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Paramecium


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Paramecium (Photo left by Y. Tsukii) is a unicellular eucaryote belonging to the phylum Ciliophora, a taxonomic group that also includes Tetrahymena, Stentor, Vorticella, and the human parasite Balantidium coli.   Ciliates are often motile by means of numerous cilia; in Paramecium these cilia cover virtually the entire cell surface.  Coordinated beating of the cilia propels the cell and sweeps food particles (e.g. bacteria) into its oral groove where food is then phagocytosed.  
Notice the prominent food vacuoles (red dye-filled spheres) seen in the photo. Ciliates have two types of nuclei, a macronucleus and one or more micronuclei (see Genetics).  Other interesting cell structures are their trichocysts (defense) and contractile vacuoles (used for osmoregulation).  
    Paramecium is a favorite research organisms of many scientists because it is easily cultured, can be grown in large numbers, is readily accessible to microscopic and electrophysiological observation, and does not pose the ethical dilemmas inherent in animal studies [1].  In particular, our research has focused on Paramecium's similarities to mammalian chemosensory nerve cells (e.g. taste and smell receptors).  As such, Paramecium is an excellent model for studying the diverse aspects of chemical sensation and response: detection of a chemical; change in  cellular membrane potential; response to the stimulus [2]. One particular advantage of Paramecium is that its swimming behavior - swim speed and turning frequency - are readily observable and, since membrane voltage and swimming behavior are intricately linked, provides insight into the cell's electrophysiology [3].  
References: 

1. Van Houten, J., Trends Neurosci. 17:62-71, 1994.
2. Van Houten, J., Ann. Rev. Physiol. 54:639-663, 1992.
3. Kung, C. and Y. Saimi, Ann. Rev. Physiol. 44:519-534, 1982

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This page was last edited on 08/14/03 .

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