Introduction to Cell Division

Every multicellular organism, however large or complex it eventually becomes, begins life as a single cell — the zygote formed at fertilisation. Everything that follows — the growth of a tiny embryo into a full-grown organism, the healing of a wound, the replacement of worn-out tissue — depends entirely on that starting cell, and the cells it produces, dividing again and again. This observation is captured in the cell theory's key statement that every cell arises only from a pre-existing cell: cells are never created from scratch, they are always the product of an earlier cell dividing. Understanding how a cell divides, and the different ways it can do so, is therefore central to understanding growth, repair, and reproduction in living organisms.