Tissues Test - 8

- The entire surface of a plant has the outer covering of epidermis.

- In some plants living in very dry habitats, the epidermis is thicker since protection against water loss is critical.

- The thick cuticle helps reduce water loss by transpiration.

- We can observe small pores here and there in the epidermis of the leaf.

- These pores are called stomata.

- Stomata are enclosed by two kidney-shaped cells called guard cells.

- They are necessary for exchanging gases with the atmosphere.

- Transpiration (loss of water in the form of water vapour) also takes place through stomata.

- Epidermal cells of the roots, whose function is water absorption, commonly bear long hair-like parts that greatly increase the total absorptive surface area.

- The root hairs greatly increase the surface area available for the uptake of water and nutrients from the soil.

- A strip of secondary meristem replaces the epidermis of the stem. Cells on the outside are cut off from this layer.

- This forms the several-layer thick cork or the bark of the tree.

- Cells of cork are dead and compactly arranged without intercellular spaces.

- A secondary meristem is a type of meristematic tissue that is responsible for the secondary growth in plants, i.e. growth in girth or thickness.

- Suberin is a waterproofing waxy substance found in higher plants.

- Suberin is a major constituent of cork.

- Its main function is as a barrier to movement of water and solutes.

• The cells of this tissue are dead.

• They are rigid, contain thick and lignified secondary walls.

• Their main function is to provide strength and support to parts of the plant.

Sclerenchyma tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts. It provides strength to the plant parts.

• Cell wall lignification is a complex process occurring exclusively in higher plants.

• Its main function is to strengthen the plant vascular body.

• This process involves the deposition of lignins.

• Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily.

• Sclereids are a reduced form of sclerenchyma cells with highly thickened, lignified cellular walls that form small bundles of durable layers of tissue in most plants.

• Sclereids are found in different shapes such as spherical, oval, or cylindrical.

• Their primary function is for mechanical support and protection.

• The substance that strengthens sclerenchyma cells is lignin.

• Lignin is cement like pigment which helps in protection and thickening of the sclerenchyma walls.

• Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily.