Asexual webster dictionary


10-Nov-2017 13:32

Paramecium reproduces asexually, by binary fission. During reproduction, the macronucleus splits by a type of amitosis, and the micronuclei undergo mitosis.

The cell then divides transversally, and each new cell obtains a copy of the micronucleus and the macronucleus.

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 microscopists, in the late 17th century.

or it may follow conjugation, a 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.

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The name "Paramecium"—constructed from the Greek παραμήκης (paramēkēs, "oblong") -- was coined in 1752 by the English microscopist John Hill, who applied the name generally to "Animalcules which have no visible limbs or tails, and are of an irregularly oblong figure." In 1773, O. Müller, the first researcher to place the genus within the Linnaean system of taxonomy, adopted the name Paramecium, but changed the spelling to Paramœcium. Species of Paramecium range in size from 50 to 330 micrometres (0.0020 to 0.0130 in) in length.

When enough food has accumulated at the gullet base, it forms a vacuole in the cytoplasm, which then begins circulating through the cell.

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.

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 question of whether paramecia exhibit learning has been the object of a great deal of experimentation, yielding equivocal results.A Paramecium propels itself by whiplash movements of the cilia, which are arranged in tightly spaced rows around the outside of the body.