Download Earthworm Dissection Lab draft

NAME: ___________________________
Earthworm Dissection Lab
Earthworm Dissection © John R. Sowash | April 2009 | Permission to redistribute granted
Pre-lab Discussion:
The earthworm belongs to a group of animals called annelids (segmented worms). The body of an annelid is usually
divided internally and externally into well-defined segments which may be separated from each other by
membranous partitions. Except for the tail and head regions, all segments are essentially alike.
Other members of this group include the clam worms and tube worms, which live in the ocean, and the leeches.
The earthworm hunts food at night and thus has been called a "night crawler." it usually extends its body from the
surface opening of a small tunnel which it makes by "eating" its way through the soil.
The rear end of the worm's body remains near the opening while the head end forages for decaying leaves and
animal debris. It has been estimated that an acre of good soil contains over 50,000 earthworms. By their continuous
foraging and tunneling these worms turn over 18 to 20 tons of soil per acre and bring over one inch of rich soil to
the surface every four to five years. Thus, indirectly, the earthworm enriches farmland and provides for more food
in a rapidly expanding population.
Purpose: To observe the structures of Lumbricus terrestris and understand how this organism displays some major
characteristics & themes of life.
Pre-Lab Questions:
1. Please fill in the following classification information on Earthworm (Lumbricus terrestris). (use
http://www.itis.gov/index.html)
a. Kingdom:
b. Phylum:
c. Class:
d. Order:
e. Family: Lumbricidae
f. Genus:
g. Species: terrestris
2. What does an earthworm eat? _____________________________________
3. Roundworms are the first organism to have a true coelom. What is a coelom?
4. Define the following terms
a. Dorsal:
b. Ventral:
BACKGROUND
1. THEME/CHARACTERISTIC OF LIFE: ______________________________________
What to know/look for:
2. THEME/CHARACTERISTIC OF LIFE: ______________________________________
What to know/look for:
3. THEME/CHARACTERISTIC OF LIFE: ______________________________________
What to know/look for:
4. THEME/CHARACTERISTIC OF LIFE: ______________________________________
What to know/look for:
5. THEME/CHARACTERISTIC OF LIFE: ______________________________________
What to know/look for:
Materials:
One specimen of Lumbricus terrestris
Dissection kit
Dissection tray
Pins
Safety: Put on a laboratory apron if desired. Handle all dissection equipment carefully. Clean all equipment when
finished. Wash your hands well after handling the specimen.
Procedure:
Throughout the procedure there are “hints” to help you later with some discussion questions.
The body of the earth worm is comprised of over 100 segments. Each segment looks like a ring. The
segments are numbered in sequence from the anterior end. Numbers in the diagrams refer to the segment
number.
1. Locate the dorsal side vs. ventral side. Hint: the dorsal is darker….why do you think that is?
2. Attempt to locate the setae on the ventral side. These may look like specks of pepper. What do you think
the purpose of these are?
3. CHOICE: Some people prefer to pin, other do not.
a. Pin worm to dissecting pan with the dorsal side facing up
b. OR do not pin; allow dorsal side to face up.
4. Using dissecting scissors, make a shallow incision in the dorsal side of the clitellum below segment 33.
5. CAUTION: Scalpels and scissors are very sharp. Report any cuts to your teacher. Using the forceps,
and scissors, spread the incision open, little by little. Separate each septum from the central tube using a
dissecting needle, and begin to pin down each loosened bit of skin. In order to see the pharynx and ganglion
(brain), you must open the worm all the way to segment 1.
WATCH THE DEMO BY YOUR TEACHER.
a. Always make shallow cuts, and “tug” the skin away from the internal organs
6. Use the figure on the next page to locate and identify the several structures. The teacher will question you!
a. five pairs of aortic arches, or hearts.
b. the median dorsal vessel. Look for smaller blood vessels that branch from the dorsal blood vessel.
c. locate the digestive system & its organs: pharynx, esophagus, crop, gizzard, and intestine.
d. To find organs of the nervous system, carefully push aside the digestive and circulatory system organs. Locate
the ventral nerve cord.
e. Trace the nerve cord forward to the nerve collar, which circles the pharynx. Locate the cerebral ganglion
under the pharynx. The ganglia above the pharynx serve as the brain of the earthworm.
f. Reproductive organs: ovaries & seminal vesicles
7. Clean Up: Wrap your specimen in a paper towel and place it in the designated area.
8. WASH YOUR HANDS THOROUGHLY. Spray and wipe the table with disinfectant.
a. five pairs of aortic arches, or hearts.
b. the median dorsal vessel. Look for smaller
blood vessels that branch from the dorsal blood
vessel.
c. locate the digestive system & its organs:
pharynx, esophagus, crop, gizzard, and
intestine. * be sure to probe the crop and
gizzard to feel it’s texture.
d. To find organs of the nervous system, carefully
push aside the digestive and circulatory system
organs. Locate the ventral nerve cord.
e. Trace the nerve cord forward to the nerve
collar, which circles the pharynx. Locate the
cerebral ganglion under the pharynx. The
ganglia above the pharynx serve as the brain of
the earthworm.
f. Reproductive organs : ovaries & seminal
vesicles
Pictures: Modern Biology, Holt & Carolina Biological
Supply, Earthworm BioKit. Modified from:
http://sps.k12.ar.us/massengale/earthworm_dissection.htm
Biology 5 Earthworm Dissection Lab Earthworm
Dissection © John R. Sowash | April 2009 |
Permission to redistribute granted
GROUP NAMES: ____________________________
1. Describe two ways in which an earthworm’s body is adapted to life in the soil.
Post Lab Questions:
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2. Annelids have the first true closed circulatory system, meaning all of their blood is contained in vessels –
including the heart. Explain why this is more efficient than an open circulatory system – a system where the blood
vessels open into a large cavity so that the blood is not always contained in vessels (or heart).
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3. The gizzard was very “hard” and the crop was “soft”. Based on an earthworm’s diet, explain why this organism
needs both structures.
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4. The worm had both ovaries and testes! Even though this hermaphrodite could self-fertilize it chooses to find a
mate instead. Why is this evolutionary significant? That is – why is it more important to have two different parents
instead of one parent? Note: earthworms do NOT care for their young.
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5. Related to the above question: Hermaphrodites are beneficial so that they can still reproduce even without a mate. If
a hermaphrodite self-fertilizes, do they use the process of meiosis or mitosis? EXPLAIN your answer, showing an
understanding of terms.
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