Science 3rd prep. 1st term unit 4 lesson 1

the importance of cell division process to living cell organisms?

Multicellular organism’s bodies contain two types of cells: somatic cells and reproductive cells. Each type is divided in a special way.

Cells in multicellular organisms are divided in different ways to achieve different purposes:

1-Somatic cells are divided by mitosis which leads to the growth of living organisms and compensation of the damaged cells.

Examples of somatic cells: - cells of ( liver, skin , kidney , ….. ) in human and animals. - cells of ( roots, stem, leaves, …… ) in plant.

2-Reproductive cells are divided by meiosis which leads to the formation of male and female gametes which are responsible for reproduction in living organisms and the transfer of genetic traits from parents to their offspring.

Examples of reproductive cells: - testis and ovary cells ( in human and animals )- Anther and ovary cells (in flowering plants).

Which part of the cell is responsible for cell division?The cell nucleus contains the genetic material of the living organism. This genetic material consists of a number of chromosomes. Chromosomes have the main role in cell division.

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The cell division

Chromosomes

Science 3rd prep. 1st term unit 4 lesson 1

General structure of the chromosome : 1- The chromosome consists of two connected threads at the centromere point each thread is called a chromatid.

2-The chromosome chemically consists of nuclear acid called D.N.A and protein. DNA carries the genetic traits of the organism.

3- Centromere it is the point of connection the two chromatid

Chromosomes: They are thread like bodies present in cell's nuclei and they represent the genetic material of the living organism.

Centromere;It is the point of connection of the two chromatids of chromosome during the cell division.

Chemical structure: Each chromatid consists of:

- a nucleic acid called (DNA) which carries the genes that carry the genetic traits of the living organism.

- Protein.

DNA It is the nucleic acid that foms the chromosomes that present in the cell nucleus and it carries the genes.

The cell Nucleus chromosomes Genes

Information about chromosomes: The number of chromosomes in living organisms is:

** different from species to another. ** fixed in members of same species.

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Science 3rd prep. 1st term unit 4 lesson 1Organism No of chromosomesHuman 46Rabbit 44Mosquito 6Fly 12Onion 16

Enriching information: Somatic cells in most living organisms contain two sets of chromosomes (one inherited from the father and the other inherited from the mother) known as the diploid number (2N),while the gametes (male gametes (sperm) female gametes (ovum) contain the haploid number (N). ** Knowing the number of chromosomes helps in identifying the animal and plant species

It is a complicated process through which the living cell divides into two cells more to aim the growth or reproduction.

1 – Mitosis

First: MitosisMitosis occurs in the somatic cells of organisms such as:

all body cells except reproductive cells and neural cells. Cells of roots , stems and leaves (in plants).

Importance : it plays an important role in: growth of living organisms compensation of the damaged cells. Competing the asexual reproduction process.

.** the cell passes through a phase called interphase before mitosis.

During interphase: the cell prepares for division the amount of genetic material (DNA) duplicates.

Phases (stages) of mitosis:DrawingEventsThe phase

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Cell division

Types of cell divison

2 - Meiosis

Science 3rd prep. 1st term unit 4 lesson 1

1-Chromatin reticulum intensifies and appears in the form of long, thin and double

األلي��افcalled a spindle is composed

extending between the two poles of the

3-The spindle fibres in the animal cell is formed from the centrosome In the plant cell, the spindle is composed from

nucleolus

Pro

phas

e

The chromosomes are arranged along the cell equator where each chromosome is connected with one of the spindle fibers at

Met

apha

se

1-Centromere of each chromosome splits

Chromatids in each chromosome then

identical groups of chromatids are formed. Ana

phas

e

a series of adverse changes occur which lead to the formation of a complete set of chromosomes that have the same number of the mother cell’s chromosomes. Nuclear threads, a nuclear network and then two new separate cells are formed. Each cell has

3-Te

loph

ase:

Note Changes in Telophase are called the adverse changes in prophase stage

How many chromosomes are there in the parental cell resulted from mitotic cell division?Both of them (2N)

Science , technology and society Liver transplantation:

liver cells are not divided in normal conditions but retain the ability to divide under certain circumstances.

For example , if the liver gets injured or a part of it is cut, the remaining cells undergo many mitotic divisions to compensate the missing part. This is the scientific basis used in liver transplantation.

*** some cells in human body are not divided at all such as nerve cells and red blood cells.

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Science 3rd prep. 1st term unit 4 lesson 1

Second: Meiosis Meiosis occurs in living organisms that reproduce by gametes.Occurrence : * In humans and animals, Its important this division occurs in the testis ةto produce the male gametes (sperms) and in the ovary to form the female

gametes (ova).

* in flowering plants this division occurs in the anther to produce the pollen grains and in the flower ovary to form an egg.

Importance :production of male gametes and females gametes to complete the sexual reproduction.

*** before starting meiosis, the cell passes through interphase where chromosomes are doubled.

Phases of meiosis:

1 – First meiotic division 2 – Second meiotic division.

First meiotic division Prophase 1 , Metaphase 1 , Anaphase 1 and Telophase 1

DrawingPropertiesThe phase

Chromatin reticulum intensifies and appears in form of distinct chromosomes, then chromosomes are arranged in homologous pairs, each pair consists of 4 chromatids are

At the end of the prophase 1, nuclear membrane disappears and every two homologous chromosomes (in the tetrad)

Each chromosome consists of two chromatids linked together by the centromere. The spindle appears and the chromesomes get

Prop

hase

I

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Science 3rd prep. 1st term unit 4 lesson 1

Chromosomes pairs arrange on the cell’s

Met

apha

se

In this phase every two homologous chromosomes start to move away from each

One of the two chromosomes migrates towards a cell pole and the other migrates

Each pole contains half the number of Anap

hase

1

At each of cell’s poles a nuclear membrane is formed around the chromosomes. So, there

Each one has half the original number of chromosomes of the parent cell. Then the cell

Telo

phas

e:

The crossing over phenomenonAt the end of prophase I, some parts of the two inner chromatids of each tetrad are exchanged to produce new genetic arrangements. This process is

called the crossing over phenomenon.

Crossing over phenomenonIt is a phenomenon that takes place at the end of prophase 1 and in which some parts of the two inner chromatids of each tetrad are exchanged to produce new genetic arrangements.

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Science 3rd prep. 1st term unit 4 lesson 1

What is the importance of the crossing over phenomenon?It contributes in genes (that carry genetic traits) exchanging between the two homologous chromosome's chromatids and distributing them randomly in the gametes.

This is an important factor for the variation of genetic traits among the members of the same species.

Second meiotic division:It aims to increase the number of produced cells. Each cell is called the (gamete), containing half the number of species chromosomes. Each cell of the two cells which resulted from the first meiotic division is divided in a way similar to mitosis division phases.

In the final phase (telophase II) of this division, four cells are produced and each of them contains half the number of chromosomes of the parent cell.

When the male gamete combines with the female gamete, the zygote is formed. It contains the original number of the organism’s chromosomes. Thus, the number of chromosomes remains constant in the cells of members of the same species.

Comparison between mitosis and meiosisMitosis Meosis

Location Occurs in all somatic cells Occurs only in reproductive (sex) cells

Importance -Growth of living organisms -Compensation of damaged cells-Completing the sexual reproduction

Formation of gametes -Sperms or pollen grains in mails -Ova or ovules in females

Resulting cells

Two cells are producedEach cell contain the same number of Chromosomes (2n)

Four cells are producedEach cell contain half number of Chromosomes (n)

Stageof division

One stage includes four phases (Prophase-Metaphase –Anaphase –Telophase)

Two stages First meiotic division Second meiotic division

Science , Technology and society

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Science 3rd prep. 1st term unit 4 lesson 1

Enriching Activity >> preparing a slide from growing tip of onion's root To different phases of mitotic cell division .

Procedures: 1 – plant onion in beaker of water until it gives out roots ( 2 -3 cm)

2 – put some roots in glass tube.

3 – add 2ml of HCl to the root for 20 minutes, then put tube in water bath (50ºC) for 7 minutes.

4 – wash the root then add 2ml fulgen solution and leave it for 30 minutes.

5 – move one growing root to clean glass slide.

6 – cut the growing tip and add 2 drops of acetic acid then cover it by cover slip.

7 – press gently on cover to mash the root tip.

8 – examine the slide by compound microscope ( see phases of mitosis division ).

Nanotechnology and cancer treatment:

Cancer occurs when the body cells are divided continuously without controlling.

- the mass resulted is called tumor - Egyptian Scientist Dr. Mustafa El Said discover a Nano-molecules which kill

this tumor called Nanotechnology that we benefit from it in:

1 – Discovering cancer disease:

- this technic starts by loading certain type of protein with nano-molecules of gold and then injecting them into the patient.

- Proteins attach on the cancerous cell surface to monitor it through a microscope.

2 – Treatment of cancer: A. by using Nano-molecules of gold as follows:

- focusing laser with a certain degree to the gold molecules, then the gold molecules absorb the light and convert it into heat which burn and kill the infected cell.

B . by using developed microscopic bombs:

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Science 3rd prep. 1st term unit 4 lesson 1

- scientists have developed smart microscopic bombs that penetrate the cancer cells and explode them from inside.

- They were used to kill the cancer cells in an experimental mice . - Treated mice live 300 days while non-treated ones live 43 days only.

Questions on lesson

Complete the following statements: 1 – the hereditary material in the ………………………………. Of the cell consists of a number of ………

2 – the chromosome chemically consists of nuclear acid called ………………. And protein.

3 – the chromosome consists of ………………… connected together at point known as ………………..

4 – the number of chromosomes is …………………………. In the individuals of the same species, while it is ……………………… from a species to another.

5 – before starting cell division, the cell passes through a phase called ………………….. in which the amount of ………………………………… duplicates.

6- at the end of prophase of mitosis, the …………………… and …………………….. disappear. 7 – in animal cell, the spindle fibers are formed by ……………………… , while in plant cell , the spindle fibers are formed from …………………………… at the cell poles.

8 – the spindle fibers are formed during the cell division in ………………………… phase and disappear in ………………………….. phase.

9 – nuclear membrane is formed at each pole of the cell surrounding by the chromosomes in the ……………………….. phase of the cell division.

10 - ……………………………. Division aims to form gametes.

11 – the somatic cells divide by……………………….. cell division, while the reproductive cells divide by ……………………………. Cell division.

12 – in human , meiosis occurs in testis to produce ……………………….., while it occurs in ovary to produce ……………………………..

13 – in plants , male gametes are called …………………………., while female gametes are called …………………………

14 – in flowering plants , the pollen grains are formed inside the ……………………. , while the ovules are produced inside the ……………………….

15 – in prophase 1 , chromosomes are arranged in ………………….. pairs, each pair consists of ………………………… chromatids which are called ……………………………..

16 – the cell which divides by ………………………… cell division gives 4 cells, while that divides by ………………………………. Gives 2 cells.

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Science 3rd prep. 1st term unit 4 lesson 1

17 – Crossing over phenomenon takes place during ………………………….. of the …………………. Division.

18 – Nano-molecules of …………………………….. metal is used to detect cells of cancer and ………………………………….. rays are used to destroy them.

Choose the correct answer1 – the type of division in somatic cell is …………………….. division. a. meiosis b. reduction c. mitosis d. no correct answer.

2 – Duplication of genetic material (DNA) occurs in ……………………… of mitosis. a. anaphase b. prophase c. interphase d. metaphase

3 – the centromere of each chromosome is divided vertically, then the two chromatids are separated from each other in the …………………………………………….a. prophase b. telophase, c. anaphase. d. metaphase.

4 – Spindle fibers appear during cell division in the …………………………. a. prophase b. metaphase c. anaphase d. telophase.

5 – meiosis division happens in the cells of the ………………………….. a. two ovaries b. two testes c. liver d. a and b

6 – meiosis is different form mitosis in that each produced cell contains ……………………. Of the parent cell. a. half the number of chromosomes. b. a twice the number of chromosomes. c. production of gametes. d. duplication of cells number.

7 – crossing over phenomenon happens in the ………………………….. a. first prophase. B. first anaphase c. second metaphase d. second anaphase.

8 – A tetrad consists of …………………………. Chromosomes. a. 2 b. 4 c. 6 d.8

9 – if the number of chromosomes in a cell of a wing of a female mosquito is 6 chromosomes, then the number of chromosomes in a sperm of a male mosquito is …………………. a. 2 b. 3 c. 6 d. 12

10 – the variation of genetic traits resulted from meiosis is due to ………………………. a. reduction of chromosomal number b. crossing over phenomenon. b. duplication of DNA d. formation of tetrads.

Give reasons for : 1 – Cellular division begins with interphase? …………………………………………………………………………………………………………………………………………………….

2 – the mitotic cell division is responsible for the growth of living organisms.

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Science 3rd prep. 1st term unit 4 lesson 1……………………………………………………………………………………………………………………………………………………

3 – shrinking of spindle fibers during the anaphase of mitosis division? …………………………………………………………………………………………………………………………………………………..

4 – the damaged nerve cells can't be compensated? …………………………………………………………………………………………………………………………………………………..

5 – the gametes are often (N) while somatic cells are often (2N)? …………………………………………………………………………………………………………………………………………………..

6 – mitosis division is important for children than meiosis? ………………………………………………………………………………………………………………………………………………..

7 – Laser is used for treatment of cancer by nanotechnology? ………………………………………………………………………………………………………………………………………………..

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