Question

Give the breif description of the life cycle of Paramecium Aurelia.

Answer 1

Life Cycle of Paramecium Aurelia:

• Paramecium aurelia is a microscopic, ellipsoidal, ciliated protozoan about 40μ broad and 130 μ long.
• Its genetic machinery consists of two diploid micronuclei each about 3 μ in diameter, and a single, polyploid macronucleus (20μ x 50μ) which contains about 500 complete sets of chromosomes.
• The macronucleus controls the physiology of the organism, whereas the micronuclei have important role in reproduction.
• P. aurelia includes both asexual and sexual reproduction in its life cycle.
• Its asexual reproduction is accompanied by binary fission, which includes the mitosis of both microunclei, amitosis of macronucleus and subsequent cytokinesis.
• The sexual reproduction of P. aurella is performed by conjugation. During conjugation pairing of two animals (conjugants) of different mating types takes place. In between both conjugants, a protuberance called preoral cone is formed in the oral region.
• The preoral cone establishes an inter-cellular cytoplasmic bridge, through which exchange of genetic material between the two individuals, takes place.
• Meanwhile, the macronucleus of each conjugant breaks down into a series of 50 or more fragments which eventually degenerate.
• Each of two micronuclei in both conjugants undergoes meiosis with the result that eight haploid nuclei are formed, but seven of them degenerate.
• The surviving nucleus of each conjugant migrates to preoral cone where it undergoes mitosis to produce two gamete nuclei.
• One of these, the stationary or female gamete nucleus returns to the interior of each conjugant, whereas the other migratory, mobile or male gamete nucleus passes into the cytoplasm of the mate.
• After this nuclear or genetic exchange, both conjugants separate, and fusion of both haploid nuclei occurs in each excom jugant.
• The diploid zygote nucleus of each exconjugant undergoes two successive mitotic divisions, forming four diploid nuclei.
• Two of the four nuclei of each exconjugant become macronuclei, while the remaining two nuclei become micronuclei.
• Soon, each exconjugant divides by transverse fission and two daughter cells, each with a macronucleus and a micronuclei are formed.
• The micronucleus of each of the daughter cells later on divides by mitosis to form two micronuclei.
• P. aurelia can undergo nuclear reorganization by internal self fertilization or autogamy without the pairing of animals.
• During autogamy, the macronucleus degenerates and both micronuclei of an individual undergo meiosis to produce eight haploid micronuclei.
• Out of eight micronuclei, seven degenerate.
• The remaining haploid nucleus divides by mitosis to form two haploid nuclei.
• Both haploid nuclei fuse to form a diploid fusion nucleus which behaves exactly in same manner as in exconjugants after conjugation.

Paramecium aurelia:

• They are unicellular organisms belonging to the genus Paramecium.
• They belongs to the phylum Ciliophora.
• They are covered in cilia which helps in movement and feeding.
• They reproduce either sexually, asexually, or by the process of endomixis.