Polysaccharides form when monosaccharides or disaccharides attach in chains. They are carbohydrate structures and generally heterogeneous. They are common in plants and are used as food and energy storage by most animals.
The most prominent example of a polysaccharide is Starch, which is composed of glucose. While it is not soluble in water, it can be digested by any animal with the specific enzyme amylase, including humans. Starch helps regulate and store energy.
Another common polysaccharide is Cellulose, the primary component of plants and especially trees. Since cellulose has a very strong molecular structure, it is not easily digested by animals; dietary fibers such as psyllium husk are examples of cellulose.
Chitin is another example; it is the smooth substance that forms crustacean and clam shells, as well as insect exoskeletons. Chitin is not easily broken down and is very common, and so acts as protection in organisms and has many industrial uses.