Monosaccharides

What gives a ripe mango or a spoonful of honey its sweet taste? It is simple sugars — that is, monosaccharides. Monosaccharides are the building units of carbohydrates. All the other carbohydrates are built when these units join to one another in different ways.

How do we recognise monosaccharides?

They exist as crystals.
They dissolve easily in water.
They taste sweet.

The three members of this group we meet most often are glucose, fructose and galactose.

Comparing the three monosaccharides

Type	Where it is found	Facts to know
Glucose	Ripe fruit, honey	Glucose is what is finally left when any starchy food is digested. It is what gets absorbed into the blood. Glucose is also what plants make in photosynthesis. Cells get energy by breaking down glucose in respiration.
Fructose	Ripe fruit, honey, pumpkin, carrot	Also known as "fruit sugar". As an unripe fruit ripens, fructose forms inside it, so the ripe fruit tastes sweet. Of all the sugars, fructose is the sweetest.
Galactose	Milk foods	Forms when the lactose in milk is digested. It is not sweet.

Extra knowledge — the shape of a glucose molecule

A six-sided ring of five carbon atoms and one oxygen atom, with hydroxyl (–OH) groups and a single –CH₂OH group attached around it. — The structure of a glucose molecule

A glucose molecule is like a ring with six corners — a hexagonal ring. Five of the six corners hold carbon atoms and one holds an oxygen atom. Several hydroxyl (–OH) groups and one –CH₂OH group are attached to the outside of the ring.

These –OH groups are why glucose dissolves easily in water. They also act as the "hands" two glucose molecules use to hold on to each other.