A simple sugar contains a single unit. Examples of monosaccharides include glucose, fructose, and galactose. Two monosaccharides may even contain the exact same chemical formula. The difference is in the way the atoms are arranged in the molecule. Substances that have the same chemical formula, but differ in structure are called isomers.
Disaccharides are sugar molecules composed of two monosaccharide units.
It is composed of a molecule of glucose bonded with a molecule of fructose. The formation of sucrose requires that one atom of oxygen and two atoms of hydrogen be released in order to provide bonding sites for the two molecules. Sometimes, carbohydrates can occur in very large and complex arrangements of bonded monosaccharides. These large molecules are called polysaccharides . Starch is a polysaccharide containing about 20 or more units.