Solved examples for class 7 science : Chapter 3

    Fibre to Fabric

    I. Multiple Choice Questions (MCQs).
    Q.1. Wool and silk are derived from
    a) animals
    b) plants
    c) microbes
    d) artificial fibres
    Answer: a) animals

    Q.2. The thick coat of hairs that grow on the bodies of sheep and goat, are known as
    a) fur
    b) wool fibre
    c) fleece
    d) all of these
    Answer: (c) fleece

    Q.3. The finest quality wool is obtained from the fleece of
    a) Angora goat
    b) Merino sheep
    c) Angora rabbit
    d) Pashmina goat

    Answer: b) Merino sheep

    Q.4. Wool fibre is made up of
    a) cellulose
    b) proteins
    c) carbohydrates
    d) all of these
    Answer: b) proteins
    Q.5. Silk was discovered in
    a) China
    b) India
    c) Australia
    d) Sri Lanka
    Answer. a)
    II. Fill in the blanks by selecting appropriate words from the given list:
    List : Mulberry, Sheep, protein, South America, Tibet

    Q.1. Cashmere goat is found in the mountains of China and ______________.

    Q.2. Alpaca and Llama camels are found in ______________.

    Q.3. ______________ are mainly reared for wool.

    Q.4. Silk fibres are made of ______________.

    Q.5. ______________ silk is the main variety of silk produced in India.
    1- Tibet,
    2- South America
    3- Sheep,
    4- protein,
    5- Mulberry

    III. Match the items of Column A with those of Column B.

    Answer: 1- b,2-d, 3-e, 4-c 5-a

    IV. Write ‘T’ for the true and ‘F’ for the false statements.
    Q.1. Wool is a soft, light, durable, elastic and a wrinkle resistant fibre.
    Q.2. Sheep are selectively bred to produce only soft under hair.
    Q.3. The population of sheep is largest in India.
    Q.4. Silkworm rearing trays are large trays made of bamboo.
    Q.5. In sericulture industry, workers are generally affected by Sorter’s disease.
    Answer: 1-T, 2- T 3-F, 4- T 5-F
    V. Very Short Answer Questions.
    Q.1. What kind of nutrient is found in wool?
    Answer: Protein
    Q.2. Write the names of any three animals from which wool is obtained.
    Answer: Goat, yak and camel.
    Q.3. Write the names of member countries of International Wool Secretariat (IWS).
    Answer: Australia, New Zealand, South Asia and Uruguay.
    Q.4. What do you understand and by the term “burrs”?

    Answer: Burrs are the small fluffy fibres which are present in the fleece of sheep.

    Q.5. Define the process of cooking in sericulture.
    Answer: The process in which a large number of cocoons are boiled to kill the worms is called cooking.

    VI. Short Answer Questions.
    Q.1. Where is in India silk farming carried out?
    Answer: In India, silk farming is carried out in the states of Assam, Bihar, Madhya Pradesh, Odisha, Karnataka and Tamil Nadu.

    Q.2. Write the factors on which the quality of silk fibre depends.
    Answer: The quality of silk fibre depends on the rearing of the silkworm (i.e. quality of Leaves fed and incubation temperature) and the reeling process that is carried out.

    Q.3. Write the factors on which the quality of wool fibre depends.
    Answer: The quality of wool fibre depends on the breed of sheep, Length, thickness, shine, colour and strength of the fibre.
    Q.4. Give a brief on animals that yield wool and about the quality of wool obtained by them.
    Answer: The finest wool is obtained from the fleece of Merino sheep. In our country. Pashmina is one of the finest quality wools, obtained from a breed of sheep, found in Kashmir and surrounding Himalayan areas. It is a fine, Light, fluffy and warm wool which is made into Pashmina shawls. The fleece obtained from the Cashmere goat found in the mountains of China and Tibet, is extremely soft and very expensive. Mohair, the fleece of Angora goat, is white, smooth and Lustrous. Angora fibre, obtained from Angora rabbit has soft and fine hair.

    Q.5. Explain the process of rearing and breeding of sheep briefly.
    Answer: Sheep are reared in dry places with Low rainfall, where the temperature is moderate. Sheep are herbivores and graze mainly on grass and weeds. They are also fed on a mixture of pulses, jowar, corn, oil cakes and Leaves. In winter, they are kept indoors and given dry fodder and Leaves. They need freshwater and fresh air to survive. During the hot weather, fans are provided in barns to keep them comfortable. A selectively bred sheep produces a large quantity of good quality wool.

    VII. Long Answer Questions.
    Q.1. Discuss the processing of wool fibres into wool briefly in a stepwise manner. Answer: The following steps are carried out to process the hair or fleece obtained from the animals into wool:
    (a) Shearing: In this process, the thick growth of hair of the sheep, along with a Layer of skin is removed. It can be done in two ways:
    ▪ Manually with a large razor, clipper or a pair of scissors.
    ▪ With the help of a shearing machine when a large number of sheep have to be sheared.
    (b) Scouring: In this step, the sheared wool is washed with a detergent in large tanks, to remove dirt, grease and sweat. In Large factories, machines are used for scouring. The washed wool is treated with an acid and dried by Low heating.

    (c) Sorting: In this process, the cleaned wool is sorted according to its texture.

    (d) Separating burrs: Burrs are the small fluffy fibres which are present in the fleece of sheep. These can also be seen on some of the sweaters we wear. The burrs are separated and the process of scouring is repeated. The hairs are then twisted into fibres.
    (e) Dyeing: The fleece of sheep and goat is naturally black, brown or white in colour. It is dyed in different colours according to requirement.
    (f) Rolling: The fibres are straightened, combed and rolled into yarn.

    Q.2. Explain the life cycle of a silkmoth.
    Answer: Life Cycle of a Silk moth
    There are four stages in the life-cycle of a silk moth – egg, larva, pupa and adult.
    The female silk moth Lays eggs which hatch into black worm-like larvae. The larva of a silk moth is known as a caterpillar or a silkworm.

    (a) The Larva feeds on mulberry leaves continuously and grows in size. During this time, it sheds its skin four times. This process of shedding the skin to grow a new one is known as moulting.

    (b) At the end of this period, it climbs the branch of the tree and attaches itself to it by weaving a net. Then it starts spinning a cocoon. The salivary glands present in Larvae’s heads secrete a sticky fluid (protein) which is wound around their bodies in a long continuous thread. The protein solidifies when it comes in contact with air and forms silk fibre. The process takes 3-7 days to complete. The Larva continues to develop inside the cocoon. This stage is called the pupa stage.

    (c) When the worm matures into an adult moth, it secretes a fluid which dissolves the silk fibres of the cocoon so that it can emerge out of it and the cycle continues.

    Q.3. (a) Discuss the processing of silk fibres into fabrics briefly.
    (b) Describe the health hazards of workers in the wool and sericulture industry.
    Answer a) Processing of cocoons to obtain silk fibres: All the cocoons are collected at one place. The pile of cocoons is used for obtaining silk fibres. The pile of cocoons is placed in hot water. Hot water makes the silk fibres of cocoons to separate out. The long silk fibres are obtained by unwinding the threads from cocoons. The process of taking out silk fibres from the cocoons for use as silk is called reeling. Reeling is done in special machine which unwind the fibres of silk from cocoons.
    Converting silk fibres into silk cloth: Silk fibres obtained from cocoons are spun (twisted) to form silk threads called silk yarn. The silk yarn is then woven on looms into silk cloth by the weavers.
    b) In the wool industry, the workers engaged in sorting, get infected by the bacteria, anthrax. It causes a deadly disease of the blood known as Sorter’s disease.
    In the sericulture industry, the workers are generally affected by respiratory diseases such as asthma and bronchitis. Apart from this severe headache, bodyache, fever, neck pain, Low back pain, eye problems are few other health disorders are also observed. During the reeling process skin infections also occur due to constant dipping of the hands in boiling water or exposing them to steam. Noise produced from the spinning and winding machines causes hearing problems.



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