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Theory:

Source of fibres:
  
In your lower class, you have learnt about some fibres get from plants. You also know that wool and silk fibres are obtained from animals. Wool is got from the fleece (hair) of yak or sheep. Silk fibres are derived from silk moth cocoons.
  
Do you know where the fibres come from on a sheep's body?
Do you know how these fibres become the woollen yarn we buy at the store to knit sweaters?
Do you know how silk fibres are transformed into silk, then woven into saris?
 
In this lesson, we will get answers to these questions.
 
Animal fibres - wool and silk:
  
Wool:
  
The wool comes from sheep, yaks, goats, and other animals. These wool-giving animals carry hair on their body. Do you know why these animals have such a thick coat of hair? Hair snags a lot of air. Air is a poor conductor of heat, as you would understand in the Heat chapter. So, hair retains these animals warm. Wool is derived from these hairy fibres.
 
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Animal (goat) fibre
  
Activity 3.1
Feel your body and arm hair and the hair on your head. Do you think there's a difference? Which one appears to be coarse, and which appears to be soft?
 
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Sheep hairs
  
Like us, the hairy skin of the sheep has two types of fibres that form its fleece:
 
(i) the coarse beard hair
(ii) the fine soft under-hair close to the skin.
 
The fine hair supplies the fibres for making wool. Some breeds of sheep possess only acceptable under-hair. Their parents are specially picked to give birth to sheep with only soft under-hair. This method of selecting parents for bringing unique characteristics in their offspring, such as soft under hair in sheep, is termed ‘selective breeding’.