Cell - Explain role of mitosis and meiosis in growth, repair, and variation

Cell division is the process by which a parent cell divides into two or more daughter cells. It is essential for growth, repair, and reproduction in living organisms.

Mitosis (Equational Division): A single parent cell divides to produce two genetically identical daughter cells. The chromosome number remains the same ($2n \rightarrow 2n$).

Role of Mitosis in Growth: It increases the number of cells in an organism, allowing a single-celled zygote to develop into a complex multicellular body.

Role of Mitosis in Repair: It replaces old, dead, or damaged cells. For example, the healing of a wound or the constant replacement of red blood cells and skin cells.

Meiosis (Reduction Division): A parent cell undergoes two successive divisions to produce four daughter cells (gametes), each having half the number of chromosomes ($2n \rightarrow n$).

Role of Meiosis in Variation: During meiosis, 'crossing over' occurs where genetic material is exchanged between homologous chromosomes. This leads to genetic recombination and variation in the offspring.

Role of Meiosis in Reproduction: It ensures that the chromosome number of a species remains constant across generations by producing haploid gametes ($n$) that fuse during fertilization to form a diploid zygote ($2n$).