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Describe cell cycle.
Answer
The cycle of cell, growth and division is called cell cycle. The cell cycle is divided into four phases.

1. First gap phase (G1 phase) or presynthetic phase.

2. Synthetic phase (S phase)

3. Second gap phase (G2 phase) or Mitotic phase (M phase)

4. Cell division phase or Mitotic phase (M phase).

The G1, S and G2 phases together constitute the Interphase. This phase takes about 95% of the duration of cell cycle. The mitotic or M phase only lasts for about an hour. 

1. G1 phase. This stage starts from the birth of the daughter cell and ends upto the time when the cell begins to synthesis of DNA. It is the phase of initial growth in which RNA and proteins are synthesised. Its duration varies from 6 to 8 hours.

2. S phase. It is the period of synthesis of DNA. It lasts for 5-6 hours.

Describe cell cycle.

Fig. Cell cycle

3. Gphase. During this phase the centrioles, mitochondria, golgi bodies and other cytoplasmic organelles are doubled. Proteins are synthesised for the formation of astral rays and spindle and energy is stored for the cell division or M phase. The duration of this stage starts from the end of S phase upto the beginning of M phase. It lasts for 4-8 hours.

4. M phase or mitosis. It is the phase when the cell division takes place and this process gives rise to two daughter cells.  collectively form the cell cycle.