Final answer:
Monosaccharides in aqueous solutions usually exist as ring structures formed through the reaction between hydroxyl and aldehyde/ketone groups. The ring structures, such as pyranose and furanose rings, are important for their stability and functionality.
Step-by-step explanation:
Monosaccharides can exist as a linear chain or as ring-shaped molecules. In aqueous solutions, they are usually found in ring forms. The ring formation occurs when a hydroxyl group (-OH) from one end of the monosaccharide reacts with an aldehyde or ketone group, creating a cyclic structure.
Glucose, for example, can form a six-membered ring called a pyranose ring, while fructose forms a five-membered ring called a furanose ring. The formation of these ring structures is essential for the stability and functionality of monosaccharides in solution.