Observation of a Living Earthworm Teacher Guide

Original Document: Observation of a Living Earthworm

Introductory Notes

Earthworms can be obtained from any bait shop, for maximum squeal effect, get the largest type, usually nightcrawlers, but the availability will depend on your area. Earthworms will not survive long if they are left out, refrigerated earthworms can last weeks.

Students often ask for gloves, but I do not provide them. Students can share the touching of the worms with their lab partners, but I try to encourage students to get over their fears and squeamishness about nature. This is biology, after all.

1. Earthworms belong to the Kingdom ___Animalia______the Phylum ______Annelida_____.

2. List two characteristics of Annelids

segmented bodies, bilateral symmetry, no backbone

3. Name two other organisms in the same Phylum Annelida. leech, marine worms

4. Place the earthworm on a moist paper towel in a dissecting pan. Observe the worm as it moves. The leading end is the anterior end, the opposite is the posterior end. Roll the worm over and observe what happens. The side that the worm prefers UP is the dorsal side. The side it prefers down is the ventral side. which side was dorsal/ventral/anterior/posterior. What other clues on the earthworm would tell you which end was which?

the direction it is moving, coloration

5. Observe the Earthworm for five minutes. Write your observations of its activity in the space below.

What is a hydrostatic skeleton? made of water

Describe how the worm moves - what muscles are necessary for the earthworm to move. Use your book as a reference to sketch the 2 muscles. longitudinal go up and down, circular go around

Now that you are familiar with your worm, it is time to give it a name. Make sure the name you choose is appropriate for the earthworm's sex.

Name of your worm ____Examples: Joe, Jordan, Jamie (anything that works for both girls and boys)______

6. Earthworms Sizes--Use a ruler to measure the length of your worm in centimeters. Worms are divided into segments. Count the number of segments on your worm (hint you may want to count a small portion of the worm and multiply). Compare your worm to three other worms in the room

  Your Worm Worm 2 Worm 3 Worm 4
Length (cm) answers vary      
Number of Segments        

Longer worms have ____more____ segments. (more, or less, or the same)

7. Locate the thickening of the earthworm's body at about segment 30. (Segments are numbered 1 to 30, one being the first segment on the head. This swelling is called the CLITELLUM

Is the clitellum located more toward the anterior or posterior of the worm? anterior

8. One the ventral side of the earthworm are small bristles called SETAE. They are too tiny to see, but you can feel them by running your fingers along the ventral side of the worm. Also note the tiny openings at around the 14th segment. These are the SEMINAL RECEPTACLES, where sperm is exchanged between two mating worms.

What is the function of setae? grip the earth, movement

What is the function of the openings at segment #14? reproduction

9. Sketch the earthworm in the space below. Label the dorsal side, ventral side, posterior and anterior ends. Also label the clitellum , setae , and seminal receptacles.

10. Study the earthworm's head. Does it appear to have any sense organs, such as eyes, ears, nose, or mouth? Do you think the earthworm is capable of sensing... (make your predictions below- yes or no)

Light? ____ Odor? ____ Sound? _____ Taste? _____ Touch? _____ answers vary, general they react to all these stimuli

11. Response to Touch (stimulation)

---Place a dry paper town on one side of the pan and a moist paper towel on the other. Stretch the worm so that it lays across both towels. Observe the earthworm's response. Which direction does it move. Perform ten trials, alternation the worm's head so that half the time it lays on the moist, and half the time it lays on the dry to start with. Record the worm's responses in the table below.

Head starts on dry

Response (moves toward wet or dry)

Trial 1

 

Trial 2

answers vary, but generally the earthworm will move toward the moist side of the tray. It will also prefer to go under the paper towel where it is dark.

Trial 3

Trial 4

Head starts on wet

Trial 1

Trial 2

 

Trial 3

 

Trial 4

 

Use the data above to write a conclusion about whether the earthworm can sense wetness or dryness. You may want to include other initial observations in your conclusions. worm prefers a moist environment

12. Remove the dry paper towel from the pan and let the worm just move around for a while. Use a pipette to drop a water droplet on its anterior end. Record its reactions. Drop water on its posterior end and record its reactions

Response to water drop on anterior end _________reacts_____

Response to water drop on posterior end _______sometimes not as strong of a reaction_______________

Should you revise you conclusions in #11. Does this test indicate that the earthworm can sense being touched?

13. Response to Odor---Obtain a Q-tip dipped in acetone (fingernail polish remover). First, wave the Q-tip near the worm's posterior end. and record the worms reaction. Then repeat this process at the anterior end. Important - Do not touch the worm, it is toxic!

Response

Ammonia anterior ______strong reaction_________

Ammonia posterior ______weak or no reaction__________________

Does the earthworm have a sense of smell? Based on your data, is the front or hind end more sensitive to odors?

14. Response to Light -- For this part of the experiment, you will be given a flashlight and the room will be darkened. Discuss with your partner and develop how you will test the worms response to light.

Describe your experiment. answers vary, they should develop a way to give the earthworm a choice between a light and dark environment

Collect data and construct data table. should look similar to the data table above

Write conclusions : earthworms prefer a dark environment