NCERT Class 7 Science Chapter 3 - Fibre to Fabric Notes

Chapter 3 - Fibre to Fabric Notes

1. 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.

2. The hairy skin of the sheep has two types of fibres that form the fleece:
• The coarse beard hair
• The fine soft under hair close to the skin. The fine hair provides the fibres for making wool.

3. 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.

4. Wool is also obtained from Yak, Angora goat, Camel, Lama and Alpaca.

5. Wool production involves various steps. Different steps are
• Shearing
• Scouring
• Sorting
• Removal of burrs
• Dyeing
• Rolled into yarn

6. The fleece of the sheep along with a thin layer of skin is removed from its body. This process is called shearing.

7. The sheared skin with hair is thoroughly washed in tanks to remove grease, dust and dirt. This is called scouring.

8. The hairy skin is sent to a factory where hair of different textures are separated or sorted. This process is called sorting.

9. The small fluffy fibres, called burrs, are picked out from the hair. The fibres are scoured again and dried. This process is called Removal of Burrs.

10. The fibres can be dyed in various colours, as the natural fleece of sheep and goats is black, brown or white. This process is called Dyeing.

11. The fibres are straightened, combed and rolled into yarn. The longer fibres are made into wool for sweaters and the shorter fibres are spun and woven into woollen cloth. This process is called Rolled into yarns.

12. The rearing of silkworms for getting silk is called sericulture.

13. Silkworms are caterpillars of silk moth which feed on leaf of mulberry.

14. During their life cycle, the worms spin cocoons of silk fibres.

15. Silk fibres are made of protein.

16. Silk fibres from cocoons are separated out by reeling the silk.

17. 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.

18. Sorter’s job is risky as sometimes they get infected by a bacterium, anthrax, which causes a fatal blood disease called sorter’s disease. Such risks faced by workers in any industry are called occupational hazards.

19. Life Cycle of Silk Moth
The female silk moth lays eggs, from which hatch larvae which are called caterpillars or silkworms. They grow in size and when the caterpillar is ready to enter the next stage of its life history called pupa, it first weaves a net to hold itself. Then it swings its head from side to side in the form of the figure of eight (8). During these movements of the head, the caterpillar secretes fibre made of a protein which hardens on exposure to air and becomes silk fibre. Soon the caterpillar completely covers itself by silk fibres and turns into pupa. This covering is known as cocoon. The further development of the pupa into moth continues inside the cocoon.

20. China leads the world in silk production. India also ranks among the leading silk producing countries.

21. According to an old Chinese legend, the empress Si-lung-Chi was asked by the emperor Huang-ti to find the cause of the damaged leaves of mulberry trees growing in their garden. The empress found white worms eating up mulberry leaves. She also noticed that they were spinning shiny cocoons around them. Accidentally a cocoon dropped into her cup of tea and a tangle of delicate threads separated from the cocoon. Silk industry began in China and was kept a closely guarded secret for hundreds of years. Later on, traders and travellers introduced silk to other countries. The route they travelled is still called the ‘silk route’.

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