The importance of mitosis to living organisms is that it allows organisms to grow in size and repair themselves. When an organism grows, its cells do not grow larger; they divide to make more of themselves through the process of mitosis, or cell division.
Mitosis does not actually divide the cell into two. It mainly divides the nuclear contents. Mitosis occurs in several stages. When a cell enters mitosis, it has already made a copy of all its DNA. The nuclear envelope surrounding the nucleus then dissolves, and the DNA line up. The two sets of DNA are pulled apart toward opposite ends of the cell. A nuclear envelope then forms around each set of DNA. The cell can now be cleaved into two cells through the process of cytokinesis.