paramecium

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paramecium

(parəmē`sĭəm), unicellular organism of the genus Paramecium, of the ciliate phylum CiliophoraCiliophora
, phylum in the kingdom Protista consisting of the ciliates, or ciliophores, complex freshwater or saltwater protozoans that swim by the coordinated beating of their cilia—short, hairlike structures that cover the cell surface.
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 found in freshwater throughout the world. Like other protozoansprotozoan
, informal term for the unicellular heterotrophs of the kingdom Protista. Protozoans comprise a large, diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple colonies and that show no differentiation into tissues.
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, paramecia, previously considered one-celled animals, are now customarily placed in kingdom ProtistaProtista
or Protoctista
, in the five-kingdom system of classification, a kingdom comprising a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms.
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. 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).

Paramecium

 

a genus embracing the simplest organisms of the class Infusoria. The elongated oval body reaches a length of 0.3 mm. It has a thick external layer of cytoplasm, the pellicle, which consists of three membranes and is covered evenly with 10,000 to 15,000 cilia. The mouth is on the side, beneath the oral groove.

The species P. bursaria undergoes intracellular symbiosis with single-celled green algae, or zoochlorella. Two species, P. caudatum and P. aurelia, are widely used in laboratory experiments. Methods for reproducing paramecia are well developed.

paramecium

[‚par·ə′mē·sē·əm]
(invertebrate zoology)
A single-celled protozoan belonging to the family Parameciidae.

Paramecium

[‚par·ə′mē·sē·əm]
(invertebrate zoology)
The genus of protozoans composing the family Parameciidae.

paramecium

any freshwater protozoan of the genus Paramecium, having an oval body covered with cilia and a ventral ciliated groove for feeding: phylum Ciliophora (ciliates)
References in periodicals archive ?
Of course, whether the paramecia are truly intelligent depends on the definition of intelligence.
Typical recordings of gravity-dependent orientation of immobilized paramecia in the hypo- and hyper-density media are shown in Figure 2a and b.
Protozoa--A group of one-celled organisms that generally do not contain chlorophyll, including amoebae, paramecia, flagellates, and certain spore-forming organisms; sometimes classified as one-celled animals.
On the microscopic level, a single soil bacterium might produce a million progeny in a week, while at the same time, protozoans such as amoebas and paramecia in the pond can number their offspring in the thousands and tens of thousands.
Youngsters navigate through the virtual reality world of a science building as they learn about aquariums, the nerves, paramecia and genetics.
Today the fifth-graders will peer through microscopes to search for paramecia, protozoa and amoebas in pond water.
The utilization of paramecia by the carnivorous plant Utricularia gibba.
The studio captured the life stages of a butterfly, the growth and flowering of poppies, the erratic movements of paramecia with time-lapse shots.
An element in the outer layer of paramecia appeared to control inherited cell characteristics.
Figures 3 and 4 illustrate the effect of bifenazate and indoxacarb on the evolution of the growth of paramecia.
Paramecia can be quite useful to have in a biology classroom.
On the other hand, the decoded genomes of single-celled organisms like yeast, paramecia, and giardia are much simpler than animal genomes.