1. 1.Cell devision
Cell Division
*Introduction
*The need for new cells
*The Cell Cycle
*Types of Cell Division
1.Mitosis
2.Meiosis
* Summary

2. Introduction
1.Definition of a Cell:
2. Growth and Development:
3.Organization:
4.Function of a cell:
The Need for New Cells
1).Growth
2).Replacement
3).Repair
4).Reproduction

3. The CELL CYCLE
The Cell Cycle
•To divide, each new cell has to undergo aphase ofGROWTHandDEVELOPMENT.
•It is after this phase that the cell attainsenough maturityandcan complete allmetabolic processes
that are necessarybefore entering the phase of cell division.
•This preparatory phase of cells is termed asInter-phase followed by cell division MITOSIS

4. INTERPHASE
•It is thelong phasein abody / somaticcell.
•Before dividing, each cell has to attain thesame size as its mother cell.
•It has 3 sub-stages:
a).G-1 Phase
b)S Phase (Synthesis Phase)
c).G-2 Phase
G-1 PHASE
•It‟s an initial growth phase or first growthphase of the cell.
•The amount of cytoplasm increases and cyto-plasmic organelles like mitochondria etc….replicates.
S-PHASE (Synthesis PHASE)
-Chromosomes are duplicated by the synthesisof more DNA
G-2 PHASE
•This growth phase is shorter.
•Proteinrequired for cell division are synthesized.
•Cell increases in size.
•Cells prepares itself to enter the next phase ofdivision “Mitosis”
•Thenucleusof cellenlargesand adefinite numberof fine, coiled thread like structures
calledchromosomes become visible.
•In fact at the beginning of mitosis the nuclearmaterial has already doubled. This stage is called
INTERPHASE , also called the Resting Stage when infact the cell is synthesizing the
chromatinsubstance.

5. Cell Cycle
What happens inINTERPHASE?
•Cell size increases.
•Nucleus of dividing cell enlarges to its maximumsize.
•Chromosomes replicate i.e. a copy of eachchromosome is created.
•Nucleolus is very clear.
•The energy for cell division is stored asproteins.
•Certain substances necessary for initiation of cell divisionare formed.

6. Cell Division
•When the cell has reached certain level of growthit enters the division phase
•Where through a sequence of events the matureparent cell divides into two daughter
cells.
•These phases are of various durations in differentcells, but the basic outline of
sequences is thesame.
•Cell division consists oftwo major stages:
1). Karyo-kinesis:Nuclear division where nucleusdivides into two.
2). Cyto-kinesis:Entire cells splits separating eachnuclei.
Types of Cell Division
•Cells in animals and plants divide in oneof the two ways described below:
1). Mitosis:that takes place in body cellsresulting in growth and development.
2). Meiosis:that takes place in gameteproducing cells resulting in gametesthat fuse forming zygote.
MITOSIS
•Mitos=Threadand
Osis= State
•Cell division process was first described bySCHLEIDEN.
•This process takes place inBody or SomaticCells of organisms.
•The basic principle is“The Chromosomenumber of cells is not altered (notchanged) in this
process.”Its justduplication.
•It‟s a complex process where mother / parentsomatic celldivides to formtwo identicaldaughter
cells.
Phases of Mitosis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

7. 1). Prophase
-”Pro”meansFirst
-Nucleusisvisiblewithlarge, shortenedmuchlikespring&thickened Chromosomes
-Nuclear Membrane&Nucleolus disappear.
- Centriolestwo minutebodies outside the nucleus separates& formsspindlefibres oastral rays
&attachestocentromereofchromosomes
- Most plant cells do nothave centrioles but stillhave a spindle network
As PROPHASEends following features are noticed
•Chromosomes:thick, clearly visible, eachchromosomes split into2 chromatids& remainin contact
throughout at the centromere.
•Nucleolus & Nuclear Membranestartsdisappearing.
•Continuousspindle fibres join both centrioles.
•Chromosomes attachtospindlebycentromeresandstart moving towardsequatorial position.
•KINETOCHORE is the siteof attachment of spindlefibres.
•CENTROMERE is thecenter of attachment of the chromatids

8. 2). Metaphase
-”Meta” means After
-Shortphase
-Chromosomes becomes mostdistinct
-DuplicationofChromosomesoccursbefore prophase, butbecomesmore evidentduring metaphase
-Chromosomes arrange themselves at the equatorial plane.

9. 3). Anaphase-
‟‟Ana‟‟ means Back
- Veryactivephase ofMitosis. Main features are
a).Homologous daughterchromosomes (2chromatids)of metaphasenowseparateand begin tomove
in the oppositedirection towards the„pole‟with thecontractionofspindle fibres.
b).Chromosomesbendaround thecentromere showing as„V‟ or „J‟ or „L‟shaped structure based
onthe length of its arms.

10. 4). Telophase
-‟Telo‟ meansEnd
- As soon as thechromatidscometogetherat the endsof the spindlenetwork, thetelophase begins.
The various changes observed during TELOPHASE are:
1).Chromosomes reach oppositepoles.Spindlenetworkdisintegratesbutcentriolesremain.
2).Chromosomesuncoil, lengthen& thus becomesthinnerturning into anetwork of less
distinctchromatin threads.
3).Nuclear membrane&Nucleolusstartsforming around 2 sets of chromosomes inboth the newly
formed daughter cells.
4).With theformationofnuclear membrane,2 nuclei are formed & the process of nuclear divisionor
KARYO-KINESIS is over. This is followed by CYTO-KINESIS
Cyto-Kinesis
- At this point thecytoplasm betweenthetwo daughternuclei constrictsi.e. a
furrow starts formingin the plasma membrane at the middle.
- Thisdeepens towardsthe interior of the cell until the cytoplasm is
splitinto2similardaughter cells.
- Inplant cellsconstriction isnot observed during cytokinesis.