Does the Rate of Regeneration in Planeria Depend Upon the Amount of Light?

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Author: Janice VanCleave

What Effect Does Light Have on the Rate of Planaria Regeneration?

Category: Biology—Reproduction

Project Idea by: Evan Sunshine and Christopher Wenz

Regeneration is the growth of new tissue or parts of an organism that have been lost or destroyed. Regeneration is a form of asexual reproduction in which a new organism is formed from one parent. Some animals, generally invertebrates (animals without backbones) such as planaria, can regenerate a complete body from small fragments of themselves. Planaria are flatworms found in freshwater such as weedy ponds, slow-moving streams, and small creeks.

Planaria regenerate from small parts cut from their bodies. For example, if a planaria's head is cut off, the beheaded body grows a new head and the separated head grows a new body. Within about 15 minutes after amputation, the cut edges are covered by epithelial cells (cells on the surface of organisms). Within about five days, distinct new parts are seen on each cut surface. A project question might be, "What effect does light have on the rate of planaria regeneration?"

Clues for Your Investigation

Planaria can be purchased from scientific catalog supply companies. Ask your teacher to order these for you. The company should also give you information about keeping the planaria alive, as well as clues on the safest way of handling, how to cut them, and how to dispose of them after the experiment. When cutting, ask for assistance from an adult. One way to help keep the planaria immobile while you work on them is to place them on an ice cube. The cut parts must be kept in pond water or a freshwater aquarium. Prepare four or more containers of cut planaria and place each container in an area receiving a different amount of light. The container in the dark will be the control. Observe the cut parts each day for two or more weeks.

Independent Variable: Amount of light

Dependent Variable: Rate of regeneration

Controlled Variables: Testing procedure, how planaria are cut, containers, temperature, environmental conditions

Control: Planaria with no light

Other Questions to Explore

  1. What effect would temperature have on regeneration of planaria?
  2. Is there a size limit on the pieces of planaria that will regenerate into complete new organisms?
  3. What effect does the direction of the cut have on planaria regeneration?

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