CBSE Class 7 Science Chapter 3 Notes Fibre to Fabric
Fibre to Fabric Class 7 Notes Understanding the Lesson
1. Silk and wool are animal fibres because silk comes from silkworms and wool is obtained from fleece, i.e., hairs of sheep, goat, yak and some other animals.
2. The wool-yielding animals bear a thick coat of hair on their body. Hair keeps these animals warm because hair trap air which does not let the heat release from their body due to its poor conductivity.
3. The hairy skin of the sheep has two types of fibres that form the fleece:
- the coarse beard hair; and
- the fine soft under hair close to the skin.
- The fine hair provides the fibres for making wool.
4. Some breeds of sheep have only fine under-hair. Their parents are specially chosen to give birth to sheep with fine under-hair only. This process of selecting parents for obtaining special characters in their offsprings, such as soft under-hair in sheep, is called selective breeding.
5. Apart from sheep, wool is also obtained from yak, angora goat, camel, Lama and alpaca.
6. Sheep are reared in many parts of our country for wool. Certain breeds of sheep have thick coat of hair on their body which yields good quality of wool. Once the reared sheep have developed a thick growth of hair, hair is shaved off for obtaining wool.
7. Wool production involves various steps. The hair of the wool yielding animals is cut and processed into wool. Different steps are shearing, scouring, sorting, grading, dyeing and making yarn.
8. The rearing of silkworms for getting silk is called sericulture.
9. Silkworms are caterpillars of silk moth which feed on leaf of mulberry.
10. During their life cycle, the worms spin cocoons of silk fibres.
11. Silk fibres are made of protein.
12. Silk fibres from cocoons are separated out by reeling the silk.
13. Reeling is done in special machines, which unwind the threads or fibres of silk from the cocoon. Silk fibres are then spun in threads and then into cloth.
Class 7 Science Chapter 3 Notes Important Terms
Cocoon: Caterpillar completely covers itself by silk fibres and turns into pupa. This covering is known as cocoon.
Fleece: Hair on the body or outer coat of sheep or yak is called fleece. It is the source of wool.
Reeling: The process of taking out threads from the cocoon for use as silk is called the reeling the silk.
Scouring: The sheared skin with hair is thoroughly washed in tanks to remove grease dust and dirt. This is called scouring.
Sericulture: The production of raw silk by raising silkworms is called sericulture.
Shearing: The process of removing fleece of the sheep along with a thin layer of skin from its body is called shearing.
Silkmoth: The silk moth develops from pupa inside the cocoon. The silk yarn or thread is obtained from the cocoon of the silk moth.
Sorting: Separation of hairy skin in different textures is called sorting.
Caterpillars: The female silk moth lays eggs; from which worm-like larva called caterpillars or silkworms are hatched.
Mulberry silk moth: The most common silk moth, Bombyx mori, is known as mulberry silk moth.