Multicellular organisms grow by producing more cells. As children, we get taller every year. That growth happens only because our bodies keep adding new cells. A sapling becomes a tree for the same reason.
But even after an organism grows up, its cells continue to divide. That's because cells wear out or get damaged.
Read more: Life Cycle of a Cell - Replacing Cells, Cell Division, Growth and Repair:, Mitosis, Specialized Sex Cells, Meiosis, Plant Sex Cells
