It's All Part of the "Body" Plan (Part 1/2)
Lesson 2 of 12
Objective: Student will compare flatworm body plan with roundworm and earthworm body plans.
In this lesson, students begin to explore the different types of body cavities by dissecting a flatworm and considering planarian development. Students also look at planarian regeneration to discover more about the aging and regeneration process. Here is an overview of what students will learn today. This is day one of a two day lesson. Day two can be found here.
Students will view a short video about planaria.
(Note: I put the audio of the video on mute and just let students watch the video without sound.)
They will answer the following questions:
- How does a planarian behave?
Sample student responses: It sides over surfaces. It swims with wavelike motion.
- How does a planarian compare to an earthworm?
Sample student responses: Both have a brain in a "head."
- How does a planarian differ from an earthworm?
Sample student responses: It is more flat. It has a mouth on the bottom of it. It has sensory organs at the top of its head.
- What happens after the planarian is given a small piece of raw liver? How does it feed?
Sample student responses: They swim around it and scrape their mouth over the liver. Its mouth looks like a tail stuck to its belly. It can retract into the belly or extend out to better reach the food.
- In your experience, how does this differ from how an earthworm eats?
Sample student responses: Earthworms burrow through the dirt eating everything as they go. Dirt goes in the mouth and castings come out of the anus.
- How does the planarian's body shape and movement allow it to live in its environment?
Sample student responses: Planarians' body shape is very streamlined. It makes it easy to swim in the water.
Students should record their responses in their lab manuals.
(Note: In past years, I have obtained live planaria. These can either be collected in the field or purchased through a supply house.)
Students will use the work of Thomas Hunt Morgan to better understand cell regeneration. Start by having students popcorn read this article.
Then have students move to the lab table and recreate Hunt Morgan's experiment using this procedure. For this portion of the lesson, students should be in groups of four. The following equipment is needed per lab group: one planarian, spring water, disposable petri dish, raw liver, paint brush, and scalpel. Using the directions in the student handout, bisect the planarian into 4 pieces. Place in a dark place under the following class period.
(Note: If you are unable to obtain planaria, use this video to view the lab procedure. Then, have students complete the lab analysis using the information in the video.)
Using the attached webquest, consider the life cycles of the following flatworms: turbellarians, trematodes, and cestodes. Students should consider how modifications in certain structures allowed flatworms to become parasites. However, by the end of the webquest, student should realize that the basic body plan is still similar.
Have students begin with The Biology of Flatworms.
Next, they should use the lung fluke as the model organism to better understand trematodes. After that, they should use the pork tapeworm as the model organism to better understand cestodes. Finally, they should conclude with important research in planarian regeneration.
Students will use whole mount prepared slides of the tapeworm and liver fluke. (Note: These can be purchased through any biological supply house.) They will observe these microscopically and compare them with the planaria.
Remind students that both the tapeworm and the liver fluke are parasitic organisms. Have them sketch the organism in their notebook and label any distinguishing structures.
On the fluke, they should identify the anterior sucker, mouth, intestine, yolk gland, uterus, ovary, seminal receptacle, and testes. Remind students that flukes have both male and female reproductive structures in the same organism, but must be fertilized by another fluke.
On the tapeworm, they should identify the scolex and proglottid. When viewing the scolex, they should notice the rostellum, hooks, and suckers. When viewing the proglottid, they should identify both male and female reproductive organs, including the testes, sperm duct, genital pore, uterus, overies, and oviduct.
Student should consider the following questions:
- why does a tapeworm not need a digestive system, but a liver fluke still has one.
- why is being a hermaphrodite would be especially advantageous for both of these internal parasites?
Summarize the results of the lab by first showing students this video.
Next, have students develop a general model that shows the different germ layers in the flatworms. Students should first whiteboard this model so they can modify it, if necessary. Once they have a complete model, they can transfer it to their lab notebook.
HOMEWORK: Students should watch the video about stem cells and tissue regeneration. Students should complete a current event worksheet.