Science 3 Marks Question

1. Neha’s mother took a thread of natural silk fabric and another thread of artificial silk fabric and burn them separately. The thread which burns giving a smell of burning hair will be natural silk (or pure silk). The thread which burns giving a smell a burning paper will be an artificial silk.
2. Yes, pure silk saree is more costly than an artificial one.
3. Neha’s mother is intelligent and knowledgeable.

1. Rearing: Rearing means helping someone to grow up.
2. Shearing: It is the process of removal of fleece along with a thin layer of skin from the body of sheep.
3. Sericulture: Sericulture refers to the rearing of silkworms to obtain silk.

Wool industry is an important source of livelihood for many people in our country. The people who do the job of sorting (separating) the fleece of sheep into fibres of different qualities are called sorters. The sorter’s job is very risky because sometimes, they get infected by the bacteria called ‘anthrax’ which cause a deadly blood disease called sorter’s disease.

1. It is used to make clothes, scarves, sarees and dresses.
2. It is used to make parachutes and bullet proof vests.
3. It is used as non-absorbable suture in surgery.

1. The risks faced by people working in any industry due to the nature of their work are called occupational hazards.
2. The people who do the job of sorting, sometimes, get infected by the bacteria called anthrax which cause a deadly blood disease called sorter’s disease.
3. Ajay is very caring, intelligent and sensible boy.

Artificial (synthetic) silk called rayon is obtained from wood pulp and it is made of modified plant material cellulose. Synthetic silk can be prepared at a large scale in factories/ mills. So, it is cheap. For obtaining pure silk, we have to rear silk moth, their larvae to get pupa. To get silk thread, we have to dip cocoon in hot water to get silk thread which is wrapped over the cocoon. The pupa inside the cocoon dies. To obtain silk for commercial purposes, a large number of cocoons (containing living pupa) are killed. As a result, natural silk is costly.

Female silk moth lays hundreds of eggs at a time, these eggs are stored carefully on strips of cloth or paper and are sold to silkworm farmers. The eggs are kept in hygienic condition and under suitable temperature and humidity, then the eggs are warmed to suitable temperature and the larva is hatched from the eggs. This is done when mulberry trees bear a fresh crop of leaves. The larvae called caterpillar eat day and night and gets bigger and bigger in size, and are kept on clean bamboo trays along with freshly chopped mulberry leaves. After 25 to 30 days caterpillars stop eating and move to a tiny chamber of bamboo in the tray to spin cocoons. The caterpillar or silkworm spins the cocoon inside which silk moth is developed.

Fibres are classified into two types on the basis of their sources. Plant fibres and animal fibres and synthetic fibres.The fibres, which are obtained from plants and animals are called natural fibres e.g., jute and wool.
Animal fibres are obtained from animals, e.g., silk and wool. Those fibres which are made by the human beings are known as Man-made or Synthetic Fibres, e.g., Rayon.

1. It captures air between its layers.
2. Because of its crimp it is bulkier and acts as insulator.
3. It readily absorbs moisture.

In first saree, one thread which burnt with a smell of burning hair is from pure silk, silk and hair are protein fibres. So, on burning these threads, a smell of burning hair comes out. In second saree, second thread which burnt with the smell of burning paper is from a cotton saree.
Since, cotton and paper both are carbohydrates and on burning, they give similar smell.

1. Female.
2. Eggs.
3. Larvae.
4. Caterpillars.
5. Silkworm.
6. Pupa.
7. Cocoon.

Shearing is the process in which fleece of the sheep along with a thin layer of skin is removed from its body. Machines similar to those used by barbers are used to shave off hair. Generally, the hair is removed during the hot weather which enables the sheep to survive without their protective coat of hair. The hair provides woollen fibres. Woollen fibres are then processed to obtain woollen yarn. Shearing does not hurt the sheep as the uppermost layer of the skin is dead.

Rearing is raising livestock like goat, cows, sheep etc. for commercial purpose by taking them out in herds for grazing , feeding them on a mixture of pulses, corn, jowar, oil cakes (material left after taking out oil from seeds) and minerals for better growth and yield of produce like meat, milk, wool. Beside this in extreme climatic condition like winter these are also provided shelter and fed on leaves, grain and dry fodder.

Fibres and fabric play a large role in everyday applications. A fibre is a hair-like strand of material. They are the smallest visible unit of a fabric and denoted by being extremely long in relation to their width. Fibres can be spun into yarn and made into fabric. A single fibre is too weak to break but when some fibres together make a fabric, it is difficult to tear. Fabric needs more energy to tear apart as compared to a single fibre.