Parenchyma Versus Aerenchyma

Parenchyma :

Parenchyma is made up of thin walled living cell. The cell wall is usually unthickened and formed of cellulose. The intercellular spaces may or may not be present.
Parenchyma is present in all the organs of plants. It fills up the spaces between different tissues and thus acts as a ground tissue or matrix.

Some of the modified parenchymatous tissues are follows:

I. chlorenchyma
II. aerenchyma


The parenchymatous tissue performs a variety of functions:

• It forms the epidermis on the outermost surface of the plant organs.
• It acts as a protective layer.
• Sometimes an impermeable layer of cutin called cuticle lines the outer surface of the epidermis. This cuticle checks he rate of transpiration.
• Guard cells of the stomata are means for exchange of respiratory gases in leaves and other organs. These guard cells are epidermal in origin.
• The epidermis and root hairs in roots are not covered by cutin. The root hairs are cylindrical outgrowths from the walls of epidermal cells of roots and increase the water absorbing capacity of roots.

Chlorenchyma :

Chlorenchyma is seen in green leaves and some other green aerial organs.
Its cells contain chloroplasts.
Chlorenchyma is differentiated into :
(a) Palisade (b) Spongy chlorenchyma

(a) Palisade:
In this tissue the cells are columnar.
The columnar cells are arranged at right angles to the upper surface of the leaf.
The intercellular spaces are relatively few.
The cells are somewhat compactly arranged.
The location of palisade in leaf and other flattened aerial, green organs is such as to receive strong, straight sun-rays.

(b) Spongy Chlorenchyma:
Spongy chlorenchyma is located in leaf and other aerial green organs in such a way as to receive mild sun rays.
Cells in spongy chlorenchyma are round or oval, parenchymatous and have large intercellular spaces.

In most leaves, the spongy chlorenchyma lies near the lower epidermis.

The cells of both palisade and spongy chlorenchyma tissues contain chloroplasts and hence perform the function of photosynthesis synthesizing glucose.



Aerenchyma :

Hydrophytes are plants growing in water or water logged habitats. E.g.Trapa, Lotus, Pistia etc. Hydrophytes have aerenchyma as one of the tissues.
Aerenchyma consists of small cells so arranged as to form large air spaces.
Due to air contained the respective plant organs become soft, light and spongy.

As a result the organs can keep themselves floating and obtain sufficient light for photosynthesis in the hydrophytes.

Some of the air spaces show special type of partition walls, which provide them mechanical strength

Extracted : TQ