NCERT Solutions for Class 7 Science Chapter 3 - Fibre To Fabric

Answer:

The rearing of silkworms for the production of silk is known as sericulture. Different types of silk , with different textures , are obtained from cocoons of different types of silk moths.

Hence, the correct answer is option (c).
 

Answer:

Mulberry silk , Tassar silk and Mooga silk are the types of silk that are obtained from cocoons of different types of silk moth. Moth silk is not a type of silk.

Hence, the correct answer is option (d).
 

Answer:

Wool comes from the hair of animals such as sheep, goat , yak , camel , rabbit , etc. It does not involve killing of animals. Whereas, silk comes from killing the cocoons. Fur and leather are animal products which are obtained from the skin of animals by killing them. Therefore, woollen shawl is the right gift for her to buy.

Hence, the correct answer is option (a).

Answer:

Silk is a natural fibre that is obtained from the cocoons of silk moth.
Hence, the correct answer is option (c).

Answer:

Wool can be obtained from the animals such as goat , yak,  camel, etc. Llama and Alpaca belong to the camel family. Moth is not a wool yielding animal/insect.

Hence, the correct answer is (d).

Answer:

Selective breeding is the process of selecting parents to obtain special characteristics or features in their off-spring is known as selective breeding. For example, some breeds of sheep possess only soft under hair.

Hence, the correct answer is option (b).

Answer:

The removal of fleece from sheep is known as shearing. It can be done manually with a razor or through a shearing machine. Therefore, the process that takes place at sheep shearing shed is removal of fleece.

Hence, the correct answer is option (a).

Answer:

The rearing, breeding and management of silkworms for the production of silk is known as sericulture.
Hence, the correct answer is option (b).

Answer:

The process of unwinding or taking out silk fibres from cocoon and combining them together to make a single thread of raw silk is known as reeling of silk.

Hence, the correct answer is option (d).

Answer:

The silkworm secretes fibre made up of protein which gets hardened on being exposed to air and become silk fibre. Silkworm completely covers itself by silk fibres. This covering is known as cocoon which is further processed to obtain silk fibres.

Hence, the correct answer is option (c).

 

Answer:

(a) Silk and wool fibres are obtained from animals.
(b) Silk fibres come from cocoon of silk moths.
(c) Wool yielding animals bear hair on their body.
(d) Hair trap a lot of air, which is a poor conductor of heat.
 

Answer:

(a) True
(b) False - In India, sheep are generally reared for obtaining wool.
(c) False - The rearing of silkworms for obtaining silk is called sericulture.
(d) True
(e) False - Yak hair are used to make woollen fabric.

 

Answer:

As the animal body has a thick coat of hair, it can trap a lot of air.  Since, air is a poor conductor of heat, it prevents the loss of heat from the body and keeps it warm.
 

Answer:

The correct match of column I with column II is as follows:

$$\begin{gathered} \left(a\right)\to \left(iii\right) \\ \left(b\right)\to \left(iv\right) \\ \left(c\right)\to \left(ii\right) \\ \left(d\right)\to \left(i\right) \end{gathered}$$

Answer:

The correct sequence of the steps in which they are carried out is as follows:

(iii) Shearing
(iv) Scouring
(v) Sorting
(i) Picking out the burrs
(ii) Dyeing in various colors

 

Answer:

The correct form can be written as:

(a) SERICULTURE
(b) SILKWORM
(c) MULBERRY
(d) REELING

Answer:

The names of wool yielding animals in each ring are as follows:

Yak- First ring
Camel- Second ring
Sheep- Third ring


 

Answer:

(a) Eggs of silk moth on mulberry leaves
(b) Silkworm
(c) Cocoon
(d) Cocoon with developing moth



 

Answer:

The proper sequence for the production of silk is as follows :

(e) Female silk moths lay eggs.
(a) Eggs are warmed to a suitable temperature for the larvae to hatch from eggs.
(d) The larvae/caterpillars or silkworms are kept in clean trays along with freshly chopped mulberry leaves.
(c) After 25 to 30 days, the caterpillars stop eating and start spinning cocoons.
(f) Cocoons are kept under the sun or boiled in water
(b) Fibres are taken out from cocoon.

 

Answer:

The correct match of column I with column II is as follows:

$$\begin{gathered} \left(a\right) \to \left(iii\right) \\ \left(b\right) \to \left(i\right) \\ \left(c\right) \to \left(ii\right) \\ \left(d\right) \to \left(iv\right) \end{gathered}$$
 

Answer:

(a) Female
(b) Eggs
(c) Larvae
(d) Caterpillars
(e) Silkworms
(f) Pupa
(g) Cocoon
 

Answer:

The thread which burns with a smell of burning hair is from a pure silk saree. This is because both silk and hair are protein fibres and hence, produce similar smell on burning. Whereas, cotton and paper both are carbohydrates, thus, the thread that burns with a smell of burning paper is from a cotton saree.
 

Answer:

"Unity is strength" is a proverb which means sticking together or being together is a source of strength. It is related with the making of fabric from fibre because a fibre is a thin strand like hair. Large number of fibres are used to make fabric. A single fibre can be easily pulled and broken whereas a fabric needs more energy to break apart.  Thus, uniting the fibres to make fabric provides strength to the material of the cloth.
 

Answer:

Various steps for processing fibres into wool are:

(i) Shearing: The removal of wool or fleece from a sheep or other wool yielding animal is called shearing. It can be done manually using a large razor or through a shearing machine
(ii) Scouring: The sheared hair is moved through tubs filled with soap and water to remove dust, dirt and grease. This is known as scouring.
(iii) Sorting: It is a process of separating hair of different textures
(iv) Cleaning of burrs: Burrs are soft fluffy fibres in wool. They are are picked out from the hair manually.
(v) Dyeing: The natural hair of sheep are brown, black or white. It is dyed in various colors.
(vi) Rolling: 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.

Answer:

Life history of silk moth can be described as:

• The female silk moth lays eggs.
• When an egg hatches, a tiny caterpillar crawls out. This is the silkworm or larva.
• The silkworm feeds on mulberry leaves and grows.
• When it is ready to enter the next stage in its life cycle, it first weaves a net to hold itself.
• It then secretes a fibre made of proteins, which hardens on exposure to air. This is the silk fibre. It covers itself completely with this fibre, to form cocoon.
• At this stage, the larva is called a pupa. The pupa grows and changes inside the cocoon.
• A few weeks later, the cocoon opens and an adult moth comes out.