CBSE – 7th Standard Science


Question Bank – Chapter 3 – Fibre to Fabric



Q.1. Where does silk fibres come from?

Ans. Some fibres obtained from plants. We have also learnt that wool and silk fibres are obtained from animals. Wool is obtained from the fleece (hair) of sheep or yak. Silk fibres come from cocoons of the silk moth.



Q.2. Where does wool comes from?

Ans. Wool comes from sheep, goat, yak and some other animals. These wool-yielding animals bear hair on their body. We also know that these animals have a thick coat of hair. Hair trap a lot of air. Air is a poor conductor of heat. So, hair keeps these animals warm. Wool is derived from these hairy fibres.


Q.3. What is selective breeding?

Ans. the hairy skin of the sheep has two types of fibres that form its fleece: (i) the coarse beard hair, and (ii) the fine soft under-hair close to the skin. The fine hair provide the fibres for making wool. Some breeds of sheep possess only fine under-hair. Their parents are specially chosen to give birth to sheep which have only soft under hair. This process of selecting parents for obtaining special characters in their offspring, such as soft under hair in sheep, is termed ‘selective breeding’.


Q.4. Explain briefly about the Animals that yield wool?

Ans. Several breeds of sheep are found in different parts of our country. However, the fleece of sheep is not then only source of wool, though wool commonly available in the market is sheep wool Yak wool is common in Tibet and Ladakh. Angora wool is obtained from angora goats, found in hilly regions such as Jammu and Kashmir. Wool is also obtained from goat hair the under fur of Kashmiri goat is soft. It is woven into fine shawls called Pashmina shawls. The fur (hair) on the body of camels is also used as wool Llama and Alpaca, found in South America, also yield wool.



Q.5. What do you understand by Rearing and breeding of sheep?

Ans. For obtaining wool, sheep are reared. Their hair is cut and processed into wool. If you travel to the hills in Jammu & Kashmir, Himachal Pradesh, Uttaranchal, Arunachal Pradesh and Sikkim, or the plains of Haryana, Punjab, Rajasthan and Gujarat, you can see shepherds taking their herds of sheep for grazing. Sheep are herbivores and prefer grass and leaves. Apart from grazing sheep, rearers also feed them on a mixture of pulses, corn, jowar, oil cakes (material left after taking out oil from seeds) and minerals. In winter, sheep are kept indoors and fed on leaves, grain and dry fodder.


Q.6. Explain the quality and texture of fibres obtained from sheeps?

Ans. Sheep are reared in many parts of our country for wool, some breeds of sheep reared in our country for producing wool. The quality and texture of the fibres obtained from them is also indicated in the table. Certain breeds of sheep have thick coat of hair on their body which yields good quality wool in large quantities. As mentioned earlier, these sheep are “selectively bred” with one parent being a sheep of good breed. Once the reared sheep have developed a thick growth of hair, hair is shaved off for getting wool.


Q.7. Mention the steps of processing of fibres into wool?

Ans. The wool which is used for knitting sweaters or for weaving shawls is the finished product of a long process, which involves the following steps:

Step I: The fleece of the sheep along with a thin layer of skin is removed from its body. This process is called shearing. Machines similar to those used by barbers are used to shave off hair. The hair provide woolen fibres.

Step II: The sheared skin with hair is thoroughly washed in tanks to remove grease, dust and dirt. This is called scouring. Nowadays scouring is done by machines

Step III: After scouring, sorting is done. The hairy skin is sent to a factory where hair of different textures are separated or sorted.

Step IV: The small fluffy fibres, called burrs, are picked out from the hair. These are the same burrs which sometimes appear on your sweaters. The fibres are scoured again and dried. This is the wool ready to be drawn into fibres.

Step V: The fibres can be dyed in various colours, as the natural fleece of sheep and goats is black, brown or white.

Step VI: 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.


Q.8. Why is wool industry also called “Occupational hazard”?

Ans. Wool industry is an important means of livelihood for many people in our country. But 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.


Q.9. Describe briefly the Life history of silk moth?

Ans. 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. 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.


Q.10. How silk yarn is obtained from the cocoon?

Ans. The silk yarn (thread) is obtained from the cocoon of the silk moth. There is a variety of silk moths which look very different from one another and the silk yarn they yield is different in texture (coarse, smooth, shiny, etc.). Thus, tassar silk, mooga silk, kosa silk, etc., are obtained from cocoons spun by different types of moths. The most common silk moth is the mulberry silk moth. The silk fibre from the cocoon of this moth is soft, lustrous and elastic and can be dyed in beautiful colours. Sericulture or culture of silkworms is a very old occupation in India. India produces plenty of silk on a commercial scale.


Q.11. Explain the Discovery of silk?

Ans. The exact time of discovery of silk is perhaps unknown. 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’.


Q.12. Explain the Processing silk?

Ans. A pile of cocoons is used for obtaining silk fibres. The cocoons are kept under the sun or boiled or exposed to steam. The silk fibres separate out. The process of taking out threads from the cocoon for use as silk is called reeling the silk. Reeling is done in special machines, which unwind the threads or fibres of silk from the cocoon. Silk fibres are then spun into silk threads, which are woven into silk cloth by weavers.

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