The common name for a group of chemicals known as carbohydrates . They are made up of carbon , hydrogen and oxygen . They are classified according to the number of sugar units which make up their structure:
• Monosaccharides (e.g. glucose, fructose, galactose) have one sugar unit
• Disaccharides (e.g. sucrose, lactose and maltose) have two sugar units
• Polysaccharides are complex carbohydrates, with many sugar molecules which are joined together.