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paramecium

 
Dictionary: par·a·me·ci·um   (păr'ə-mē'shē-əm, -sē-əm) pronunciation
 
n., pl. -ci·a (-shē-ə, -sē-ə) or -ci·ums.

Any of various freshwater ciliate protozoans of the genus Paramecium, usually oval and having an oral groove for feeding.

[New Latin Paramēcium, genus name, from Greek paramēkēs, oblong in shape : para-, alongside; see para–1 + mēkos, length.]


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General features of a paramecium.
(click to enlarge)
General features of a paramecium. (credit: © Merriam-Webster Inc.)
Any of the free-living, single-celled protozoans that make up the genus Paramecium. Most are about the size of the period at the end of this sentence. They vary in shape and are surrounded by a rigid protein layer (pellicle) covered with hundreds of cilia that beat rhythmically to propel them and to direct bacteria and other food particles into their oral groove. Food particles are collected into food vacuoles, where digestion takes place. Two (occasionally three) contractile vacuoles close to the surface near the ends of the cell expand and contract as they discharge metabolic wastes and excess fluid. Paramecia have two kinds of nuclei: a large macronucleus (the centre of all metabolic activities) and at least one small micronucleus (which stores the genetic material necessary for sexual reproduction).

For more information on paramecium, visit Britannica.com.

 
Columbia Encyclopedia: paramecium
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paramecium (parəmē'sĭəm) , unicellular organism of the genus Paramecium, of the ciliate phylum Ciliophora found in freshwater throughout the world. Like other protozoans, paramecia, previously considered one-celled animals, are now customarily placed in kingdom Protista. The paramecium has a stiff outer covering that gives it a permanent slipper shape. It swims rapidly by coordinated wavelike beats of its many cilia—short, hairlike projections of the cell. A paramecium normally moves forward in a corkscrew fashion but is capable of reversing direction when it encounters adverse conditions. This trial-and-error behavior (backing up and then continuing forward in a slightly different direction until an optimum path is found) is conspicuous when the animal is observed through a microscope.

Paramecia and other ciliates are the most complex of all single-celled organisms. The paramecium has an external oral groove lined with cilia and leading to a mouth pore and gullet; food (typically smaller organisms, such as bacteria) is digested in food vacuoles. There are also an anal pore, two contractile vacuoles that regulate the water content of the cell, and two nuclei. The larger nucleus, or macronucleus, is thought to regulate most cell functions, while the smaller nucleus, or micronucleus, is involved in reproduction. Paramecia usually reproduce asexually by cell division but can also exchange genetic information via a process called conjugation, in which two individuals unite at the oral grooves and exchange micronuclei that serve as little packages of DNA, after which the cells divide, yielding daughter cells with DNA from each of the parents.

Bibliography

See A. Jurand and G. C. Selman, The Anatomy of Paramecium aurelia (1964).


 
Veterinary Dictionary: Paramecium
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A genus of ciliate protozoa.

 
Wikipedia: Paramecium
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Paramecia

Paramecium aurelia
Scientific classification
Domain: Eukaryota
Kingdom: Protista
Phylum: Ciliophora
Class: Ciliatea
Order: Peniculida
Family: Parameciidae
Genus: Paramecia
Müller, 1773
Species

Paramecium aurelia
Paramecium bursaria
Paramecium caudatum
Paramecium tetraurelia

Paramecia, also known as Lady Slippers, due to their appearance, are a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 50 to 350 μm in length, Simple cilia cover the body, which allow the cell to move with a synchronous motion (like a caterpillar). There is also a deep oral groove containing inconspicuous compound oral cilia (as found in other peniculids) used to draw food inside. They generally feed on bacteria and other small cells. Osmoregulation is carried out by a pair of contractile vacuoles, which actively expel water absorbed by osmosis from their surroundings.

Paramecia are widespread in freshwater environments, and are especially common in scums. Certain single-celled eukaryotes, such as Paramecium, are examples for exceptions to the universality of the genetic code (translation systems where a few codons differ from the standard ones).

Contents

Physiology

The paramecium approximates a prolate spheroid[1], rounded at the front and pointed at the back. The pellicle is a stiff but elastic membrane that gives the paramecium its definite shape. Covering the outer edge are whiplike structures, called cilia. On the side beginning near the front end continuing down half way is the oral groove, which collects food until it is swept into the cell mouth. There is an opening near the back end called the anal pore. The contractile vacuole and its radiating canals — referred to previously for osmoregulation of the organism, are also found on the outside of a paramecium.The paramecium is very commonly mistaken as a blepharisma.

The paramecium contains cytoplasm, trichocysts (“thread capsules”), the gullet, food vacuoles, the macronucleus.

Locomotion

In order for the paramecium to move forward, its cilia beat at an angle, backwards in unison. This means that the paramecium moves by spiraling through the water on an invisible axis. The paramecium can also move backwards when the cilia beat forward at an angle in unison.

When the paramecium runs into a solid object, the cilia change their direction and beat forward, causing the paramecium to go backward. The paramecium turns slightly and goes forward again. If it runs into the solid object again it will repeat this process until it can get past the object.

Gathering food

Paramecia feed on microorganisms like bacteria, algae, and yeasts. To gather its food, the paramecium uses its cilia to sweep up food along with some water into the cell mouth after it falls into the oral groove. The food goes through the cell mouth into the gullet. When enough food has accumulated at the gullet base, it forms a food vacuole in the cytoplasm, and travels through the cell, through the back end first. As it moves along, enzymes from the cytoplasm enter the vacuole to digest the contents, digested nutrients then going into the cytoplasm, and the vacuole shrinks. When the vacuole reaches the anal pore, it ruptures, expelling its waste contents to the exterior.

Symbiosis

One of the most interesting known symbiotic relationships is that of Paramecium aurelia and its bacterial endosymbionts. The bacteria infect the protozoa, and they produce toxic particles that kill sensitive strains, but not killer strains. See also the Chlorella symbiosis with Paramecium bursaria.

Giant amoebas, for instance, have types of endosymbiotes, which seem to function as mitochondria in these amoebas. Another example involves protozoa bacteria that produce cellulases to assist the host protozoan with cellulose digestion (similar to those found in some in termites).

Genome

The paramecium genome has been sequenced (species: Paramecium tetraurelia), providing evidence for three whole-genome duplication.[2]

In some ciliates, like Stylonychia and Paramecium, only UGA decoded as a stop codon, while UAG and UAA are reassigned as sense codons.[3]

Learning

The question of whether paramecia exhibit learning has been the object of a great deal of experiment, yielding equivocal results. In one of the most recent experiments published[4], the authors, by using a voltage as a reinforcement, concluded that paramecium may indeed learn to discriminate between different brightness levels.

References

  1. ^ O. F. Muller [1]
  2. ^ Aury, J. M., O. Jaillon, et al. (2006). "Global trends of whole-genome duplications revealed by the ciliate Paramecium tetraurelia." Nature 444(7116): 171-8. [2]
  3. ^ Lekomtsev, S, Kolosov, P., et al. (2007) "Different modes of stop codon restriction by the Stylonychia and Paramecium eRF1 translation termination factors", PNAS, 104(26):10824-9 [3]
  4. ^ Armus, H.L., Montgomery, A.R., Jellison, J.L. (2006) "Discrimination Learning in Paramecia (P. caudatum)" , The Psychological Record, 56,489-498[4]

External links


 
Translations: Paramecium
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Dansk (Danish)
n. - tøffeldyr

Nederlands (Dutch)
pantoffeldiertje

Français (French)
n. - paramécie

Deutsch (German)
n. - Pantoffeltierchen

Ελληνική (Greek)
n. - παραμηκίο (εμβαδόζωο, πρωτόζωο)

Italiano (Italian)
paramecio

Português (Portuguese)
n. - paramécio (m) (Zool.)

Русский (Russian)
род пресноводных инфузорий-го- лотрихов

Español (Spanish)
n. - paramecio

Svenska (Swedish)
n. - paramecium (mikroskopiskt djur)

中文(简体)(Chinese (Simplified))
草履虫

中文(繁體)(Chinese (Traditional))
n. - 草履蟲

한국어 (Korean)
n. - 짚신벌레

日本語 (Japanese)
n. - ゾウリムシ

العربيه (Arabic)
‏(الاسم) منعول, نعائلي : نوع من الحيوانات الأحاديه الخليه والشبيهه بالخف في شكلها‏

עברית (Hebrew)
n. - ‮סנדלית (יצור חד-תאי)‬


 
 

 

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/  Read more
Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Paramecium" Read more
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