Question

What chemical substance is deposited in the secondary wall of sclerenchyma?
A)Myelin
B)Lignin
C)Lymph
Collagen

Answer 1

Hint : It is a complex polymer of amino acids deposited in the cell wall of the plant cell. It provides flexibility, great tensile and compressive strength.

Complete answer :
Sclerenchyma is a hard supporting tissue, formed of long, narrow, fibre-like cells with pointed ends. These cells are dead with thick lignified walls (i.e., deposited with lignin) that gradually lose protoplasm.
Nucleus and cytoplasm are absent in sclerenchyma. The cell wall of sclerenchyma is formed of cellulose and hemicellulose. It is thickened due to the secondary deposition of lignin (i.e. have lignified cell walls ). Lignin acts as cement and hardens the cell wall. The lignified cell wall has pits. Lignin makes the cell wall impermeable and doesn’t allow substances to pass through it. As a result, heavily lignified cells are without living cytoplasm.
Lignin is basically deposited in tracheids, vessels, fibres of xylem and phloem and sclerenchyma. However, lignin composition varies among species, phylogenetic groups, cell types, developmental stages and even seasonal growth.
Myelin is an insulating layer that forms around the nerves including the brain and spinal cord. It is made up of protein and fatty substances that’s why it can’t be considered as the answer as it is not found on the secondary wall of sclerenchyma. Lymph is not a protective covering it is a fluid connective tissue. They help in providing immunity rather than acting as an outer covering. Collagen Is found in bones, muscles, skins, and tendons and it holds the body together. It also doesn’t act as outer covering.

Thus, the correct option is B i.e., Lignin.

Note : Lignins are resistant to acid hydrolysis, readily oxidized, soluble in hot alkaline and bisulfite. It is a natural polymer exist in all terrestrial plants although some aquatic organisms may contain lignin like components.