Cell division is a fascinating biological process, and is the building block for complex life. The amount of time it takes for cell division to completely take place ranges widely, depending on the species involved: some bacteria, for example, can complete cell division in 20 minutes, while mammals such as humans may take 12-24 hours. This is a reflection of the complexity of the cells, but also the purpose of the cell division: bacteria need to divide rapidly to reproduce and grow, while adult humans are not in a growth stage, and therefore do not need to produce as many new cells.

There are two primary types of cell division. The type of cell division most people have in mind when they think of cells dividing is mitosis, a process in which a single parent cell divides itself into two identical daughter cells. This is accomplished by doubling the chromosomes within the parent cell and then physically splitting the cell in two. The other type of cell division is called meiosis, and it results in an end product of four daughter cells which can be used for reproduction, as each daughter cell only contains half of the necessary DNA for life.

In the case of bacteria and rapidly growing organisms like a fetus or a young animal, cell division takes place much more rapidly. The organism cannot grow and thrive without a rapid replication of cells, especially in the case of an embryo. Fully grown organisms divide cells on a much slower scale, to slowly renew the body, except in areas like the skin and bone marrow, which are constantly generating new cells. If an injury is sustained, the cells can divide more quickly to heal the area.

Cell division can get out of control. This rapid growth of cells is known as cancer, and produces characteristic clusters of cells that take the form of tumors and other growths which can kill if left untreated. The reason for out of control cell division is unknown, although scientists have shown that some substances can stimulate rapid cell division. These substances, or carcinogens, are required by law in many places to be labeled as a health risk. The mutated cells which double into cancers must also be completely eliminated from the body for the risk to be reduced to zero, as the cells may continue to reproduce if left alone. For this reason, many cancer treatments are very radical, to ensure that all of the harmful cells are excised from the body to prevent a recurrence.