Lysine is an essential amino acid because

Options

A. It is very rare
B. It has a high nutritive value
C. It is an important cinstituent of all proteins
D. It is not formed in the body and has to be provided through diet

Answer

### Step-by-Step Solution:

1. **Definition of Essential Amino Acids**:
- Essential amino acids are those that cannot be synthesized by the body and must be obtained through diet.

2. **Specific Case of Lysine**:
- Lysine is classified as an essential amino acid because the human body cannot produce it on its own.

3. **Importance of Lysine**:
- Lysine plays a crucial role in various bodily functions, including normal growth and muscle turnover. It is also involved in the formation of carnitine, which is important for energy production in cells.

4. **Dietary Requirement**:
- Since lysine cannot be synthesized by the body, it must be included in the diet to meet the body's needs for this amino acid.

5. **Conclusion**:
- Therefore, lysine is considered an essential amino acid because it is not produced by the body and must be obtained through dietary sources.