Question

The monomer unit of chitin in fungal cell wall is
A. Mannitol
B. Acetyl glucosamine
C. Ascorbic acid
D. Glucuronic acid

Answer 1

Hint: A characteristic feature that places fungi in a different kingdom than plants and animals is that their cell wall has chitin. Chitin’s monomer unit has significance in various biological systems.

Complete Answer:
- Fungus is a eukaryotic organism present worldwide and includes microorganisms like yeasts, rusts, smuts, mushrooms and molds. The fungal cell wall is rigid and is made up of glucans and chitin. Glucans are found in plants while chitin is present in the exoskeleton of arthropods. Fungi are the only organisms that combine both these structural molecules on their cell wall.
- Chitin is a long-chain polymer of N-acetylglucosamine, a derivative of glucose. These units form covalent linkages. Chitin may be described as cellulose with one hydroxyl group on each monomer replaced with an acetyl amine group. This feature allows increased hydrogen bonding with adjoining polymers, providing the polymer matrix increased strength.
- N-Acetylglucosamine is a secondary amide between glucosamine and acetic acid. Its polymer form, chitin, is the main component of radula in molluscs, breaks of cephalopods etc. Chitin is used as a flocculating agent in wastewater. Humans and other mammals have chitinase and chitinase-like protein that can degrade chitin.

Additional information: Mannitol is a kind of sugar alcohol used as a sweetener and medication. It is commonly used to increase urine production, diuretics.
- Ascorbic acid or Vitamin C is a reducing and antioxidant agent that fights bacterial infections and protects body cells from damage.
- Glucuronic acid is a soluble compound produced from the liver of humans. It facilitates the transport of hormones and drugs. It also helps in metabolism of microorganisms, plants and animals.

Thus, the correct answer is option B, ‘acetyl glucosamine’.

Note: Chitin is a very versatile molecule. It can form solid structures on insect wings on its own, or can combine with other components like $CaCO_3$ to make very strong substances like shells. In fungus, chitin helps to retain their shape and provides them strength.