Which one of the following is a protein fibre?

Silk is a natural protein fibre obtained from the cocoons of silkworms, primarily the Bombyx mori species [c1, c2]. Chemically, silk consists of two main proteins: fibroin, which forms the continuous filament, and sericin, a gum that cements the filaments together [c1, t2, t4]. All animal-derived fibres, including silk and wool, are protein-based, whereas plant-derived fibres like cotton, jute, and hemp are cellulosic [t1, t4]. Cotton is composed of natural cellulose and is a seed fibre [t1]. In contrast, Nylon and Polyester are synthetic fibres produced through chemical synthesis (polymerization) using petroleum by-products [t3, t7]. Specifically, Nylon is a synthetic polyamide, and Polyester is a synthetic polymer [c3, t7]. Therefore, among the given options, only silk is a protein fibre [t2, t6].

Sources

1. [1] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 9: Agriculture > Production > p. 95
2. [2] NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 4: The Age of Industrialisation > TYPES OF FARMING > p. 87
3. [3] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 28: Manufacturing Industry and The Iron and Steel Industry > Groups of Industries > p. 279
4. [4] https://ncch.gov.mn/Files/Method/identification_of_fibres_and_fabrics_SCHWENCK.PDF