MITOSIS AND MEIOSIS
Each cell thus acquires its structure and ability to function because of the organisation of its membrane and organelles in specific ways. The cell thus has a basic structural organisation. This helps the cells to perform functions like respiration, obtaining nutrition, and clearing of waste material, or forming new proteins. Thus, the cell is the fundamental structural unit of living organisms. It is also the basic functional unit of life.
Cell division
New cells are formed in organisms in order to grow, to replace old, dead, and injured cells, and to form gametes required for reproduction. The process by which new cells are made is called cell division. There are two main types of cell division:
1. mitosis and
2. meiosis.
The process of cell division by which most of the cells divide for growth is called mitosis. In this process, each cell called the mother cell divides to form two identical daughter cells (Fig. 5.7). The daughter cells have the same number of chromosomes as the mother cell. It helps in the growth and repair of tissues in organisms.
Figure 5.7: Mitosis
Specific cells of reproductive organs or tissues in animals and plants divide to form gametes, which after fertilisation give rise to offspring. They divide by a different process called meiosis which involves two consecutive divisions. When a cell divides by meiosis it produces four new cells instead of just two (Fig. 5.8). The new cells only have half the number of chromosomes than that of the mother cells. Can you think as to why the chromosome number has reduced to half in daughter cells?
Figure 5.8: Meiosis
Source: This topic is taken from NCERT TEXTBOOK