Class 7 Science Notes Chapter 3 (Fibre to Fabric) – Science Book

Okay, let's prepare detailed notes for Chapter 3: Fibre to Fabric, focusing on aspects relevant for government exam preparation based on NCERT Class 7 Science.

NCERT Class 7 Science: Chapter 3 - Fibre to Fabric

Focus: This chapter deals primarily with animal fibres, specifically Wool and Silk. (Plant fibres like cotton and jute were covered in Class 6).

1. Introduction to Animal Fibres

• Definition: Fibres obtained from animals are called animal fibres.
• Key Examples: Wool and Silk.
• Composition:
  • Wool: Primarily protein.
  • Silk: Primarily protein.

2. Wool

• Source: Obtained from the fleece (hair) of sheep, goat, yak, camel, llama, and alpaca.

  • Sheep: Most common source of wool.
  • Yak: Wool is common in Tibet and Ladakh.
  • Angora Goat: Source of Mohair fibre (found in hilly regions like Jammu & Kashmir).
  • Goat (Kashmiri Goat): Source of fine, soft Pashmina wool (used for Pashmina shawls).
  • Camel: Fur on the body is also used as wool.
  • Llama and Alpaca: Found in South America, also yield wool.

• Types of Fibres in Fleece: Sheep have two types of fibres:

  • The coarse beard hair.
  • The fine soft under-hair close to the skin (This is the fibre used for making wool).

• Selective Breeding:

  • Definition: The process of selecting parent animals with desired characteristics (like soft under-hair) to obtain offspring with those specific traits.
  • Purpose: To breed sheep that yield only fine soft under-hair.

• Rearing and Breeding of Sheep:

  • Regions in India: Sheep are reared in hilly regions (Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Arunachal Pradesh, Sikkim) and plains (Haryana, Punjab, Rajasthan, Gujarat).
  • Diet: Sheep are herbivores, preferring grass and leaves. Rearers also feed them a mixture of pulses, corn, jowar, oil cakes, and minerals.
  • Shelter: Kept indoors during winter and fed on leaves, grain, and dry fodder.
  • Goal: To obtain sheep with a thick coat of hair (fleece) for good quality wool.

• Processing Fibres into Wool: This involves several steps:

  • Step I: Shearing
    • Definition: Removal of the sheep's fleece along with a thin layer of skin.
    • Tools: Machines similar to those used by barbers.
    • Timing: Usually done during hot weather so sheep can survive without their protective coat.
    • Pain: Does not hurt the sheep (like getting a haircut) as the uppermost layer of skin is dead. Hair grows back.
  • Step II: Scouring
    • Definition: Thorough washing of sheared skin with hair in tanks.
    • Purpose: To remove grease, dust, and dirt.
    • Method: Now mostly done by machines.
  • Step III: Sorting
    • Definition: Separating hair of different textures.
    • Process: Hairy skin is sent to a factory where sorting is done.
  • Step IV: Cleaning of Burrs
    • Definition: Removing small, fluffy fibres called burrs from the hair. (These are the same burrs that sometimes appear on sweaters).
    • Process: Fibres are scoured again and dried.
  • Step V: Dyeing
    • Definition: Colouring the fibres.
    • Reason: The natural fleece is usually black, brown, or white. Fibres are dyed in various colours.
  • Step VI: Rolling into Yarn
    • Definition: Straightening, combing, and rolling the fibres into yarn.
    • Outcome: Longer fibres are made into wool for sweaters; shorter fibres are spun and woven into woollen cloth.

• Occupational Hazard:

  • Sorter's Disease: Wool industry workers involved in sorting fleece can sometimes get infected by a bacterium called Anthrax, which causes a fatal blood disease. This is an occupational risk.

3. Silk

• Source: Obtained from the cocoons of silkworms (larva/caterpillar stage of the silk moth).

• Nature: Silk fibres are animal fibres made of protein.

• Sericulture:

  • Definition: The rearing of silkworms for obtaining silk.

• Life History of the Silk Moth: (Understanding this cycle is crucial)

  • Stage 1: Egg: The female silk moth lays hundreds of eggs at a time.
  • Stage 2: Larva (Caterpillar or Silkworm): Eggs hatch into larvae. They feed voraciously on mulberry leaves and grow rapidly in size.
  • Stage 3: Pupa:
    • The caterpillar stops eating and weaves a net to hold itself.
    • It swings its head from side to side in the shape of the figure eight (8).
    • During these movements, it secretes a fibre made of protein which hardens on exposure to air, becoming silk fibre.
    • The caterpillar covers itself completely with this silk fibre, forming a cocoon.
    • The caterpillar develops into a pupa inside the cocoon.
  • Stage 4: Moth: The pupa develops into an adult moth inside the cocoon. The moth emerges from the cocoon to continue the life cycle.

• Silk Yarn: Obtained from the cocoon of the silk moth.

• Varieties of Silk:

  • Different types of silk moths yield different textures of silk (coarse, smooth, shiny, etc.).
  • Examples: Tassar silk, Muga silk, Kosa silk, etc., are obtained from cocoons spun by different types of moths.
  • Mulberry Silk Moth: The most common silk moth. The silk fibre from its cocoon is soft, lustrous, elastic, and can be dyed beautifully.

• From Cocoon to Silk (Processing):

  • Step 1: Rearing Silkworms:
    • Female moths lay eggs, which are stored carefully on strips of cloth or paper and sold to silkworm farmers.
    • Farmers keep eggs under hygienic conditions and suitable temperature/humidity.
    • Eggs are warmed to a suitable temperature for hatching.
    • Larvae (silkworms) are kept in clean bamboo trays with freshly chopped mulberry leaves.
    • After 25-30 days of feeding, they stop eating and move to tiny chambers (twigs/racks provided in the tray) to spin cocoons.
  • Step 2: Processing Silk:
    • A pile of cocoons is collected.
    • Reeling the Silk: Cocoons are kept under the sun, boiled, or exposed to steam. This kills the pupa inside and separates out the silk fibres.
    • The process of taking out threads from the cocoon for use as silk is called reeling the silk.
    • Reeling is done using special machines that unwind the delicate threads (filaments) from the cocoon.
  • Step 3: Making Silk Fabric:
    • Silk filaments are spun (twisted) into silk threads (yarn).
    • These threads are then woven into silk cloth by weavers.

• Discovery of Silk (Traditional Account): Believed to have been discovered in China by Empress Leizu. China kept it a secret for centuries but it eventually spread through trade routes (like the Silk Road).

4. Key Terms Recap

• Fleece: The hairy coat of animals like sheep.
• Rearing: Bringing up and looking after animals.
• Shearing: Removing the fleece from sheep.
• Scouring: Washing sheared wool to remove impurities.
• Sorting: Separating wool fibres based on texture.
• Sericulture: Rearing silkworms to obtain silk.
• Silkworm: The larva/caterpillar stage of the silk moth.
• Cocoon: The protective covering made of silk fibre spun by the silkworm around itself during the pupa stage.
• Pupa: The stage in a silk moth's life cycle between larva and adult moth, spent inside the cocoon.
• Reeling: The process of unwinding silk filaments from the cocoon.
• Selective Breeding: Choosing parents with desired traits to produce offspring with those traits.

5. Important Points for Exam Preparation:

• Know the specific animals that provide wool (Sheep, Yak, Angora Goat, Kashmiri Goat, Camel, Llama, Alpaca) and the special types of wool (Mohair, Pashmina).
• Memorize the exact sequence of steps in processing wool: Shearing -> Scouring -> Sorting -> Cleaning Burrs -> Dyeing -> Rolling.
• Understand the life cycle of the silk moth (Egg -> Larva/Silkworm -> Pupa/Cocoon -> Moth) and what happens at each stage, especially cocoon formation.
• Know the definition of Sericulture and Reeling.
• Remember that silkworms primarily feed on Mulberry leaves.
• Be aware of the different types of silk (Mulberry, Tassar, Muga, Kosa) and that Mulberry silk is the most common.
• Know that both wool and silk are protein fibres.
• Remember the occupational hazard associated with wool sorting (Sorter's disease/Anthrax).

These notes cover the essential information from NCERT Class 7, Chapter 3, structured for effective revision for government exams. Focus on definitions, processes, sources, and key terms.