Fiber To Fabric Class 7 NCERT Chapter Guide

Understanding Animal Fibers: Wool and Silk

Unlike plant fibers such as cotton and jute that you studied in Class 6, wool and silk are animal fibers. Wool comes from the fleece (hair) of animals like sheep, goats, yak, and camels. The hairy skin of sheep has two types of fibers: the coarse beard hair and the fine soft under-hair close to the skin. It is this fine under-hair that is selectively bred to produce wool. Silk, on the other hand, comes from the cocoons of the silk moth (Bombyx mori). The process of rearing silkworms for the commercial production of silk is known as sericulture. Both wool and silk are made of complex proteins, which make them strong, warm, and highly breathable.

From Sheep to Sweater: The Step-by-Step Processing of Wool

1. Shearing — The fleece of the sheep, along with a thin layer of dead skin, is carefully shaved off the animal's body. This is typically done in hot weather so that the sheep can survive comfortably without their warm protective coat. Shearing does not hurt the sheep, just like getting a haircut doesn't hurt us.
2. Scouring — The sheared skin and hair are thoroughly washed in large tanks of water containing detergents. This process removes grease, dust, dirt, and sweat from the fibers. Today, scouring is largely done using automated machinery.
3. Sorting — The scoured hair is sent to factories where hair of different textures, lengths, and qualities is separated and sorted out into clean categories.
4. Burr Cleaning — Small, fluffy fibers called burrs (similar to the tiny lint balls that appear on your sweaters) are hand-picked out from the wool. The remaining fibers are scoured again and dried, making them ready to be drawn into clean wool yarn.
5. Dyeing — Since the natural fleece of sheep and goats is mostly black, brown, or white, the processed fibers are dyed in a wide and vibrant range of artificial colors using textile-grade dyes.
6. Rolling and Spinning — The cleaned, dried, and colored fibers are straightened out, combed, and rolled into yarn. The longer fibers are spun into high-quality wool for sweaters, while shorter fibers are spun and woven into woolen clothes.

The Life History of a Silk Moth

Comparing Wool and Silk

Exam Watchout: Common Mistakes to Avoid

Many students lose marks by confusing Sericulture with Apiculture (rearing honeybees) or Pisciculture (rearing fish). Remember: Sericulture is strictly the commercial rearing of silkworms for silk production.

Another common error is writing that shearing hurts the sheep. Always explain that shearing removes only the topmost, dead layer of skin, making it completely painless for the animal, much like a human haircut! Also, keep the correct sequence of wool processing in mind: Shearing -> Scouring -> Sorting -> Cleaning of burrs -> Dyeing -> Rolling.

Practice Questions with Solutions

• Q: What is meant by the term 'selective breeding' with reference to wool production? A: Step 1: Define breeding. Breeding is the process of producing offspring through sexual reproduction. Step 2: Explain 'selective' breeding in context. To get sheep with specific desirable characteristics (like very soft under-hair), scientists and farmers select parent sheep that already possess those high-quality traits. Step 3: Combine and formulate final definition. Final answer: Selective breeding is the process of selecting parents for obtaining special characters in their offspring, such as soft under-hair in sheep to produce high-quality wool.
• Q: Explain how silkworms produce the silk thread. A: Step 1: Identify the stage. The silk thread is produced during the caterpillar stage when it prepares to enter the pupa stage. Step 2: Describe the action of secreting the substance. The caterpillar swings its head in a figure-eight pattern. Step 3: State the nature of the secretion. It secretes fibers made of a protein which hardens into silk upon exposure to air and wind. Final answer: The caterpillar secretes a liquid protein through its glands while swinging its head in a figure-of-eight motion. This protein hardens upon contact with air, forming the continuous thread that makes up the protective cocoon.
• Q: Why does shearing not hurt the sheep? A: Step 1: Understand skin structure. The skin of animals is composed of layers, with the outermost layer being dead skin cells. Step 2: Relate this to shearing tools. Shearing tools shave off the fleece along with only this uppermost dead layer of skin. Step 3: Draw a real-life parallel. Compare it to a human haircut or shaving a beard, which doesn't hurt because there are no active nerve endings in dead tissue. Final answer: Shearing does not hurt the sheep because the uppermost layer of the skin from which the fleece is removed consists of dead cells, and the sheep's wool grows back just like human hair.
• Q: What is 'reeling' of silk and how is it carried out? A: Step 1: Define the start point. Raw cocoons must be processed to separate the delicate silk fibers from the pupa. Step 2: Describe the heat treatment. The cocoons are kept under the sun, boiled, or exposed to steam to loosen the silk threads. Step 3: Describe the final extraction. Special machines unwinding the long silk threads from the cocoon. Final answer: Reeling is the process of taking out silk threads from the cocoon. Cocoons are first boiled or kept under steam to loosen the protective sericin gum, and then automated machines unwind the delicate fibers to prepare raw silk yarn.

Frequently Asked Questions