The process by which cells increase their number is called cell division.

Cell division is a vital process that allows organisms to grow, repair damaged tissues, and reproduce. It is a tightly regulated process that ensures the accurate distribution of genetic material from the parent cell to the daughter cells. The two main types of cell division are mitosis and meiosis.

Mitosis:
Mitosis is a type of cell division that occurs in somatic (non-reproductive) cells. It results in the formation of two identical daughter cells, each with the same number of chromosomes as the parent cell. The process of mitosis involves several stages:

1. Interphase: This is the phase before cell division where the cell prepares for division by growing in size, duplicating its DNA, and synthesizing proteins.

2. Prophase: In this stage, the chromatin (uncoiled DNA) condenses to form visible chromosomes. The nuclear membrane disintegrates, and the centrioles move to opposite poles of the cell, forming spindle fibers.

3. Metaphase: During metaphase, the chromosomes align along the equator of the cell. The spindle fibers attach to the centromeres of each chromosome, ensuring their proper distribution.

4. Anaphase: In anaphase, the spindle fibers contract, separating the sister chromatids of each chromosome. The separated chromatids are pulled towards opposite poles of the cell.

5. Telophase: Telophase marks the end of mitosis. The chromosomes reach opposite poles of the cell, and a nuclear membrane forms around each set of chromosomes. The cytoplasm begins to divide.

6. Cytokinesis: In this final stage, the cytoplasm fully divides, resulting in the formation of two separate daughter cells. Each daughter cell contains a complete set of chromosomes.

Meiosis:
Meiosis is a specialized type of cell division that occurs in reproductive cells (gametes). Its purpose is to reduce the chromosome number by half, ensuring the production of genetically diverse offspring. Meiosis consists of two successive divisions, known as meiosis I and meiosis II, resulting in the formation of four haploid daughter cells.

In conclusion, cell division is a complex process that involves the replication and distribution of genetic material to ensure the growth and reproduction of organisms. Mitosis is responsible for the growth and repair of somatic cells, while meiosis is involved in the production of gametes for sexual reproduction.