What kind of sugar units make up a monosaccharide?

A monosaccharide consists of one sugar unit, which makes it the simplest form of carbohydrate. This single sugar unit can either be an aldose, containing an aldehyde group, or a ketose, containing a ketone group. Monosaccharides cannot be hydrolyzed into simpler sugars, which distinguishes them from disaccharides and polysaccharides, which are composed of two or more sugar units, respectively. Common examples of monosaccharides include glucose, fructose, and galactose, all of which primarily serve as building blocks for more complex carbohydrates and are essential for various metabolic processes in living organisms.