A cell is the structural and functional unit of life. New cells arise from the pre-existing cells by the process of cell division Cell division is an important phenomenon that occurs in all living organisms. In unicellular organisms, cell division directly produces two individuals thus; it is a means of reproduction.
In multi-cellular organisms, there are two types of cells the somatic cells or the body cells (which form the body of the organism) and the reproductive cells (gamete-producing cells). In multi-cellular organisms, life begins from a single cell, the zygote, which divides and re-divides into a number of cells to form a complete organism.
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Why Cells Divide?
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The cells divide to produce new cells. The new cells are produced for:
i. Growth:
Cell division produces new cells which grow and form a cluster of similar cells to form tissues and organs. This is essential for the growth of an organism.
ii. Replacement of Dead Cells:
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The existing cells in our body are destroyed regularly. These cells should be replaced by the new cells for the normal functioning of the body. Cell division helps in the replacement of dead cells.
iii. Repair of Tissues:
In case of injuries or normal wear and tear of tissues, cells divide and new cells fill up the broken cut ends to heal wounds. Thus, cell division is essential for the repair of the tissues.
iv. Reproduction:
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New cells arise from pre-existing cells. The sex cells (sperms and eggs) are formed because of cell division (meiosis). These sex cells form zygote after fertilization. Thus, cell division is essential for reproduction.
Types of Cell Division:
Two types of cell division occur in organisms mitosis and meiosis.
Mitosis occurs in somatic cells (as well as reproductive cells such as in spermatogonia and oogonia before entering meiotic cycle) leading to growth and development.
Meiosis occurs in reproductive cells leading to gamete formation.
Karyokinesis and Cytokinesis:
The cell division includes two events nuclear division or karyokinesis leading to division of parent nucleus into daughter nuclei; followed by the division of cytoplasm or cytokinesis leading to the division of the parent cell into daughter cells.