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A simple sugar that cannot be decomposed.

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Welcome to the realm of carbohydrates!

Carbohydrate food sources

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Carbohydrates are the most abundant source of energy found in most foods.

Remember: "carbohydrates" refers to the fact that most contain carbon, hydrogen, and oxygen in a 1:2:1 ratio, making an empirical formula of CH2O - it is not a hydrate!


The simplest carbohydrates, or simple sugars, are plentiful in fruits. A monosaccharide is a carbohydrate consisting of a single sugar unit.

Common examples of simple sugars are glucose and fructose. Why are these referred to hexoses? How do the structures differ?

Note: in the images below, there is a carbon (C) wherever the structure bends - it's just the shorthand way of drawing the structures!

Linear forms of monosaccharides glucose and fructose

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The following structures are also glucose and fructose:

Cyclic form of monosaccharides glucose and fructose

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How does this compare to the first set of structures? Why are they different?

Pentoses, such as the structures shown below, are also an important group of monosaccharides.

Structure of the monosaccharides ribose and deoxyribose

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For more information on monosaccharides and to check your answers, click here.


Monosaccharides are the foundation of more complex carbohydrates. How can two cyclical sugars be linked together? (Hint: use the following image to help you explain)

Condensation of glucose and fructose creates sucrose

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Sucrose, or table sugar, is a disaccharide. Lactose, which is found in milk, and maltose are also common disaccharides. How are disaccharides broken down during digestion?

To check your answers and to find more information on disaccharides, click here.


A polysaccharide is a complex carbohydrate polymer formed by linking multiple monosaccharide monomers.

Tip: "mono" means one or single, "di" means two, and "poly" means many. These prefixes refer to the number of monosaccharides of each type of carbohydrate!

One of the best known polysaccharides is starch - a staple in most diets. The following are two forms of starch:

Structure of amylose and amylopectin

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How do amylose and amylopectin differ from each other?

Glycogen has even more branches of glucose monomers. What is the function of glycogen?

Cellulose is another polymer of glucose and can consist of hundreds to thousands of monomers. It is the structural component of cell walls of green plants and is the single most common organic molecule on Earth!

Ball and stick structure of cellulose

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How does cellulose differ from starch? What does the structure look like? How is cellulose used in everyday life?

You can check your answers and find more info on polysaccharides here!

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