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Live Leeches

Miss Heidi H. Haugen
Access Excellence-Genentech
Adapted from: "Those Amazing Leeches" by Cheryl M. Halton (Dillon Press, Inc.-1989)

Focus Question

"How does a live leech respond to light, odor, and vibrations?"


Introduction

Leeches are classified as annelids, or segmented worms. They are related to earthworms and share many traits. Both leeches and earthworms are hermaphrodites (have both male and female reproductive organs). In addition, both have an organ called a clitellum which forms a cocoon to protect fertilized eggs called embryos. Earthworms use setae (small stiff bristles) along each side of their body to move and burrow in the ground. Most leeches utilize suckers at each end of the body for moving or attaching to a host. Earthworms have bodies with a series of connected rings called annuli. As the earthworms grows, an additional ring is added to the end of its body. The segments are separated inside the worm by thin body walls. Leeches have 32 segments regardless of their age. Each segment has from 3 to 5 annuli. Leeches do not have internal walls separating its segments, allowing them to store a large amount of blood. There are a number if sense organs that leeches use to detect feeding opportunities. Colored dots, segmental receptors, on the leech's body are sensitive to water and/or ground movements/vibrations. Eyespots or ocelli are light-sensitive cells found on all parts of the leech. Leeches are extremely sensitive to light and shadows passing above them. The eyes of a leech are found only on the leech's head and are made up of groups of ocelli. There are other cells on a leech that are sensitive enough to detect even tiny amounts of substances such as skin, oils, and blood.

Procedure

Getting to know your leech:

(Be sure to let your leech rest after each mini-experiment)

  1. Fill a petri dish ~3/4 full of water (obtained from your teacher). Select a leech from the "leech jar". Name your leech . Place the leech in the petri dish. Observe the leech and record movement. Does the leech move in a particular way? Look at both the dorsal and ventral sides of the leech. Diagram your leech in detail and Identify-label the anterior and posterior end of your leech. Summarize your findings.

  2. Count the segments on the leech. How many segments does your leech have? Use a magnifying lens to see the structures of a leech more closely. Locate and label the Clitellum. What is the purpose of the Clitellum?

  3. Locate the sense organs or areas of these organs on the leech. These areas are not easily observed. If possible, label the segmental receptors, ocelli, and the eyes.

Leeches and Light:

  1. Place your leech in a 600ml beaker. Allow the leech to remain undisturbed for about 5 minutes in a well lighted room.
  2. Pass your hand over the container so that a shadow falls on the leech. Observe and record the leeches' actions.

Leeches and Odor Detection:

  1. Take a clean, empty 600ml beaker and make a fingerprint on one side of the inside of the container. Be sure that only the one fingerprint is visible.
  2. Mark the fingerprint area on the outside by circling it with a grease pencil.
  3. Add water, obtained from your teacher, and your leech to the container. Observe the leech closely. Record your observations. What structures on the leech are involved with the detection of odor?
  4. Now try adding a few drops of dilute beef broth to a 600ml beaker containing water, obtained from your teacher, and your leech. How many drops does it take to excite the leech? Record the information.
  5. Now try adding a few drops vinegar to a 600ml beaker containing water, obtained from your teacher, and your leech. How many drops does it take to excite the leech? Record the information.
  6. Now try adding a few drops of red food coloring to a 600ml beaker containing water, obtained from your teacher, and your leech. How many drops does it take to excite the leech? Record the information.

Leeches and Vibrations:

  1. Place your leech into a 600ml beaker containing water, obtained from your teacher. Allow the leech to remain undisturbed for at least 5 minutes. Use a plastic ruler or tongue depressor to stir up the water surface. Observe and record the leeches actions. What parts of the leech are receptive to water movement? Why would leeches have organs that are sensitive to water vibrations?

Observations/Records

record your observations/summaries and answers to questions in the procedure on a separate sheet of paper.

Getting to know your leech:

  • Does the leech move in a particular way?
  • How many segments does your leech have?
  • What is the purpose of the Clitellum?

Leeches and Light:

  • No questions in this section.

Leeches and Odor Detection:

  • What structures on the leech are involved with the detection of odor?
  • How many drops of vinegar does it take to excite the leech?
  • How many drops of red food coloring does it take to excite the leech?

Leeches and Vibrations:

  • What parts of the leech are receptive to water movement?
  • Why would leeches have organs that are sensitive to water vibrations?

Conclusion/ Analysis

(please answer the following on a separate sheet of paper)

  1. What is the adaptive advantage to the leeches' responses to light, odor, and vibrations?
  2. What do the terms anterior, posterior, dorsal, and ventral mean?
  3. What do you like best about leeches?
  4. In 1884 scientists discovered a very powerful natural anticoagulant, hirudin, in the salivary glands of the medicinal leech-Hirudo medicinalis. Why do you think these leeches contain hirudin?
  5. Graph the substances used in odor detection and how many drops of each substance took to excite the leech.


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