Tissue and it's classification

Tissue: A group of cells performs the duty of manufacturing food; another group stores it, while the other group conducts the transport of food materials. There is further a group of cells that gives mechanical strenght to some organs. In many cases it is observed that a group of cells originating from a single origin remain closely attached in a place and collectively perform a similar type of function. This type of cells in a group is called tissue. In multicellular organisms division of labour is the main cause of formation of tissue.
Type of tissue: Cells of all tissues do not have the power of cell division but some of them have. Therefore tissues are of two types in terms of the power of cell division.

1. Meristamatic tissue &

2. Permanent tissue.

1. Meristamatic tissue :

Meristamatic cells compose the Meristamatic tissue. The cells of this tissue divide repeatedly. These tissues are found in the tress. Due to their presence plants increase in size very rapidly. Other permanent tissues are originated from Meristamatic tissue.

Characrteristics of Meristamatic tissues:Characrteristics of  Meristamatic tissues are as follows :

1. Cells possess the power of cell division.

2. Usually the cells are rectangular of oval.

3. Cell wall is made of cellulose and is thin.

4. Nucleus is large and the cytoplasm is denser.

5. Usually no vacuole is seen in the cell.

6. Usually there is no intercellular space in Meristamatic tissue, so the cells are arranged compactly.

2. Permanent tissue:

Cells of permanent tissues are not capable of cell division, for which they are called Permanent tissue. They are originated from Meristamatic tissues. All tissues other than the Meristamatic ones are permanent tissues.

Characteristics of Permanent tissue:

1. Cells of these tissues have no power of division.

2. Cells are well developed and properly shaped.

3. Cell wall is comparatively thick.

4. Nucleus of the cells are bigger and cytoplasm is dense.

5. Usually there are vacuoles in the cell.

6. There may have intercellular spaces in between cells.

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Whether the child will be a son or daughter

Now we can understand easily that the father or mother is responsible for the birth of a son or daughter. Both male and female have 44 autosomes, a pair of sex chromosome. Sex chromosome of a female is XX and that of the male is XY. The male gamete (sperm) bears X and Y chromosome. But the female gamete (egg) bears X and X. If the X bearing egg of the female is united (fertilize) with Y bearing sperm of the male, the child will have XY. A child having such chromosomes will be a male child. It is seen that if there is no Y chromosome, the child will never be a son. There is no Y chromosome in a female; Y chromosome is present only in male. So if a couple do not have any male child, the husband is responsible not the wife.

A figure on this ssue shows:

 

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Male-Female determining Chromosome

Every living being has a definite number of chromosomes. In human beings there are 23 pairs of chromosome. Among them 22. pairs are similar in both male and female, these are Autosomes . Members of the remaining pair of chromosome are different in male and female. This pair of chromosome determines the sex of human beings. As they determine the sex, so they are called X and y sex chromosome or sex determining chromosome. One of the sex chromosomes is X chromosome and the other is Y chromosome. If the sex chromosome pair is XY, the child will be male (son), and if it is XX, the child will be female (daughter). In Drosophylla (a fly) also XX indicate female and XY male. So in case of determining the sex, the role of  X and Y chromosome is vital.

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Different Stages of Mitosis

Mitosis is a continuous process. The process is completed by a complex  method. According to the sequence and stages, this continuous process is divided into five stages. The stages are:

(1)Prophase,

(2) Pro-Metaphase,

(3) Metaphase,

(4) Anaphaseand

(5) Telophase.

               Ø  Prophase: At this stage, the nucleus swells up.Chromosomes begin to be dehydrated. As a result, the chromosomes gradually become shorter and thicker. Then they are visible under microscopes. At the end of this stage nucleolus and nuclear membrane become disappear.

 

 

 Ø  Pro-Metaphase : At the beginning of this stage. the fibrous protein converse toform a bi-polar spindle apparatus. Each chromosome is then become attached to a fibre of the spindle apparatus by its centromere. Each fibre of the spindle apparatus is called spindle fibre. The fibre to which the chromosomes are attached is called traction fibre. As they are attached with the chromosomes so they also called hromosomal fibre. In animal cell aster rays re radiated from centrioles present at two poles.

   

  
Ø  Metaphase: Chromosomes are arranged at the equatorial plane of the spindle. The

centromere of each chromosome remains at the equatorial plane and the two arms are placed towards two poles. At this stage, the chromosomes become maximum thick and short. Two chromatids of a chromosome become maximum thick and short. Two chromatids of a chromosome become clearly visible and the centromere is divided in to two parts.

    

    
  Ø  Anaphase: Two separate chromatids of a chromosome move towards the opposite pole of the spindle apparatus. Centromere goes ahead at the movement of the chromatids towards the pole and the arms follow them. when the daughter chromosomes reaches near the poles the anaphase stage ends.

   

 Ø  Telophase: Daughter chromosomes take position at two opposite poles.Chromosomes gradually take water and become elongated, thin and long. Nuclear membrane develops encircling the chromosomes. Nucleolus reappears at the secondary constriction of the Sat chromosome. Spindle apparatus disappears. At the end of this stage, gradually a cell wall develops at the equatorial region of the cell. As a result, the mother cell divides into two daughter cells. In case of animal cells, instead of formation of cell wall the cell membrane is constricted inwardly and the cell divides into two.

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