Polysaccharides – Class 12 | Chapter – 9 | Biology Short Notes Series PDF

Polysaccharides are major classes of biomolecules. They are long chains of carbohydrate molecules, composed of several smaller monosaccharides. These complex bio-macromolecules functions as an important source of energy in animal cell and form a structural component of a plant cell. It can be a homopolysaccharide or a heteropolysaccharide depending upon the type of the monosaccharides.

Characteristics of Polysaccharides

  1. Many of the polysaccharides are insoluble in water.

  2. These are not sweet.

  3. These are hydrophobic.

  4. These do not form crystals on desiccation.

  5. Polysaccharides can be extracted in the form of a white powder.

  6. These have a high molecular weight as carbohydrates.

  7. These are compact and osmotically active inside the cells.

  8. The hydrogen to oxygen ratio in them is 2:1 and they consist of hydrogen, carbon and oxygen. 

Functions of Polysaccharides

  1. Structural Functions- Common sources of energy are nutrition polysaccharides and most of the organisms can easily break down starch into glucose. However, some complex polysaccharides are not very digestible that are known as dietary fibre and these provide important elements in the diet for humans. There are soluble fibre and insoluble fibre that are associated with various functions in the body. The former is responsible for lowering cholesterol levels (bad) in the blood, normalizing blood lipid levels and reducing sugar response after eating. The latter or insoluble fibre reduces the risk of diabetes.

  2. Storage Functions- Storage polysaccharides are starch, glycogen and insulin. A glucose polymer that is insoluble in water is Starch. Both humans and animals have amylases to digest starches easily. Starch can be found in potatoes, rice, wheat and maize. Glycogen is the long-term store for energy and works the best in animal and fungal cells. The primary energy storage takes place in the adipose tissue and glycogen is made by the liver and muscles and also within the brain and stomach by glycogenesis. Glycogen serves as an energy reserve for animals and is the main form of carbohydrate stored in the animal body. It is insoluble in water and yields glucose on hydrolysis.

Types Of Polysaccharides

Polysaccharides are categorized into two types:

  • Homopolysaccharides.
  • Heteropolysaccharides.


A polysaccharide that contains the same type of monosaccharides is known as a homopolysaccharide. Some of the important homopolysaccharides are:

  1. Glycogen: It is made up of a large chain of molecules. It is found in animals and fungi.
  2. Cellulose: The cell wall of the plants is made up of cellulose. It comprises long chains of ꞵ-glycosides.
  3. Starch: It is formed by the condensation of amylose and amylopectin. It is found largely in plants, fruits, seeds, etc.
  4. Inulin: It is made up of a number of fructofuranose molecules linked together in chains. It is found in the tubers of dahlia, artichoke, etc.


A polysaccharide that contains different types of monosaccharides is known as a heteropolysaccharide. Some of the important heteropolysaccharides are:

  1. Hyaluronic Acid: It is made up of D-glucuronic acid and N-acetyl-glucosamine. It is found in connective tissues and skin.
  2. Heparin: It is made up of D-glucuronic acid, L-iduronic acid, N-sulfo-D-glucosamine and is largely distributed in mast cells and blood.
  3. Chondroitin-4-sulfate: Its component sugars are D-glucuronic acid and N-acetyl-D-galactosamine-4-O-sulfate. It is present in the cartilages.
  4. Gamma globulin: N-acetyl-hexosamine, D-mannose, D-galactose are the component sugars of this polysaccharide. It is found in the blood.

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By Team Learning Mantras