Science Cordova Grade-7 Ch-3 [Fibre to Fabric]

Q1. Very Short Answer Type Questions:

a. Name the steps involved in the production of wool from sheep?

Ans.

Sheering
Scouring
Sorting
Combing
Dyeing
Spinning

b. Which is the strongest natural fibre?

Ans. Silk

c. What are the basis to decide the quality of wool obtained from sheep?

Ans. The quality of wool is judged on the basis of thickness, length, shine, strength, and fineness of the fibres.

d. Name the process of rearing of silkworms for obtaining silk.

Ans. Sericulture.

Q2. Short Answer type-I questions:

a. What is meant by selective breeding?

Ans. Selective breeding, also known as artificial selection, is a process used by humans to develop new organisms with desirable characteristics.

b. What is meant by scouring?

Ans. The process of washing the fleece of sheep to remove dust, dirt, sweat, grease, etc., is called scouring.

c. Give two characteristics of wool.

Ans. Wool has a high tensile strength and has high elasticity.

It can absorb large amount of water.

It is light weight and can be easily dyed.

d. What is silk. How is it obtained?

Ans. Silk is a fine, strong, soft and shining fibre obtained from silkworms. It is separated from cacoons of silkworms which is made of protein.

e. Why are the cacoons boiled in hot water or treated in ovens.

Ans. To kill the pupa inside cacoons, these are boiled in hot water. If they are not killed and allowed to grow, they will break the cacoon and thereby reduce the length of the silk fibre.

f. Why do we not wait for the silk moth to hatch and then boil the cacoon?

Ans. This is because if the cacoon breaks, it cause damage to its silk threads and hence lowers the quality of silk.

g. Why do we need to boil the cacoon for extraction of silk?

Ans. Cocoons are set in boiling water to disintegrate the glue that passes one strand of silk to the layers beneath. This permits a single silk strand to be unrolled from the case.

Q3. Short Answer type-II Questions:

a. Why does Sheering not hurt the sheep?
Ans. Sheering does not hurt the sheep because the uppermost layer of the skin of sheep is dead.

b. Differentiate between silk and wool.
Ans. Wool is hair of animals like sheep. It soaks in water.

Silk is a fibre secreted by an insect named silk-worm. It does not soak in water.

c. What are raw silk and spun silk?
Ans. Reeled silk before the gum is removed is called raw silk.
A yarn or fabric made from short unreeled silk fibre that have been degummed is called spun silk.

d. With the help of flow chart, describe the life cycle of a silkworm.