In this investigation, you will explore the features of a living earthworm (Lumbricus terrestris). During the investigation, it is important that you keep your earthworm moist using a paper towel. This is because earthworms obtain oxygen through their skin. Also, handle the worms gently, the goal is to gather information without harming the specimen.
Can an Earthworm Tell Up from Down?
Observe the earthworm as it moves. Earthworms do not have appendages (like arms or legs), but they do have bilateral symmetry. That means they have a left and a right side, a front and a back, and a top and a bottom. The scientific names for these regions are:
Top = Dorsal Bottom = Ventral Front = Anterior Back = Posterior
1. How can you tell the dorsal from ventral side?
2. How can you tell the anterior from posterior side?
3. Label the sides of earthworm using the scientific names:
4. Geotaxis is the movement of an organism in response to gravity. Keeping the health and safety of your specimen in mind, describe how it responds to being flipped over as well as how it responds to being tilted in the tray.
Do All Earthworms Share the Same Features?
Many organisms have different morphotypes, or variations within a species. For example, coloration in black bears can range from brown to gray to black. Some organisms also display sexual dimorphism, where the females of the species look different from the males. For example, a male lion will have a large mane, but
females do not.
Place your earthworm next to the earthworm from the group next to you. Carefully observe their features, focus on things like size, color, number of segments, and other external features.
1. What do they have in common?
2. What are differences you can observe between the worms?
3. Earthworms are hermaphrodites, meaning they have both male and female sex organs (testes and ovaries). The thickening of the body at about segment 30 is called the clitellum. Exchange of sperm occur in this region, with each worm fertilizing its partners eggs. Locate the clitellum on your earthworm and compare it to other worms. Consider the following:
Is the clitellum visible on all earthworms?
Is the clitellum in the same location on all worms?
Is it the same size?
How can you explain any observed differences?
What Senses Does the Earthworm Have?
Like all members of the animal kingdom, earthworms are heterotrophs, meaning they must obtain food. A plant is an autotroph, it can make its own food from
sunlight. Animals use their senses to find food and avoid danger. In this section, you will determine what the earthworm can sense in its environment. Behaviors occur in response to a stimulus, such as light or temperature.
Response to Moisture
Place a dry paper towel on one side of the tray, keeping a moist towel on the opposite side. Observe the earthworm. Does it move to one side or another? Does it spend more time on one side? Describe your observations.
Response to Light
Darken an area of the tray or use a flashlight to make a bright area. Describe how the worm reacts to the light and the dark.
Response to Odor
Dip a q-tip in rubbing alcohol and place it near the head region. Caution: do not touch the skin, it will burn the worm! Does the earthworm react to this stimulus? Is this test sufficient enough to determine if the worm has a sense of smell? Why or why not?
Response to Temperature
Use a cold pack or ice to design an experiment to test the earthworm's response to temperature. Describe your observations:
Final Analysis - CER
Experimental Question: What senses does the earthworm have?
CLAIM (answer the experimental question using a complete sentence)
EVIDENCE (summarize from your observations)
REASONING: (link the claim to the evidence or to scientific principles, answer WHY this would be the case)
Write a short definition for each of the following terms:
1. Appendages ________________________________________________________________
2. Bilateral Symmetry ____________________________________________________________
3. Geotaxis ____________________________________________________________________
4. Hermaphrodite ______________________________________________________________
5. Heterotroph ________________________________________________________________
6. Morphotype ________________________________________________________________
7. Sexual dimorphism __________________________________________________________
8. Stimulus ___________________________________________________________________