Carbohydrates are typically used by living organisms as a source of energy.

The term carbohydrate refers to either a single sugar molecule or several sugar molecules bonded together.

Glucose is a common sugar molecule used to make carbohydrate polymers.


carbohydrate foods  

Monosaccharides: Ready Energy

Monosaccharides are carbohydrates with a single sugar molecule.

Glucose is an important monosaccharide in living organisms.

Glucose is the energy source of choice and is "burned" by cells to produce energy.


structure of glucose



Disaccharides: Varied Uses

A disaccharide contains two monosaccharides bonded together.

Sucrose (table sugar) and lactose (milk sugar) are disaccharides. 


Polysaccharides as Energy Storage Molecules

Polysaccharides are polymers of monosaccharides.

Some polysaccharides function as short term energy storage molecules.

Plants store glucose as starch.

Animals store glucose as glycogen.

Polysaccharides as Structural Molecules

Cellulose is the most abundant polysaccharide on earth because it comprises the cell walls of plants. It, like glycogen and starch, is made up of many glucose monomers connected together. However, the glucose molecules of cellulose are linked together differently than the glucose molecules of starch and glycogen.

It cannot be digested by humans because we don't have the correct enzymes to break these different types of bonds that hold them together. Other organisms (cows, rabbits, horses, termites) have microorganisms in their digestive systems which do have the right type of enzymes to break down cellulose and these animals are able to get nutrition (calories) from it.






 Structure of starch


 Structure of glycogen


Structure of cellulose

Toggle open/close quiz question

If a cell wanted to break down cellulose, which of the following is true?
    a.All cells can break apart cellulose, it would just need to use hydrolysis to break the cellulose apart
    b.The cell would need the correct enzyme in order to use hydrolysis to break down the cellulose
    c.The cell would need to have the correct enzyme in order to break the cellulose down using dehydration synthesis
    d.All cells can break down cellulose using dehydration synthesis


Extra Help


 More about sugars