Paramecia are widespread in freshwaterbrackishand marine environments and are often very abundant in stagnant basins and ponds. Because some species are readily cultivated and easily induced to conjugate and divide, it has been widely used in classrooms and laboratories to study biological processes. Paramecia were among the first ciliates to be seen by microscopistsin the late 17th century.
They were probably known to the Dutch pioneer of protozoologyAntonie van Leeuwenhoekand were clearly described by his contemporary Christiaan Huygens in a letter of Joblot gave this creature the name "Chausson"or "slipper", and the phrase "slipper animalcule" remained in use as a colloquial epithet for Parameciumthroughout the 18th and 19th centuries.
Ehrenbergin a major study of the infusoria published inrestored Hill's original spelling for the genus name, and most researchers have followed his lead.
Species of Paramecium range in size from 50 to micrometres 0. Cells are typically ovoid, elongate, foot- or cigar-shaped. The body of the cell is enclosed by a stiff but elastic membrane pellicleuniformly covered with simple
Asexual reproduction in parameciumhairlike organelles which act like tiny oars to move the organism in one direction. Nearly all species have closely spaced spindle-shaped trichocysts embedded deeply in the cellular envelope cortex that surrounds the organism.
Typically, an anal pore cytoproct is located on the ventral surface, in the posterior half of the cell. In all species, there is a deep oral groove running from the anterior of the cell to its midpoint.
This is lined with inconspicuous cilia which beat continuously, drawing food inside the cell. A few species are mixotrophsderiving some nutrients from endosymbiontic algae chlorella carried in the cytoplasm of the cell. Osmoregulation is carried out by contractile vacuoleswhich actively expel water from the cell to compensate for fluid absorbed by osmosis from its surroundings.
A Paramecium propels itself by whiplash movements of Asexual reproduction in paramecium cilia, which are arranged in tightly spaced rows around the outside of the body. The beat of each cilium has two phases: "Asexual reproduction in paramecium" densely arrayed cilia move in a coordinated fashion, with waves of activity moving across the "ciliary carpet", creating an effect sometimes likened to that of the wind blowing across a field of grain.
The Paramecium spirals through the water as it progresses.
When it happens to encounter an obstacle, the "effective stroke" of its cilia is reversed and the organism swims backward for a brief time, before resuming its forward progress. This is called the avoidance reaction. If it runs into the solid object again, it repeats this process, until it can get past the object.
It has been calculated that a
Asexual reproduction in paramecium expends more than half of its energy in propelling itself through the water. This low percentage is nevertheless close to the maximum theoretical efficiency that can be achieved by an organism equipped with cilia as short as those of the members of Paramecium. Paramecia feed on microorganisms like bacteria, algae, and yeasts.
To gather food, the Paramecium makes movements with cilia to sweep prey organisms, along with some water, through the oral groove, and inside the mouth opening. The food passes through the cell mouth into the gullet. When enough food has accumulated at the gullet base, it forms a vacuole in the cytoplasm, which then begins circulating through the Asexual reproduction in paramecium. As it moves along, enzymes from the cytoplasm enter the vacuole to digest the contents; digested nutrients then pass into the cytoplasm, and the vacuole shrinks.
When the vacuole, with its fully digested contents, reaches the anal pore, it ruptures, expelling its waste contents to the environment. Some species of Paramecium form mutualistic relationships with other organisms.
Paramecium bursaria and Paramecium chlorelligerum harbour endosymbiotic green algae, from which they derive nutrients and a degree of protection from predators such as Didinium nasutum. The genome of the species Paramecium tetraurelia has Asexual reproduction in paramecium sequenced, providing evidence for three whole-genome duplications.
The question of whether paramecia exhibit learning has been the object of a great deal of experimentation, yielding equivocal results. However, a study published in Asexual reproduction in paramecium to show that Paramecium caudatum may be trained, through the application of a 6.
Like all ciliates, Paramecium has a dual nuclear apparatus, consisting of a polyploid macronucleusand one or more diploid micronuclei. The macronucleus controls non-reproductive cell functions, expressing the genes needed for daily functioning. The micronucleus is the generative, or germline nucleus, containing the genetic material that is passed along from one generation to the next.
Paramecium reproduces asexually, by binary fission. During reproduction, the macronucleus splits by a type of amitosisand the micronuclei undergo mitosis. The cell then divides transversally, and each new cell obtains a copy of the "Asexual reproduction in paramecium" and the macronucleus.
Fission may occur spontaneously, in the course of the vegetative cell cycle. Under certain conditions, it may be preceded by self-fertilization autogamy or it may follow conjugationa sexual phenomenon in which Paramecium of compatible mating types fuse temporarily and exchange genetic material.
During conjugation, the micronuclei of each conjugant divide by meiosis and the haploid gametes pass from one cell to the other.
The gametes of each organism then fuse to form diploid micronuclei. The old macronuclei are destroyed, and new ones are developed from the new micronuclei. Autogamy or conjugation can be induced by shortage of food at certain points in the Paramecium life cycle.
In the asexual fission phase of growth, during which cell divisions occur by mitosis rather than meiosis, clonal aging occurs leading to a gradual loss of vitality. In some species, such as the well studied Paramecium tetraureliathe asexual line of clonally aging paramecia loses vitality and expires after about fissions if the cells fail to undergo autogamy or conjugation.
The basis for clonal aging was clarified by transplantation experiments of Aufderheide. In contrast, transfer of cytoplasm from clonally young paramecia did not prolong the lifespan of the recipient. These experiments indicated that the macronucleus, rather than the cytoplasm, is responsible for clonal aging. Other experiments by Smith-Sonneborn,  Holmes and Holmes,  and Gilley and Blackburn  demonstrated that, during clonal aging, DNA damage increases dramatically also reviewed by Bernstein and Bernstein.
In this single-celled protist, aging appears to proceed as it does in multicellular eukaryotes, as described in DNA damage theory of aging. When clonally aged P. During either of these processes the micronuclei of Asexual reproduction in paramecium cell s undergo meiosis, the old macronucleus disintegrates and a new macronucleus is formed by replication of the micronuclear DNA that had recently undergone meiosis.
There is apparently little, if any, DNA damage in the new macronucleus. These findings suggest that clonal aging is due, in large part, to a progressive accumulation of DNA damage see DNA damage theory of aging ; and that rejuvenation is due to the repair of this damage in the micronucleus during meiosis. Meiosis appears to be an adaptation for DNA repair and rejuvenation in these paramecia.
From Wikipedia, the free encyclopedia. For the
Asexual reproduction in paramecium alga, see Paramecia alga. In Witzany, Guenther; Nowacki, Mariusz. Characterization, Classification, and Guide to the Literature.
Antony van Leeuwenhoek and his "Little Animals" Asexual reproduction in paramecium. Description et usages de Plusieurs Nouveaux Microscopes, tant simple que composez in French. An History of Animals. British and other freshwater ciliated protozoa. Journal of Experimental Biology. Proceedings of the National Academy of Sciences. Journal of General Microbiology. Journal of Eukaryotic Microbiology.
Witzany G, Nowacki M eds. Biocommunication of Ciliates, Springer, Dordrecht, pp. Evidence of functional changes in the macronucleus with age".
Mechanisms of Ageing and Development. Mesodiniea MesodiniumMyrionecta.