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SCIENCE | Class 7 (Startup Science) Solutions; Chapter 3: Materials of Daily Use.

 **A. Answer in Detail**


1. Differentiate between plant and animal fibres. 

Ans: Plant fibres are derived from plants, while animal fibres are obtained from animals.  

- Sources:  

  •   - Plant fibres: Cotton (from cotton plant), jute (from jute plant), flax (linen).  
  •   - Animal fibres: Wool (from sheep, goats), silk (from silkworms).  
- Composition:  
  •   - Plant fibres are primarily made of cellulose.  
  •   - Animal fibres consist of proteins (e.g., keratin in wool, fibroin in silk).  
- Properties:  
  •   - Plant fibres are breathable and absorbent but less durable.  
  •   - Animal fibres are elastic, insulating, and stronger.  


2. How is wool obtained from sheep? 

Ans: Wool is obtained from sheep by the following process-

  • - Shearing: The thick coat of hair (fleece) is shaved off using electric clippers.  
  • - Scouring: The fleece is washed in tanks to remove dirt, grease, and impurities.  
  • - Sorting: Fibres are graded based on texture and quality.  
  • - Carding: Fibres are combed to align them into thin sheets called slivers.  
  • - Spinning: Slivers are twisted into yarn using spinning wheels or machines.  


3. Explain the life cycle of silk moth.

1. Egg: Female silk moth lays eggs on mulberry leaves.  

2. Larva (Silkworm): Eggs hatch into larvae that feed on mulberry leaves for 25–30 days.  

3. Pupa: The silkworm secretes silk to spin a cocoon around itself for protection during metamorphosis.  

4. Adult Moth: The pupa develops into a moth, which emerges from the cocoon, mates, and lays eggs.  


4. How are silk fibres obtained from cocoons?

Ans: Silk Fibres are obtained from cocoons by -

  • - Cocoons are boiled in water to soften the sericin (a protein glue) binding the silk threads.  
  • - The softened threads are carefully unwound in a process called reeling.  
  • - Multiple filaments are combined and twisted to form a strong, usable silk thread.  


5. How do silkworms spin cocoons?

  Ans:

Silkworms secrete a liquid protein (fibroin) from their silk glands, which hardens into fine threads upon contact with air. Using their spinnerets (organs near the mouth), they move their heads in a figure-8 pattern to spin the cocoon, which takes 2–3 days.  




 **B. Answer Briefly**


1. Why do you need clothes?

  Ans:

Clothes protect us from weather (heat, cold, rain), ensure modesty, and reflect cultural/social identity.  


2. What are animal fibres? Give two examples.

Ans:  

Animal fibres are protein-based fibres obtained from animals. Examples: Wool (sheep), Silk (silkworms).  


3. How does wool fibre keep our body warm?

Ans:  

Wool traps air between its fibres, creating an insulating layer that retains body heat. In this way wool keeps our body warm.


4. What are the three grades of silk produced? 

Ans: The three grades of silk produced are- 

Mulberry silk (highest quality), Tussar silk, and Eri silk.  


5. What is throwing?

Ans:

Throwing is the process of twisting raw silk filaments into strong, usable threads.  


6. Name a few varieties of silk.

Ans: Few varieties of silk are- 

Mulberry, Tussar, Eri, Muga, and Charka silk.  


7. Name two breeds of sheep found in India. Also give the names of the states in which they are found.

Ans:

- Lohi: Punjab and Rajasthan.  

- Nali: Haryana and Punjab.  


 C. Answer in One Word or a Few Words


**C1. Match the two columns.**  

1. Silk moth → (iii) Bombyx mori  

2. Cocoon → (i) Silk fibre  

3. Food for silk moth → (v) Mulberry leaves  

4. Fleece → (vi) Hair of sheep  

5. Shearing → (ii) Removal of thick coat of hair  

6. Nail silk → (iv) Inferior quality of silk  


**C2. State whether the following statements are True (T) or False (F).**  

1. Wool is obtained only from sheep. → **F** (also from goats, camels)  

2. Sericulture is a process of rearing of silkworm. → **T**  

3. Removing fleece of sheep from its body is called scouring. → **F** (called shearing)  

4. Silk threads are secreted from silk glands. → **T**  

5. Sheep feed on mulberry leaves. → **F** (sheep eat grass; silkworms eat mulberry leaves)

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