Tuesday, July 26, 2011

CBSE Class-7th Science Fibre to Fabric

CBSE _ NCERT Class-7th Science  Chapter: Fibre to Fabric

Why a cotton garment cannot keep us as warm in winter?
Cotton clothes are thin and do not have spaces in which air can be trapped. thus Cotton clothes do not prevents heat coming out of our body.
What is a fibre?

A fibre is a long strong thread, which is obtained from natural sources or man made sources.
Fibres are classified into two types on the basis of their sources. Plant fibres and animal fibres and synthetic fibres.

The fibres, which are obtained from plants and animals are called natural fibres e.g., jute and wool.
Animal fibres are obtained from animals, e.g., silk and wool.

Those fibres which are made by the human –beings are known as Man-made or Synthetic Fibres, e.g., Rayon.

Match the following:
1. Scouring-->          Cleaning sheared skin
2. Mulberry leaves-> Food of silkworm
3. Yak ->                  Wool yielding animal
4. Cocoon ->             Yields silk fibers.
Explain the process of making yarn from fiber ?

The process of making yarn from fiber is called spinning. In this process,fibers from a mass of cotton wool are drawn out and twisted. this brings the fibers together to from a Yarn. 

Why sheep have a thick coat of hair?

Thick coat of hair trap a lot of air. Air is a poor conductor of heat, So, hair keeps sheep warm

What are the different sources of wool?

The fleece of sheep is not the only source of wool. Angora wool is obtained from angora goats. The fur (hair) on the body of camels is also used as wool like Llama and Alpaca.

Name the some Indian bread of sheep

1. Lohi  2. Rampur bushair  3 . Nali   4. Bakharwal    5. Marwari  6. Patanwadi

Which parts of the black sheep have wool?

The hairy skin called fleece have wool in black sheep.

What is meant by the white fleece of the lamb?

White fleece means the hairy skin which is white in colour.

What is wool?

The soft, curly fibres obtained from the fleece of sheep, goat and yak etc., are known as wool.

What is selective breeding?

Certain breeds of sheep have thick coat of hair on their body which yields good quality wool in large quantities. As  these sheep are “selectively bred” with one parent being a sheep of good breed.
The process of selecting parents for obtaining special characters in their offspring is known as selective breeding.

Name the protein which is the chief component of wool fibres.

Keratin is the chief component of wool fibres

What is shearing? How it is done?

The process of removing the fleece of the sheep along with a thin layer of skin is from its body is called   shearing. It is done by using shearing machine

Which animal material is used to weave fine, soft shawls called Pashmina shawls?

The under fur of Kashmiri goat is used to weave fine, soft shawls called Pashmina shawls.

Why shearing of wool done only in summer?

Usually shearing of wool is done only in summer as sheep do not to survive without their protective coat of hair in winter.

Why wool yielding animals have a thick coat of hair?

A thick coat of hair helps in trappinga lot of air. As, air is a poor conductor of heat, it keep these animals warm.

Does shearing does hurt the sheep?

Shearing does not hurt the sheep because the uppermost layer of the skin is dead. Also, the hair of sheep grows again just as our hair does.

What is scouring?     
The sheared skin with hair is thoroughly washed in tanks to remove grease, dust and dirt. This is known as scouring.

How we get wood fibres from sheep?

The processing of fibres into wool involves the following steps:

Step I:  Shearing: - At first hair are removed using shearing machine

Step II: scouring   : - Hair is washed in tanks to remove grease, dust and dirt. This process is called scouring.

Step III: After scouring, sorting of hair is done on the basic of different textures

Step IV: The small fluffy fibres, called burrs, are picked out from the hair

Step V: The fibres then dyed in various colours, according to choice

Step VI: The coloured fibres are straightened, combed and rolled into yarn

What are the main hazards of wool industry?

Workers in wool industry get infected by a bacterium, anthrax, which causes a fatal blood disease called sorter’s disease

What is sericulture?

The rearing of silkworms for obtaining silk is called sericulture

Discuss the process of obtaining silk?

For obtaining silk, moths are reared and their cocoons are collected to get silk threads.

The cocoons are boiled to separate out silk fibres from cocoon.

Threads obtain from the cocoon spun into silk threads, which are woven into silk cloth by weavers.

The process of taking out threads from the cocoon for use as silk is called reeling the silk

Why caterpillars should not be collected with bare hands? 

Caterpillars should not be collected with bare hands because skin of caterpillars may cause allergy.

Why caterpillars need to shed their skin when they grow bigger?

The caterpillars eat their own shed skin during their growing stage and have no other food option. So they need to shed their skin when they grow bigger enter the next stage of its life history called pupa.

Why does silk have different varieties?

Silk-producing moth eats up different kinds of leaves, which accounts for the different varieties of silk. Thus, tassar silk, mooga silk, kosa silk, etc., are obtained from cocoons spun by different types of moths.

Fill in the blanks-
(i) --  China        --is the largest producer of silk.
(ii) Silk is a poor ---conductor of heat.
(iii) – Suint  ---is a dried perspiration found in raw wool.
(iv) A-- yar --is a long continuous thread.

Choose  the True statements
(a) Yarn is made of fibers
 (b) Spinning is a process of making fibers
(c) Jute is the outer covering of coconut.
(d) The process of removing seed  from cotton called ginning
(e) Weaving yarn makes a piece of fabric
 (f) Silk fiber is obtained from the stem of a plant
 (g) Polyester is a natural fiber
(h) The fleece are combed to remove Burrs
(i)  Muga is the strongest variety of Wool or Silk

(a) Yarn is made of fibers.(True)
(d) The process of removing seed  from cotton called ginning.(True)
(e) Weaving yarn makes a piece of fabric.(True)
(h) The fleece are combed to remove Burrs.(True)
(i) Muga is the strongest variety of Silk

Define: weaving, ginning, spinning

The process of arranging two sets of yarns together to make a fabric is called weaving.
The process of making yarn from fibres is called spinning
Cotton fibres are separated from the seeds by combing this process is called ginning 

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