There are four main categories of macromolecules (extremely large molecules) which includes proteins, lipids, nucleic acids, and carbohydrates. The monomer of carbohydrates is called a monosaccharide (mono- meaning one; sacchar meaning sugar). By joining monosaccharides together through glycosidic covalent bonds (a dehydration reaction), polysaccharides are formed. The carbohydrates that are formed have a variety of functions such as energy storage and support/structure.
Two examples of carbohydrates with a structural function include cellulose and chitin. Cellulose is found in the cell walls of plants and is not found at all in animals. Cellulose is a rod-like polymer of glucose. The second example of a carbohydrate with a structural function is found in animals. This carbohydrate is called chitin. Chitin is found in the exoskeletons. Similar to cellulose, chitin is a polymer of glucose (the difference us that each glucose in chitin has an attached amino acid).
The second function of carbohydrates is for energy storage. Starch is the energy storage polysaccharide found in plants. Just like the previous polysaccharides mentioned, starch is composed of multiple glucose molecules bonded by glycosidic bonds. The energy storage polysaccharide found in animals is named glycogen. Glycogen is stored in the liver of animals. The reason why my cat was chosen to represent the term glycogen is because of the reason that glycogen is found only in animals.