In Class 8 Science Ch 3 Synthetic Fibres and Plastics, we explore the world of synthetic fibers and plastics, which have become integral to our daily lives. This chapter covers the various types of synthetic fibers, their properties, and how they are used in a wide range of applications, from clothing to industrial products. We also discuss plastics, including their different types, uses, and the significant environmental challenges posed by plastic waste. Understanding the production, advantages, and disadvantages of synthetic materials will help us appreciate their impact on both society and the environment.
Class 8 Science Ch 3 Synthetic Fibres and Plastics
D. Give reason for the following
1. Wool is ideal for making winter clothing.
Ans: Wool is a poor conductor of heat and hence keeps the body warm. Air, being a bad conductor of heat, gets trapped in the holes present in a woollen garment. Thus, woollen clothes protect us from cold in winter.
2. Sheep are usually sheared during warm weather.
Ans: The hair present on the sheep helps in keeping the animal warm in winters. Hence, sheep are usually sheared in warm weather.
3. Wool industry workers often develop sorter disease.
Ans: Anthrax is a disease of sheep and other animals that is caused by a bacterium called anthrax. Shearers and wool sorters who handle sheep and their fleece are at a high risk of getting anthrax. Therefore, anthrax is also called the sorter’s disease. In humans, anthrax causes dark pimple-like boils on the skin and can lead to skin, lung and intestinal infections or to a fatal blood infection.
4. Some varieties of sheep are selectively bred.
Ans: The cocoons are either exposed to steam, heated in an oven or carefully boiled in water. This process kills the pupae before they can emerge from the cocoon by cutting through the fibres. Sericin is the natural gum that holds the silk fibres together. Boiling the cocoons separates the silk fibres from each other.
5. Some breeds of sheep only have thick coat of fine underhair. These sheep yield good-quality wool in large amounts. Such varieties of sheep are selectively bred by choosing their parents to give birth to sheep that yield only good-quality wool.
E.
1. What are natural fibres?
Ans: Natural fibres are obtained from natural sources such as plants and animals. Cotton and jute are obtained from plants, while silk and wool are obtained from animals.
2. Which breed of the sheep provides the finest quality wool?
Ans: Merino
3. Define selective breeding.
Ans: The process of selecting parents and breeding them for obtaining special characteristics in the offspring is called selective breeding.
4. Name the most common silkworm.
Ans: Bombyx mori
5. What is sericin?
Ans: Sericin is the natural gum that holds the silk fibres together.
F.
1. List three characteristics of wool fibres.
Ans: 1. Wool has the following characteristics.
i. It is durable, elastic and does not wrinkle easily. Therefore, woollen garments retain their shape with use.
ii. It is a poor conductor of heat and hence keeps the body warm. iii. It absorbs water. This property makes it easy to dye wool.
2. Name three animals of the camel family from which wool is obtained.
Ans: Alpaca, llama and Vicuna
3. Does shearing cause a sheep any pain?
Ans: Shearing does not hurt the sheep as the hair that are sheared are dead.
4. What is grading of wool?
Ans: The wool fibres are grouped based on their length, fineness, colour, texture and other characteristics. This process is called grading. Different grades of wool are used to make different woolen products
5. How does a silkworm make its cocoon?
Ans: When the caterpillar of the silkworm is mature, it stops feeding and begins to turn into a pupa. The pupa secretes a thin, continuous filament-like substance from its salivary glands. The substance is made of a protein that hardens when exposed to air. This hardened secretion becomes silk fibre. The pupa swings its head from side to side in the form of the figure of eight and spins around itself a case of silk fibre called a cocoon.
Class 8 Science Ch 3 Synthetic Fibres and Plastics
G.1. Describe the steps involved in the production of wool.
Ans: Steps involved in the production of wool:
Shearing: The process by which the fleece of the sheep is removed is called shearing. It may be done using either clippers or a shearing machine.
Scouring: The process by which the sheared fleece is treated to remove dust, dirt and grease is known as scouring. The sheared skin and hair are thoroughly washed in a series of tubs to clean them. Nowadays, machines are used for this process.
Sorting: Hair of different textures are separated from each other by sorting. Small fluffy fibres called burrs are removed. The wool fibres that remain are scoured once more and dried.
Grading: The wool fibres are grouped based on their length, fineness, colour, texture and other characteristics. This process is called grading. Different grades of wool are used to make different woolen products.
Dyeing: As the natural fleece of sheep and goat are black, brown or white, the fibres obtained from them are dyed in various colours.
Carding and spinning: The fibres are straightened, combed by passing them through rollers. This process is called carding. The fibres are then twisted to make yarn by the process of spinning. A spinning frame is used for this purpose. The yarn is wound onto paper cones or spindles for easy use in weaving and knitting machines.
Weaving and knitting: Yarns are knitted or woven by hand or in machines to make fabric. Knitting uses a single yarn, while weaving uses two or more yarns. Therefore, longer woollen fibres are suitable for knitting, while shorter fibres are suitable for weaving.
2. Describe the life cycle of the silk moth with the help of labelled diagrams.
Ans: The following are the stages of the life cycle of a silk moth
• Egg stage: The female silk moth lays hundreds of eggs on the leaves of the mulberry plant. They hatch in about 7–14 days.
• Larval stage: The eggs hatch into larvae or caterpillars that are the silkworms. The caterpillars feed on mulberry leaves and grow over 3–4 weeks. The caterpillar sheds its skin four times during this phase as it grows bigger in size. This process is called moulting.
• Pupal stage: Once the caterpillar is mature, it stops feeding and begins to turn into a pupa. The pupa secretes a thin, continuous filament-like substance from its salivary glands. The substance is made of a protein that hardens when exposed to air. This hardened secretion becomes silk fibre. The pupa swings its head from side to side in the form of the figure of eight and spins around itself a case of silk fibre called a cocoon. The colour of the cocoon depends on what the silkworm eats.
• Adult stage: The pupa continues to develop inside the cocoon for about 15 days and grows into a moth. Finally, the fully formed moth pierces open the cocoon and emerges. The lifespan of the adult is only about 3–10 days. Adult moth Mating Laying eggs Hatching Feeding Caterpillar Cocoon formation Emergence of a moth
3. What is sericulture? Describe how silkworms are related as part of the process of sericulture.
Ans: The rearing of silkworms for the production of silk is called sericulture. To obtain silk, silkworms are reared, and silk fibre is extracted from their cocoons and processed.
The rearing of silkworms and production of silk involves the following steps.
• The hundreds of eggs laid by a female silk moth are collected on strips of cloth or paper. They are kept under suitable conditions of temperature and humidity to help them hatch.
• The silkworms that hatch from the eggs are placed in clean bamboo trays that are lined with fresh mulberry leaves.
• The silkworms are fed mulberry leaves for about 25 to 30 days. Newspapers are spread over the trays to absorb excess moisture from the leaves. The trays are cleaned regularly every few days. The silkworms grow and moult four times.
• When mature, the silkworms stop eating and begin to spin cocoons. They are shifted to bamboo trays that have small chambers or frames. Each silkworm spins its cocoon in a part of the frame. The spinning of cocoons takes about 3–7 days. Silk moths develop inside these cocoons.
Class 8 Science Ch 3 Synthetic Fibres and Plastics
4. How is silk obtained from the cocoons of silkworms?
Ans: Silk is extracted and processed from the cocoons in the following way:
• The silkworm cocoons are sorted according to colour, size, shape and texture. They usually range from white and yellow to greyish in colour.
• The cocoons are either exposed to steam, heated in an oven or carefully boiled in water. This process kills the pupae before they can emerge from the cocoon by cutting through the fibres. Sericin is the natural gum that holds the silk fibres together. Boiling the cocoons separates the silk fibres from each other. This process is called degumming.
• The cocoons are taken out of the water and silk fibres are extracted by a process called reeling. Reeling involves carefully unwinding the continuous strand of silk that makes the cocoon as a single unbroken thread. Reeling is usually done in special machines. As the silk strand is too fine to use, 3–10 strands from different cocoons are reeled together to produce a silk thread of suitable thickness. This silk is called reeled silk.
• The silk is dyed in different colours. It is then spun into yarns which can be woven into silk fabric. Silk yarn from which sericin has not been removed by boiling is called raw silk. Raw silk is lustrous but has a coarse texture.
Class 8 Science Ch 3 Synthetic Fibres and Plastics
5. What is an occupational hazard? Explain the various occupational hazards faced by workers in wool processing and sericulture industries.
H. Both wool and silk are poor conductor of heat.They both help us keep warm in winters.However ,winter clothing is made of wool.why?
Ans: The diseases caused due to the occupation are called as occupational hazards.
Various occupational hazards are associated with the silk industry, some of which are:
• Handling cocoons in boiling water by hand without wearing gloves can cause the skin to peel off or form blisters, which can lead to skin infections.
• The vapours from boiling cocoons and fumes of diesel and the strong chemicals used for dyeing silk fibres can cause irritation in eyes, skin infections and respiratory problems.
H. It is a poor conductor of heat and hence keeps the body warm.
As we come to the end of this chapter, it’s clear that Class 8 Science Ch 3 Synthetic Fibres and Plastics play a major role in our everyday lives. From the clothes we wear to the packaging materials we use, these man-made substances have become almost impossible to live without. However, understanding the advantages and disadvantages of Class 8 Science Ch 3 Synthetic Fibres and Plastics is essential—not just for exams, but for becoming responsible users and aware citizens.
We’ve learned how synthetic fibres are created from chemicals and how they differ from natural fibres in terms of strength, durability, and cost. At the same time, we explored how plastics are versatile, lightweight, and used in countless applications. But it’s equally important to remember that Class 8 Science Ch 3 Synthetic Fibres and Plastics, while useful, also contribute to environmental problems like pollution and non-biodegradability. This brings a clear need for proper disposal, recycling, and responsible usage.
In conclusion, by studying Class 8 Science Ch 3 Synthetic Fibres and Plastics, we gain not just scientific knowledge, but also the awareness to make smarter choices as consumers. Whether it’s choosing eco-friendly alternatives or understanding how to recycle better, our daily actions matter. The chapter on Class 8 Science Ch 3 Synthetic Fibres and Plastics reminds us that science is not just about facts—it’s about how we use that knowledge to improve the world around us.
Class 8 Science Ch 3 Synthetic Fibres and Plastics
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