## **Core Concept**
Inulin is a type of polysaccharide, specifically a fructan, which is a homopolymer composed of fructose units. It serves as an energy storage molecule in many plants. Inulin is not digestible by human enzymes but can be fermented by gut microbiota.

## **Why the Correct Answer is Right**
The correct answer, , indicates that inulin is composed of fructose units. Inulin is synthesized from sucrose through the action of the enzyme sucrose:fructan 6-fructosyltransferase (1-FFT), resulting in a polymer chain of fructose molecules linked by β(2→1) glycosidic bonds. This polymer can vary in length but typically consists of 2 to 60 fructose units.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because inulin is not a polymer of glucose units; glucose polymers are known as starch or glycogen in animals and plants.
- **Option B:** This option is incorrect because while galactose is a simple sugar, inulin is specifically known to be composed of fructose units, not galactose.
- **Option C:** This option is incorrect because although mannose is an important sugar in glycoproteins and glycolipids, inulin is specifically a polymer of fructose.

## **Clinical Pearl / High-Yield Fact**
Inulin is used clinically as a marker of extracellular fluid volume and for measuring the glomerular filtration rate (GFR) because it is freely filtered by the kidneys but neither reabsorbed nor secreted. A key point to remember is that inulin clearance closely approximates the GFR, making it a valuable tool in renal physiology assessments.

## **Correct Answer:** . Fructose