What is the primary difference between glucose and fructose as sugars?

The primary difference between glucose and fructose as sugars is that both are indeed categorized as monosaccharides. They are the simplest forms of carbohydrates, meaning they cannot be broken down into smaller sugar units. Both sugars share a similar molecular formula, C6H12O6, but they differ in structure. Glucose is an aldohexose, which means it has an aldehyde group at one end, while fructose is a ketohexose, containing a ketone group. This distinction in structure leads to differences in how each sugar is metabolized in the body, but the fundamental classification of both as monosaccharides is the most critical difference to note in this context.

The other options do point out various characteristics of glucose and fructose, but they do not accurately convey the primary difference in their classification as sugars.