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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.

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 [pic] Nucleus [pic] chromosomes [pic] Genes

Information about chromosomes:

The number of chromosomes in living organisms is:

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

|Organism |No of chromosomes |

|Human |46 |

|Rabbit |44 |

|Mosquito |6 |

|Fly |12 |

|Onion |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.

[pic]

First: Mitosis

Mitosis 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:

|Drawing |Events |The phase |

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

| |strings (chromosomes). |Prophase |

| |2-A network of filamentous fibres الألياف الخيطية called a spindle is composed | |

| |extending between the two poles of the cell. | |

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

| |cell, the spindle is composed from intensifying the cytoplasm at the cell poles. | |

| |4-At the end of this phase, the nucleolus and nuclear membrane disappear. | |

|[pic] |The chromosomes are arranged along the cell equator where each chromosome is | |

| |connected with one of the spindle fibers at its centromere. |Metaphase |

| | | |

|[pic] |1-Centromere of each chromosome splits lengthwise into two halves. | |

| |Chromatids in each chromosome then separate from each other. |Anaphase |

| |2-Spindle fibers begin to shrink and two - | |

| |identical groups of chromatids are formed. Each group migrates towards | |

| |one of the cell’s poles. | |

|[pic] |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 |3-Telophase: |

| |threads, a nuclear network and then two new separate cells are formed. Each cell has | |

| |the same number of chromosomes (2n). | |

| | | |

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. |

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

|Drawing |Properties |The phase |

|[pic] |Chromatin reticulum intensifies and appears in form of distinct chromosomes, then | |

| |chromosomes are arranged in homologous pairs, each pair consists of 4 chromatids are |Prophase I |

| |called a tetrad. الرباعي. | |

| | | |

| |At the end of the prophase 1, nuclear membrane disappears and every two homologous | |

| |chromosomes (in the tetrad) start to move away from each other. | |

| | | |

| |Each chromosome consists of two chromatids linked together by the centromere. The | |

| |spindle appears and the chromesomes get connected with spindle fiber. | |

|[pic] |Chromosomes pairs arrange on the cell’s equator. | |

| | |Metaphase |

| | | |

|[pic] |In this phase every two homologous chromosomes start to move away from each other as | |

| |the spindle fibers shrink انكماش. |Anaphase 1 |

| | | |

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

| |the other pole. | |

| | | |

| |Each pole contains half the number of chromosomes of the parent cell. | |

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

| |are two nuclei. |Telophase: |

| | | |

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

| |enters into the second meiotic division. | |

The crossing over phenomenon

At 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 phenomenon |

|It 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. |

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 meiosis

| |Mitosis |Meosis |

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

|Importance |-Growth of living organisms |Formation of gametes |

| |-Compensation of damaged cells |-Sperms or pollen grains in mails |

| |-Completing the sexual reproduction |-Ova or ovules in females |

|Resulting cells |Two cells are produced |Four cells are produced |

| |Each cell contain the same number of Chromosomes (2n) |Each cell contain half number of Chromosomes (n) |

|Stageof division |One stage includes four phases |Two stages |

| |(Prophase-Metaphase –Anaphase –Telophase) |First meiotic division |

| | |Second meiotic division |

Science , Technology and society

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:

- 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.

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 answer

1 – 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.

……………………………………………………………………………………………………………………………………………………

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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Cell division

[pic]

[pic]

2 - Meiosis

Types of cell divison

The cell division

Chromosomes

1 – Mitosis

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