science f4 chapter 3 :3.1 cell body

8/7/2019 science f4 chapter 3 :3.1 cell body

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CHAPTER 3 : HEREDITIY

AND VARIATION

CELL DIVISIONCELL DIVISION


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CHROMOSOMES

Nucleus of a cell contains many smallthread-like structures called chromosomes.

Chromosomes are made up ofdeoxyrobonucleic acid (DNA) and protien. Chromosomes contain heredity material

called genes.

The nucleus of each organisms cellcontains chromosomes which always exist in

pairs.


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For examples,A human somatic cell contains 23 pairs of

chromosomes. In each pair of chromosomes is inheritedfrom the father and one from the mother.

All somatic cell of the same type oforganisms have the same number ofchromosomes.


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GENES

Genes are heredity material or heritablecharacteristics located on chromosomes.

A gene is a DNA unit which functions to code theheritable characteristics, (passes heridityinformation from one generation to another)

Genes are in pairs. One gene is inherited from thefather and one from the mother.

Genes determines the characteristics like bodyheight, hair colour, fingerprint and appearance.


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Relationship between gene,

chromosome and DNA

Built up

of

Containing of

Containing

Forming

Determining


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LOGOType of cell division

2 type of cell divisionMitosis

A cell division process which takes placeonly in somatic cells

Meiosis the process of cell division to produce

gametes with half of the number ofchromosomes of the parent cell.

Only occur in the reproductive organs.


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Mitosis

The chromosomes in the nucleus

shorten, fatten and become clearly

visible.


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Mitosis

Chromosome replication occurEach thread-like chromosome is called achromatid

Chromatid are joined at the centromereThe nuclear membrane dissappears..


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Mitosis

Spindle fibre form

Chromosome lined up along theequatorial plane


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Mitosis

Spindle fibre pull the chromatids

so that they separate and moveto opposite poles of the cell.

At the same time, cells begin to

divide.


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Mitosis

The new nuclear membrane are

formed.Two daugther cells areproduced.


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Meiosis


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Meiosis I

Chromosomes in nucleusshorten and fatten.

First division


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Meiosis I

Replication and crossing over inchromatids occur

First division


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Meiosis I

Chromosomes arranged in thecentre of the cell in an equatorial

plane.Nuclear membrane disappearsSpindle fibre formed

First division


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Meiosis I

Chromosome move to oppositepoles of the cell

Cell begins to split into two

First division


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Meiosis I

Two daugther cells are formedNuclear membrane is formedagain

First division


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Meiosis I

Chromosomes are arranged incentre of the cell

Nuclear membrane disappears

Seconddivision


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Meiosis I

Chromatids separateCell begins to split

Seconddivision


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Meiosis I

Nuclear membrane is formed again4 daughter cells are formedEach daughter cell contains half

the number of chromosomes of theparent cells

Each daughter cell shows variation

Seconddivision


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Importance of mitosis and meiosis

Importance of mitosis Mitosis forms a new cells for growth Mitosis forms new cells to replace cells or tissues which

are damaged or have died Mitosis enables hereditary material in parent cell to bepassed to daughter cells. This process is to ensures

that the number of chromosomes in a daughter cell is

identical to that of the parent cell.

Mitosis enables axesual reproduction in someorganisms, like the binary fission in amoeba and

vegatative reproduction in plants.


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Importance of meiosis

Meiosis ensures that the number of chromosomesis diploid (2n) in the zygote when the nucleus of a

sperm fuses with the nucleus of an ovum during

fertilisation.

Combination of different chromosomes andcrossing over which occur causing variation to take

place in the next generation.


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Comparison between meiosis and

mitosis

MEIOSIS MITOSIS

SIMILARITIES

Chromosome replication takes place

Cell division occurs

New cells are produced


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LOGOMeiosis DIFFERENCES Mitosis

During the

formation of

gametes

When this process

happen

During the

formation of

somatic cells

Testes and

ovaries

Where this process

happens in animals

Somatic cells

Anther andovary

Where this processhappens in plants

Tip of the rootand shoot


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Meiosis Differences mitosis

Twice Number of cells division once

Occurs

during firstcell division

only

Replication process Occurs

Four Nu. Of daughter cellsproduce two


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LOGOHalf Nu. Of chromosomes in

daughter cells compared

to those of parent cell

Same

Different Genetic make up in

daughter cells compared to

those of parent cell

Same

Happens Crossing over Does not

happen


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LOGODo it yourself!!!

Answer the following questions in your exercise book.

1. Why are the characteristics among brothers and sisters

born of the same parents different?Mengapakah terdapat perbezaan sifat antara adik-beradik

yang dilahirkan oleh ibubapa yang sama?

2. Name two variations which distinguish you from yourbrothers and sisters.

nyatakan dua variasi yang membezakan anda daripada

adik-beradik anda.


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LOGOFill in the blanks with suitable words

1. ___________ are thread-like structures found in the nucleiof animal and plant cell.

2. Chromosomes contain heredity material called ________.3. _________is a cell division process to form new cells in

the body.4. __________ is a cell division process to form gametes.5. In human being, mitosis occurs in _____, while meiosis

occurs in reproductive organs like ______and ______.

6. Mitosis produces ________ daugther cells, while meiosisproduces _________daugther cells.7. __________which occurs during meiosis causes variation

among the same species.


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LOGOEnhancement Exercise

Diagram 1 shows a type of cell division which occurs in thehuman body.

Diagram 1 a) state the type of cell division shown in diagram 1. b) state any two of the importance of this cell division.


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c) name the organ in a female body wherethe above process occurs.

d) how many daughter nuclei are producedat the end of this process?

e) How many chromosomes are there inthe daughter cells?

science f4 chapter 3 :3.1 cell body

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