chitin

definition: 
A fibrous substance consisting of polysaccharides, which is the major constituent in the exoskeleton of arthropods and the cell walls of fungi.
sentence: 
There are a few other animal carbohydrates, notably chitin, the substance which constitutes the hard outer casing of insects and crustaceans.
difficulty: 
medium
toefl frequency: 
1
toefl classification: