(1.2) Cell Division(p22-27)

Cell Division

• Cells must divide to survive.• There is a limit to how large a cell can grow.• If the amount of material in a cell is too large

the cell dies.

Cell DivisionWhen a cell divides

- two new cells are created

- each cell is identical to the original cellThe set of instructions each

cell inherits is stored in a unique molecule called DNA (deoxyribonucleic acid).

DNA• DNA in the nucleus of the cell contains the

hereditary material.• DNA molecules have a shape like that of a

ladder.• To fit inside the nucleus DNA forms compact

coiled threads called chromatin.• To reproduce the chromatin packs together to

form chromosomes.• Chromosomes pass on hereditary information

when a cell divides.

DNA• Chromatin are thin threads of DNA.• If the DNA in one of your cells is uncoiled it

would be 2 m long!

ChromatinDNA

Cell Cycle

• The series of events in the life of a cell is called the cell cycle.

• Two main stages:i) growth - called interphaseii) division - consisting of

mitosis and cytokinesis

Growth Stage

• During interphase the cell:- grows- carries out its usual functions- makes copies of its DNA and organelles to

prepare for cell division• Most cells spend most of their lives in

interphase.• Interphase ends when a cell begins to divide.

Division Stage

Two phases of cell division:1.Mitosis

- the contents of the nucleus separate into 2 identical copies.

2. Cytokinesis- cytoplasm and organelles divide into 2 identical, separate copies- each cell now starts its own cell cycle

Cell Division - It’s Important

Through cell division livings things undergo three important functions:i) growthii) maintenanceiii) repair

ClassworkText• p 23 LC #1-3• p 25 LC #1-3• p 27 LC #1,3

Quiz: Next class on section (1.1) - cell parts, diffusion and osmosis