Which of the following can't be included under glucan?

Options

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

Answer

To determine which of the following cannot be included under glucan, we need to understand what glucans are. Glucans are homopolysaccharides made up of glucose units. Let's analyze each option step by step.

### Step-by-Step Solution:

1. **Definition of Glucan**:
- Glucans are homopolysaccharides composed solely of glucose units. The term "homo" indicates that all the monomer units are the same (in this case, glucose), and "polysaccharide" indicates that it consists of multiple sugar units (more than 10).

2. **Identifying Glucans**:
- **Starch**: Starch is a homopolysaccharide made up of glucose units. Therefore, it is included under glucans.
- **Cellulose**: Cellulose is also a homopolysaccharide composed of glucose units. Thus, it is also included under glucans.
- **Glycogen**: Glycogen is another homopolysaccharide made up of glucose units, so it is included under glucans as well.
- **Pectin**: Pectin is a heteropolysaccharide, which means it is made up of different types of sugar units, not just glucose. Therefore, pectin cannot be included under glucans.

3. **Conclusion**:
- Among the options provided, pectin is the only one that cannot be classified as a glucan because it is a heteropolysaccharide.

### Final Answer:
Pectin cannot be included under glucan.