The chemical nature of 'Silk' is

Question

Accepted Answer

The correct answer is **3. Protein**.

### Explanation:

Silk is a natural fiber produced by certain insects, most notably silkworms. The primary component of silk is a protein called fibroin, which is secreted by the silkworm during the process of spinning its cocoon.

#### Why Silk is Considered a Protein:
1. **Composition**: Silk is made up of amino acids, which are the building blocks of proteins. The specific sequence and arrangement of these amino acids give silk its unique properties, such as strength, elasticity, and luster.
2. **Biological Function**: Proteins serve various functions in living organisms, including structural roles. In the case of silk, it provides structural support to the cocoon, protecting the developing silkworm.
3. **Chemical Structure**: The chemical structure of silk includes long chains of amino acids linked by peptide bonds, characteristic of proteins.

#### Why Other Options are Incorrect:
1. **Carbohydrate**: Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen, typically serving as energy sources or structural components in living organisms (e.g., starch, cellulose). Silk does not fit this category as it does not serve primarily as an energy source.
  
2. **Lipid**: Lipids are a diverse group of hydrophobic molecules, including fats, oils, and waxes, primarily used for energy storage and as structural components of cell membranes. Silk does not have the characteristics of lipids, as it is not hydrophobic and does not serve the functions typical of lipids.

3. **Fatty Acid**: Fatty acids are carboxylic acids with long hydrocarbon chains, which are components of lipids. They are not proteins and do not relate to the structure or function of silk.

In conclusion, silk is classified as a protein due to its amino acid composition and biological functions, making option 3 the correct answer.