Mitosis.

Mitosis is the process in which a cell's nucleus replicates and divides in preparation for division of the cell. Mitosis results in two cells that are genetically identical. Mitosis is necessary for growth for repair and replacement of damaged or worn out cells. All multi-cellular animals; plants, fungi, and protists, which begin life as single cells, carry out mitosis to develop into complex organisms containing billions of cells. Mitosis occurs in fully-grown organisms by maintaining …

…growth factor, for example, stimulates the growth of nerve cells during embryonic development, but has no effect on other cells. Others, such as epidermal growth factor, control division in a variety of cells. Understanding the production of growth factors and their precise mode of activity pose significant research challenges. As scientists learn more about the mechanisms for normal cell division, they gain insight into the causes of the unregulated cell growth that leads to cancer.