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Cell Division Part 2

Cell Biology - Cell Division Part 2

Mitosis:
It is a second phase of cell cycle and further divided into four phases:
1.  Prophase
2.  Metaphase
3.  Anaphase
4.  Telophase


Prophase:
·  It is a beginning phase and condensed chromosomes and nucleolus are observed
·  At the end of this phase, condensed chromosomes appears as two chromatids holding together with centromere and nucleolus disappears completely
·  Chromosomes migrates towards the nuclear membrane
·  If Centrosome is present, two units of it separate and migrate towards opposite poles. Plant cell do not contain Centrosome.
·  Centriole located at two different poles develop a bipolar spindle made up of cytoplasmic fibers which is made up of proteins
·  Nuclear membrane disintegrate and chromosomes spreads in all over the cell area


Metaphase:
·  It is also called as prometaphase
·  Centromere of each chromosome migrates and attached to the equatorial plane of the bipolar spindle
·  Chromatids float free


Anaphase:
·  Centromere of each chromosome holds two chromatids and divides
·  Each chromatid has its own centromere and they migrate towards opposite poles due to contraction of spindle fibers
·  Chromatid with its independent centromere is known as a chromosome
·  At the end of the phase, the number of chromosomes are same as the number of chromosomes occurred in the original cell


Telophase:
·  Each chromosomes uncoils and chromatin network appears
·  A nucleolus develops on the nucleolar organizer region of a specific chromosome
·  At the end, nuclear membrane is reformed and two nuclei exist at two polar region


Cytokinesis:
·  It is a process of dividing nuclear region and disappearance of cytoplasmic spindle
·  In plant cell, Cytokinesis occurs at the centre of the cell and middle lamella made up of protein is developing from centre towards periphery of the cell. A cell wall is later formed on two sides of middle lamella.
·  In animal cell, Cytokinesis occurs by constriction of cytoplasm from peripheral region towards centre of the cell and finally two cells become separated. 


Significance of Mitosis:
·  The number of chromosomes is same in both the cell
·  Cells maintain their cell size
·  Degenerated cells are replaced and growth and development occurs
·  Single cell develops its multicellular body by forming tissues and organs


Self study:
Example-1: In which of the following cell division, the number of chromosomes remain same as it was in the parent cell?
a)  Mitosis
b)  Meiosis
c)  Interphase
d)  Metaphase

Answer: In mitosis type of cell division, the number of chromosomes remains same as it was in the parent cell.


Example-2: In prophase, two Centriole locates at two poles and develops _________________
a.  Cytoplasmic fibers
b.  Chromatin
c.  Bipolar spindle
d.  Centrosome

Answer: In prophase, two Centriole locates at two poles and develops bipolar spindle.


Example-3: In which of the following phase, nucleolus develops on the nucleolar organizer region?
a)  Metaphase
b)  Telophase
c)  Prophase
d)  Anaphase

Answer: In Telophase, nucleolus develops on the nucleolar organizer region.


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