Question

What is cell division? Why is cell division necessary?

Answer 1

Hint: Cell division is the very important process in reproduction and growth. All organisms start their life from a single cell. Fertilized egg or zygote is single celled. It divides repeatedly to form a large number of cells.

Complete answer:
Cell division is a process by which a parent cell divides into two or more daughter cells. Cell division is usually a part of a large cell cycle. There are two types of cell division:
Mitosis:
-It is also called somatic division because it occurs during formation of somatic cells or body cells.
-Mitosis is an equational division in which a parent cell divides into two identical daughter cells. Each of which contains the same number and kind of chromosomes as are present in the parent cell.
-The development of an individual from zygote to adult stage takes place through mitotic cell divisions.
-It occurs in two steps:-
Karyokinesis (nuclear division)
 Cytokinesis (division of cytoplasm)

Mitosis is divided into four stages:-
Prophase,
metaphase,
anaphase and
telophase.
Cytokinesis is of two types:-
Cleavage cytokinesis (occurs in animals and some lower plants).
Cell plate cytokinesis (occurs in plants)

Meiosis:
-The reduction division occurs only in the reproductive cells at the time of gamete formation.
-By this process four daughter cells are formed from the single parent cell and are genetically different from the parent.
-The chromosome number in them (the daughter cell or gametes) reduces to half (haploid).
Meiosis consist of two cell division:- Meiosis I and Meiosis II

Meiosis I	Meiosis II
Prophase I	Prophase II
Metaphase I	Metaphase II
Anaphase I	Anaphase II
Telophase I	Telophase II

Cell division is necessary because of following reason:-
-A cell has to divide to maintain continuity from one generation to another generation.
-In multicellular organisms, it plays an important role in the formation of gamete.
-Old and worn out cells are regularly repaired by means of cell division.
-In unicellular organisms like amoeba, cell division is the means of reproduction whereas in multicellular organisms; it is the means of tissue growth and maintenance.
-Mitosis maintains a similar number and type of chromosomes in all cells.
-Meiosis produces lots of variation due to independent assortment of chromosomes and crossing over.

Note: Rudolf Virchow gave cell lineage theory that new cells arise by division of pre-existing ones:- omnis cellulae cellula. As a result of meiosis four cells are formed and due to mitosis only two
Meiosis produces lots of variation due to independent assortment of chromosomes and crossing over.
cells are formed.