Observe the outermost layer of cells in plants
What do you notice?
This is the single layer of cells called epidermis .
They are flat with outer and side walls are thicker than the inner wall
It is present all through the plant and protects the plant parts .
Since it has to protect, these cells do not have intercellular spaces .
The epidermal cells on the aerial surface (part facing outward) secrete a waxy, water-resistant layer .
This aids :
- Protection against loss of water
- Mechanical injury
- Invasion by parasitic fungi
The epidermis is thicker in dry areas to protect plants from water loss. They also have a layer of chemical substance called cutin which gives the plant waterproof quality .
Observe this image;
Look at the small pores present between the epidermal cells .
These are called stomata .
- The pore called stomata is enclosed by two kidney-shaped cells called guard cells .
- Exchange of gases (respiration in plants) takes place through stomata.
- Transpiration (loss of water in the form of water vapour) also takes place through stomata
There are root hairs extending from the epidermal layer .
Why is this so?
The root epidermis is responsible for water absorption
To increase surface area of absorption , they bear long hair-like structures called root hair.
Have you observed the outer layer of a branch of a young plant and that of a tree?
Why are they different?
The outer protective tissue of plants undergo certain changes with time
A strip of secondary meristem replaces the epidermis of the stem.
Cells on the outside are cut off from this layer to form several-layer thick cork (bark of the tree)
- Cork cells are dead
- Cells are compactly arranged
- They do not have intercellular spaces
- They have a chemical called suberin in their walls
- Suberin makes sure that gases and water cannot pass through
- Thus it protects the plants from mechanical injury and water loss by evaporation.