Monday 31 January 2022

NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric

                       Fibre to Fabric

In this chapter we learn about wool and silk obtained from animals. Wool is obtained from the fleece (hair) of sheep or yak. Silk fibres come from cocoons of the silk moth. 

Animal fibres — wool and silk 

पशु रेशे - ऊन और रेशम

WOOL- Wool is natural fiber which comes from sheep, yak and other animals. Wool is basically the hair of these animals. Hairs are good conductors of heat or very bad conductors of air. Hence hairs keep these animals warm.

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 provides the fibres for making wool. Some breeds of sheep possess only fine under-hair, which is good for manufacturing woolens.

Selective breeding- it is the process of selecting specific parents or breed of animal to give specific character or quality offspring which can be used to produce good quality products from them. It is similar to buying high yielding seeds for farming. 

  1. Sheeps are found in Ladakh, Kashmir and Jammu, tibet. Their wool is called sheep wool which is very common.

  1. Goats in jammu and kashmir also give wool

  • Angora goats give the wool name Mohair.

  • Cashmere goats give cashmere wool, and pashmina shawl are made from them.

  1. Camels are also used to obtain wool, their  fur (hair) on the body is used as fiber to use wool, like Llama and Alpaca, found in South America, also yield wool. 

From fibres to wool 

रेशों से ऊन तक

Hairs of sheeps, goats,camels and yaks have been cut to produce wool. Let's learn how a sheep gets ready to give wool. Hilly areas like Jammu & Kashmir, Himachal Pradesh, Uttaranchal, Arunachal Pradesh and Sikkim, or the plains of Haryana, Punjab, Rajasthan and Gujarat are main sources of wool in our country. 

 Shepherds feed their sheeps and goats by various ways first they take them to grassland for grazing. 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.

Certain breeds of sheep have thick coat of hair on their body which yields good quality wool in large quantities. Once the reared sheep have developed a thick growth of hair, hair is shaved off for getting wool.

Processing fibres into wool

फाइबर से ऊन बनाना

After shredding hair there are many steps for making wool:

बालों को काटने के बाद ऊन बनाने के कई चरण होते हैं:

Step 1- The fleece of the sheep along with a thin layer of skin is removed from its body . This process is called shearing. Machines like barbar used to shave hair, don't worry sheep don't get hurt. It is similar to how we cut our hair or men shave their beard. 

Sheeps get shaved in summer so that they can't die in winter. Now these hairs are processed to make woollen yarns.

Step 2-  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 3-  After scouring, sorting is done. The hairy skin is sent to a factory where hair of different textures are separated or sorted.

Step 4- 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 5- The fibres can be dyed in various colours, as the natural fleece of sheep and goats is black, brown or white.

Step 6-  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.

The processing of fibre into wool can be represented as follows: Shearing → Scouring → Sorting → Cleaning of burrs ↓ Rolling ← Dyeing.

SILK- silk is also another fiber which we get from living beings i.e silkworms. Silkworms spin the ‘silk fibres’. The rearing of silkworms for obtaining silk is called sericulture. 

Life history of silk moth

In the pupa stage 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.

The caterpillar completely covers itself by silk fibres and turns into pupa. This covering is known as cocoon. Silk fibres are used for weaving silk cloth, this soft silk yarn is as strong as a comparable thread of steel.

There are different types of silks :

Tassar silk

Mooga silk 

Kosa silk

These different types of cocoons are 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 keeping various kinds of silk worms to obtain silk from is a very old occupation of India. 

From cocoon to silk 

For obtaining silk, moths are bred, taken care of and their cocoons are collected to get silk threads.

Rearing silkworms: A female silk moth lays hundreds of eggs at a time. The eggs are stored on paper and cloth than sold to farmer. Now these eggs need to be kept at a specific temperature so they hatch and feed on mulberry leaves, these larvae or caterpillars eat night and day till 25 to 30 days after these eating days they go into a bamboo chamber of bamboo in the tray to spin cocoons. 

The caterpillar or silkworm spins the cocoon inside which develops the silk moth.

कैटरपिलर या रेशमकीट कोकून को घुमाता है जिसके अंदर रेशम कीट विकसित होता है।

Processing silk: A pile of cocoons is used for obtaining silk fibres. The cocoons are kept under the sun or boiled or exposed to steam. 

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.

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