Cell division is also known as mitosis. It occurs in cells with a nucleus, known as Eukaryotic cells. It is a process by which cells produce new, genetically identical cells that are smaller than the parent cell due to the division of the cytoplasm. However, this process is necessary to replace old, worn out cells. It is also necessary during the process of growth. When an organism grows, for example a human, the bone cells divide forming new bones cells and once the skeleton has grown, the muscles and skin cells also divide, eventually adding height to the organism. Cell division is also important in organisms like bacteria, which are Prokaryotic cells because they lack a nucleus. In this case, cell division is known as binary fission and is a method of asexual reproduction. One cell gives rise to two daughter cells. This is a way of producing more individuals. Neurons also known as nerve cells stop being able to reproduce shortly after birth. However, before that time, neurons are produced by mitosis.