4 science 2 rpk- chap 5 cell division (part 1)

8/9/2019 4 Science 2 Rpk- Chap 5 Cell Division (Part 1)

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BIOLOGY FORM 4

SMKRPK 4 SCIENCE

2


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` Cells are the basic units of life in all living things.

` Cells in living things do not last forever, for they;

` A) wear out sometimes,

` B) get damaged (through cuts, by ultravioletradition or by hazardous environmental pollutant.

` C) grow old naturally and die


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` Cell division occurs actively in the meristems atthe tips of the roots and shoots.

` Active cell division which takes place in these

places leads to faster growth and elongationof plant.


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` Binary fission, e.g in Paramecium sp.

` It reproduces through mitosis.


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` Cell division can be divided into 2 stages:

Cytoplasmic division also known as cytokinesis

Nuclear division Cytoplasmic division

MITOSIS


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` Each cell contains nucleus.


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` The nucleus containschromosomes.

` Each chromosome consistsa long DNA molecule whichcarries genes in a linearsequence.

` DNA contains geneticinformation which will beinherited to daughter cell.

` Parents cells divide formingdaughter cells.


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CELL

CYCLE

Interphase

M phase

G1

S

G2

Mitosis

Cytokinesis

Prophase

Metaphase

Anaphase

Telophase


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` Interphase is

the period

betweendivisions, and is

further divided

into 3

subphases: G1,S, G2


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` Means gap or growth phase 1

` In this phase, cells grow rapidly.` New organelles are synthesized such as

mitochondria and choloroplast.

` Metabolic rate of the cell is high.

` The chromosome appear as thread-likestructures called chromatin.


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` S phase means DNA synthesis

` The DNA in nucleus undergoes replication.

` Each duplicated chromosome now consists oftwoidentical sisterchromatids which contain

identical copies of the chromosomes DNA

molecule.


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` The cells continues to grow and remain

metabolically active .` The cell accumulates energy & complete its final

preparation for the next stage of cell division.


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` Mitosis is the stage within the cell cycle when the

DNA (or chromosomes) of a cell divides into two

separate nuclei.

` The four main distinctive phases of mitosis are:a) Prophase

b) Metaphase

c) Anaphase

d) Telophase


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` Chromatids (replicatedchromosomes) condenseand become visible in alight microscope.

` The nucleolusdisappears.

` Paired centrioles(centrosome) move to

the opposite end of thecell.

1) PROPHASE1) PROPHASEEarly ProphaseEarly Prophase


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` Nuclear membrane

disappears.

` Spindle forms.

` Asters (shortmicrotubules) radiating

from centrioles) form.

Late prophaseLate prophase


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` Sisterchromatids line up

at the spindle equator.

` Each centromere attaches

itself to thespindle fibre.

At the end of metaphase, the

centromeres divide.


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` The separated

chromatids, now called

chromosomes are

pulled apart towards theopposite poles by the

contraction of spindle

fibres.

`

Anaphase is completedwhen chromosomes

arrive at the poles.


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` Chromosomes reach the poles

of the cell and cannot be seen

clearly.

` The spindle fibres disappear.

` Nuclear membrane reforms

around the chromosomes and

the nuclelolus reappears in

each nucleus.

` Telophase may lead straight

into cytokinesis.


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` Is the separation of parents cell cytoplasm atthe end of a mitosis.

` The organelles and other content of the parent cell

are equally divided between the two daughter

cells.` Cytokinesis in animal cell and plant cell are

different.


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` The cell membrane at the

midpoint of the parent cell

constricts in to form a

cleavage furrow(division furrow)

` Constriction continues,

and finally cytoplasm are

separated and two

daughtercells formed.


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` Vesicles (produced bythe Golgi body)containing carbohydratesgather at the equator ofthe parent cell.

` The vesicles fusetogether to form a cellplate.

` Cellulose builds on eachside of cell plate forming

the cell walls of twodaughter plants cells.


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`Compare and contrast Mitosis

and Cytokinesis of Animal Cells

with Plant cells.


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Animal Cells Aspects Plant Cells

1. Centrosomes

2. Cell plate

3. Furrowing ofcytoplasm

4. Location

5. Shape ofcells produced


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` What if the cells fail to divide or begin to divideat the wrong time or divide uncontrollably??

` When a cell divides through mitosis repeatedly,without control & regulation, it can produce

cancerous cells.` A cancerous cells divides uncontrollably to form atumour, an abnormal mass of cells.

` Tumor cells have no function but instead

interfere with the normal activity of surroundinghealthy cells, like restricting blood flow to them.


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` Some tumours remaininactive an arerelatively harmless, and

we call these benign(not cancerous)tumours.

` Grow slowly

Benign tumors Malignanttumors

` Consists of cancercells.

` Grow slowly but capableof very rapidgrowth.

` Can invade and destroyneighbouring cells


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` Dangerous when theycompress surroundingtissue.

` A benign tumour near ablood vessel couldrestrictthe flow ofblood.

` In the abdomen it couldimpair digestion.

` In brain, it could causeparalysis.

Benign tumors Malignanttumors

` Some cancerous cell breakfree from a tumour and canspreadlocally or through

bloodstream & lymphaticsystem to other parts ofbody.

` When this happen, secondarytumours develop in otherbody tissues.

` Example: A breast cancercan spread to bone tissue.


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Benign

tumors

Malignanttumors


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GeneticCarcinogen

s

Radiation Age

Viruses


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` Cloning is a natural process.

` Many unicellular organisms and plants can reproduceasexually through mitosis to produce clones.

` For example:

Some unicellular organisms undergo budding and binary fissionto produce new organism.

Some plants reproduce vegetatively through stems, roots andleaves.

` Clone share the same genetic contentandchromosomal number with one another as well as withthe parent organism.


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` Plants can be cloned through tissue culture.` Tissue culture-process of growing cells

artificially in laboratory; modern & efficient wayin cloning plants.

` Produce genetically identical clones


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1) A piece of tissue, called explant,

is taken from parent plant.

Ex: Small cut of carrot tissue

2) It is sterilised to prevent gowth of

pathogens (such as bacteria &

fungus)

3) It is placed onto a growth

medium (gel containing nutrients &

growth regulators)

4) The tissue cells divide by mitosis

to produce the mass of loosely

arranged & undiiferentiated cells

called callus.

Tissue culture


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Callus is stimulated with shoot and

root stimulating hormones to formmultiple shoots and roots

The plantlets (little plants) are

planted in sterile compost to grow


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` A branch of medicineconcerned with the treatment

of disease.` Ex: A part of a person-skin,

heart, liver or even just a fewcells-are duplicated toproduce clones.

` The cloned tissue is used toreplace a damaged ordiseasedtissue without therisk of tissue rejection.

a) Reproductivecloning

` Produce entireanimal that is

geneticallyidentical to theparent animal.


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` The most effective technique for cloning animals.

` Zygote-a fertilised egg. Zygote divides into two or

more cells called embryo.

HOW ?

A good milking cow is stimulated with hormones to release

many fertile eggs, which are then collected.

Sperms are collected from a prize bull


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The eggs are then fertilised by sperms

outside the uterus (in vitro fertilisation)

in a culture (using a tube or petri dish.

The fertilised eggs called zygote are

allowed to develop into multicellular

embryos

The embryos is split into individual cells,

each cell further divides to form more

embryos.

The embryos are implanted into surrogate

mothers to develop.

Identical calves are born naturally from their surrogate

mothers.


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` Embryo cloning uses only parents with good

characteristics, hoping that these characteristics would

pass down to theiroffspring.


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` It combines a somatic cell nucleus with an egg(nucleus of egg is removed), and the embryo

produced is cloned.

` :


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` Dolly, the sheep is the firstcloned mammal has died

on 14th February 2003

after developing a lung

disease. She was only 6years old when she died.

` Under normal

circumstances, sheep can

live for 10 to 16 years, soshe died at relatively young

at the age of six.


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A cell was taken from the mammary

gland of female Finn Dorset sheep.

An egg was obtained from another

female sheep (Scottish Blackface). The

nucleus is removed.

Fuse the cell and egg with electric

current

The egg was implanted into a third ewe

(female sheep),&

few months later,Dolly was born


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Advantages

ofcloning


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Disdvantages

ofcloning

4 science 2 rpk- chap 5 cell division (part 1)

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