begin collecting data. She may provide you
with a template to get you started on this first lab.
Conduct the experiment according to the directions on the front of this sheet.
Results and Analysis: Answer the following questions in your lab notebook. Use full sentences but
you do not need to write out the question if the answer refers back to the question.
1. What is a stimulus? In this experiment, what is the stimulus?
2. Which kind of surface, wet or dry, does the worm prefer? Use your data and actual numbers to
answer this.
3. Did it matter which end (anterior or posterior) was on the wet or dry towel? Explain your answer
using your data.
4. Why do you think the worm responded this way to the moisture? In other words, what advantage
does the worms behavior serve for its survival?
5.
Was this a controlled experiment? Explain why or why not.
6. Describe any errors in your experiment or things that did not go as planned. Do you think they
affected your results? Why or why not?
7. What is another stimulus that you would like to test the earthworm’s reaction to? Describe how
you would conduct this experiment.