Why are epidermal and cork cell called protective tissue?

Epidermal cells and cork cells are two types of cells in the outermost layer of the cells. Epidermal cells are arranged in a single layer to cover the whole plant body during primary growth. Cork cells are produced by the cork cambium during secondary growth of plants. Both epidermal cells and cork cells contain water-repellent substances to prevent the water loss from the plant body. The main difference between epidermal and cork cells are the occurrence of each type of cells in the plant body.

As plants grow older, the outer protective tissue undergoes certain changes. A strip of secondary meristem replaces the epidermis of the stem. The outer layer of young tree stem is made up of living cells called epidermis.

Cells on the outside are cut off from this layer. This forms the several-layer thick cork or bark of the tree. Cells of bark are dead and compactly arranged without intercellular spaces.

Both bark and epidermis forms the components of simple permanent tissue whose main function is in protection. In the woody plants the epidermis of the stem is replaced by periderm whose major component is the cork.

Reason why epidermis and cork are called protective tissue:

a) Since the entire surface of a plant has outer covering of epidermis. It protects all the parts of the plant.

b) Epidermal cells on the aerial parts of the plant often secrete a waxy, water-resistant layer on their outer surface.

c) This aids in protection against loss of water, mechanical injury and invasion by parasitic fungi.

d) Cork cells have a chemical substance called suberin that makes them impervious to gases and water.

e) They also help the plant from attack by harsh environmental conditions like extreme hot temperature.