## **Core Concept**
Cellulose is a type of polysaccharide, specifically a homopolysaccharide composed of glucose units. The digestibility of polysaccharides depends on the type of glycosidic bonds and the anomeric configuration. Humans lack the enzyme that can break certain types of glycosidic bonds.

## **Why the Correct Answer is Right**
The correct answer, , refers to the beta-1,4-glycosidic bond present in cellulose. This bond is resistant to human digestive enzymes because human enzymes can primarily break alpha-1,4 and alpha-1,6 glycosidic bonds. The beta-anomeric configuration in cellulose, specifically beta-1,4 linkages, cannot be cleaved by human enzymes due to the structural specificity of these enzymes. This is why humans cannot digest cellulose.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option does not directly relate to the reason cellulose is not broken down in human digestion. The alpha-1,4-glycosidic bond is found in glycogen and starch, which are easily broken down by human enzymes.
- **Option B:** This option refers to another type of glycosidic bond but does not accurately represent the reason for the indigestibility of cellulose.
- **Option D:** This option might seem related but does not accurately describe the glycosidic bond in cellulose or the reason for its indigestibility.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **dietary fiber**, which includes cellulose, provides bulk to the stool and helps in the movement of food through the digestive system but is not a significant source of calories or nutrients for humans. This is because humans lack the enzymes to break down the beta-glycosidic bonds found in fiber.

## **Correct Answer: .**