Monday 31 January 2022

NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric

                       Fibre to Fabric

In this chapter we learn about wool and silk obtained from animals. Wool is obtained from the fleece (hair) of sheep or yak. Silk fibres come from cocoons of the silk moth. 

Animal fibres — wool and silk 

पशु रेशे - ऊन और रेशम

WOOL- Wool is natural fiber which comes from sheep, yak and other animals. Wool is basically the hair of these animals. Hairs are good conductors of heat or very bad conductors of air. Hence hairs keep these animals warm.

The hairy skin of the sheep has two types of fibres that form its fleece: (i) the coarse beard hair, and (ii) the fine soft under-hair close to the skin.The fine hair provides the fibres for making wool. Some breeds of sheep possess only fine under-hair, which is good for manufacturing woolens.

Selective breeding- it is the process of selecting specific parents or breed of animal to give specific character or quality offspring which can be used to produce good quality products from them. It is similar to buying high yielding seeds for farming. 

  1. Sheeps are found in Ladakh, Kashmir and Jammu, tibet. Their wool is called sheep wool which is very common.

  1. Goats in jammu and kashmir also give wool

  • Angora goats give the wool name Mohair.

  • Cashmere goats give cashmere wool, and pashmina shawl are made from them.

  1. Camels are also used to obtain wool, their  fur (hair) on the body is used as fiber to use wool, like Llama and Alpaca, found in South America, also yield wool. 

From fibres to wool 

रेशों से ऊन तक

Hairs of sheeps, goats,camels and yaks have been cut to produce wool. Let's learn how a sheep gets ready to give wool. Hilly areas like Jammu & Kashmir, Himachal Pradesh, Uttaranchal, Arunachal Pradesh and Sikkim, or the plains of Haryana, Punjab, Rajasthan and Gujarat are main sources of wool in our country. 

 Shepherds feed their sheeps and goats by various ways first they take them to grassland for grazing. Apart from grazing sheep, rearers also feed them on a mixture of pulses, corn, jowar, oil cakes (material left after taking out oil from seeds) and minerals. In winter, sheep are kept indoors and fed on leaves, grain and dry fodder.

Certain breeds of sheep have thick coat of hair on their body which yields good quality wool in large quantities. Once the reared sheep have developed a thick growth of hair, hair is shaved off for getting wool.

Processing fibres into wool

फाइबर से ऊन बनाना

After shredding hair there are many steps for making wool:

बालों को काटने के बाद ऊन बनाने के कई चरण होते हैं:

Step 1- The fleece of the sheep along with a thin layer of skin is removed from its body . This process is called shearing. Machines like barbar used to shave hair, don't worry sheep don't get hurt. It is similar to how we cut our hair or men shave their beard. 

Sheeps get shaved in summer so that they can't die in winter. Now these hairs are processed to make woollen yarns.

Step 2-  The sheared skin with hair is thoroughly washed in tanks to remove grease, dust and dirt. This is called scouring. Nowadays scouring is done by machines. 

Step 3-  After scouring, sorting is done. The hairy skin is sent to a factory where hair of different textures are separated or sorted.

Step 4- The small fluffy fibres, called burrs, are picked out from the hair. These are the same burrs which sometimes appear on your sweaters. The fibres are scoured again and dried. This is the wool ready to be drawn into fibres.

Step 5- The fibres can be dyed in various colours, as the natural fleece of sheep and goats is black, brown or white.

Step 6-  The fibres are straightened, combed and rolled into yarn . The longer fibres are made into wool for sweaters and the shorter fibres are spun and woven into woollen cloth.

The processing of fibre into wool can be represented as follows: Shearing → Scouring → Sorting → Cleaning of burrs ↓ Rolling ← Dyeing.

SILK- silk is also another fiber which we get from living beings i.e silkworms. Silkworms spin the ‘silk fibres’. The rearing of silkworms for obtaining silk is called sericulture. 

Life history of silk moth

In the pupa stage it first weaves a net to hold itself. Then it swings its head from side to side in the form of the figure of eight (8). During these movements of the head, the caterpillar secretes fibre made of a protein which hardens on exposure to air and becomes silk fibre.

The caterpillar completely covers itself by silk fibres and turns into pupa. This covering is known as cocoon. Silk fibres are used for weaving silk cloth, this soft silk yarn is as strong as a comparable thread of steel.

There are different types of silks :

Tassar silk

Mooga silk 

Kosa silk

These different types of cocoons are spun by different types of moths. The most common silk moth is the mulberry silk moth.The silk fibre from the cocoon of this moth is soft, lustrous and elastic and can be dyed in beautiful colours.

Sericulture or culture of silkworms is keeping various kinds of silk worms to obtain silk from is a very old occupation of India. 

From cocoon to silk 

For obtaining silk, moths are bred, taken care of and their cocoons are collected to get silk threads.

Rearing silkworms: A female silk moth lays hundreds of eggs at a time. The eggs are stored on paper and cloth than sold to farmer. Now these eggs need to be kept at a specific temperature so they hatch and feed on mulberry leaves, these larvae or caterpillars eat night and day till 25 to 30 days after these eating days they go into a bamboo chamber of bamboo in the tray to spin cocoons. 

The caterpillar or silkworm spins the cocoon inside which develops the silk moth.

कैटरपिलर या रेशमकीट कोकून को घुमाता है जिसके अंदर रेशम कीट विकसित होता है।

Processing silk: A pile of cocoons is used for obtaining silk fibres. The cocoons are kept under the sun or boiled or exposed to steam. 

The process of taking out threads from the cocoon for use as silk is called reeling the silk. Reeling is done in special machines, which unwind the threads or fibres of silk from the cocoon.

Wednesday 26 January 2022

Nutrition in Plants (पौधों में पोषण) Full Chapter Class 7 Science | NCERT Science Class 7 Chapter 1

         Nutrition in Plants

What are nutrients?

carbohydrates, proteins, fats, vitamins and minerals are components of food. These components of food are called nutrients and are necessary for our body. 

Every living being required food, Plants can make their own food or synthesis, while animals and human being cant produce their food own, therefore animals and human directly or indirectly depends on plants for their food. 


Plants are only beings who make food by taking components from surroundings i.e water, crabondixiode, sunlights and other minerals from environments. 

Food is one way or mode by which living organisms take nutrition.The nutrients enable living organisms to build their bodies, to grow, to repair damaged parts of their bodies and provide the energy to carry out life processes.

Those living beings  who made their own food by taking components or simple substances from the environment are called autotrophic (auto = self; trophos = nourishment) nutrition. Therefore, plants are called autotrophs.

Animals and most other organisms take in food prepared by plants. They are called heterotrophs (heteros) = other.


Leaves are the food factories of plants. Therefore, all the raw materials must reach the leaf. Water and minerals present in the soil are absorbed by the roots and transported to the leaves.

Carbon dioxide from air is taken in through the tiny pores present on the surface of leaves. These pores are surrounded by ‘guard cells’. Such pores are called stomata.

Water and other minerals are transported through vessels inside the stems and roots to leaves.The leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight.

Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis.It is a unique process on the earth. The solar energy is captured by the leaves and stored in the plant in the form of food. Thus, the sun is the ultimate source of energy for all living organisms.

 Photosynthesis there would not be any food. The survival of almost all living organisms directly or indirectly depends upon the food made by the plants.Oxygen which is essential for the survival of all organisms is produced during photosynthesis, therefore without photosynthesis we can't imagine life on earth.

During the process oxygen is released. The presence of starch in leaves indicates the occurrence of photosynthesis. Starch is also a carbohydrate. 

Algae are green in colour. They contain chlorophyll which gives them the green colour. Algae can also prepare their own food by photosynthesis.

Synthesis of plant food other than carbohydrates

Carbohydrates  are used to synthesise other components of food such as proteins and fats. Plants synthesise carbohydrates through the process of photosynthesis.

Proteins are nitrogenous substances which contain nitrogen.These are absorbed by the plants along with water. farmers adding fertilisers rich in nitrogen to the soil. In this way the plants fulfil their requirements of nitrogen along with the other constituents.


There are some plants which do not have chlorophyll. They cannot synthesise food. Like humans and animals such plants depend on the food produced by other plants. They use the heterotrophic mode of nutrition. Example a plant named Cuscuta (Amarbel). It does not have chlorophyll. It takes ready-made food from the plant on which it is climbing.Cuscuta is called the parasite.

There are certain plants which can trap insects and digest them. A pitcher plant which has a pitcher-like or jug-like structure is the modified part of the leaf. A leaf above the pitcher acts as lid whenever any insect trapped inside that pitcher, which has hairs inside it which tanges the insect later digestive juices of the plant digest it. 

Such insect-eating plants are called insectivorous plants.


There are certain organisms which absorb the nutrients from dead and decaying matter called saprotrophic nutrition. Such organisms with saprotrophic mode of nutrition are called saprotrophs. 

Fungi is one example. Fungi also grows on bread, pickles, leather, clothes and other articles that are left in hot and humid weather for a long time. The fungal spores are generally present in the air. When they land on wet and warm things they germinate and grow.

Symbiosis-  It is a process of food sharing or food production where organisms live together and share both shelter and nutrients in exchange without harming each other.

For example, certain fungi live inside the roots of plants. The plants provide nutrients to the fungus and, in return, the fungus provides water and certain nutrients.


As we know plants and crops absorb nutrients like nitrogen, potassium, phosphorus,from soil to grow. While crops need much more nutrients from soils.

This continued farming and plantation growth sucks out the nutrients from plants. Therefore continued practise of adding nutrients to soil is very important like adding manure and fertilizers. 

Mainly nitrogen needs to replenish more for this, Farmers grow leguminous plants or crops like  gram, peas, moong, beans and other legumes to replenish nitrogen. Now the roots of these plants have a bacterium called Rhizobium.

Rhizobium cannot make its own food. So it often lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen. In return, the plants provide food and shelter to the bacteria. They, thus, have a symbiotic relationship. This association is of great significance for the farmers. 

Summary Ends

सारांश समाप्त

Synthetic Fibres and Plastics (सिंथेटिक फाइबर और प्लास्टिक) Full Chapter Class 8 Science | NCERT Science Class 8 Chapter 3


There are two types of fibres:

फाइबर दो प्रकार के होते हैं:

Natural Fiber is fibre which is obtained by plants and animals, like cotton, wool, silk, etc.

Synthetic fiber is man- made fiber. It’s  a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer like rayon, nylon and polymer.

Polymers occur in nature also. Cotton, for example, is a polymer called cellulose. Cellulose is made up of a large number of glucose units.

Types of Synthetic Fibres:

    सिंथेटिक फाइबर के प्रकार:

Ryonrayon or artificial silk is man-made copy fibre of silk, it is made by chemical treatment of wood pulp. Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. 

It is cheaper than silk and can be woven like silk fibres. It can also be dyed in a wide variety of colours. Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.

Nylon: it is the first fiber which is 100% man-made without taking any component from animals and plants. It was invented in 1931 and made by mixing coal, water and air. 

Nylon fibre was strong, elastic and light. It was lustrous and easy to wash. So, it became very popular for making clothes. It is used to make -socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains,  parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.

Polyester and Acrylic:

पॉलिएस्टर और एक्रिलिक:

Polyester: Polyester is another synthetic fibre. Fabric made from this fibre does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material.Terylene is a popular polyester. It can be drawn into very fine fibres that can be woven like any other yarn.

PET (polyethylene terephthalate) is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.

Polyester (Poly+ester) is actually made up of the repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell. Fabrics are sold by names like polycot, polywool, terrycot, etc. As the name suggests, these are made by mixing two types of fibres. Polycot is a mixture of polyester and cotton. Polywool is a mixture of polyester and wool.

Acrylic: it is basically artificial woolen and warm like wool. Clothes made from acrylic are relatively cheap. They are available in a variety of colours. Synthetic fibres are more durable and affordable which makes them more popular than natural fibres. 

Characteristics of Synthetic Fibres

Some benefits of synthetic fibers are:

Dry up quickly


Less expensive

Readily available

Easy to maintain

If there are many benefits of synthetic fibers but there is one big disadvantage is melting on heating.  If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of the person wearing it. We should, therefore, not wear synthetic clothes while working in the kitchen or in a laboratory.



Plastic is also a polymer like the synthetic fibre. Plastic articles are available in all possible shapes and sizes as you can see. Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires. 

Polythene (Poly+ethene) is an example of a plastic. It is used for making commonly used polythene bags.

We have seen there is one plastic which can be bent and another which can’t be bent and gets broken. Lets understand these two types plastics:

Thermoplastics- it is a form of plastic with a very low melting point, this plastic gets deformed easily on heating and can be bent easily. Polythene and PVC are some of the examples of thermoplastics. These are used for manufacturing toys, combs and various types of containers.

Thermosetting plastics- these plastics, when moulded once, can not be softened by heating. It means its melting point is high. Two examples are bakelite and melamine. Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc. Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics.

Plastics as Materials of Choice

 Nowadays plastic is everywhere from kitchen to operation theater. This is because of their light weight, lower price, good strength and easy handling. Being lighter as compared to metals, plastics are used in cars, aircrafts and spacecrafts, too. List is never ending. 

Here we why plastic is extensively used:

  • Plastic is Non-reactive- plastic doesn't react and erodes in the open. Unlike metals, it reacts in the open like if iron is kept in the open it gets eroded.

  • Plastic is Light, Strong and Durable - Plastic is very light, strong, durable and can be moulded into different shapes and sizes, it is used for various purposes. Plastics are generally cheaper than metals. They are widely used in industry and for household articles.

  • Plastics are Poor Conductors - plastics are poor conductors of heat and electricity. That is why electrical wires have plastic covering, and handles of screwdrivers, handles of frying pans are also made of plastic.

  • Plastics find extensive use in the healthcare industry. Some examples of their use are the packaging of tablets, threads used for stitching wounds, syringes, doctors’ gloves and a number of medical instruments.

  • Special plastic cookware is used in microwave ovens for cooking food. In microwave ovens, the heat cooks the food but does not affect the plastic vessel. 

  • Teflon is a special plastic on which oil and water do not stick. It is used for non-stick coating on cookware.

  • Fire-proof plastics: Although synthetic fibre catches fire easily, it is interesting to know that the uniforms of firemen have a coating of melamine plastic to make them flame resistant. 


Plastics and the Environment 

A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable

A material which is not easily decomposed by natural processes is termed non-biodegradable.

Therefore, according to definition plastic is non-biodegradable and doesn't go with the environment. plastic takes several years to decompose, it is not environment friendly. It causes environmental pollution.

It also doesn't get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution.

How can we limit the use of plastic?

  • Avoid the use of plastics as much as possible. Make use of bags made of cotton or jute when you go shopping.

  • The biodegradable and nonbiodegradable wastes should be collected separately and disposed off separately.

  • It is better to recycle plastic waste. Most of the thermoplastics can be recycled.

  • Use the 5 R principle. Reduce, Reuse, Recycle, Recover and Refuse. Develop habits which are environment friendly. 

  •  Do not throw plastic bags in the water bodies or on the road. 

  • Try to minimise the use of plastic materials e.g., use a steel lunch box instead of a plastic one. 

हम प्लास्टिक के उपयोग को कैसे सीमित कर सकते हैं?

  • जितना हो सके प्लास्टिक के इस्तेमाल से बचें। खरीदारी के लिए जाते समय रुई या जूट के बैग का प्रयोग करें।

  • बायोडिग्रेडेबल और नॉनबायोडिग्रेडेबल कचरे को अलग-अलग एकत्र किया जाना चाहिए और अलग-अलग निपटाया जाना चाहिए।

  • प्लास्टिक कचरे को रिसाइकिल करना बेहतर है। अधिकांश थर्माप्लास्टिक को पुनर्नवीनीकरण किया जा सकता है।

  • 5 आर सिद्धांत का प्रयोग करें। कम करें, पुन: उपयोग करें, रीसायकल करें, पुनर्प्राप्त करें और मना करें। ऐसी आदतें विकसित करें जो पर्यावरण के अनुकूल हों।

  •  प्लास्टिक की थैलियों को जलाशयों में या सड़क पर न फेंके।

  • प्लास्टिक सामग्री के उपयोग को कम से कम करने का प्रयास करें, उदाहरण के लिए, प्लास्टिक के बजाय स्टील लंच बॉक्स का उपयोग करें।

Summary Ends.

सारांश समाप्त।


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