Paramecium: Wikis

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From Wikipedia, the free encyclopedia

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

Paramecium aurelia
Paramecium bursaria
Paramecium caudatum
Paramecium tetraurelia

Paramecium is 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 from the cell absorbed by osmosis from their surroundings.

Paramecia are widespread in freshwater environments, and are especially common in scums. Recently, some new species of Paramecia have been discovered in the oceans.

Certain single-celled eukaryotes, such as Paramecium, are examples for exceptions to the universality of the genetic code: in their translation systems 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 hairlike 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, the gullet, food vacuoles, the macronucleus.

Locomotion

Cilia are the locomotive part in the paramecium. 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.

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 is 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.

Communication by electromagnetic radiation

Paramecium may be able to communicate via radiation. This may be true of other single-celled organisms as well. In an experiment conducted in 2008, Daniel Fels at the Swiss Tropical Institute in Basel, demonstrated that Paramecium caudatum grown in complete darkness in glass tubes, which prevented the passing of chemical signals, were able to influence feeding behavior and growth rates of neighbours in other tubes, suggesting that electromagnetic signals were involved. It appears that the microbes use at least two frequencies on which to communicate,[5] one of which was in the ultraviolet (UV) range.[6] The structures within the organisms that make this possible have not been identified. Fels suggests that signals of this sort could lead to novel noninvasive medical techniques.[5]

References

  1. ^ O. F. Muller
  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. [1]
  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
  4. ^ Armus, H.L., Montgomery, A.R., Jellison, J.L. (2006) "Discrimination Learning in Paramecia (P. caudatum)" , The Psychological Record, 56,489-498[2]
  5. ^ a b Choi, Charles (June 2009). "News Scan Briefs: Electromagnetic Chatter". Scientific American. http://www.scientificamerican.com/article.cfm?id=in-brief-jun09. Retrieved 2009-11-04. 
  6. ^ Fels, Daniel (April 1 2009). "Cellular Communication through Light". PLoS ONE. http://www.plosone.org/article/info:doi%252F10.1371%252Fjournal.pone.0005086. 

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

PARAMECIUM, 0. F. Muller, (often misspelt Paramaecium,. Paramoecium), a genus of aspirotrochous ciliate Infusoria, characterized by its slipper-like shape, common in infusions, especially when they contain a little animal matter. It has two dorsal contractile vacuoles, each receiving the mouths of five radiating canals from the inner layer of the ectosarc, and a large ovoid meganucleus, and one or two micronuclei. From its abundance, the ease with which it can be cultivated and observed, its relatively simple structure and adequately large size (-- in.), it is most frequently selected for elementary study and demonstration, as well as for purposes of research.


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Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Paramecium aurelia

Taxonavigation

Main Page
Cladus: Eukaryota
Regnum: Protista
Subregnum: Biciliata
Infraregnum: Alveolata
Phylum: Ciliophora
Subphylum: Intramacronucleata
Classis: Oligohymenophorea
Subclassis: Peniculia
Ordo: Peniculida
Subordo: Parameciina
Familia: Parameciidae
Genus: Paramecium

Vernacular names

English: Paramecium
עברית: סנדלית
Polski: Pantofelek

Simple English

[[File:|thumb|200px|Paramecium]] Paramecium is one of the best-known protists, often taught in school biology courses. Paramecium is a ciliate genus. They are a clade of protists which move by the synchronous waves of tiny projections from their cuticle. These projections are called cilia (singular: cilium).[1][2] The species range from 50 to 350 μm in length.[3] They live in freshwater ponds, and eat bacteria, and other protists such as single-celled algae.

Paramecium species usually have bacterial symbionts, and some species have green algal symbionts.

Reproduction

Reproduction in Paramecium has been researched for many years. Paramecium has two nuclei (a large macronucleus and a single compact micronucleus).[4] They cannot survive without the macronucleus and cannot reproduce without the micro-nucleus.[1] Reproduction is either accomplished by binary fission (asexual), conjugation (sexual),[1] or, rarely, by endomixis, a process of self-fertilisation. During binary fission a fully grown organism divides into two daughter cells.[1] Conjugation consists of the temporary union of two organisms and the exchange of micro-nuclear elements[1]. Without the rejuvenating effects of conjugation a paramecium ages and dies.[1] Only opposite mating types, or genetically compatible organisms, can unite in conjugation.[1]

This reproductive system is unique to ciliates, and is one of the reasons why we think the Protista is not a natural clade, but just a convenient collection of single-celled organisms of various origin.

Paramecium aurelia

This species consists of 14 "syngens", each genetically isolated from every other, and biochemically unique. Each syngen has two mating types.[5] The syngens are so similar in appearance that they have not been given separate species names.[6]

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Paramacium
  2. 101 Science.com: Paramecium Caudatum
  3. A μm is a millioneth of a metre.
  4. Paramecium
  5. Sonneborn T.M. 1938. Mating types in Paramecium aurelia. Proc Am Philos Soc 79, 411-434.
  6. King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics, 7th ed. Oxford. p322

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