An Overview of Class 7 Science Fibre To Fabric Worksheets
FAQs on Class 7 Science Fibre To Fabric Worksheets
1. What are the most important steps involved in processing sheep fleece into woollen yarn for the CBSE Class 7 exam?
As per the 2025-26 syllabus, the key steps in processing fibres into wool are crucial for exams. The process includes:
Shearing: The process of removing the fleece of the sheep along with a thin layer of skin. This is usually done in hot weather.
Scouring: The sheared fleece is thoroughly washed in tanks to remove grease, dust, and dirt.
Sorting: The washed wool is sent to a factory where hair of different textures is separated or sorted.
Burr Removal: Small fluffy fibres, called burrs, are picked out from the hair.
Dyeing: The fibres are dyed in various colours as the natural fleece is typically black, brown, or white.
Spinning: The fibres are straightened, combed, and rolled into yarn. Longer fibres are made into wool for sweaters, and shorter fibres are spun and woven into woollen cloth.
2. Explain the complete life cycle of a silk moth. Which stage is commercially important for silk production?
The life history of a silk moth is an expected question. The four distinct stages are:
Egg: The female silk moth lays hundreds of eggs on mulberry leaves.
Larva (Caterpillar/Silkworm): The eggs hatch into larvae, which feed voraciously on mulberry leaves and grow in size. They shed their skin (moult) four times.
Pupa: The caterpillar secretes a protein fibre that hardens on exposure to air. It spins this fibre around itself to form a protective casing called a cocoon. The stage inside the cocoon is the pupa.
Moth: The pupa develops into an adult moth, which emerges by breaking the cocoon.
The cocoon stage is the most important for commercial silk production, as the single, long thread of the cocoon is unwound to get silk fibre.
3. Differentiate between natural silk and artificial silk. How can you test this difference?
Distinguishing between natural and artificial silk is a key concept. The main differences are:
Source: Natural silk is an animal protein fibre obtained from the cocoon of silkworms. Artificial silk, like rayon, is a synthetic fibre made from processed plant cellulose (wood pulp).
Texture: Natural silk is very soft, smooth, and lustrous, while artificial silk can feel slightly coarser.
Cost: Natural silk is significantly more expensive than artificial silk.
Burn Test: This is a crucial test. When burned, natural silk smells like burning hair and leaves a brittle, black ash. Artificial silk smells like burning paper and leaves a soft, grey ash.
4. What is sericulture and why is it important?
Sericulture is the science and practice of rearing silkworms for the production of raw silk. It is an agro-based industry that involves cultivating mulberry plants to feed the silkworms, raising the silkworms until they spin cocoons, and then processing these cocoons to extract silk fibres. It is important as it provides a valuable natural fibre for the textile industry and is a major source of employment for many people, especially in rural areas.
5. Why doesn't the process of shearing hurt the sheep?
Shearing does not hurt the sheep for the same reason that a haircut does not hurt humans. The fleece is removed using clippers, similar to those used by barbers. This process only cuts the hair. The uppermost layer of a sheep's skin is dead, so cutting the wool fibres from this layer is completely painless. Shearing is also timed to be done in warmer weather, ensuring the sheep do not suffer from the cold after losing their protective coat.
6. What are the occupational hazards associated with the wool and silk industries?
This is a higher-order thinking question that might appear in exams. Workers in these industries face specific health risks:
In the wool industry, workers involved in sorting fleece (sorters) are at risk of a fatal blood disease called anthrax, also known as Sorter's disease. This is caused by the bacterium *Bacillus anthracis* sometimes found in the fleece of infected animals.
In the silk industry, workers who unwind the silk from cocoons (reelers) often have to dip their hands in boiling water, which can cause blisters and burns. They may also suffer from respiratory issues like asthma due to inhaling vapours from the boiling cocoons.
7. Why is wool considered a better insulator than cotton, making it suitable for winter clothing?
Wool is a superior insulator compared to cotton due to its physical structure. Wool fibres have a natural crimp (waviness) which creates many tiny air pockets within the fabric. Air is a poor conductor of heat. These trapped air pockets prevent the body's heat from escaping into the cold surroundings, thus keeping us warm. Cotton fibres are smoother and less crimped, so they cannot trap as much air, making them less effective at providing insulation.
