When you grow, your cells don't get bigger. You just have more of them. In fact, if you think about it, you started life as one single cell! So where do all these new cells come from? Most body cells can divide to make two perfect copies. These new cells can go on to divide again and again. Through cell division existing cells can make huge numbers of new cells quickly. They do this anywhere your body is growing, or to replace damaged or worn out cells. First, a cell has to make a duplicate set of genes. All the genes in a cell's chromosomes need to be copied perfectly. Then the cell can split into two new cells, each with a complete set of genes. These new cells can divide over and over again until there is the right number of cells. When you think what is actually happening, it's no surprise that growing sometimes seems like such hard work! This kind of cell division is called mitosis. It makes cells that are identical copies, complete with a full set of 23 pairs of chromosomes. Cell division by mitosis