In botany, plant fibres used for textiles and ropes are mainly made up of which structural substance?

Introduction / Context:
Plant fibres such as cotton, jute and flax are widely used in making cloth, ropes and other materials. Understanding what these fibres are made of helps connect basic chemistry with everyday materials. This question checks knowledge of cellulose as the main structural component of plant cell walls and fibres.

Given Data / Assumptions:

• Plant fibres are obtained from parts like seed hairs, stems or leaves.
• Plant cell walls contain characteristic structural materials.
• Collagen and many proteins are typically associated with animals, not plants.

Concept / Approach:
Plant cell walls are primarily composed of cellulose, a complex carbohydrate. Cellulose molecules form long chains that bundle together into strong fibres, giving rigidity and strength to plant tissues. Fibres used in textiles are essentially bundles of these cellulose rich cells. Collagen is an animal protein, and vitamins are micronutrients present in small amounts, not structural components. Storage proteins are more important in seeds for nutrition than for making tough fibres.

Step-by-Step Solution:
Step 1: Recall that plant cells have a cell wall made mainly of cellulose. Step 2: Understand that fibres from plants are specialised cells with thick cell walls. Step 3: Link the strength and flexibility of these fibres to the presence of cellulose microfibrils. Step 4: Compare with collagen and proteins, which are structural materials in animals, not in plant cell walls. Step 5: Conclude that cellulose is the correct substance forming plant fibres.

Verification / Alternative check:
Textbooks and reference sources describe cotton as almost pure cellulose. Jute and flax also contain high percentages of cellulose along with some other polysaccharides. Industrial chemistry uses this property to produce paper, rayon and other materials from plant cellulose. These examples confirm that cellulose is the key component of plant fibres.

Why Other Options Are Wrong:
Option a mentions collagen, which is a fibrous protein found in animal connective tissues such as tendons and skin, not in plants.
Option b talks about storage proteins like gluten, which are important in seeds and grains for nutrition but do not form the main structure of fibres used in textiles.
Option d refers to vitamins, which are present only in tiny amounts and act as co factors in biochemical reactions rather than as structural materials.

Common Pitfalls:
Learners sometimes assume that any strong string like material must be made of protein because many animal fibres are protein based, such as wool and silk. This can cause confusion when shifting from animal to plant examples. Recognising that plant structural strength relies on polysaccharides, especially cellulose, helps avoid this error.

Final Answer:
Plant fibres are mainly composed of cellulose, the main structural carbohydrate of plant cell walls.