Cell cycle

The ordered sequence in which this happens is the cell cycle. For this topic, you need to understand its three overall stages; you do not need to learn the named phases within mitosis.

A cell does not spend all its time dividing. It passes through a cell cycle: it grows and prepares for division, separates its copied chromosomes, then splits into two cells. Mitosis is the part in which the nucleus divides.

To grow, it must produce more cells, so its cells repeatedly pass through the cell cycle and divide. Cell division also allows worn-out or damaged cells to be replaced.

A multicellular organism grows mainly by increasing its number of body cells. These new cells do not appear from nowhere: every new cell is produced when an existing cell passes through the cell cycle and divides.