Question

Explain various phases of mitosis

Answer 1

Gr. Mitos = Wrap thread
This is the most common type of cell division that occurs both in somatic and germ cells. It results in the formation of two equal daughter cells in which the chromosomes number remains unchanged. The term “mitosis” was coined by Walther Flemming (1882).

The mitosis can be studied as follows-

A) Karyokinesis:

It involves division of the nucleus. It is further divided into four phases –

1. Prophase – The chromosomes become visible like thin and long threads due to dehydration. The centromere is distinct. The nuclear membrane and the nucleolous finally get disintegrated. Both the centrioles reach ultimately to the opposite poles. The centrosphere part forms the arsters and the spindle fibres (Fig. 11.3).
2. Metaphase – Further shortning and thickning of the chromosomes due to spiralization and chromatids become distinct. Attachment of the spindle fibres to the centromere parts of the chromosomes. The chromosomes get arranged at the equitorial plate (Meta phasic plate) with help of the spindle fibres.
3. Anaphase – The centromeres divide to form daughter chromosomes. The daughter chromosomes separate and begin to move towards the opposite poles. Gradually, the daughter chromosomes reach to the respective poles
4. Telophase – Disappearance of the asters and the spindle fibres. Reformation of the nuclear membrane and the nucleolous. The chromosomes become long and thread like due to despiralization. Finally, the chromosomes become invisible due to hydration. The parent cell has two distinct nuclei in this stage.

(B) Cytokinesis:

The karyokinesis is followed by cvtokinesis which divides the cytoplasm into two almost eqal parts. the cytokiness is different in the animal cells and plant cells. In the plant cells the cytkinesis beings wth the formation of cell plate. In the animal cells, it beings with the formation of a peripheral groove. In plant cells, the granules of calcium & magnesium pectate get accumulated during formation of cell plate.

Significance of Mitosis:

1. The mitosis helps in body growth by forming new cells.
2. In mitosis, the number of the chromosomes remain unchanged. Hence, the duaghter cells become similar to the parent cell.
3. The mitosis help to maintain proper karvoplasmic index in a cell.
4. The mitosis helps in the repairing of worn out tissues & healing of wounds.