Question

What are the general characteristics of sclerenchyma tissue? Which type of cells of this tissue are the cause of grittiness of the pulp of pear?

Answer 1

Hint: sclerenchyma is a Greek word that means hard tissue. Sclerenchyma is a simple permanent tissue ( it is made up of single kinds of cells) that is composed of dead cells. The walls ( that is outer layer) of sclerenchyma consist of the deposition of cellulose, hemicellulose and lignin.

Complete answer:
Some characteristics features of sclerenchyma are:
a. Cells of sclerenchyma are called sclerenchymatous cells. They are usually dead ( non-green) and without protoplasts. During maturation, the cells lose their protoplasm and become dead.
b. Cells are elongated and narrow and possess highly thickened cell walls. Their walls are made up of substances like cellulose, hemicellulose and a specialised organic material lignin which provides mechanical strength to the plant and its parts. Lignin deposition is so thick that the cell walls tend to become strong, rigid and impermeable to water.
c) Walls of the sclerenchymatous cells possess few to numerous pits.
two types of cells are found in sclerenchyma:
a. Sclerenchymatous fibres: These are the highly elongated cells which have pointed or oblique ends. Their elongated and narrow shape makes them look like fibres. These are the thick-walled cells and, in some cases,, the cell wall becomes so much lignified that the lumen (inner space or cavity) is greatly reduced
These fibres generally occur in groups or bundles, in various parts of the plants like stems. They are usually found associated with xylem and phloem of the vascular bundles. These provide the mechanical strength to the organs that possess them.
b. Sclereids: These are spherical, oval or cylindrical cells with highly thickened cell walls. The cell walls are so thickened that the lumen of the cells is always reduced and obliterated
Sclerenchyma tissue that is sclereids is responsible for the grittiness of pulp of fruits.

Note: Sclereids are present in:
 Fruit walls of nuts like walnut, almond, etc.
Pulp of fruits like guava, pear and sapota (cheeku) etc. The 'gritty' (crisp) texture of these fruits is due to the presence of hard cells or sclereids in their pulp.
Seed coats of legumes like peas, beans, etc. (Seed coats are the outer protective coverings of seeds), Leaves of tea.