Not all polysaccharides are based on glucose. The basic unit of starch and cellulose is glucose. But inulin is a kind of fructooligosaccharide, which exists in the roots of compositae plants. Agar is a kind of polygalactose, which is a polysaccharide contained in some seaweeds.

Polysaccharide is a complex and huge carbohydrate, which is formed by condensation and dehydration of multiple monosaccharide molecules. All carbohydrates and their derivatives that conform to the concept of polymer are called polysaccharides. Polysaccharides are widely distributed in nature and are also very important. Some are the components that make up the cell walls of animals and plants, such as peptidoglycan and cellulose;

Some nutrients used as animal and plant storage, such as glycogen and starch; Some of them have special biological activities, such as heparin in human body has anticoagulant effect, and polysaccharide in pneumococcal cell wall has antigen effect.

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Polysaccharides such as starch and glycogen can be used as biological energy storage materials. Heteropolysaccharide forms proteoglycan with protein through valence bond, which plays a biological role, such as being used as a body lubricant, identifying cells of heterogeneous tissues, and the basic components of blood group substances.

Polysaccharide compounds widely exist in animal cell membranes and cell walls of plants and microorganisms. They are high-molecular polymers formed by connecting aldehyde groups and ketone groups through glycosidic bonds, and they are also one of the four basic substances that constitute life.

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