With the help of suitable diagrams, explain the mitosis in detail.

Mitosis is the cell division in somatic cells in which one cell divides into two daughter cells, each with the same number of chromosomes as the parent cell. It has two parts: karyokinesis (division of the nucleus) and cytokinesis (division of the cytoplasm).

Karyokinesis has four phases:

1. Prophase: chromosomes condense and become visible as thread-like structures, each made of two sister chromatids. The centrioles move to opposite poles and spindle fibres start forming. The nuclear membrane and nucleolus begin to disappear.
2. Metaphase: the nuclear membrane disappears completely. Chromosomes become fully condensed and arrange themselves in the equatorial plane of the cell. Spindle fibres attach to the centromere of each chromosome.
3. Anaphase: the centromere of each chromosome splits, and sister chromatids separate. They are pulled to opposite poles by the spindle fibres, and now each is a separate chromosome.
4. Telophase: chromosomes reach the poles and uncoil (become thin). Nuclear membrane and nucleolus reappear around each set, so two nuclei are formed. Spindle fibres disappear.

Cytokinesis: the cytoplasm divides. In animal cells, a furrow forms in the middle and the cell is pinched into two. In plant cells, a cell plate forms in the middle.

Diagrams: draw one labelled diagram for each phase: prophase (condensed chromosomes, centrioles, disappearing nuclear membrane), metaphase (chromosomes in the middle with spindle fibres), anaphase (chromatids moving to the poles), telophase (two nuclei forming) and cytokinesis (two daughter cells).

Mitosis helps in growth, repair of tissues and replacement of old cells.