CELL DIVISION

           Growth and development are characteristic features of cells. During this period, the cells increase both in numbers and size. Most of the living organisms are made up of number of cells therefore, if a single cell has to become multicellular, they must undergo repeated cycles of growth and division. Such cycle is known as cell cycle. This helps the organism not only to increase the cell number and size but also transfer genetic information from parents to off springs (sexual reproduction).

Hence, cell division is important in a living organism for

Growth and development

Reproduction and

Tissue renewal (in mature organisms)

The cell cycle is essentially divided into two periods – (a) Interphase and (b) Division phase 

(a)Interphase

1. It is known as non-division phase or resting phase.

2. It lasts for more that 95% of the duration of cycle.      

3. Although it is called as resting phase, but the cell is biochemically very active. During this phase, the cell prepares itself for the ensuring cell division and synthesizes various biomolecules including two similar copies of DNA.

4. It‘s divided into G₁ phase (“First –Gap”) , the  S phase (Synthesis) and G₂ phase (Second Gap)

 (b)Division phase

1. It is also known as M. phase or Mitosis phase.

2. It lasts for only 5% of the duration of cycle.

3. The division phase consists of two phases –M-phase (or Mitosis phase) with division of nucleus or karyokinesis and division of cytoplasm or cytokinesis. M-phase is further subdivided into Prophase (“meta” –between), Ana-phase (“ana-back) and Telophase (“end”). Howard and Pele divided cell cycle into these four phases.