A disaccharide is formed by the chemical bonding of two monosaccharides. This process is known as dehydration synthesis or condensation reaction, where a molecule of water is released as the two sugar molecules combine.
To elaborate, monosaccharides are simple sugars like glucose and fructose. When they join together through a glycosidic bond, they create a disaccharide like sucrose (table sugar), which is composed of glucose and fructose. The formation of this bond is crucial for creating larger carbohydrates and provides energy sources for living organisms.