Page 32 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

Stage 2: The eggs hatch and the larvae emerging from them are called silkworms.

These silkworms are voracious feeders and feed on mulberry leaves and quickly grow

in size.
Stage 3: The next stage in their life cycle is that of pupa. In this stage, the larvae 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, it secretes a fibre, called Fibroin, made
of a protein. This fibrehardens on exposure to air and becomes the silk fibre. Soon

the silkworm covers itselfcompletely by the silk fibre. This covering is known as a

cocoon.
Stage 4: After the complete

development, the cocoon splits open

and a beautifulsilkmoth comes out
of it. However, it is from this cocoon

that silk fibres are obtained, but the

developing silkworm is killed. Some

silkworms are allowed to live and
mature into silk moths so that they can

lay eggs to produce more silkworms.

2. Explain the steps that are involved in the processing of fibres into wool.
Ans. The following steps are involved in the processing of fibre into wool.

Step 1: Shearing– The process of removing and collecting the hair along with a thin
layer of skin is called shearing. It can be done manually

with a large razor or with a machine. It is done in
summer season so that hair of the sheep grow again

before the onset of winter. Shearing does not hurt the
sheep because the uppermost layer of the sheep’s

skin is dead. A sheep can produce 1 to 3 kg of wool.
Step 2: Scouring– The skin with hair is called ‘raw’ or

‘grease wool’ and is washed to remove dust particles
and dirt. This process is called scouring. The main

purpose of scouring is to remove the impurities from
the wool. Scouring is carried out with or without

chemicals, at room temperature or at appropriate
higher temperatures with the addition of suitable

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