Only some cells in multicellular organisms retain the ability tom divide. Those that do, do not divide continuously, but undergo a regular cycle of division separated by periods of cell growth. This is known as the cell cycle and has three stages:
1. Interphase which occupies most of the cell cycle, and is sometimes known as the resting phase because no division takes place.
2. Nuclear division when the nucleus divides either into two (mitosis) or four (meiosis).
3. Division of the cytoplasm (cytokinesis) which follows nuclear division and is the process by which the cytoplasm divides to produce two new cells (mitosis) or four new cells (meiosis).
The length of a complete cell cycle varies greatly amongst organisms. Typically, a mammalian cell takes about 24 hours to complete a cell cycle, of which about 90% is interphase.
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