**Core Concept**
Chitin is a polysaccharide composed of a long chain of N-acetylglucosamine units, which is a key structural component of exoskeletons in arthropods, such as insects and crustaceans. It is also a major component of the cell walls of fungi. The unique structure of chitin allows it to provide rigidity and strength to these organisms.

**Why the Correct Answer is Right**
The correct answer is that chitin is a polysaccharide. Chitin is synthesized in the cell membrane by the enzyme chitin synthase, which catalyzes the transfer of N-acetylglucosamine units from UDP-N-acetylglucosamine to the growing chitin chain. The resulting chitin fibers are then secreted out of the cell and assembled into a strong and flexible matrix. This matrix provides the structural framework for the exoskeletons of arthropods and the cell walls of fungi.

**Why Each Wrong Option is Incorrect**
* **Option A:** Not applicable, as this option is missing.
* **Option B:** Incorrect, as chitin is not a type of protein. While chitin is synthesized by enzymes in the cell membrane, it is a carbohydrate, not a protein.
* **Option C:** Incorrect, as cellulose is a polysaccharide composed of glucose units, not N-acetylglucosamine units. Cellulose is a key component of plant cell walls, but it is not related to chitin.

**Clinical Pearl / High-Yield Fact**
Chitin is an example of a biomaterial that has inspired the development of new medical technologies, such as wound dressings and tissue engineering scaffolds. Its unique properties make it an attractive material for biomedical applications.

**Correct Answer: B. Chitin is a polysaccharide.**