Which of the following belongs to the class of natural polymers?

All of these

The correct answer is option 4. All of these.

All of the options provided belong to the class of natural polymers.

Let us delve into each of the options:

1. Proteins: Proteins are large biomolecules composed of long chains of amino acids. Amino acids are organic compounds containing both an amino group \((-NH_2)\) and a carboxyl group \((-COOH)\). These amino acids are linked together by peptide bonds to form polypeptide chains, which then fold into complex three-dimensional structures. Proteins play crucial roles in various biological processes, including structural support, enzyme catalysis, immune response, and cellular signaling.

2. Rubber: Natural rubber is a polymer of isoprene units, which are hydrocarbons with the molecular formula \(C_5H_8\). Rubber molecules consist of long chains of repeating isoprene units linked together by carbon-carbon double bonds. Natural rubber is produced by certain plants, such as the rubber tree (Hevea brasiliensis), and it exhibits elastic properties, making it suitable for various applications, including tires, seals, and adhesives.

3. Cellulose: Cellulose is a complex carbohydrate and the main structural component of the cell walls in plants. It is composed of long chains of glucose molecules linked together by β-1,4-glycosidic bonds. Cellulose molecules form microfibrils, which provide strength and rigidity to plant cell walls. Cellulose is abundant in nature and serves as a structural material in plants. It is also used commercially to produce paper, textiles, and other materials.

These three examples—proteins, rubber, and cellulose—are all natural polymers because they are derived from biological sources and are composed of long chains of repeating units. They exhibit diverse structures and properties, reflecting their roles in biological systems and industrial applications.