Download Earthworm Dissection

Name
Class
Date
Skills Practice Lab
Earthworm Dissection
Among the most familiar invertebrate animals are the earthworms, members of
the phylum Annelida. The word annelida means “ringed” and refers to a series
of rings, or segments, that make up the bodies of the members of this phylum.
Internally, septa, or dividing walls, are located between the segments. There
may be more than 100 segments in an adult earthworm.
One system of the earthworm that cannot be observed in the lab is the respiratory system. The earthworm has no gills or lungs. Gases are exchanged between
the circulatory system and the environment through the moist skin.
In this lab, you will dissect an earthworm in order to examine the observable
external and internal structures of earthworm anatomy.
OBJECTIVES
Name the organs that make up various systems of the earthworm.
Show the correct procedure for dissection of an earthworm.
Relate the earthworm’s structures to its behavior for survival.
MATERIALS
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
dissecting pins
dissection tray
forceps
gloves
hand lens
lab apron
paper towel
preserved earthworm
safety goggles
scalpel
scissors
teasing needle
twist tie
water
plastic storage bag
Procedure
1. Put on safety goggles, gloves, and a lab apron.
2. Place a paper towel in the bottom of a dissection tray, and moisten it with
water. Place an earthworm on the towel. Identify the dorsal side, which is the
worm’s rounded top, and the ventral side, which is its flattened bottom. Turn
the worm ventral side up, as shown in Figure 1.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
97
Skills Practice
Chapter Labs
Title
Name
Class
Date
Earthworm Dissection continued
FIGURE 1 VENTRAL VIEW OF EARTHWORM
Mouth
Segment
Setae
Septum
Female genital
pore
Sperm groove
Clitellum
1
Prostomium
9
11
15
Openings of
seminal
receptacles
Male genital
pore
26
32
3. Use a hand lens as you observe all parts of the worm, externally and internally. Find the anterior end by locating the prostomium, which is a fleshy
lobe that extends over the mouth. The other end of the worm’s body is the
posterior end, where the anus is located.
4. Look for the worm’s setae, which are the tiny bristlelike spines located on
every segment except the first and last one.
5. Review the following information about the clitellum.
The clitellum is a swelling of the body found in sexually mature worms and is
active in the formation of an egg capsule, or cocoon. Eggs are produced in the
ovaries and pass out of the body through female genital pores. Sperm are
produced in the testes and pass out through tiny male genital pores. During
mating, sperm from one worm travel along the sperm grooves to the seminal
receptacles of another worm. Fertilization of the eggs takes place outside the
body as the cocoon moves forward over the body, picking up the eggs of one
worm and the sperm of its mate.
6. Locate the clitellum, which extends from segment 33 to segment 37. Refer to
Figure 1 to locate and identify the external parts of the earthworm’s reproductive system.
7. Find the pair of sperm grooves that extend from the clitellum to about segment 15, where one pair of male genital pores is located. Look also for one
pair of female genital pores on segment 14. There is another pair of male
genital pores on about segment 26. Try to find the two pairs of openings of the
seminal receptacles on segment 10. Note: These openings are not easy to see.
8. Turn the earthworm dorsal side up. Add water to the tray so that the earthworm remains moist. Using a scalpel and scissors, make a shallow incision in
the dorsal side of the clitellum at segment 33. CAUTION: Scalpels and
scissors are very sharp. Report any cuts to your teacher.
9. Using the forceps and scalpel, spread the incision open, little by little.
Separate each septum from the central tube by using a teasing needle, and pin
down each loosened bit of skin. Continue the incision forward to segment 1.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
98
Skills Practice
Chapter Labs
Title
Name
Class
Date
Earthworm Dissection continued
10. Review the following information about the circulatory system.
The pumping organs of the circulatory system are five aortic arches, sometimes called hearts. Circulatory fluids travel from the arches through the
ventral blood vessel to capillary beds in the body. The fluids then collect in
the dorsal blood vessel and re-enter the aortic arches.
11. Use Figure 2 to locate and identify the five pairs of aortic arches. Then find
the dorsal blood vessel. Look for smaller blood vessels that branch from the
dorsal blood vessel.
FIGURE 2 DORSAL VIEW OF DISSECTED EARTHWORM
Esophagus
Crop
Dorsal blood
vessel
Clitellum
Pharynx
Hearts
Gizzard
Intestine
12. Review the following information about the digestive tract.
The earthworm takes in a mixture of soil and organic matter through its
mouth, which is the beginning of the digestive tract. The mixture enters the
pharynx, which is located in segments 1–6. The esophagus, in segments 6–13,
acts as a passageway between the pharynx and the crop. The crop stores food
temporarily. The mixture that the earthworm ingests is ground up in the
gizzard. In the intestine, which extends over two-thirds of the body length,
digestion and absorption take place. Soil particles and undigested organic
matter pass out of the worm through the rectum and anus.
13. Locate the digestive tract, which lies below the dorsal blood vessel. Refer to
Figure 2 to locate the pharynx, esophagus, crop, gizzard, and intestine.
14. Review the following information about the nervous system.
The nervous system consists of the ventral nerve cord, which travels the
length of the worm on the ventral side, and a series of ganglia, which are
masses of tissue containing many nerve cells. The nerve collar surrounds the
pharynx and consists of ganglia above and below the pharynx. Nervous
impulses are responsible for movement and responses to stimuli. Each segment contains an enlargement, or ganglion, along the ventral nerve cord.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
99
Skills Practice
Chapter Labs
Title
Name
Class
Date
Earthworm Dissection continued
15. To find organs of the nervous system, gently push aside the digestive system and
circulatory system organs. Use Figure 3 to locate the ventral nerve cord. Trace
the nerve cord forward to the nerve collar, which circles the pharynx. Find one
pair of ganglia under the pharynx and another pair of ganglia above the pharynx.
The ganglia above the pharynx serve as the brain of the earthworm.
FIGURE 3 EARTHWORM NERVOUS SYSTEM
Nephridia
Ventral nerve cord
Ganglion
Nerve
collar
Ganglion
Pharynx
Ventral blood
vessel
Esophagus
Hearts
Crop
Gizzard
Dorsal blood
vessel
16. Use Figure 3 to locate some nephridia, which are found in pairs in each
body segment. There are two in every segment. These tiny, white fibers on the
dorsal body wall carry out excretory functions.
17. Use Figure 4 to locate and identify a pair of ovaries in segment 13. Look for
two pairs of tiny testes in segments 10 and 11. To find these organs, you will
again have to push aside some parts already dissected.
FIGURE 4 EARTHWORM REPRODUCTIVE SYSTEMS
Segment
3
4 5 6 7 8 9 10 11 12 13 14 15
Crop
Pharynx
Prostomium
Mouth
Septum
Esophagus
Ovary
Testes
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
100
Skills Practice
Chapter Labs
Title
Name
Class
Date
Earthworm Dissection continued
18. Dispose of your materials according to your teacher’s instructions.
19. Clean up your work area, and wash your hands before leaving the lab.
Analysis
1. Identifying Relationships What is the name of the pumping organs of an
earthworm?
2. Describing Events Trace the parts of the digestive tract through which food
passes.
3. Identifying Relationships Which parts of the earthworm serve as its brain?
How are these parts connected to the rest of the body?
4. Analyzing Data Which of the parts of the earthworm’s body that you saw are
included in the excretory system?
5. Examining Data How can you find out whether an earthworm eats soil?
Conclusions
1. Interpreting Information Among the earthworm’s structural adaptations are
its setae. How do you think the earthworm’s setae make it well adapted to its
habitat?
2. Drawing Conclusions How is the earthworm’s digestive system adapted for
extracting relatively small amounts of food from large amounts of ingested soil?
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
101
Skills Practice
Chapter Labs
Title
Name
Class
Date
Earthworm Dissection continued
Extension
Building Models On a separate sheet of paper, draw and label the parts of the
earthworm you observed, and color code the systems. Use green for the reproductive system, yellow for the digestive system, blue for the excretory system,
and red for the nervous system.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
102
Skills Practice
Chapter Labs
Title
TEACHER RESOURCE PAGE
Skills Practice Lab
Earthworm Dissection
Teacher Notes
TIME REQUIRED Two 45-minute periods
SKILLS ACQUIRED
Identifying and recognizing patterns
Inferring
Interpreting
Measuring
Organizing and analyzing data
RATINGS
Teacher Prep–4
Student Setup–3
Concept Level–3
Cleanup–3
Easy
1
2
3
4
Hard
THE SCIENTIFIC METHOD
Make Observations Students observe the external and internal structures of
earthworm anatomy.
Analyze the Results Analysis questions 2–5 require students to analyze their
results.
Draw Conclusions Conclusions question 2 asks student to draw conclusions
from their data.
Form a Hypothesis Analysis question 5 and Conclusions questions 1 and 2 ask
students to form a hypothesis based on their results.
MATERIALS
Materials for this lab can be ordered from WARD’S. Use the Lab Materials
QuickList Software on the One-Stop Planner CD-ROM for catalog numbers
and to create a customized list of materials for this lab.
Do not use live earthworms for this lab. They cannot be humanely dissected.
SAFETY CAUTIONS
• Discuss all safety symbols and the caution statement with students.
• Instruct students on the correct, careful handling of all dissecting instruments,
especially the scalpel. Do not allow students to use razor blades.
• Prolonged contact with WARDSafe, which should be used to store the specimens, may be irritating to skin and eyes and may cause allergic reaction in
hypersensitive individuals. Discontinue use if redness or swelling occurs. In
case of contact, flush with water, including under eyelids, for 15 minutes.
Contact physician if irritation or redness persists. May be toxic if swallowed.
If conscious, drink 8–10 oz (240–300 mL) water to dilute material. Induce
vomiting. Get prompt medical attention.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
125
Skills Practice
Chapter Labs
Title
TEACHER RESOURCE PAGE
Earthworm Dissection continued
• Do not use specimens preserved with formaldehyde.
DISPOSAL
Wrap the remains of dissected earthworms in newspaper, place them in a plastic
bag, and tie the bag securely. Inform the school custodian of the bag’s contents,
and hand it over personally for its safe disposal.
TECHNIQUES TO DEMONSTRATE
Emphasize to students that dissection is not “cutting and slicing.” Rather, it is
making careful incisions to expose parts, and then using a probe to separate
organs from their coverings. Point out that the intent of dissection is to carefully
unwrap the animal’s structures without causing any damage.
Demonstrate to students the correct techniques for dissection. Emphasize
that the scalpel is sharp so that incisions can be controlled. Have students use
scalpels cautiously so that internal organs are not destroyed before they can be
observed.
Students might have difficulty observing a dissection demonstration. Use an
opaque projector or an instructional video or software if students have difficulty
observing an actual dissection. If a video or software is used, allow students to
refer to it as needed throughout the dissection.
TIPS AND TRICKS
This lab works best in group of two to four students.
Between lab periods, cover each specimen pinned to the dissection tray with a
paper towel dampened with water or WARDSafe. Store the specimen in a plastic
bag that is tied securely. Use a felt-tip marker to write students’ names directly on
the dissection trays or plastic bags.
If you do not wish to have students perform this dissection, or if some students
object to dissection, alternative methods of studying these structures are available.
These include models, filmstrips, videotapes, and computer simulations.
Allow students who have difficulty with scientific terminology to use their
observations to infer the functions of the parts of the earthworm. Have students
sketch each part for which they can infer a function. Check students’ sketches
and the functions they identify for accuracy. You can also pair these students
with students who have little difficulty with the terminology.
For the Extensions item, students will find that the most prominent features
are the full length of the dorsal blood vessel and the intestine, which ends with
the anus. Less prominent but present are pairs of nephridia, which are found in
every segment.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
126
Skills Practice
Chapter Labs
Title
TEACHER RESOURCE PAGE
Name
Class
Date
Skills Practice Lab
Earthworm Dissection
Among the most familiar invertebrate animals are the earthworms, members of
the phylum Annelida. The word annelida means “ringed” and refers to a series of
rings, or segments, that make up the bodies of the members of this phylum.
Internally, septa, or dividing walls, are located between the segments. There may
be more than 100 segments in an adult earthworm.
One system of the earthworm that cannot be observed in the lab is the respiratory system. The earthworm has no gills or lungs. Gases are exchanged between
the circulatory system and the environment through the moist skin.
In this lab, you will dissect an earthworm in order to examine the observable
external and internal structures of earthworm anatomy.
OBJECTIVES
Name the organs that make up various systems of the earthworm.
Show the correct procedure for dissection of an earthworm.
Relate the earthworm’s structures to its behavior for survival.
MATERIALS
•
•
•
•
•
•
•
•
dissecting pins
dissection tray
forceps
gloves
hand lens
lab apron
paper towel
•
•
•
•
•
•
•
preserved earthworm
safety goggles
scalpel
scissors
teasing needle
twist tie
water
plastic storage bag
Procedure
1. Put on safety goggles, gloves, and a lab apron.
2. Place a paper towel in the bottom of a dissection tray, and moisten it with
water. Place an earthworm on the towel. Identify the dorsal side, which is the
worm’s rounded top, and the ventral side, which is its flattened bottom. Turn
the worm ventral side up, as shown in Figure 1.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
127
Skills Practice
Chapter Labs
Title
TEACHER RESOURCE PAGE
Name
Class
Date
Earthworm Dissection continued
FIGURE 1 VENTRAL VIEW OF EARTHWORM
Mouth
Segment
Setae
Septum
Female genital
pore
Sperm groove
Clitellum
1
Prostomium
9
11
15
Openings of
seminal
receptacles
Male genital
pore
26
32
3. Use a hand lens as you observe all parts of the worm, externally and internally. Find the anterior end by locating the prostomium, which is a fleshy
lobe that extends over the mouth. The other end of the worm’s body is the
posterior end, where the anus is located.
4. Look for the worm’s setae, which are the tiny bristlelike spines located on
every segment except the first and last one.
5. Review the following information about the clitellum.
The clitellum is a swelling of the body found in sexually mature worms and is
active in the formation of an egg capsule, or cocoon. Eggs are produced in the
ovaries and pass out of the body through female genital pores. Sperm are
produced in the testes and pass out through tiny male genital pores. During
mating, sperm from one worm travel along the sperm grooves to the seminal
receptacles of another worm. Fertilization of the eggs takes place outside the
body as the cocoon moves forward over the body, picking up the eggs of one
worm and the sperm of its mate.
6. Locate the clitellum, which extends from segment 33 to segment 37. Refer to
Figure 1 to locate and identify the external parts of the earthworm’s reproductive system.
7. Find the pair of sperm grooves that extend from the clitellum to about segment 15, where one pair of male genital pores is located. Look also for one
pair of female genital pores on segment 14. There is another pair of male
genital pores on about segment 26. Try to find the two pairs of openings of the
seminal receptacles on segment 10. Note: These openings are not easy to see.
8. Turn the earthworm dorsal side up. Add water to the tray so that the earthworm remains moist. Using a scalpel and scissors, make a shallow incision in
the dorsal side of the clitellum at segment 33. CAUTION: Scalpels and
scissors are very sharp. Report any cuts to your teacher.
9. Using the forceps and scalpel, spread the incision open, little by little.
Separate each septum from the central tube by using a teasing needle, and pin
down each loosened bit of skin. Continue the incision forward to segment 1.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
128
Skills Practice
Chapter Labs
Title
TEACHER RESOURCE PAGE
Name
Class
Date
Earthworm Dissection continued
10. Review the following information about the circulatory system.
The pumping organs of the circulatory system are five aortic arches, sometimes called hearts. Circulatory fluids travel from the arches through the
ventral blood vessel to capillary beds in the body. The fluids then collect in
the dorsal blood vessel and re-enter the aortic arches.
11. Use Figure 2 to locate and identify the five pairs of aortic arches. Then find
the dorsal blood vessel. Look for smaller blood vessels that branch from the
dorsal blood vessel.
FIGURE 2 DORSAL VIEW OF DISSECTED EARTHWORM
Esophagus
Crop
Dorsal blood
vessel
Clitellum
Pharynx
Hearts
Gizzard
Intestine
12. Review the following information about the digestive tract.
The earthworm takes in a mixture of soil and organic matter through its
mouth, which is the beginning of the digestive tract. The mixture enters the
pharynx, which is located in segments 1–6. The esophagus, in segments 6–13,
acts as a passageway between the pharynx and the crop. The crop stores food
temporarily. The mixture that the earthworm ingests is ground up in the
gizzard. In the intestine, which extends over two-thirds of the body length,
digestion and absorption take place. Soil particles and undigested organic
matter pass out of the worm through the rectum and anus.
13. Locate the digestive tract, which lies below the dorsal blood vessel. Refer to
Figure 2 to locate the pharynx, esophagus, crop, gizzard, and intestine.
14. Review the following information about the nervous system.
The nervous system consists of the ventral nerve cord, which travels the
length of the worm on the ventral side, and a series of ganglia, which are
masses of tissue containing many nerve cells. The nerve collar surrounds the
pharynx and consists of ganglia above and below the pharynx. Nervous
impulses are responsible for movement and responses to stimuli. Each segment contains an enlargement, or ganglion, along the ventral nerve cord.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
129
Skills Practice
Chapter Labs
Title
TEACHER RESOURCE PAGE
Name
Class
Date
Earthworm Dissection continued
15. To find organs of the nervous system, gently push aside the digestive system and
circulatory system organs. Use Figure 3 to locate the ventral nerve cord. Trace
the nerve cord forward to the nerve collar, which circles the pharynx. Find one
pair of ganglia under the pharynx and another pair of ganglia above the pharynx.
The ganglia above the pharynx serve as the brain of the earthworm.
FIGURE 3 EARTHWORM NERVOUS SYSTEM
Nephridia
Ventral nerve cord
Ganglion
Nerve
collar
Ganglion
Pharynx
Ventral blood
vessel
Esophagus
Hearts
Crop
Gizzard
Dorsal blood
vessel
16. Use Figure 3 to locate some nephridia, which are found in pairs in each
body segment. There are two in every segment. These tiny, white fibers on the
dorsal body wall carry out excretory functions.
17. Use Figure 4 to locate and identify a pair of ovaries in segment 13. Look for
two pairs of tiny testes in segments 10 and 11. To find these organs, you will
again have to push aside some parts already dissected.
FIGURE 4 EARTHWORM REPRODUCTIVE SYSTEMS
Segment
3
4 5 6 7 8 9 10 11 12 13 14 15
Crop
Pharynx
Prostomium
Mouth
Septum
Esophagus
Ovary
Testes
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
130
Skills Practice
Chapter Labs
Title
TEACHER RESOURCE PAGE
Name
Class
Date
Earthworm Dissection continued
18. Dispose of your materials according to your teacher’s instructions.
19. Clean up your work area, and wash your hands before leaving the lab.
Analysis
1. Identifying Relationships What is the name of the pumping organs of an
earthworm?
The pumping organs are called aortic arches.
2. Describing Events Trace the parts of the digestive tract through which food
passes.
Food passes from the mouth to the pharynx, esophagus, crop, gizzard, intestine, and then wastes leave through the anus.
3. Identifying Relationships Which parts of the earthworm serve as its brain?
How are these parts connected to the rest of the body?
The ganglia above the pharynx serve as the earthworm’s brain. They are
connected to the rest of the body by way of the ventral nerve cord.
4. Analyzing Data Which of the parts of the earthworm’s body that you saw are
included in the excretory system?
The nephridia are included in the excretory system.
5. Examining Data How can you find out whether an earthworm eats soil?
Cut into the intestine and expose the contents.
Conclusions
1. Interpreting Information Among the earthworm’s structural adaptations are
its setae. How do you think the earthworm’s setae make it well adapted to its
habitat?
The earthworm uses its setae to anchor itself in the soil during locomotion.
2. Drawing Conclusions How is the earthworm’s digestive system adapted for
extracting relatively small amounts of food from large amounts of ingested soil?
Digested food is absorbed in the intestine, which extends over two-thirds of
the body length, thus affording a large surface area for absorption.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
131
Skills Practice
Chapter Labs
Title
TEACHER RESOURCE PAGE
Name
Class
Date
Earthworm Dissection continued
Extension
Building Models On a separate sheet of paper, draw and label the parts of the
earthworm you observed, and color code the systems. Use green for the reproductive system, yellow for the digestive system, blue for the excretory system,
and red for the nervous system.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Program
BioSources
Title
Lab Program
132
Skills Practice
Chapter Labs
Title