MITOSIS-TEXT

MITOSIS

BIOLOGY

Mitosis is a somatic or vegetative cell division and the daughter  cells resemble the mother cell in every aspect. Organs formed by this type of division such as liver, kidney, brain, skin, etc. are called vegetative organs because they do not participate directly in reproduction.

Growth of any organ system in plant or animal is due to increase in cell number by mitosis. Cells from young ad tender organs such as shoot, tips, bud, root tips, tissues of young animals the divided more rapidly than the cell from old and mature organs. This is the reason for a greater rate of growth in young organs .

Before the cell division occurs various changes are seen in the cell. Major change is the doubling of the number of chromosomes. Only after this is completed, the cell divide, so the the daughter cell will have the same number of chromosomes as the mother cells..

This is essential you have already learnt that chromosomes carry the genes. Genes carry the genetic information and are responsible  for the inheritance of parental features. They also regulate all the function of the cell by directing and controlling all the proteins in the cells.

Before cell division begins, the non-diving or resting cells are said to be in interphase. This phase in the life of the cell is called interphase.

Chromosomes in the nucleus of interphase cell are in a highly decondensed state and form a diffuse network of filaments called chromatin.  Most of the cells spend a considerable portion of their life in interphase.Mitosis is of brief duration and once the division is complete, both the daughter cells usually enter into interphase.

Once mitosis is initiated it proceeds without any interruption till the cell division is complete and daughter cells are formed.Based on the changes occurring in the five stages have been recognized in mitosis .1. prophase     2. Metaphase     3. Anaphase   4. Telophase  and 5. Cytokinesis.

 

Prophase :

      This is the first stage of cell division. Before prophase starts the chromosomes are in a decondensed state and appear as a diffuse network of filaments. During prophase, the chromosomes start condensing.

As a results, the shape of the chromosomes becomes definite and distinct. Each chromosomes has two arms called chromatids. The two chromatids are joined together by centromere. While these changes are occurring the nucleous and rest of the structure in the  nucleus disappear gradually.

Meanwhile the centrioles move to the  opposite side of nucleus. In plants cells, where centrioles are usually absent the they appear at this stage of cell division. From each centriole fine thread like fibres appear. These fibres are called spindle fibres. Acentriole with spindle fibres is called an aster. The spindle fibres grow towards the centre of the cell.

2. Metaphase:

Chromosomes now move to the centre of the cell and arrange themselves in a row. This looks like a plate and is called quitorial plate. Some of the spindle fibres are attached to the  centromere of each chromosome. Rest of the fibres grow towards opposite pole and join the centriole on the opposite side. Each chromosome is attached to fibres from the two opposite poles.

3. Anaphase:

At this spindle fibres pull the chromosomes to opposite ends. As a results the centromere splits and are pulled a part along with chromatids. As a result, half the original number of chromosomes  move to each of the two opposite poles.

4. Telophase:

By the beginning of this phase, the chromosomes complete movement and will be at each end of the cell. Nuclear membrane, nucleolus and other nuclear structure reappear. Chromosomes begin decondensation process. By the end of telophase, cell will be having two nuclei, one on each side. Spindle fibres now disappear.

5. Cytotinesis:

A new membrane is formed at the quitorial plate during this phase. This didivide the cell in two daughter cells. Thus at the end of mitosis, two daughter cells which are extractly similar to the mother cell are formed. This first four stages of cell division involve changes in nucleus and division of nuclear components equally between daughter cells.

Hence, these  four phases prophase, metaphase, anaphase and telophase of cell division are together called karyokinesis. Means division of  nucleus. The last stage is called cytokinesis as the cytoplasm is the only component undergoing division in this stage of mitosis.

POINTS TO REMEMBER:

Mitosis is a somatic cell.

Doubling of the number of chromosomes is the major event before cell division.

Interphase is the period when the cell grows in size nd performs the physiological functions. Chromation is in a decondensed state in the nucleus of an interphase cell.

During prophase, centrioles move to the opposite poles of the cells and spindle fibres formed from the centrioles.

During metaphase, chromosomes  move to centre of the cell and form equatorial plate. Spindle  fibres grow in length and attach themselves to the centromere  of each chromosome..

During anaphase, the chromosomes are pulled apart and each half moves to the opposite side of the cell.

During telophase, the nuclear membrane appears around the chromosomes and chromosomes decondense into chromatin.

During cytokinesi, a membrane or a cell wall appears in the middle of the cells and divides the cytoplasm of the cell into two. With this the cell division is completed and two daughter cells are formed. During mitosis, kayokinesis occurs before cytokinesis.

THANKYOU,

NANDITH AKUNURI

CELL DIVISION MITOSIS AND MEIOSIS - TEXT

CELL DIVISION MITOSIS AND MEIOSIS

BIOLOGY

Take a seed and break it open. There is no plant inside the seed. Similarly, if you break open an egg, there is no chick inside. But the seed when sown in soil and watered, gives a plant which may grow into a tree. Similarly, the egg, when incubated, gives a chick. have you ever thought how this is possible?

 Plants or animals make their beginning from a single called zygote. This single cell divides and produces two cells.. they divide again and produce fur cells, the four cells give rise to eight cells-these cells divided several thousands of times to produce a plant or animal which has several thousands of cells. This process is called development and occurs by cell division. You already learnt that cells are frome from pre-existing cells.

The cells produced from the egg or zygote are of two types. Vegetables or somatic cells and reproductive or germ cells. Various organs in the body are derived from these two cell types.

As you can see, the germ cell give rise to organs involved in the production of male and female gametes while the somatic cells give rise to almost all the organs except those producing male and female gametes. These cells that divide are called parental or mother cells and the resulting cells i.e the products of cell division are called daughter cells.

All the somatic cells divide by a process of mitosis while the germs cells divide by a process called meiosis or reduction division. The major difference between the mitosis and meiosis is the number of chromosomes in the daughter cells.

In mitosis, daughter cells have exactly the same number of chromosomes as the parental cell..

In meiotic division, daughter cells have exactly half the number of chromosomes of the parental cell cells.

Details about mitosis and meiosis and how they occur are given in the next two videos.

THANKYOU,

NANDITHA AKUNURI

CELLS ORGANIZE TO FORM TISSUES-TEXT

CELLSORGANIZE TO FORM TISSUES

BIOLOGY

As mentioned earlier, a pile of bricks do into represent a house. Similarly, a mass of cells do not form an organism. These cells must be organized into proper body parts. In all the multicellular organisms, this process of organizing the cells into the body parts starts after the differentiation.

All the cells designated to carry out a similar function will have a similar structure and are grouped together to form a tissue. Several tissues are organized to form an organ. And several organs into organs system and finally into organism.

Let us now study the tissue organization..

In unicellular organisms, all the body functions are carried out by by a single cell. In very primitive  multicellular organisms. As in some body of the algae such as volvox, hundred of cells are grouped together to form a colony.

In the colony carryout reproductive and these are called reproductive cells- Thus the work to be done in the colony is divide among the cells and this is a primitive form of differentiation. In the modern multicellular organism, this division of work or labour is much more complicated.

A tissue is a group of cells having similar structure and carry out a similar function and they have a common origin. Usually, a tissue has several thousands of cells arranged closely.

These cells are packed in frame work called extracellular matrix. This is made up of proteins and carbohydrates provide mechanical support for the cells in the tissues and keeps the cells in position. All the cells in a tissue communicate with each other to efficiency carry out the function as single unit. Plant and animal tissues are different in their structure and functions .

THANKYOU,

NANDITHA AKUNURI

SEEDS AND SEEDS –ACTIVITY-8

SEEDS AND SEEDS –ACTIVITY-7

SEEDS AND SEEDS –ACTIVITY-6