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Paramecium Swimming Behavior

Paramecium is a unicellular organism motile by means of numerous cilia that cover its cell surface. Under normal conditions, these cilia beat in a coordinated fashion to rapidly move the cell forward at rates of up to 2 mm/sec. These bouts of forward swimming are periodically interrupted by turns (also called avoidance reactions), during which the cilia briefly reverse their normal forward stroke. The cell therefore briefly jerks and at times even tumbles before resuming its forward motion. The cell now swims in whatever direction it happened to face at the end of its turn. Under some conditions, Paramecium cells can even swim backwards! When several avoidance reactions follow close together, the repeated backward strokes of the cilia actually propel the cell in a reverse direction. This motion is easily identified, both in the orientation of the cell (the posterior/darker end now leading the way) and in the motion being less smooth than forward swimming.

    Because of its relatively large size (for a microorganism!), this swimming behavior is easily observable under a dissecting microscope and easily recorded with a microscope-mounted camera. This permits researchers to make careful and detailed observations of Paramecium's swimming behavior, measuring average swim speed, turning frequency, and duration of backwards swimming (if observed).

    The combination of forward swimming and turning enable Paramecium to swim toward (chemoattraction) or away from (chemorepulsion) chemicals in their environment.  Researchers often use a T-maze to test whether a substance is a chemoattractant or a chemorepellant. In this assay, a chemical to be evaluated is placed into the "TEST arm of the T-maze, a control solution into the "CONTROL" arm, and Paramecium cells into the center (stopcock) section. Once the stopcock is turned to connect the left and right arms of the T-maze, cells can swim into either arm. After 15 - 30 minutes, the number of cells on either side is counted and a percentage, known as the index of chemokinesis, is calculated. We have recently adapted this procedure for use in the high school classroom1.

 

1. de Ondarza, J. and N.L. Elwess. A Matter of Taste: Investigating sensory modalities in the protozoan Paramecium. The Science Teacher 69:36 - 40, 2002.

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This page was last edited on 12/04/02 .

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