Very similar is the situation by repairing (or mostly replacing) tissues and cells that are either damaged, bad, missing or old. That happens not only by some “strange” organisms (for example by the sea star when one or more of its arms are being cut), but you can also observe it on yourself, for example when you cut your finger. Well, if you cut it down as a whole, it will not grow back to you, of course, that can happen neither to most plant nor to most animal or fungi. Therefore I used the word strange for describing the skill of some beings to replace the whole organ. This ability is present by only a small part of the whole multicellular organisms system. The third, also very important function of mitosis is the asexual reproduction of organisms as whole (not only their parts), when the new offspring grows directly from the parent and is genetically identical to it. This kind of reproduction, used by many types of plants (different kinds of berries, banana palm, potato, the flower fuchsia and many other) and a few kinds of animals (for example one sea brown sun-like animal with a very interesting name which I cannot remember on), is exploited very often as the only way how to reproduce certain, mentioned upper, plants.
Although being very important, mitosis has a bad side, sort of a bad importance, as well; I mean the uncontrolled division, which ends with the disease cancer. Normally, there is a major external factor for control of the cell division – the physical contact. When, for example, filling a gap of skin being cut, cells divide until they touch each other, then they stop dividing and that is how a layer one cell thick is formed. By the uncontrolled division cells fail to stop growing and even dividing on contact with other cells. They create masses called malignant tumors that attack and invade healthy tissues. These tissues are then “killed” (destroyed) – that is why and how cancer is so dangerous for the organism.
The mitosis, consisting of its four phases, is very important not only by reproduction of whole organisms, but also by repairing some of their parts. It is considered to be at least equal to the meiosis and the sexual reproduction. However, it has a bad side, as well, and that is the maybe most problematic disease, the cancer. .