Cell division is the first stage of growth in living organisms whereby cells divide to form new cells. In unicellular organisms cell division is a process of asexual reproduction. It leads to an increase in the total number of individuals. On the other hand, in multicellular organisms the division of all cells, other than the reproductive cells, is known as mitosis. In mitosis is cell division an aspect of growth and is accompanied by cellular enlargement and differentiation.
Two phases are very prominent in cell division, nl. karyokinesis, where the nucleus divide and cytokinesis, where the cytoplasm divide. Mitosis usually requires an hour or two for completion. The period between two cell divisions during which the cell grows and duplicates its chromosome material is called the Interphase. An interphase followed by cell division is known as the Cell cycle.
In plants, special cells divide in a region just behind the tip of the radicule or plumule, or in buds, so that new cells are formed that can grow and develop. The result is that the roots and stem increase in size (length and width) and buds can develop into flowers or into branch stems and leaves.
In animals, for example in human beings, mitosis takes place in special tissues in organs.
During the development of the embryo, there is continual mitotic division and growth of the cells, starting with the division of the fertilized egg. These divisions takes place in:
the skin,
long bones, and
in the lymph glands.
The formation of new cells is necessary for the following reasons:
multicellular plants and animals start life as single cells, the zygotes or fertilized egg cells; the process of Mitosis gives rise to many cells which differentiate to form tissues, organs and organ-systems of the organism.
mitosis results in an increase in size and growth of an organism,
cell reproduction is used to form new cells to renew certain tissues and to replace worn out cells
mitosis is also used as a form of asexual reproduction in some organisms like in unicellular Amoeba and multicellular Hydra as well as vegetative reproduction in plants.
mitosis results in the formation of two daughter cells with identical nuclei and chromosomes,
the stages in the division of the nucleus are called karyokinesis (karyon, nucleus and kinesis splitting or dividing)
the division of the cytoplasm is called cytokinesis,
at the end of mitosis, two daughter cells are formed that have identical nuclear material and the daughter cells are a result of cytokinesis which are half the size of the original parent cell,
the daughter cells have to grow to reach the size of the parent cell.