Which one of the following polysaccharides is composed of `beta`-glycosidic link ?

Options

A. Starch
B. Glycogen
C. Dextrin
D. Cellulose

Answer

To determine which polysaccharide is composed of beta-glycosidic links, we can follow these steps:

### Step 1: Understand the Types of Glycosidic Links
Glycosidic links can be classified into two types based on the orientation of the hydroxyl group on the first carbon of the monosaccharide:
- **Alpha-glycosidic link**: The hydroxyl group on the first carbon is below the plane of the ring.
- **Beta-glycosidic link**: The hydroxyl group on the first carbon is above the plane of the ring.

### Step 2: Identify the Monosaccharides in the Polysaccharides
We need to identify the monosaccharides that make up the given polysaccharides:
- **Cellulose**: Composed of beta-D-glucose.
- **Starch**: Composed of alpha-D-glucose.
- **Glycogen**: Composed of alpha-D-glucose.
- **Dextrin**: Composed of alpha-D-glucose.

### Step 3: Analyze the Polysaccharides
Now, we will analyze each polysaccharide:
- **Cellulose**: Contains beta-D-glucose, which forms beta-glycosidic links (specifically, beta-1,4-glycosidic linkages).
- **Starch**: Contains alpha-D-glucose, which forms alpha-glycosidic links.
- **Glycogen**: Contains alpha-D-glucose, which forms alpha-glycosidic links.
- **Dextrin**: Contains alpha-D-glucose, which forms alpha-glycosidic links.

### Step 4: Conclusion
Based on the analysis, the polysaccharide that contains beta-glycosidic links is **cellulose**.

### Final Answer
**Cellulose** is the polysaccharide composed of beta-glycosidic links.

---