4. Cytokinesis and significance of mitosis

Mitosis completes duplicated chromosomes into daughter nuclei, But the cell itself is divided into daughter cells.

The process of mitosis is a great significance in the life of an organism.
 

Maintenance of chromosome number: Mitosis involves an equational division resulting in diploid daughter cells' formation with the same chromosome number as that of a mother cell. It helps to maintain the diploid ($2n$) number of chromosomes in daughter cells.

 

Growth: All the somatic cells are formed by mitosis, and thus it plays a vital role in the growth, organ development and increase in body size of a multicellular organism.

 

Repair: This process helps to repair the damaged and wounded tissue by renewal the lost cells.

 

Regeneration: It is involved in the replacement of old and dead cells by forming new cells.

 

Reproduction: Unicellular organisms are multiplies by this method.

• Cells of the eye lens, nerve cells of  cerebral cortex and most muscle cells last a lifetime but once dead are not replaced.
• Epithelial cells lining the gut last only about $5$  days.
• Average life of other gut cells is about $15$ years.
 

• Skin cells  - about every two weeks.
• Bone cells - about every ten years.
• Liver cells - about every $300$ – $500$ days.
• Red blood cells last for about $120$ days and are replaced.