science note cell division grade 10

Cell-division

The formation of new cells from persisting cell is called cell division. It is of two types. They are as follows.
i) Mitosis cell division (mitotic cell division)
ii) Meiosis cell division (meiotic cell division)
i) Mitosis cell division (mitotic cell division)

The cell division in which daughter cells are formed from a mother cell is called mitosis cell division (mitotic cell division). In this cell division, the number of chromosomes in each daughter cell is equal to the number of chromosomes in each mother cell. This cell division occurs in somatic cell.
ii) Meiosis cell division (meiotic cell division)

The cell division in which four daughter cells are formed from the a mother cell is called Meiosis cell division (meiotic cell division).In this cell division, the number of chromosomes in each daughter cell is half in comparison to the number of chromosomes in mother cells. This cell division occurs in reproductive cell.
In details.

i) Mitosis cell division (mitotic cell division)

i) Mitosis cell division (mitotic cell division) completes in four phases. They are as follows.
i) Prophase
ii) Metaphase
iii) Anaphase
iv) Telephase
i) Prophase

a) Chromosomes becomes shorter and thicker
b) The nucleus membrane starts to disappear and spindle fibre starts to appear.

ii) Metaphase
a) Chromosomes become further shorter and thicker.
b) Nucleus membranes completely disappear and spindle fibres completely appear.
c) Chromosomes remains attached at a point is called centromere.

iii) Anaphase
a) cenromere divides and chromosomes starts to move towards opposite poles by the contraction of spindle fibre.
b) Chromosomes becomes further shorter and thicker.
c) Migrated chromosomes appears in U,V,I and J shape.

iv) Telephase
a) Migrated chromosomes reach completely to opposite poles.
b) Nuclear membranes start to appear and spindle fibres start to disappear.
c) Chromosomes become thin, long and thread like structure.

Note:
Interphase:
It is the initial stage of cell division and is known as resting stage of cell. In this cell stage, all metabolic activities occurs except division. Chromosomes become long, thin and thread like structure. Nucleus membrane is distinct at this stage. In this stage, replication of chromosomes takes place. So, it is possible to have equal number of chromosomes in mother cell and two daughter cells.
Importance of Mitosis cell division (mitotic cell division)

a) It helps in wound healing.
b) It helps in growth and development of body of living being.
c) It helps in the replacement of old, dead and decaying cells.
d) It helps in asexual reproduction.
e) It helps to maintain genetic stability.

i) Meiosis cell division (meiotic cell division)
It completes in two stages. They are as follows.
a) Meiosis (I)
b) Meiosis (II)

a) Meiosis (I)
It completes in four stages. They are as follows.
a) Prophase (I)
b) Metaphase (I)
c) Anaphase (I)

d) Telephase (I)
A) Prophase (I)

It completes in five sub-phases. They are as follows.
i) Leptotene
a) Chromosomes become thin, long and thread like structure.
b) The size and volume of nucleus increases.

ii) Zygotene
a) Chromosomes become shorter and thicker.
b) Paring of homologous chromosomes takes place which is called synapsis. (Synapsis occurs)

iii) Pachytene
a) Chromosomes become shorter and thicker.
b) The exchange of genetic materials between homologous chromosomes takes place Which is called crossing over. (Crossing over takes places)

iv) Diplotene
a) Chromosomes become further shorter and thicker.
b) Crossing over takes place.
c) The separating chromosomes are stilled attached at one or more points which is called chaismata.
d) The paired homologous chromosomes began to move away from each other.

v) Diakinesis
a) The chromosomes become further shorter and thicker.
b) Nuclear fibre starts to disappear.
c) Spindle fibre starts to appear.

B) Metaphase (I)
a) Chromosomes become further shorter and thicker.
b) Nuclear membranes completely disappear and spindle fibres completely appear.
c) Chromosomes remains attached at a point is called centromere.

C) Anaphase (I)
a) cenromere divides and chromosomes starts to move towards opposite poles by the contraction of spindle fibre.
b) Chromosomes becomes further shorter and thicker.
c) Migrated chromosomes appears in U,V,I and J

D) Telephase (I)
a) Migrated chromosomes reach completely to opposite poles.
b) Nuclear membranes start to appear and spindle fibres start to disappear.
c) Chromosomes become thin, long and thread like structure.

Meiosis (II)
i) Meiosis cell division (meiotic cell division) completes in four phases. They are as follows.
i) Prophase (II)
ii) Metaphase (II)
iii) Anaphase (II)
iv) Telephase (II)

i) Prophase (II)
a) Chromosomes becomes shorter and thicker
b) The nucleus membrane starts to disappear and spindle fibre starts to appear.

ii) Metaphase (II)
a) Chromosomes become further shorter and thicker.
b) Nuclear membranes completely disappear and spindle fibres completely appear.
c) Chromosomes remains attached at a point is called centromere.

iii) Anaphase (II)
a) cenromere divides and chromosomes starts to move towards opposite poles by the contraction of spindle fibre.
b) Chromosomes becomes further shorter and thicker.
c) Migrated chromosomes appears in U,V,I and J shape.

iv) Telephase (II)
a) Migrated chromosomes reach completely to opposite poles.
b) Nuclear membranes start to appear and spindle fibres start to disappear.
c) Chromosomes become thin, long and thread like structure.

Importance of meiosis cell division (meiotic cell division)
a) It helps in the formation of male and female gamete.
b) It helps in the formation of spores.
c) It brings variation and evolution in the livings beings due to crossing over.

Note (1): Crossing over: The exchange of genetic materials between homologous chromosomes during pachetene  and diplotene, sub-phases of prophase (I) of meiosis cell division(meiotic cell division) is called crossing over.

Importance of crossing over
a) It brings evolution and variation in the living beings.
Note (2): Syanpsis: Pairing of homologous chromosomes during zygotene, sub-phase of prophase (I) of meiosis cell division (meiotic cell division)
Note (3): Chaismata: The point through which crossing over takes place is called chaismata.
Note (4): Karyokinesis: The division of nucleus is called karyokiness.
Note (5): Cytokines: The division of cytoplasm is called cytokines.
Note (6): Homologous chromosomes: The identical male and female parent chromosomes that occurs in pair is called Homologous chromosomes

The Ends