What do the different types of permanent tissues do?

Parenchyma

Parenchyma is a type of simple permanent tissue composed of living cells with thin cell walls. The cells are usually oval or round in shape and loosely packed to create intracellular spaces. The cell walls are composed of cellulose. 

Parenchyma participates in photosynthesis due to their chlorophyll content. They also have storage functions and contribute to the overall mechanical support of the plant. 

Collenchyma

Collenchyma consists of living cells with thickened cell walls composed of cellulose, pectin and water. It is primarily present in leaf stalks and beneath the epidermis. The collenchyma has a high refractive index resulting from its pectin content. These cells are elongated and tightly packed with very little intracellular space.

Collenchyma provides the plant body with mechanical strength, elasticity, and tensile strength, and contributes to the flexibility of plants. It also plays a role in the manufacture of sugar and sugar storage in the form of starch. Additionally, it helps prevent leaves from tearing due to the wind, and can dedifferentiate to form cork cambium or phellogen.

Sclerenchyma

Sclerenchyma tissue is composed of dead cells with very thick cell walls that have a high lignin accumulation. These cells lack protoplasm and have no intracellular space.

The primary function of sclerenchyma is to provide the plant’s main structural elements with vital mechanical support and rigidity. The thick, lignified walls make the plant structures stiff and hard.