Question

Araban/Xylan is
A. Tetrosan
B. Pentosan
C. Hexosan
D. Heptosan

Answer 1

Hint: Xylan is a group of hemicellulose present in plant cells. They provide raw material for the preparation of complex polysaccharides. They are anticoagulant and antiviral in nature.

Complete Answer:
It is the third most abundant biopolymer on earth. It is found in the secondary cell wall of dicots and the cell wall of all grasses.
- Composition: It is a polysaccharide which is made up of beta 1, 4 linked xylose which is a pentose sugar or pentosan. Most xylans contain branches of L-arabinofuranose, acetyl D-glucopyranosyl and 4,O-methyl glucuronosyl residues. The biosynthesis of Xylans involves glycosyltransferase.

Role of Xylan in plant cell:
- It helps in maintaining the integrity of the plant cell wall.
- It helps in increasing the cell wall recalcitrance to enzymatic digestion.
- It helps plants to defend against herbivores and pathogens.
- It plays a significant role in plant growth and development.

Commercial uses:
- It plays a significant role in the bread industry as it affects the hardness of dough.
- A xylose derivative can be used as a natural sugar.
- Xylan is a major source of renewable energy in making biofuels.
- It has potential prebiotic property.
- Hexosan is the group of hemicelluloses that hydrolyses hexose sugar.

Thus the correct answer is (B). Araban/Xylan is pentosan.

Note: The xylan present in hardwood is around 10-35% and that in softwood is around 10-15%. The xylan along with cellulose and lignin provides rigidity to the cell wall.