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Cell Cycle and Cell Division

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What is G0 (quiescent phase) of cell cycle?

The G0 or quiescent phase is the inactive stage that some cells enter in the adult animals. the stage is characterised by cells that do not exhibit division or proliferation but are metabolically active. They only proliferate when called on to do so depending on the requirement of the organism. 


What is the average cell cycle span for a mammalian cell ?

24 hours is an average duration. The cell division phase lasts only for one hour while interphase lasts for 95% of the duration of the cycle. 

Describe the events taking place during interphase. 

Interphase is the resting stage of the cell cycle. It covers 95% of the total duration of a cell cycle. It involves a series of changes that prepare a cell for division. It is the period during which the cell experiences growth and DNA replication in an orderly manner. Interphase is divided into three phases.

(i) Gphase

(ii) S phase

(iii) Gphase

Gphase - It is the interval between mitosis and initiation of DNA replication. It is the stage during which the cell grows and prepares its DNA for replication. In this phase, the cell is metabolically active but there is no replication of the DNA.

S phase - It is known as the synthesis phase as it is the stage during which DNA synthesis occurs. In this phase, the amount of DNA (per cell) doubles, but the chromosome number remains the same.

Gphase - In this phase, the cell continues to grow and prepares itself for the division. The proteins and RNA required for mitosis are synthesised during this stage.


How does cytokinesis in plant cells differ from that in animal cells?

Cytokinesis in animal cell

Cytokinesis in plant cell

1. It occurs by furrow method.

2. The constriction in plasmalemma is formed by contraction of microfilaments.

3.Cleavage starts at the periphery and then moves inward, dividing the cell into two parts.

1. It occurs by cell plate method.

2. No constriction is formed.

3. Cell plate formation starts at the centre of the cell and grows outward, toward the lateral walls.



Can there be mitosis without DNA replication in ‘S’ phase ?

No, mitosis cannot occur without DNA replication in S phase. For the formation of new cells additional DNA is required and it is very necessary to maintain the chromosomal number in the dayughter cells. thus, mitosis cannot occue without the duplication of DNA in the S phase