Final answer:
Monosaccharides are different because they have different structures, although they have the same molecular formula. Glucose, galactose, and fructose are isomeric monosaccharides with slightly different arrangements of atoms. These structural differences impact their properties and functions.
Step-by-step explanation:
Monosaccharides are small, simple sugars that are the building blocks of carbohydrates. While all monosaccharides have the same molecular formula of (CH2O)n, they are different because they have different structures. For example, glucose, galactose, and fructose are isomeric monosaccharides, meaning they have the same chemical formula but have slightly different arrangements of atoms. These structural differences affect their properties and functions in living organisms.