Download WormDissectionLesson

Worm Dissection
Lesson # _8___ in a series of
___10__ lessons
Brief Lesson Description: Students will dissect an earthworm to learn about the body systems and
lifestyle of the worm.
VA-SOL Standard(s):
LS. 1 The student will demonstrate an understanding of scientific reasoning, logic, and the nature of
science by planning and conducting investigations in which:
j) current applications are used to reinforce life science concepts
LS. 4 The student will investigate and understand how organisms can be classified. Key concepts include:
c) the distinguishing characteristics of major animal phyla
d) the characteristics that define a species
Next Generation Science Standard(s): LS1.A: Structure and Function
Grade/ Grade Band: 7th
Topic: Invertebrate Anatomy
Essential Question: How does the inside of an invertebrate compare to us?
Specific Learning Objectives:
 Students will be able to name the organs that make up the systems of the earthworm.
 Students will be able to explain the functions of the various organs
 Students will be able to compare function of earthworm organs to those of humans.
Narrative / Background Information
Prior Student Knowledge based on the learning trajectory/scope and sequence:
Students will know the characteristics of invertebrates
Students will understand that a worm is an example of an invertebrate
This is the first time students have dissected in our class much of the instruction will also focus on
techniques and behavior during a dissection
Science & Engineering Practices: How and where in the 5-E
Safety Instructions:
Planning and Carrying Out
sequence are you explicitly
 Students should be
Investigations
teaching the Nature of Science.
careful when handling
 Scientific Investigations
scissors
use a Variety of Methods
 Students must read all
(stated before students
instructions for each step
begin dissection)
of the dissection to
remain safe
 Goggles should be worn
 No food or drink near
dissection
Pre-conceptions/misconceptions based on peer-reviewed research and conversation with experienced
CT:
Students apply the label of animals almost exclusively to vertebrates (Gabel, 1994).
LESSON PLAN – 5-E Model
ENGAGE: (How do you spark their interest and assess their prior knowledge) 5 minutes
When students walk into the room they will collect the Knowledge Rating sheet from the front counter.
Students will spend then fill in the chart noting their familiarity with the vocabulary terms to be
discovered throughout the lab investigation. Students will then watch a short video highlighting ten
facts about Earthworms.
EXPLORE: (How are their investigating/tinkering/manipulating/researching science?) 40 minutes
“Scientific Investigations use a variety of methods, from our video yesterday, we need to make sure
we are careful when using the tools, and that we are respectful during the process of dissecting.” I will
remind students of safety instructions before beginning the earthworm dissections. Students need to
exercise caution when using the dissection scissors, and must respect the organism and not mutilate the
animals, but carefully follow dissection procedures. Students will then work in similar ability pairs to
explore the internal and external anatomy of the earthworm. I will call student groups up to the front of
the room to collect their lab supplies, at this point I will further remind students of the lab safety
requirements and expectations of the lab.
EXPLAIN: (How are the students discussing science, and how are you shaping these discussions?)
While dissecting the earthworm, students will answer questions and elaborate on processes in their lab
packet. Students will be required to turn in their own lab packet. I will give students a 5 minute warning
to monitor timing, and to allow students time to clean up their lab stations.
ELABORATE (How are you placing the scientific information in a new context): 5 minutes
Once students have finished cleaning their lab station, they will begin to answer the final lab questions.
Students will complete summary lab questions and apply their knew knowledge to describe the function
of earthworms in the environment. These questions will be assigned for homework and the lab packet
will be collected the next day and graded as assessed by teacher key.
EVALUATE: (How are you assessing the students’ understanding of the lesson?)
Formative Monitoring (Questioning /Discussion): I will listen to student conversations and questions
throughout the dissection, and redirect and assist as necessary. I will look at student responses
throughout the lab to check for understanding during the process.
Summative Assessment (Quiz / Project / Report): Student lab reports will be collected and graded in
correspondence to the teacher key.
List Specific Accommodations based on IEPs and Teacher Discussions:
Directions will be repeated/rephrased
Extended time for select students with IEPS to complete lab
Differentiation for G&T: Students will complete regular lab packet
Differentiation for Students with Special Needs and IEPs: Student lab packet will include some pre-filled
information and include additional probing questions
Materials
Safety goggles
Paper towels
Preserved earthworms
Dissection trays
Dissecting pins
Forceps
Probe
Hand Lens
Scissors
Earthworm Fact Video (from C. Dawson)
References
Gabel, Dorothy, ed. Handbook of Research on Science Teaching and Learning. New York: Macmillan, 1994. 184
Name ______________________________________
KNOWLEDGE RATING – Worms
Place a check under the column describes your understanding of today’s vocabulary words.
Have Seen
Or Heard
regeneration
host
parasite
anus
segment
flatworms
round worms
segmented
worms
Can Say
Can Define
Can Spell
Can Use In A
Sentence
Don’t Know
At All
Earthworm Dissection
Name: ______________________________ Date: ________________ Period: ______________
Specific Learning Objectives:
•
Students will be able to name the organs that make up the systems of the earthworm.
•
Students will be able to explain the functions of the various organs
•
Students will be able to compare function of earthworm organs to those of humans.
Materials
• Earthworm
• Dissection pan
• Dissection scissors
• Dissection pins
• Probe
• Disposable gloves
• Protective eyewear
Procedure
One lab partner will read the procedure aloud while the other follows the instruction. Lab partners should take turns performing
both these roles during the dissection.
External Anatomy
The word annelida means “ringed” and refers to the 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
worm.
1. Straighten the earthworm out across the dissection tray, placing the ventral side down.
a. The ventral side appears flatter than the other sides of the earthworm.
b. The dorsal side is the worm’s rounded top.
* Run your fingers along the ventral and dorsal surfaces of the preserved worm from anterior to posterior and from posterior to
anterior on each surface.
2. Describe your observations.
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3. Identify the anterior and posterior ends of the earthworm.
a. The anterior end features the prostomium, which is a fleshy lobe that extends over the mouth.
b. The posterior end features the anus, the end of the digestive tract.
4. Locate the clitellum, which extends from segment 33 to segment 37. The clitellum is a swelling of the earthworm near its
anterior side.
5. Place a dissection pin in both ends of the earthworm to secure it in place.
6. Sketch your earthworm in the space below. Label the following parts of the worm:
• Anterior • Posterior • Clitellum • Mouth• Anus
7. Record the following data:
a. Number of segments from anterior end to clitellum: ____________
b. Length of earthworm: ____________ cm
The clitellum (segment 33-37) is a swelling of the body found in sexually mature worms and is active in the formation of a mucus
egg capsule, or cocoon. Eggs are produced in the ovaries and pass out of the body through female genital pores (segment 14).
Sperm are produced in the testes and pass out through tiny male genital pores (segments 15 and 26). During mating, sperm from
one worm travel along the sperm grooves to the seminal receptacles of another worm. This cross-fertilization is known as
hermadrophritism. 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.
Internal Anatomy
8. Locate the clitellum and insert the tip of the scissors about 3cm posterior.
9. Cut carefully all the way up to the head. Try to keep the scissors pointed up, and only cut through the skin. Be careful not to
damage any of the internal organs.
10. Spread the skin of the worm out, gently tear the septa (little thread like structures that hold the skin to organs below it)
11.Place pins in the skin to hold it apart.
12. Locate the internal reproductive organs. The seminal vesicles, where sperm cells are produced, are large and cream colored.
They are located on either side of the esophagus. Smaller seminal receptacles receive sperm cells and are located posterior to the
larger vesicles also on either side of the esophagus.
13. Try to locate the pair of ovaries in the thirteenth segment. They are quite small and difficult to see. You will need a dissecting
microscope or hand lens.
The earthworm takes in a mixture of mineral and organic matter known as soil 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 takes place.
Soil particles and undigested organic matter pass out of the worm through the anus.
14.The digestive system starts at the mouth. You will trace the organs all the way to the anus and identify each on the worm.
a. Find the mouth opening, the first part after the mouth is the pharynx, you will see stringy things attached to either side
of the pharynx (pharyngeal muscles).
b. The esophagus leads from the pharynx but you probably won’t be able to see it, since it lies underneath the heart.
c. You will find two structures close to the clitellum. First in the order is the crop, followed by the gizzard. The gizzard
leads to the intestine, which is as long as the worm and ends at the anus.
15.Describe the function of each digestive organ and label the diagram below:
Digestive Organ Function
Crop
Mouth
Pharynx
Intestine
Gizzard
Anus
Esophagus
Pharyngeal
Muscles
16.Use your scissors to open the crop and gizzard. Examine the contents of these organs.
17. Trace the parts of the digestive tract through which food passes from beginning to end.
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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.
18. Locate the nervous system, which lies on the ventral surface. Locate the ventral nerve cord and cerebral ganglion
Excretory functions are carried on by nephridia, which are found in pairs in each segment. Closely inspect the segments on the
external surface, near the setae, see the nephridia openings. Internally, they appear as tiny coiled white fibers on the dorsal body
wall of each segment. The earthworm has no gills or lungs. Gases are exchanged between the circulatory system and the
environment through the moist skin. In humans, kidneys serve as excretory organs.
19. Using the information in the excretory paragraph, infer why earthworm come out of the soil during heavy rains and explain
why it is important that they return to the soil when it get hot.
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Clean your work area as directed by your teacher.
Post-Lab
Answer the following questions in complete sentences.
1. In which organ (crop or gizzard) did you find the contents to be most ground up and why?
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2. How could you find out whether an earthworm eats soil or not?
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3. Your dissection of the earthworm did not go beyond segment 32. What would you observe if you dissected the remainder of the
worm to its posterior end?
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4. Reflect on the process of the lab dissection. Explain what safety steps you took, and describe what was most interesting to you
and why.
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DIAGRAMS
EXTERNAL EARTHWORM
INTERNAL EARTHWORM
View A
View B