 Now, we will talk about the importance of cell division. Why cell division occur? There are three major objectives, development and growth, regeneration and asexual reproduction. Cells need to divide. There are few parts of our bodies or animals bodies which do not grow. They do not require a cell division as we previously talked about the neurons and nerve cells. They do not divide. They remain in G0 phase throughout their lives, so they do not divide, they do not make division. But many other cells of the body, they require a continuous growth, for example our skin cells, they need continuous growth, our skin cells are continuously falling down and new cells are forming, cells in our stomach, they are also very important cells and they are exposed to different pHs due to entrance of the food, its digestion and other processes. So the cells of stomach need to be replaced again and again in all of these tissues like the stomach or in our mouth or cheek cells on our skin and many other cell types they need to grow and for growth they need to divide and this is very important that they divide in same type of cells with same number of chromosomes. So mitosis is a very, very important process which is required for the tissue and the organ growth. For the tissue growth, for the growth of the organism as a whole, there is another requirement if sometimes organisms body is wounded, it is injured. For example we hit our hand on some hard surface and our finger is injured and animal has injured, when it is injured its skin cells are cut off, its muscles they are broken down or something and they have to be replaced. For wound healing we also need cell division, just like that many times the plants they are also wounded, eaten up by for example an animal cut down by a bio kit or otherwise they also need to replace their parts. So mitosis is very important in the growth of the tissues and in the wound healing. There is another very important process in which mitosis helps, few organisms can replace or remake their lost parts. For example starfish which have usually 5 arms, if its one arm is broken or cut off or we can say amputated by a predator it can remake its whole arm by the process of we call regeneration. It can regenerate its whole arm, it is able to regenerate the arm with the help of the cell division or the mitosis because we know that mitosis is the cell division in the somatic cells the cells other than the germline cells. In some other organisms the regeneration also takes place for example the lizards they also can replace their lost tail. Many times what happened that a lizard is escaping from its predator it is successful to escape but the predator somehow breaks down its tail. Lizards also replace their tail with the help of mitosis the cell division. So it means that organisms can divide their cells to produce new cells for the tissue growth, for the wound healing and for the regeneration of their lost parts. Lizards also use mitosis, few organisms also use mitosis for the asexual reproduction. There are few unicellular organisms which asexually reproduce by the help of this simple cell division the mitosis. So mitosis or cell division is a very important process. Now we see that what happen if there are errors in mitosis. There may be different types of errors in the mitosis cell division like particularly mostly what could happen that when the chromosomes divide at the centromere during the NFA's. When the chromosomes of course we know that each chromosome at that time consist of sister chromatids and for going towards the poles it have to be broken apart or it have to be cut off from the centromere into two sister chromatids and each sister chromatid have to go towards one pole. If sometimes or somehow by a mistake they are not cut off they are not broken at centromere and the whole duplicated chromosome goes towards one side then in one cell there will be more chromosome in one daughter cell there will be more chromosome and in the other daughter cell there will be less. Most probably these cells will not be able to survive. Now this process of cell division is highly regulated as we have seen in the process of mitosis and in the process of cell cycle particularly that there are different check points controlling mechanisms which always check that whether the cell is cell has completely or correctly completed the process as required for example during the G1 checkpoint which checks that whether all the materials required for DNA synthesis are complete or before the M phase or the division phase in the G2 phase are all the materials which are required for the mitosis the karyokinesis are they complete but sometimes what happen and in the M checkpoint the mitosis checkpoint itself which checks that whether the nuclear division is correctly completed but sometimes what happen that this regulation fails and if somehow at some place this regulation is not correct then the result will may be uncontrolled growth of cells the worst sequence is the uncontrolled growth of cells. If the cell cannot stop dividing after M phase it do not enter into a proper G0 phase and rest for sometime and then go to the interface in as normal but it grows randomly. It happens due to mutations there are certain types of mutations due to which mitosis the process of mitosis continues uncontrolled and the check points they are not properly checking their places where they have to check that whether everything is correct the result is this is the uncontrolled growth of cells not in the form of normal layers of cell but in the form of heaps the result of this is tumors we call these heaps of cells tumors if these tumors are just present but but they are they are not like growing further or they are damaging start damaging other tissues and second thing they do not break off from their places. These tumors are called benign tumors but sometimes what happens that these tumors they become we call malignant they become cancerous they start growing very fast their size increases a lot and the cells from these tumors they break off and go to the blood circulation and through blood circulation they reaches other tissues and make tumors there as well so when these these cells which are broken off from the original tumor they go to different tissues and they can make secondary tumors at these places we call them we call this state or situation metastasis which is the spread of the cancerous cells or the cancer which is the very dangerous stage at which our treatment of this cancer become very very difficult so uncontrolled growth of cell may result in very serious consequences.