Which monosaccharide is commonly known as blood sugar?

Glucose is commonly referred to as blood sugar because it is the primary sugar involved in energy metabolism and is a critical source of energy for the body's cells. It is found in the bloodstream, where it circulates and is used by various cells and tissues. The body regulates glucose levels through insulin and other hormones to maintain homeostasis, ensuring that cells receive sufficient energy for their functions.

Glucose also serves as a fundamental building block for more complex carbohydrates and is a vital participant in several metabolic pathways, including glycolysis, which generates energy in the form of ATP. This makes glucose crucial not just for immediate energy needs but also for overall metabolic health.

The other options represent different monosaccharides with specific roles, but they do not serve as the primary energy source in the same way that glucose does in the bloodstream. For instance, galactose is found in milk and dairy products, ribose is important in the structure of RNA, and fructose, while also a sugar in the body, is primarily processed by the liver and not as directly involved in regulating blood sugar levels as glucose.