Why do Cells Divide?
Humans have about 10^14 cells. There are many types of cells in our body in each and every organ. For example, skin has skin cells, hair has hair cells, and the kidney has kidney cells, and so on. In adult humans, adult nerve and muscle cells do not divide at all. Liver cells divide once a year. Blood cell precursors in the bone-marrow divide more than once per day, and the same holds true even for cells lining the gut.
For growth to happen, body cells either have to increase their size, or divide, but all cells (besides a few certain cells) choose to divide in nature. Cells divide for a few reasons. Cells divide to replace the old worn out cells with new cells. Cells during their metabolism obtain nutrients, and get rid of waste through a process called diffusion. Diffusion will be faster in a short distance, and slower over long distances. So if the size of the cell increases instead of dividing, due to its giant nature, the diffusion will be too slow and the wastes would poison the cell to death. Deoxyribonucleic acid, or DNA, is already programmed into every cell to provide the code for the proteins necessary for the cell’s survival. If the cell size increases, the proteins needed for building the cell membrane would be more, and the available DNA would not be sufficient. So the cell divides to generate another copy of DNA that can manage to code for proteins of the new cell. Proper surface area to volume ratio should be maintained for each cell to carry out its functions and survive. This ratio should be small to enable the cell to excrete the wastes properly, and get sufficient nutrients for the cell’s metabolism. So, to maintain surface area to volume ratio, cells divide. It is a universal truth that in nature ‘all cells come from preexisting cells’. So cells divide in order to make new cells from the existing one cell, and resemble it.
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