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| Cell Cycle |
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| Every cell that is capable of undergoing division passes through a cyclic sequence of events involving growth and division. It is called Cell Cycle. It encompasses the entire sequence of events that occur in a cell from the time it is formed from its parent cell till the time of its own division into daughter cells. |
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| Cell cycle has three main stages namely: |
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| Interphase |
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| This is a period of intense synthesis and growth in the cell. The cell produces many materials required for its own growth and activities. The genetic material DNA replicates during interphase. |
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| Karyokinesis |
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| It is the process of nuclear division, which involves separation of chromatids and their redistribution as chromosomes into daughter cells. |
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| Cytokinesis |
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| It is the process of division of the cytoplasm to result in the formation of daughter cells. |
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| fig. 17.1 - The Cell Cycle |
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| The length of the cycle depends on the nature of cell and various external factors like temperature food and oxygen availability. Bacterial cells may divide every 20 minutes, epithelial cells living the small intestine divide once in 8 to 10 hours, onion root tip cells take about 20 hours to divide. Some specialised cells like the nerve cells never divide. |
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