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Responses of Annelids or Segmented Worms to Various Stimuli

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Author: Janice VanCleave

Segmented worms such as the earthworm belong to the phylum Annelida. These worms have a more advanced body structure than most worms. The body of the earthworm is like two tubes, one inside used for digesting food and one outside serving as the body wall. The earthworm has a mouth but no nose, eyes, or ears. Yet it responds to odors and to changes in moisture, temperature, and light.

In this project, you will have the opportunity to unravel these paradoxes by observing and testing an earthworm's responses to various stimuli. You will also test the learning ability of earthworms. Note: No earthworms should die from any of the experiments in this project. Handle the worms with care. At the conclusion of the project, place the worms outside in a shady area of soil.

Getting Started

Purpose: To observe an earthworm in a simulated (near-natural) soil environment.

Materials

  • 3 cups (750 ml) of potting soil
  • l-quart (l-liter) glass jar with lid
  • 1 cup (250 ml) of water
  • 8 to 10 earthworms (from a bait shop, or dig your own)
  • apple peelings
  • sheet of newspaper
  • rubber bands
  • hammer
  • large nail

Procedure

  1. Pour the soil into the jar.
  2. Moisten the soil with water and keep it moist during the entire project
  3. Put the worms into the jar.
  4. Responses of Annelidas Segmented Worms

  5. Place the apple peelings on the surface of the soil and keep the worms supplied with peelings during the entire project.
  6. Fold the newspaper so that it fits around the outside of the jar. Secure it with the rubber bands.
  7. Use the hammer and nail to make five or six holes in the lid of the jar.
  8. Secure the lid and place the jar in a cool place (see Figure 18.1).
  9. Remove the paper and observe the jar every day for two weeks.

Results

The worms start wiggling immediately and burrow into the soil. A network of tunnels can be seen in the soil. The apple peelings disappear, and casts (undigested soil deposits) appear on the surface of the soil.

Why?

Earthworms spend their lives in one small area of the ground. In some places there are 50,000 worms per acre of soil. An earthworm's diet consists of the animal and vegetable matter in the soil, which is pulled into the worm's mouth by muscles in its body. Nutrients are extracted as the soil passes through the earthworm's digestive tube and out the other end. In this way, earthworms are very beneficial because their tunneling and digestive process loosens and aerates the soil.

Try New Approaches

  1. How does low temperature affect the activity of the worms? Place the jar of worms in a refrigerator. Make daily observations of the movement of the worms inside the jar for one week. Keep the worms in the refrigerator for the remainder of the project. The body temperature of worms changes with their environment. Their metabolism is reduced in cold temperatures, so they become more lethargic. Thus, more worms can be contained in a smaller area for longer periods of time.

Design Your Own Experiment

  1. Which end of the earthworm is more sensitive to odor? Moisten a paper towel and lay it on a table. Place one worm on it. Wet a cotton ball with fingernail polish remover. Hold the wet cotton ball near, but not touching, the anterior end (the more pointed and darker end) of each worm. Repeat at the posterior end (rear end) and at segments between the ends.
  2. Does the earthworm prefer wet or dry surfaces? Lay two pieces of wet and dry paper towels next to each other, but not touching, on a table. Place an earthworm across the two surfaces, anterior end on the wet towel, and observe the response. Then reverse the worm's position so that the anterior end is on the dry towel. Again, observe the response.
  3.  
    1. Does the earthworm respond faster at a higher or a lower body temperature? Prepare two containers of worms by placing soil and three worms in two separate baby food jars. Place one jar in a refrigerator and keep the other at room temperature. After 24 hours, use the worms from each jar to test their response to odor and preference for wet or dry paper.
    2. Use a stereomicroscope (dissecting microscope) to measure the change in heart rate of the worms at different body temperatures. Place one worm at a time under the microscope. Find the earthworm's dorsal aorta (the blood vessel running along the uppermost region of the back). You should see a wavelike contraction moving from the posterior end to the anterior end. Each wave is a single "heartbeat" Count the beats in one minute. Measure the temperature of the soil. Make additional temperature changes by sitting the containers in a bowl of ice water. Do not heat the water because you will injure the worms. Prepare a graph using temperature as the independent variable (x-axis) and heartbeat as the dependent variable (y-axis).
  4. Responses of Annelidas Segmented Worms

  5. Can an earthworm learn simple, consistent choices when confronted with alternatives? Use shoe boxes to construct a T-maze (see Figure 18.2). Cover the top with several layers of red cellophane and restrict direct light on the maze. Use a "D" cell battery and wire to supply a brief electric shock when the worm touches the wire. Earthworms can learn to take the arm of the maze leading to the reward (darkness and moisture) and away from the punishment (light, dryness, sandpaper, and electric shock). The development of this response is slow and will require many trials. Separate the worms that are learning the maze and place them in their own container. It is thought that earthworms can learn to make the correct choice 90% of the time. How well do your worms learn? How long do they retain what they learn? Display the maze and photographs showing the worms during a typical learning lesson as well as a graph comparing the trials for each worm in training.

Get the Facts

  1. The American earthworm belongs to the genus Lumbricus. Charles Darwin first showed that this worm is important because it aerates the soil by digging tunnels and aids in the growth of plants by dragging seeds from the surface into the damp soil where they can germinate. Use an encyclopedia to find out more about the benefits of earthworms. How deep do they tunnel? How much soil do they bring to the surface annually?
  2. Earthworms have a nervous system but no obvious sense organs such as eyes. But the worms do respond to light stimuli. How? Use a biology text to find information about the sensory responses of worms. Also read the experiment titled "Night Crawlers" (pp. 124–125) in Janice VanCleave's Biology for Every Kid (New York: Wiley, 1990).
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