Question

Why do cells increase in number and not in size?

Answer 1

The growth of any living organism occurs by the process of mitotic cell division. During mitosis, one cell divides to form two identical daughter cells. All cells perform mitosis and in this way the number of the cells in the body increases and causes the organism’s growth. To maintain homeostasis in the body, the size of the cells is controlled by various mechanisms.

Complete answer:
The growth of any living organism occurs through cell division. The growth rate of the cell is controlled by a variety of genes. As the cell grows, the surface area to the volume ratio gets smaller. If the cell continues to grow beyond a certain limit, entry of oxygen and food materials across the membrane will be slowed down. Larger cells will require specialized organs to increase the surface area available for exchange processes. Since this is not possible, cells grow only to a certain size and after that it divides.
Cell division leads to exponential increase in cell number. More cells mean more synthesis of biomolecules, without disturbing the homeostasis of the organism. This is the reason why cells increase in number and not in their size.

Note:
Some cells can grow to very large sizes through a specialized cell cycle called endoreplication. In this division, the genome is replicated during the S phase but there will be no M phase or cytokinesis. The resulting cell will have many copies of the genome and become polyploid. Polyploidy is a common phenomenon seen in cancer cells. The oocytes of egg laying animals are also unusually large in size.