Note on Mitosis

 

Mitosis is a process by which a cell divides into two cells. All organisms grow by cell division. It takes place in all parts of plants and animals.

 

It has two parts:

 

1. A) Karyokinesis (Division of Nucleus)

1. B) Cytokinesis (Division of Cytoplasm)

 

 

1. A) Kagokinesis:

 

It is the division of nucleus and has followings phases:

 

Prophase:

 

1. i) In this phase coiling of chromosomes starts and they becomes shorter and thicker.

 

1. ii) Microtubules in cytoplasm arrange to form spindle.

 

iii) In animal cells fibers originate forming a star shaped aster.

 

1. iv) Spindle fibers, centrioles and aster form mitotic apparatus.

 

1. v) In this phase nuclear membrane and nucleoli disappear.

 

1. vi) In this phase chromosomes consists of chromatids attached on centromere.

 

 

Metaghase:

 

1. i) Chromosomes arrange themselves on equator and become more visible.

 

1. ii) Chromosomes are attached on their centromere to one spindle fiber from each pole.

 

 

Anaphase:

 

1. i) Spindle fiber shrinks and becomes short.

 

1. ii) Chromatids start separating.

 

iii) Each separated chromatid doubles itself to form chromosomes of daughter cell.

 

1. iv) Chromosomes moves to their opposite poles.

 

 

Telophase:

 

1. i) Chromosomes reached to their opposite poles.

 

1. ii) They become less visible.

 

iii) The nucleoli reappear.

 

1. iv) The nuclear membrane reappears.

 

1. B) Cytokinesis:

 

 

This is the division of cytoplasm.

 

1. i) In plant cells cytoplasm divides by the formation of cell plate, which extends across the equatorial plane until the two daughter cells becomes separated.

 

1. ii) In animal cells cytoplasm divides by furrowing or inward pinching of the membrane resulting into two daughter cells. Thus two daughter cells formed are identical to their parent cell in all respect.

 

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