Final answer:
The example of a monosaccharide is glucose, which serves as an essential energy source for organisms. Sucrose and lactose are disaccharides, not monosaccharides, and starch is a polysaccharide. Lactose is made up of glucose and galactose connected by a glycosidic bond.
Step-by-step explanation:
An example of a monosaccharide is glucose. Monosaccharides are the simplest form of carbohydrates, consisting of single sugar molecules. Glucose (C6H12O6) is a primary source of energy for living organisms and a product of photosynthesis. Other common monosaccharides include fructose, found in fruits, and galactose, which is a component of lactose, or milk sugar. While glucose, galactose, and fructose all share the same chemical formula, they are distinct compounds known as isomers due to their differing arrangements of atoms.
Contrastingly, sucrose, lactose, and starch are not monosaccharides. Whereas sucrose and lactose are disaccharides, composed of two monosaccharide molecules, starch is a polysaccharide, which is a complex carbohydrate composed of many glucose units linked together.
To address a question from related topics, lactose is a disaccharide formed by the bond between glucose and galactose, which is known as a glycosidic bond.