Notes On Animal Fibre - Silk - CBSE Class 7 Science
What is cool in summer and warm in winter? The Chinese guarded the making of this fabric with their life What fabric are we talking about? Yes! We are talking about silk, the queen of textiles. Silk is a type of an animal fiber produced by the silkworm. Discovery of silk Chinese legend has it that empress Si-lung-Chi was worried about the damaged mulberry leaves in her garden. Emperor Huang-ti found out that the white worms were eating up the mulberry leaves and spinning shiny cocoons. A cocoon accidentally dropped into the empress’s cup of hot tea, and the delicate tangle of threads separated from the cocoon, thus leading to the discovery of silk. Thus, the silk industry was born in China. This was kept secret for hundreds of years. later this was introduced in other countries by traders and travelers much later. The route they travelled was called the silk route. Properties of Silk Silk is an elastic, lustrous protein fibre. The soft silk thread is as strong as a comparable steel thread. Types of Silk Different types of silk moths yield different types of silk yarn, such as mulberry silk, tassar silk, eri silk and moonga silk.The most common silk moth is the mulberry silk moth. It’s Latin name is Bombyx mori. Let us discuss about the life cycle of silk moth. Life Cycle – Silk Moth Actually silkworms are not worms, but the larvae or caterpillars hatched from the eggs of the silk moth. The life history of a silk moth starts when a female silk moth lays eggs. The larvae or caterpillars hatched from the eggs of the silk moth. These silkworms feed on fresh mulberry leaves the silkworm grows in size and then becomes a pupa. In the pupa stage, it weaves a net to hold itself.  It then swings its head from side to side, secreting a fibre that hardens on contact with air. This fibre is made of a protein and becomes the silk fibre. The caterpillar covers itself completely with silk fibre and turns into a pupa, this covering is known as the cocoon. The moth continues to develop within the cocoon. The silk thread or yarn is obtained from the silk moth’s cocoon. Rearing Silkworms Sericulture Sericulture, or silk farming, is the rearing of silkworms for the production of raw silk. Silkworms are reared under suitable conditions of temperature and humidity to obtain silk threads from their cocoons. The female silk moth lays hundreds of eggs. These are stored on strips of cloth or paper. Mulberry leaves are the staple diet of silkworms. When the mulberry tree bears a fresh crop of leaves, the eggs are warmed suitably so that the larvae hatch from them. The larvae, caterpillars or silkworms are then stored in clean bamboo trays and are fed freshly chopped mulberry leaves. They eat day and night, and grow to enormous sizes.   The bamboo trays are provided with small racks or twigs to which the cocoons can be attached. This happens usually after 25 to 30 days when the caterpillars stop feeding and move to the twigs to spin cocoons. The silk moth develops inside these cocoons. Interesting fact about Caterpillar As the caterpillars grow bigger, they shed their skin. The skin of the caterpillar does not grow along with it. So, it sheds its skin, and underneath the old one is a new skin. Caterpillars may shed skin four or five times! Processing Silk Extracting silk from the cocoon is called processing silk. The first step is to separate the silk fibre from the cocoon. For this, they need to be exposed to warmth. Piles of cocoons are kept under the sun, boiled or exposed to steam. The warmth causes the silk fibre to separate from the rest of the cocoon. The next step is called reeling the silk, which is the process of delicately unwinding the fibre from the cocoon. Reeling is also done in special machines. The silk thread is then bleached and dyed into many shades. The silk fibre is then spun into silk thread, which is then woven into silk cloth by weavers.

#### Summary

What is cool in summer and warm in winter? The Chinese guarded the making of this fabric with their life What fabric are we talking about? Yes! We are talking about silk, the queen of textiles. Silk is a type of an animal fiber produced by the silkworm. Discovery of silk Chinese legend has it that empress Si-lung-Chi was worried about the damaged mulberry leaves in her garden. Emperor Huang-ti found out that the white worms were eating up the mulberry leaves and spinning shiny cocoons. A cocoon accidentally dropped into the empress’s cup of hot tea, and the delicate tangle of threads separated from the cocoon, thus leading to the discovery of silk. Thus, the silk industry was born in China. This was kept secret for hundreds of years. later this was introduced in other countries by traders and travelers much later. The route they travelled was called the silk route. Properties of Silk Silk is an elastic, lustrous protein fibre. The soft silk thread is as strong as a comparable steel thread. Types of Silk Different types of silk moths yield different types of silk yarn, such as mulberry silk, tassar silk, eri silk and moonga silk.The most common silk moth is the mulberry silk moth. It’s Latin name is Bombyx mori. Let us discuss about the life cycle of silk moth. Life Cycle – Silk Moth Actually silkworms are not worms, but the larvae or caterpillars hatched from the eggs of the silk moth. The life history of a silk moth starts when a female silk moth lays eggs. The larvae or caterpillars hatched from the eggs of the silk moth. These silkworms feed on fresh mulberry leaves the silkworm grows in size and then becomes a pupa. In the pupa stage, it weaves a net to hold itself.  It then swings its head from side to side, secreting a fibre that hardens on contact with air. This fibre is made of a protein and becomes the silk fibre. The caterpillar covers itself completely with silk fibre and turns into a pupa, this covering is known as the cocoon. The moth continues to develop within the cocoon. The silk thread or yarn is obtained from the silk moth’s cocoon. Rearing Silkworms Sericulture Sericulture, or silk farming, is the rearing of silkworms for the production of raw silk. Silkworms are reared under suitable conditions of temperature and humidity to obtain silk threads from their cocoons. The female silk moth lays hundreds of eggs. These are stored on strips of cloth or paper. Mulberry leaves are the staple diet of silkworms. When the mulberry tree bears a fresh crop of leaves, the eggs are warmed suitably so that the larvae hatch from them. The larvae, caterpillars or silkworms are then stored in clean bamboo trays and are fed freshly chopped mulberry leaves. They eat day and night, and grow to enormous sizes.   The bamboo trays are provided with small racks or twigs to which the cocoons can be attached. This happens usually after 25 to 30 days when the caterpillars stop feeding and move to the twigs to spin cocoons. The silk moth develops inside these cocoons. Interesting fact about Caterpillar As the caterpillars grow bigger, they shed their skin. The skin of the caterpillar does not grow along with it. So, it sheds its skin, and underneath the old one is a new skin. Caterpillars may shed skin four or five times! Processing Silk Extracting silk from the cocoon is called processing silk. The first step is to separate the silk fibre from the cocoon. For this, they need to be exposed to warmth. Piles of cocoons are kept under the sun, boiled or exposed to steam. The warmth causes the silk fibre to separate from the rest of the cocoon. The next step is called reeling the silk, which is the process of delicately unwinding the fibre from the cocoon. Reeling is also done in special machines. The silk thread is then bleached and dyed into many shades. The silk fibre is then spun into silk thread, which is then woven into silk cloth by weavers.

#### Activities

Activity1: Pem.org has developed an about silkworm life cycle, silk cultivation and fashioned in silk with interseting images from the ancient times. The simulation is based on images. You can learn the concept through images which excelently desingned in understanding the concept. Go to Activity Activity2: Kji.iitm.ac has developed an interactive simulation regarding the life cycle of silkworm. The simulation is totally image based about each stage of silkworm. Go to Activity Activity3: Springer.com has developed an interesting simulation regarding life cycle of silkworm through intersingf images and explanation for the each stage of silkworm life cycle. The simulation containes interesting question through the quiz. Go to Activity

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