Notes, Exercises, Videos, Tests and Things to Remember on Reproduction in Paramecium
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It reproduces asexually by transverse binary fission and sexually by conjugation.
It is a common method of reproduction in Paramecium which occurs during favourable condition. A fully grown Paramecium is divided into two daughter individuals. Division occurs at the right angle to the longitudinal axis of the body. Nuclear division is followed by the cytoplasmic division.
Paramecium stop feeding and its oral groove disappears. Macronucleus divides by amitosis and micronucleus divides by mitosis. After division, they move towards the opposite end. At the same time, the constriction develops at the middle part of the body which divides cytoplasm into two equal parts. In this way, two daughter Paramecium are produced. One form anterior end called protor and another from posterior end called opisthe. They are of equal size and contains a complete set of cell organelles as in parents. Oral groove and cytopharynx are newly formed. One contractile vacuole goes to protor and another to opisthe. Other two are newly formed.
The whole process is completed within 2 hours and may occur one to four times a day.
It is a temporary union of two individuals for mutual exchange of genetic materials. It occurs during unfavourable conditions. It involves following steps:
In this way, 8 parameciums are produced as a result of conjugation. They are metabolically active and can undergo repeated binary fission.
In conjugation new and metabolically active macronucleus is produced by reorganization of micro nuclear materials.
In conjugation old, weak and defective macronucleus is replaced by new one which can control metabolism growth and the environment. Because of this paramecium is rejuvenated i.e it gains the previous vigority.
In conjugation, genetic materials are exchanged between Paramecium of opposite mating types. It brings variation in daughter individuals due to genetic recombination.