Division Of Labour In Multicellular Plants

Division Of Labour In Multicellular Plants :

Tissue and Tissue System

Tissue : In unicellular organisms a single cell does all the functions. There is no chance of division of labour on the basis of cell. In contrast, this kind of division is found in multicellular living body. In this case, it is observed that 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.



Types 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 :

• Meristamatic tissue &

• 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 or 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. Meristamatic tissues are present at the apex of roots and stems. According to their position they are Apical meristems and accroding to their origin they are Primary meristems, because they are originated from the embryonic stage. Stem and root increase in length by the division of cells of these tissues. In the roots and stems of gymnosperms and dicotyledonous plants there develops a new Meristamatic tissue, they are called 'Secondary meristems. According to their position they are Secondary meristems. Due to the cell division of these tissues the breath of the root and stem increase i.e. the root and stem gradually become broader in breath

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.

Types of permanent tissue :

Permanent tissues are of three types, namely -

• Simple tissue,
• Complex tissue and
• Secretory tissue.

(a) Simple tissue: Tissues of same kinds compose simple tissue. Simple tissues are of three types, namely Parenchyma: Characteristics of parenchyma tissue are as follows:

* Cells are almost uniform in length, breath and depth.

* Cells are round, oval or polygonal in shape.

* Cell wallls are evenly thick.

* Cells are living and contain sufficient protoplasm.

* There may have intercellular spaces between adjacent cells. Permanent - tissues that Thin cell wall contain chlorophyll are called Chlorenchyma. The chlorenchyma of leaf IS called Messophyll. Parenchymatous tissues with large air spaces In aquatic plants are Aerenchyma.

Functions:

* Chlorenchyma manufactures food materials. * They store reserve food.

* They help ,in transporting the food materials. Parenchyma in the epidermis act as a defensive organ. Position: Usually pith, pith rays, epidermis and most of the cortex are made of this tissue.

Collenchyma: Characteristics of collenchyma tissues are as follows:

√ Cells are to some extent elongated. '

√ Cells are living with protoplasm.

√ Cell wall is unevenly thick, thickness is greater at eorners of the cells.

√ There maybe intercellular spaces between adjacent cells Functions:

￾ Cells with chlorophyll manufacture food.

￾ It gives mechanical strength ' to the growmg organ. Position: It is found under the epidermis, in the petioles and veins of leaves and in the flower stalks.

Sclerenchyma: Characteristics of Sclerenchyma are as follows: ￾ Cells elongateq and the ends are pointed.

￾ Cell walls being lignified become thick and the thickness is uniform. Mature cells are dead and without nucleus and protoplasm.

￾ In transverse section they are polygonal.

Functions:

￾ To give mechanical strength to different organs of the plant is the main function.

￾ Some dead cell may store excretory substances of plants.

￾ Sometimes it forms hard outer wall to protect the inner soft portion, e.g. seeds of coconut and date-palm Position : They are present in cortex, phloem and pericycle.