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Types of Cell Division Cells in animals and plants divide in

one of the two ways described below:

1). Mitosis: that takes place in body cells

resulting in growth and development.

2). Meiosis: that takes place in gamete

producing cells resulting in gametesthat fuse forming zygote.

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MITOSIS Mitos means Thread & Osis means State Cell division process was first described by

SCHLEIDEN. This process takes place in Body (Somatic)

Cells of or anisms.

The basic principle is The Chromosomenumber of cells is not altered (not changed)in this process. Its just duplication.

Its a complex process where mother / parentsomatic cellsomatic cell divides to form two identicaldaughter cells.

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Phases of Mitosis

1). Prophase (P)

.3). Anaphase (A)

4). Telophase (T)

(PMAT)

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1). PROPHASE

- Pro means First- Nucleus is visible with large,

shortened much like spring &thickened Chromosomes.- Nuclear Membrane &Nucleolus disappear.-

bodies outside the nucleusseparates & forms spindlefibres or astral rays &attaches to centromere ofchromosomes.- Most plant cells do not havecentrioles but still have aspindle network.

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As PROPHASE ends followingfeatures are noticed

Chromosomes: thick, clearly visible, each

chromosomes split into 2 chromatids & remainin contact throughout at the centromere.

disappearing.

Continuous spindle fibresjoin both centrioles.

Chromosomes attach to spindle bycentromeres and start moving towardsequatorial position.

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KINETOCHORE is the siteof attachment of spindle

fibres.

CENTR MERE s t ecenter of attachment of

the chromatids.

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2). METAPHASE- Meta means After

- Short phase

- Chromosomes

becomes most distinct.- Duplication ofChromosomes occurs

e ore prop ase, ubecomes more evidentduring metaphase.

- Chromosomes arrange

themselves at theequatorial plane.

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3). ANAPHASE

- Ana means Back- Very active phase of Mitosis.Main features are

a). Homologous daughterchromosomes (2 chromatids)of metaphase now separateand begin to move in the

oppos e rec on owar s epole with the contraction ofspindle fibres.

b). Chromosomes bend around

the centromere showing as Vor J or L shaped structurebased on the length of its arms.

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4). TELOPHASE

- Telo means End

- As soon as the

chromatids cometogether at the endsof the spindle

network, thetelophase begins.

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The various changes observed during

TELOPHASE are:1). Chromosomes reach opposite poles. Spindle

network disintegrates but centrioles remain.

2). Chromosomes uncoil, lengthen & thus becomesthinner turning into a network of less distinctchromatin threads..

forming around 2 sets of chromosomes inboth the newly formed daughter cells.

4). With the formation of nuclear membrane, 2 nuclei

are formed & the process of nuclear division orKARYO-KINESIS is over. This is followed byCYTO-KINESIS.

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CytoCyto--KinesisKinesis

- At this point thecytoplasm between the twodaughter nuclei constricts

i.e. a furrow starts formingin the plasma membrane atthe middle.

-

interior of the cell until thecytoplasm is split into 2similar daughter cells.

- In plant cells constrictionis not observed duringcytokinesis.

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Importance of Mitosis

- Helpful in growth of tissues, organs

and thus organism.

- Used for repair of damaged tissues and

.- It is the method by which lower animals

reproduce.

- Hereditary characters are maintainedby the replication of chromosomes.

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Characteristics of Mitosis

- It takes place in Somatic / Body cells.

- It helps in tissue growth.

- 2 e ual similar dau hter cells are

formed.

- Chromosome number is preserved.

- Daughter cells are identical to parentcell.

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Difference in Plant and Animal Mitosis

Plant Mitosis1. Centrioles are absent in

Plant Mitosis.2. No contractile ring is

found.

Animal Mitosis1. Centrioles are present in

Animal Mitosis.2. Formation of contractile

ring between 2 nuclei of the

formed.4. In Telophase there is a

formation of Cell Plate forthe process of cytokinesis.

5. Nuclear and Cell divisionare found in specialregions called Meristems.

3. Cell constriction is formedin the late Telophase for theprocess of Cytokinesis.

4. No cell plate is formed.5. Cells divide everywhere, all

the time