Monosaccharides are simple sugars with only one sachharide unit. These cannot be hydrolysed into simpler forms. A monosaccharide containing an aldehydic group (–CHO) in its molecule is called aldose. The glucose and galactose are aldoses. A monosaccharide which contains a keto group (> C = O) in its molecule is called ketose. Fructose is a ketose.