Carbohydrates also occur in various combined forms that are present as structural components in many plants and bacteria. A class of compounds commonly known as glycoproteins are composed of carbohydrates covalently linked to proteins. These include serum proteins, Some hypophyseal hormones and many other which have physiological roles to play.

Several slimy substances, known as mucoids, are also rich in carbohydrate content and consist of several short chains of oligosaccharids. Several blood group specific substances associated with the red blood cells