Which of the following carbohydrates cannot be directly utilised by the human body as a source of energy?

Options

A. Starch
B. Cellulose
C. Glycogen
D. All of these

Answer

To determine which carbohydrate cannot be directly utilized by the human body as a source of energy, we will analyze the given options: starch, cellulose, glycogen, and the option "all of this."

### Step-by-Step Solution:

1. **Understanding Starch**:
- Starch is a polysaccharide made up of glucose units.
- The human body has enzymes, such as amylase, that can break down starch into simple glucose molecules.
- Since glucose is a primary source of energy for the body, starch can be directly utilized.

2. **Understanding Cellulose**:
- Cellulose is also a polysaccharide, but it is composed of glucose units linked in a way that humans cannot digest.
- The human body lacks the necessary enzymes to break down cellulose into simple glucose molecules.
- Therefore, cellulose cannot be directly utilized by the human body as a source of energy.

3. **Understanding Glycogen**:
- Glycogen is the storage form of glucose in the human body.
- It is readily converted back into glucose when the body needs energy.
- As glycogen can be broken down into glucose, it can be directly utilized by the body.

4. **Conclusion**:
- Among the options provided, starch and glycogen can be utilized by the human body as sources of energy.
- Cellulose, on the other hand, cannot be utilized due to the lack of enzymes necessary for its digestion.
- Therefore, the correct answer is **cellulose**.

### Final Answer:
**Cellulose cannot be directly utilized by the human body as a source of energy.**

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