Paramecium – Description of Habitat, Structure and Reproduction

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Paramecium caudatumBiology Notes | Zoology
Paramecium – Description of Habitat, Structure and Reproduction Process
For: Science Class 11

Habitat
Paramecium is found in fresh water. It is widely distributed and commonly found animal. Its body is unicellular. The shape of the cell is like a sole of slipper. Therefore, it is called slipper animalcule.

Structure

Pellicle: It is outer most covering. It is thin and elastic. It is made up of a kind of gelatinous substance. The surface of pellicle has hexagonal structure and each hexagonal structure consists of cilia outer side and trichocyst inner side. Its function is to provide shape to the cell and to give elasticity to the cell.

Cilia: The outer layer is covered with fine hair like structure called cilia. The cilia arise from the cytoplasm and penetrate pellicle. The base of the cilia has nodule called kinetosome. The cilia help in locomotion and capture food.

Trichocyst: The trichocysts are spindle shaped structure, which arrange at right angle towards inner side of pellicle. They are considered as defense organs. They are discharged out as needle like structures when the paramecium is stimulated.

Oral groove: The oral groove is oblique aperture which runs backward and situated at 2/3rd part of the body. Base of oral groove is called vestibule and is conical shaped. The vestibule connects an opening called cytostome. The cytostome opens into gullet. It is tube like structures and called as cytopharynx. The gullet terminates in food vacuole.

Cytopyge: There is small opening called cytoproct or cytopyge is present behind oral groove. It acts as anus of the paramecium through which undigested matters from the cell is passed out.

Cytoplasm: Cytoplasm is differentiated into two parts. The outer part is thin and called ectoplasm, inner part is granular called endoplasm. The ectoplasm consists of trichocysts and base of cilia. Endoplasm consists of cell organelles and cell inclusions.

Nucleus: In the endoplasm, there are two nuclei. One is larger kidney shaped called macronucleus or mega nucleus which helps in vegetative reproduction. There is another is smaller round or spherical nucleus in the cavity of large nucleus called micronucleus, which helps in sexual reproduction.

Contractile Vacuole: There are two contractile vacuoles one at each end. The contractile vacuole consists of 5-10 radial canals, which appear as star like structure. Each radial canal has three parts i.e. ampulla, terminal and injecting canal.

Function of contractile vacuole
It helps in absorption of water from the body and pour into the vacuole. The vacuole contracts time to time to throw out the excess water from the body. It is the organ of osmoregulation.

Reproduction
The paramecium reproduces both sexually and asexually

Sexual reproduction
It takes place by conjugation method. During the process following events occur

  • Two paramecia come close and get attached together from side of oral groove by some sticky substances. The Paramecia that take part in conjugation are called conjugants.
  • At the point of attachment, pellicle degenerates to form cytoplasmic bridge.
  • After formation of cytoplasmic bridge, the macronucleus of each conjugant disappeared.
  • The micronucleus undergoes meiosis division in each conjugant to give four nuclei.
  • In each conjugant out of four nuclei, three nuclei degenerate and only one remain functional.
  • The remaining one nucleus of each conjugant undergoes mitosis division to produce two nuclei. Out of two nuclei, one is larger and other is smaller.
  • Small nucleus of each conjugant migrates crosswise between two paramecia through cytoplasmic bridge. That nucleus is called migratory nucleus or male nucleus. The larger nucleus remains stationary and called stationary nucleus or female nucleus.
  • The migrated nucleus fuses with stationary nucleus in each conjugant to form zygote nucleus.
  • Now two paramecia separate together and then they are called exconjugant.
  • In each exconjugant the zygote undergoes mitosis division 3 times to produce 8 nuclei.
  • Out of eight nuclei, four becomes larger and 4 becomes smaller in each exconjugant. The larger nuclei are termed as macronucleus and smaller is micronucleus.
  • Out of four micronucleus 3 degenerate and one remains functional.
  • The functional micronucleus in each exconjugant divides into two and the conjugant divide by binary fission into two daughter paramecia from each exconjugant. The macronuclei are shared equally.
  • Again the micronuclei of two daughter paramecia divide into two and macronuclei are again shared and later the paramecia divide again to produce 8 paramecia.

Significance of conjugation
The vitality is stored, the hereditary materials or characters are exchanged between two paramecia. There are some other methods of sexual reproduction

Autogamy
It takes place in single individual. The micronucleus divides into two and fuses to form synkaryuon or zygote. Then the Paramecium starts to divide to produce daughter paramecia.

Hemixis
In this method fragmentation and division of macronucleus takes place without any activity of micronucleus.

Cytogamy
It takes place in two individuals. In this process micronucleus divides 3 times to produce 8 nuclei. in which 6 degenerate and remaining 2 fuse together to give zygote.

Asexual Reproduction
It takes place by binary fission method . At first, micronucleus divides into 2 nuclei by mitosis. Macronucleus divides into 2 by mitosis. The cytpharynx also divides into 2 parts. The cytoplasm is also divided into 2 parts. Then transverse constriction is made from two sides. New contractile vacuoles are formed. The constriction meet at centre and two daughter paramecia re produced.

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