December 3, 2015

Junior Inter Zoology - Important 4 Marks Questions for IPE Exams

Q: Draw labelled diagram of Paramecium.

Q: Describe the process of transverse binary fission in Paramecium.
A: Transverse binary fission takes place in Paramecium during favourable conditions.
The division of nucleus during binary fission is known as karyokinesis and that of
cytoplasm is called cytokinesis.

Paramecium is commonly called slipper animalcule and is a common protozoan in fresh water bodies. It has an oral groove, cytostome and cytopharynx on the oral surface,
besides two contractile vacuoles (one in the anterior part and the other in the posterior part). There are two nuclei, viz., macronucleus (large, bean shaped, polyploid) and a micronucleus (small, round, diploid). Body is covered by pellicle, below which infra ciliary system and trichocysts are present. Cilia are present all over the body.

During binary fission, Paramecium stops feeding. Then micronucleus divides by mitosis and macronucleus by amitosis. Oral groove disappears. Now a constriction appears in the middle, grow deep and divides the parent Paramecium into two daughter Paramecia. The daughter formed from the anterior half of the parent is called proter and that is formed from the posterior part is called opisthe. Proter receives the cytostome and cytopharynx and anterior contractile vacuole of the parent. Opisthe receives the posterior contractile vacuole of the parent. Proter develops a new oral groove, and a contractile vacuole in the posterior part. Opisthe develops an oral groove, cytostome and cytopharynx, and a contractile vacuole in the posterior part.

Transverse binary fission in Paramecium is called homothetogenic fission because, the
plane of fission is at right angles to the long axis of the body. The fission is also called perikinetal fission because it occurs at right angles to the kineties.

If conditions are favourable, binary fission is completed in about two hours and
Paramecium can produce about four generations of daughter Paramecia in a day.

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