Permanent Tissue - Simple Permanent Tissues (Supporting Tissue)

Permanent Tissue

• Cells of meristematic tissues change their shape & size to get specialised in performing other functions in plants body. This process is called Differentiation.

• Once the cells of meristematic tissue divide to a certain extent, they become specialized for a particular function.

Permanent tissues are of two types:

Simple tissues and Complex tissues

(i) Simple tissues: This type of tissue is composed of same type of cells.

These are again of four types:

(a) Parenchyma simple tissues:

• These tissues are responsible for photosynthesis, storage of food, gaseous exchange and floating of plants.
• They are a group of living cells with cell wall made of cellulose.
• The parenchyma cells have large intercellular spaces between them.
• There are thin walls that surround each cell.
• They are found in leaves and newly formed branches.

(b) Collenchyma simple Tissues:

• These tissues are responsible for providing flexibility to the plants so that they can bend easily.
• They are a group of living cells with cell wall made of cellulose and pectin.
• They have a little intercellular space in between them.
• The cells present in these tissues are broad and irregularly thick at corners.
• They are present in leaves and stems of a plant.

(c) Sclerenchyma Simple Tissues:

• These tissues are responsible for making plants hard and rigid.
• They are made up of dead cells having cell wall made of lignin.
• The cells do not have any intercellular spaces.
• The cells have a long structure with thick walls.
• They are found in stems, veins of the leaves and coverings of nuts and seeds.

Chlorenchyma

These tissues are similar to that of parenchyma but they also contain chlorophyll in them.

Due to the presence of chlorophyll, they are capable of performing the process of photosynthesis in plants.

Aerenchyma

• They are found in aquatic plants.
• They are also similar in structure to that of the parenchyma but they have large air cavities in them.
• These cavities allow the aquatic plants to float in water.
• The cell walls of dead cells have a substance called lignin in them which provides rigidity to the cells. Lignin acts as the cement for the cells.

Stomata

Stomata are pore-like structures that are present in the epidermis of the leaves.

These pores are enclosed by two cells that have a similar shape as a kidney. These are called Guard Cells of Stomata. Guard cells are modified epidermal cells.

Guard cells are responsible for the exchange of gases and transpiration.

Epidermis:

• The outermost layer of the cell is known as the Epidermis.
• It covers the entire plant.
• It is a thin layer of single cells but in places with less water, the epidermis of the plants can become thick in order to avoid frequent water loss.
• The cells are flat and they have no intercellular spaces between them.
• The outer walls of the epidermal cells are thick and the inner walls are thin.
• The epidermal cells often have long hair-like structures in roots which facilitate the absorption of water.
• The main function of the epidermis is to protect the plants from fungi, water loss and any injuries by secrets a wax-like water-resistant substance called as Cuticle on the surface of the plants which protects the plants.

Cork Simple Tissues:

• These types of tissue consist dead cells with no intercellular spaces. They form the outer layer of old tree trunks.
• Cork cells have a chemical called suberin in their walls that makes them impervious to gases and water.
• Cork tissue protects plants from injuries, germs and water loss.
• Cork being light in weight is used for making several products like bottle stoppers and shuttle cork.

Simple Permanent Tissues:

Tissues made of one type of cell, which looks like each other.

1) Parenchyma:

• These tissues provide support to plants and store food and water. They are loosely packed and have large intracellular space.
• Parenchyma with chlorophyll which performs photosynthesis is called chlorenchyma.
• The parenchyma with large air spaces to give buoyancy is called aerenchyma.

2) Collenchyma:

• This tissue provides mechanical support.
• It is thickened at the corners and have very little intercellular space.
• It provides flexibility allowing easy bending of various parts of a plant without breaking.

3) Sclerenchyma: 

• This tissue makes the plant hard and stiff.
• It is thickened due to lignin and has no intercellular space.
• Cells of this tissue are dead.
• It is commonly seen in the husk of the coconut.

4) Guard cells and Epidermal tissue:

• This tissue provides protection and helps in the exchange of gases.
• Guard cells are present around the stomatal pore. They can be kidney or dump-bell shaped.
• Epidermal tissues are flat and have no intracellular spaces. The epidermal tissues of roots help in the absorption of water and minerals. They are modified in desert plants to help them in adaptation. They have a thick waxy coating of Cutin. This aids in protection against loss of water, mechanical injury, and invasion by parasitic fungi.