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Open-Ended Inquiry • Design Your Own Lab
Chapter 10 Lab Regeneration
in Planaria
Problem
How potent are the stem cells in planaria?
Introduction
Planarians are freshwater flatworms that are able to regenerate body parts. Figure 1
shows the external anatomy of a planarian. When a planarian is cut, stem cells collect
at the site of the injury. Stem cells have the ability to differentiate into other types of
cells. Stem cells that can form any tissue in an organism’s body are totipotent. Stem
cells that can differentiate into some, but not all, cell types are multipotent.
In this lab, you will design an experiment to determine how potent planarian stem
cells are. Then you will share your results with the rest of the class. From these
combined results, you should be able to infer where stem cells are found in a
planarian’s body.
Figure 1 External anatomy of planarian
Skills Focus
Form a Hypothesis, Design an Experiment, Draw Conclusions
Materials
• fresh water or spring water
• planarians
• petri dishes
• glass-marking pencil
• forceps
• scalpel
• dissecting microscope
• glass microscope slide
• lens paper
• pipette
• small paintbrush
• clear ruler
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Safety
A scalpel is an extremely sharp instrument. Never hold a flatworm with your
fingers while making a cut. If you are using glass petri dishes or pipettes, check
for cracks or chips. Alert your teacher if you break a glass object. Wash your
hands thoroughly with soap and warm water before leaving the lab.
Pre-Lab Questions
1. Apply Concepts What would you expect to observe if the stem cells in
planarians are totipotent? What would you expect to observe if the stem
cells are multipotent?
2. Control Variables What will you use as a control in your experiment?
Explain why you need this control.
3. Infer Two planarians are cut at different locations. Regeneration occurs in
one planarian, but not in the other. Based on these results, what might you
infer about stem cells in planarians?
Procedure
Part A: Care and Handling of Planarians
Your teacher has been caring for the planarians while they were adjusting to
their new environment. Your teacher may ask you to care for the planarians as
you observe them for one or two weeks. You will also need to know the most
effective way to make cuts.
1. Water Planarians need to be kept in fresh water or bottled spring water in a
dark area at room temperature. The water should be changed every other
day. Use a pipette to remove the old water from the petri dish and to add
new water. CAUTION: Never add tap water or distilled water to the petri
dish.
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2. Food The planarians need to be fed once a week. Your teacher may assign you
the task of feeding the planarians. If so, place a small piece of food in each petri
dish. Do not let uneaten food sit for more than four hours. Clean the bottom of
the dish with a paper towel and add a fresh supply of water.
3. Moving Planarians Use a pipette to move a planarian from one dish to another.
Be sure to transfer the planarian quickly or it may attach itself to the inside of the
pipette. CAUTION: If a planarian attaches itself to a petri dish, do not use a hard
object to scrape it off the dish. Use a small paintbrush instead.
4. Making Cuts Figure 2 shows a vertical cut and a horizontal cut. It also shows
the difference between a partial cut and a complete cut. A vertical cut is
generally more difficult to make than a horizontal cut. Try using a glass slide
with lens paper wrapped around it as a cutting surface. If you are making a
partial cut, leave the scalpel in the cut for 5–10 seconds to prevent the cut from
sealing back up immediately.
Figure 2 Examples of cuts
Part B: Design an Experiment
Assume you will have three planarians to work with.
5. Form a Hypothesis How potent are stem cells in planaria? Record the
hypothesis you will test to answer this question.
Hypothesis:
6. Control Variables Decide which independent variable you will investigate—the
type of cut or the location of the cut. Record your independent and dependent
variables.
Independent Variable:
Dependent Variable:
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7. Describe Your Plan Record the details of your plan below, including how
you will track changes in the dependent variable. Use Figure 3 to record the
cuts you intend to make.
Experimental Design:
Figure 3 Planned cuts
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8. Organize Data Construct a data table in the space below. Depending on the cuts
you make, you may have as many as five planarians to observe. Leave room for
up to two weeks of observations.
9. Disposal After handling the planarians, wash your hands thoroughly with soap
and warm water. When the experiment is over, follow your teacher’s instructions
for cleanup and disposal of materials.
Analyze and Conclude
1. Infer What evidence do you have that planarians have more than one type of
tissue in their bodies?
2. Apply Concepts What must happen to the stem cells before the different kinds
of tissues can be regenerated?
3. Evaluate How complete was the regeneration process? Refer to the diagram of
planarian anatomy in Figure 1 to help you evaluate the results.
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4. Draw Conclusions Use your results to explain why your hypothesis was
supported or why it was not supported.
5. Analyze Data As a class, look at the results from all the experiments. What
can you conclude about the location of stem cells in a planarian’s body?
6. Apply Concepts Why can the human body heal a cut on a finger but not
regenerate a finger that is cut off?
Extend Your Inquiry
Planarians naturally swim away from bright light. How could you demonstrate that regenerated
eyespots are functional?
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