Materials Included In Kit

Additional Materials Required

Safety Precautions

This activity is not considered hazardous, but always follow appropriate laboratory safety rules. Eye protection and gloves should be worn. Take caution whenever working with a razor blade. Wear gloves and eye protection and follow all normal laboratory guidelines. Wash hands thoroughly after completing the activity.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The planaria used in this activity may be disposed of according to Flinn Suggested Biological Waste Disposal Type IV. 

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This activity will require two classroom periods to set up. Additional class time will be needed to record the observations in Part IV.
• The black construction paper should be cut in half before student use.
• Planaria may be ordered from Flinn Scientific, Catalog Nos. LM1094 class size 30, and LM1095 class size 100, or collected locally. Search for planarians on the undersides of rocks in the riffle portions of streams. Place canned dog food or liver in a nylon stocking and tie it to a rock in the riffle portion of the stream. Collect the stocking covered with planaria the next day. Keep the planaria in spring or pond water and in a cool place.
• The forceps or foam-tipped wand may be used to pass out the planaria to student groups.
• It is best to use spring water or pond water for the experiments in this kit.
• Here are a few tips for long term cultures of planaria:
  • Planaria thrive best in large jars or culture dishes containing clear pond water or spring water (do not use tap or distilled water). Add a couple of leaves or bottom dwelling aquarium plants to the culture to provide a place to hide, then introduce planaria. The cultures should be aerated by forcing air gently through clean pipet or an aquarium pump.
  • Culture should be placed out of direct sunlight.
  • Maintain cultures at room temperature (68–72 °F).
  • Feed planaria once every day or every other day with small pieces of meat (such as liver) or hard-boiled egg yoke. Supply only as much food as can be consumed in approximately 30 minutes and remove any uneaten food to avoid bacterial blooms in the water.
  • Approximately half of each culture container’s water should be replaced weekly to help ensure long-term culture survival.
  • Since planaria are very sensitive organisms to culture, set up two separate culture containers and keep them in different areas of the room. This may help ensure that at least one culture survives if the other crashes.
• As an extension to Part III, have the students cut planaria in half as seen in Cut 1 in Figure 3 and see how each half responds to the Light versus Dark procedure.
• Demonstrate the planaria cuts for Part IV in front of students, if desired.
• Scalpels may be used in place of the razor blades, if desired.
• If a video microscope is available, project the planaria before and after the cuts are made. Otherwise have students look at them at the demonstration table.
• In Part IV, each planaria cut should be made on a microscope slide in a drop of water.
• Some planaria will likely fission during this activity. They do this by sticking their posterior end to the dish and quickly swim away. The “tail” portion will break away from the main body and another whole planarian will eventually form.
• Do not feed the planaria during Part IV. During regeneration, planaria do not feed. Adding food will just foul the water, leading to possible death of the planaria.

Answers to Questions

Part I. General Planarian Observations

Length of planarian ___1.7___ mm
Average length of planaria in classroom ___1.5___ mm
Does the planarian move in the Petri dish? If so, how does it move?

The planarian moved slowly around the edges of the Petri dish. As it moved, its body was stretched and recoiled in an “inch worm”–type fashion.

Is the planarian active or inactive?

This planarian was active.

How does the planarian react to current?

Answers will vary. The planarian moved away when the current was provided. It also shrank and became curled.

Part II. Left or Right Handed Is your planaria left or right handed? ___Right___ 

Part III. Light vs. Dark From the observations, do planaria prefer light or dark areas? Why?

Dark areas. All planaria moved toward the dark side of the Petri dish when given the option. They may be sensitive to light.

Part IV. Regeneration Did any of the cut Planaria regenerate? If so, which ones?

Yes. The “heads” and “tails” of the planaria showed regeneration. The partial heads seemed to fuse back together.

Why do you think these regenerated and others did not?

It seemed that the “heads” and “tails” regenerated much easier. This may be due to the locations in which the planaria were cut (e.g., locations of nerves).

Were the rates of regeneration different for each type of cut? If so, explain.

Yes. The “heads” pieces seemed to regenerate much faster than any of the other cuts. The planarian that has been cut in half lengthwise did not survive.

Introduction

Are two heads really better than one? Explore the amazing capability of planaria regeneration! Three interesting studies with planaria will also be performed.

Concepts

• Planaria
• Stimulus
• Growth and development
• Regeneration
• Cell division

Background

Planaria can be found under rocks and logs in many bodies of fresh water. Although they are very simple organisms, planaria have the astonishing ability to regenerate body parts. Planaria (planarian—single) are flat-bodied worms belonging to the phylum Platyhelminthes that are typically 1–6 mm in length. Their systems consist of a simple digestive–excretory system, nervous system (including a simple “brain”) and eyespots on top of their heads (see Figures 1 and 2). These eyespots appear to be two large, crossed eyes making the planaria look more intimidating to potential predators. The black dot seen within the eyespot is actually the functioning eye.

Planaria reproduce both sexually and asexually by fission (splitting in half) and regenerate all body parts that were lost during the division. Planaria are also particularly responsive to stimuli. They are even capable of successfully navigating a maze with multiple choices.

Experiment Overview

Four activities will be performed in this experiment—general observations of planaria, left or right-handedness of planaria, a light versus dark activity and planaria regeneration.

Materials

Safety Precautions

This activity is not considered hazardous, but always follow appropriate laboratory safety rules. Take caution whenever working with a razor blade. Wear gloves and eye protection and follow all normal laboratory guidelines. Wash hands thoroughly after completing the activity.

Procedure

Part I. General Observations

1. Obtain a planarian in a shallow pool of water in a Petri dish.
2. Observe the planarian using a magnifying glass. Draw the planarian and label the eyespots, anterior (head), and posterior ends in the Planarian Activities Worksheet.
3. Obtain a ruler and measure the length of the planarian (in mm). Record the measurement in the Planarian Activities Worksheet.
4. Once all student groups have measured their planaria, determine the average planarian size for your classroom. Record the average planarian size in the Planarian Activities Worksheet.
5. Observe the planarian for several minutes. Does the planarian move in the Petri dish? How does it move? Is the planarian active or inactive? Answer the questions in the Planarian Activities Worksheet.
6. Obtain a disposable pipet. Create a current in the water by placing the stem of the pipet in the water and slowly squeezing and releasing the bulb of the pipet. How does the planarian react? Answer the questions in the Planarian Activities Worksheet.
7. Save this planarian for use in Part II.

Part II. Left- or Right-Handed

1. Planarians display a right-handed or left-handed nature. Using a foam-tipped wand or forceps, flip the planarian onto its back in the water of the Petri dish.
2. Observe which direction, left or right, the planarian flips over to recover itself. If it rolls to your right, it is right-handed. If it rolls to your left, it is left-handed.
3. Repeat steps 1 and 2 four more times. Record all observations in the Planarian Activities Worksheet.
4. Is your planarian left or right handed? Record your answer in the Planarian Activities Worksheet.
5. Save the planarian for use in Part III.

Part III. Light vs. Dark

1. Obtain two more planaria from your teacher.
2. Place the specimens in the water of the Petri dish with your original planarian.
3. Obtain a black piece of paper and a light source.
4. Cover half of the Petri dish with black paper.
5. Place the light source directly above the Petri dish.
6. Make sure the three planarians in the Petri dish start on the “light” side of the Petri dish.
7. Observe the planaria for three minutes and then record all observations after three minutes in the Planarian Activities Worksheet.
8. Repeat steps 4–7 two additional times. Record all observations in the Planarian Activities Worksheet.
9. Save these three planaria for use in Part IV.

Part IV. Regeneration

1. Obtain three additional Petri dishes and three more planaria from your teacher. Place all six planaria in the Petri dish used in Part III.
2. Using a marker, label the Petri dish containing the six planaria “partial heads.” Label the three remaining Petri dishes as follows—heads, tails and lengthwise.
3. Place a shallow layer of spring or pond water in each Petri dish.
4. Three types of cuts will be made—a mid-length cut, lengthwise cut and partial lengthwise cut.
5. Obtain a microscope slide. Using a pipet, place a drop of water on the slide. This slide will be used as the platform for the planarian dissections.
6. Using a foam-tipped wand or forceps, place one planarian on the drop of water on the microscope slide.
7. Using a razor blade, cut the planarian in half about mid-length (Cut 1) (see Figure 3). Use extreme caution when using the razor blade.
   {10815_Procedure_Figure_3}
8. Using a foam-tipped wand or forceps, move the head piece into the dish labeled “heads” and the tail piece into the “tails” dish.
9. Repeat steps 5–8 using another planarian.
10. Cut two planaria, one at a time as described above, in half lengthwise (Cut 2) (see Figure 3). Place these pieces into the dish labeled “lengthwise.”
11. Make partial lengthwise cuts on the last two planaria (one at a time as described). Begin at the anterior (head) end and cut in a posterior direction until about mid length. The heads will be split but the tails will be intact (Cut 3) (see Figure 3). Place these two planaria back into the “partial heads” dish.
12. Place all dishes in a dark, cool place.
13. Check the dishes every few days for the next two to three weeks. Add additional sand and spring water as needed.
14. Record all observations in the Planarian Activities Worksheet.

Student Worksheet PDF

10815_Student1.pdf