Paramecium
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Paramecium
Classification of Animals Non Chordates of Class 11
Paramecium is a holotrichous ciliate protozoan.
It is commonly called as Slipper animalcule.
Body is covered with a thin, firm, flexible membrane called pellicle.
Cilia in the posterior end are longer called caudal tuft.
Trichocysts are peculiar bottle-shaped organelles present in the ectoplasm of Paramecium. Trichocysts are the organelles of offence and defence.
Macronucleus is one, large, kidney-shaped, controls vegetative functions (metabolism).
Micronuclei, one (P. caudatum), two (P. aurelia) and several (P. multimicronucleatum) are only concerned with reproduction.
Oral apparatus consists of Cytopharynx and cytostome (mouth), cytopyge or cytoproct (anus).
Nutrition or food intake in Paramecium is holozoic. It is a filter feeder.
Most favourite food is Tetrahymena, another ciliate protozoa. Tetrahymena is a protozoan used in biological research.
Paramecium moves in wavy line. It involves rotation and gyration.
Paramecium shows negative response and moves against water current.
Paramecium reproduces by transverse binary fission and nuclear reorganisation.
Binary fission occurs during favourable condition. It is faster multiplication, completes about in half an hour (upto three divisions per day).
Paramecium undergoes several kinds of nuclear reorganisation such as conjugation, autogamy, cytogamy etc. These processes are to overcome aging or senescence which is caused due to repeated binary fissions.
In Paramecium nuclear reorganisation takes place for rejuvenation.
Conjugation occurs between two mating types of same species of Paramecium. It is a modified form of cross fertilisation. Each conjugant produces a female stationary and a male migratory nucleus by three successive divisions of its micronucleus.
They are called pronuclei. Conjugation of Paramecium involves exchange of micronuclei. Synkaryon is the diploid nucleus formed by the fusion of stationary and migratory nuclei in conjugant.
Synkaryon divides thrice to form eight nuclei. Each Paramecium (exconjugant) at the end of the conjugation produces four daughter Paramecia.
Autogamy is the process of self-fertilisation. It occurs in a single animal of P. aurelia.
Endomixis occurs in P. aurelia. It is asexual reproduction and one individual produces four daughter Paramecia.
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