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|Chapter Five: Cell Reproduction|
During their lifetime, cells undergo a process of growth which ends either in death or reproduction. Since the general stages of this cycle are the same for all eukaryotic cells, it has been called the cell cycle. It has two main stages. The first stage, mitosis, refers to the division of the nucleus and the DNA. The other stage is called interphase (which literally means "the phase between each division"), which is in turn divided into three smaller periods. The three periods, listed in the order in which they occur, are G1, S, and G2.
After a cell divides, the daughter cells enter a period of growth called the G1 period. Since each daughter cell is roughly half the size of the normal-sized parent, the daughter cells must grow and synthesize new organelles. Once the cell has grown to normal size, it may remain stagnant (stationary) in the G1 phase. However, usually some change (which is currently being researched) occurs in the cell which causes it to enter the S phase. The S phase simply refers to the time when the cell's DNA is replicated in preparation for cell division. Once this is completed, the cell enters the G2 phase, in which it synthesizes the structures required for cell division.