Carbohydrates are essentially simple sugars. Glucose, Fructose, Maltose, Sucrose and  Lactose are forms of sugars.

The smallest building block of a carbohydrate is a Monosaccharides.

Mono = One

Saccharide = Sugar

Fructose and Glucose are both monosaccharides. If we look at a Fructose molecule and a Glucose Molecule, the amount of Carbon, Hydrogen and Oxygen molecules are the same.  

The only difference is how they are arranged.

Fructose

Glucose

When we put two monosaccharides together, we form a Disaccharide.

Sucrose, Maltose and Lactose are three Disaccharides.  

Maltose = Glucose and Glucose

Sucrose = Glucose and Fructose

Lactose = Galactose and Glucose

These two monosaccharides are joined by a Covalent bond.

When we get a chain of monosaccharides we form a Polysacchardie.

Starch and Glycogen are 2 forms of polysacchardies.

In humans we store glucose as Glycogen, while in plants, they store glucose as Starch.

You’ll see that although both of them store glucose, the way the molecules are structured is very different.

While starch is in straight layers, glycogen branches off.