Earthworm Dissection

 

Appropriate for a high school environmental studies classroom

 

Adapted from www.bjbarton.com/lessons/earthworm.pdf

 

Purpose:

The purpose of this lab is to study the internal and external anatomy of the common earthworm.

 

Objectives:

After completion of this lab, students will be able to

            -identify specific organs and body systems of the earthworm

            -relate these organs and systems to their particular functions

 

Standards:

            National:

-         A1, A3, A5, B1, D4, D6, E3-6

-         See National Science Education Standards for descriptions

            New Hampshire:

-         1a, 2b, 2d, 3a, 3d, 6a

-         See New Hampshire Science Curriculum Framework for descriptions

                          

Background knowledge needed:

Students should know why they are studying the earthworm, especially in relation to its importance in IPM.  Earthworms are one of the three main classes of annelids, classified mainly by their body segmentation, or division of the body into a series of repeated segments that look similar to a set of joined rings.  Earthworms obtain nutrients by “eating” their way through soil and extracting vital nutrients as the soil passes through the digestive tube.  They rid themselves of undigested material by mixing it with mucus and secreting this “casting” through the anus.  Farmers value earthworms because they till the earth as they pass through the soil, stirring it up and constantly shifting nutrients around.  The castings that they release also help to improve the texture of the soil.  Both of these factors allow for a better environment for plants to grow in.  It has also been found that plants growing in soils containing earthworms are more successful and tend live longer, growing larger than plants in soils depleted of earthworms.  (Campbell and Reece 2002).

 

Materials Needed:

Preserved earthworms

Hand lens

Scalpel

Forceps

Dissection needles

Straight pins

Dissecting pan or block of soft wood

Worksheet with a picture of the interior structures of the earthworm, with spaces for

students to fill in the names of the organs as they find them

Attached question sheet

 

Optional:

Lab coats, eye protection, rubber gloves

 

Grouping of Students:

Students should be grouped in pairs, each pair with their own earthworm to dissect.  Either the teacher or the students can choose these pairs, as long as safe lab techniques are being used.

 

Preparation for Experience:

The worms will need to be ordered prior to the day of the dissection.  Students should also either already have knowledge of safety precautions for working in a lab, or need to be taught prior to the experiment.  Tools should be cleaned before the lab begins.

 

Outline of Experience:

Introduction/Orientation: The students need to be excited and motivated about this lab in order for them to get the most out of it.  They should know the importance of the earthworm for farmers in general, especially for those farmers who utilize IPM practices.  This is a great opportunity for them to work closely with a partner, and each pair has certain responsibilities and goals that promote a certain amount of independent work, where they get to make their own decisions and do the actual lab themselves.

Body of lesson:  Each pair of students should gather all the instruments required for the lab, and find a space to work in.  The teacher will then pass out one earthworm to each pair.  During the lab the teacher should walk freely around the classroom, making sure to observe every pair to help them with any potential problems and answering any questions.  The following protocol should be followed:

1.)   Place the worm with the dorsal surface (bottom) facing up in the dissecting pan or on the block of wood

2.)   Use the scalpel to make a long, shallow incision slightly to one side of the midline, from the mouth to about halfway down the worm- be careful not to cut too deeply!

3.)   With the forceps and needles, carefully pull apart the sides of the incision, and pin the skin to the bottom of the dissecting pan or wood.

4.)   Following the previous incision, cut down the rest of the worm, again being careful not to cut too deeply, and pin the skin to the pan or wood so that the interior of the worm is exposed.

5.)   The students then study the different body structures and systems of the worm,

   labeling them on the worksheet.

Conclusion:  The lab itself should last at least forty minutes, giving students

plenty of time to analyze and study the worm’s interior and exterior.  Time needs to be allowed for the set-up and clean up of the lab.  If a pair of students finishes early, and completes the worksheet before time is up, they can be allowed to dissect and study individual organs if they like, or try to identify various organ systems in the worm.  Once all the pairs are finished with the actual dissection, they need to correctly dispose of their worm, clean any tools they used, and put all the instruments away where they belong.  The class should then return to their seats and use the remaining class time to go over the worksheet and answer any questions the students might have.

 

Assessment Plan:  Each student is expected to find and label certain body features of the earthworm during the experiment, documenting this on a handout provided by the teacher.  They should also answer the questions on the attached worksheet after completion of the lab.

 

Extensions, Adaptations, Alternatives, Next Steps:

As stated before, if a pair of students finishes the worksheet early, and has found all the organs before the designated ending time of the dissection, they may then dissect and study different organs of the worm, as long as they still respect the worm and don’t just play with it.  If a particular student or group of students is uncomfortable actually performing the dissection, but is willing to observe it, pair him/her up with another person who is willing to dissect the worm.  If someone does not want to be a part of the lab at all because they are uncomfortable with the dissection, they should be allowed to leave the room and fill out the worksheet using various textbooks or other references.  They should be present once the lab has been cleaned up, during the time when the teacher wraps up the lab, goes over the worksheet, and answers any questions.

 

References:

            Barton, B.J. (2003).  Mohave High School. Retrieved January 21, 2004 from the World Wide Web: http://www.bjbarton.com/lessons/earthworm.pdf

Campbell, N., Reece, J. (2002). Biology. 6th ed.  Benjamin Cummings: San Francisco, California.

           

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Questions for Earthworm Dissection

 

1.) What are the major organ systems that you were able to find in your earthworm?

 

 

 

 

 

 

 

2.) What organ system does the heart belong to, and what is its purpose?

 

 

3.) What organ system does the kidney belong to, and what is its function?

 

 

4.) Name the organs of the digestive system.  How do earthworms extract the nutrients from their food?

 

 

 

 

 

 

5.) What organ system is most closely connected to the respiratory system?  Why?

 

 

 

 

 

 

 

6.) Draw and label the basic nervous system of an earthworm.  What is its major function?