Short AnswerType Questions
1.What is meant by selective breeding what is its purpose
2. What is silk How do we get silk from cocoon?
3. (a) What are raw silk and spun silk
(b) On burning silk, it gives out the smell of burning hair. Give reason.
4 With the help of a flow chart only , describe the life cycle of a silkworm.
5. a) What is sorter's disease
(b) Why is this disease called occupational disease?
6. (a) Why do wool-yielding animals have a thick coat of hair on their bodies?
(b) why is shearing done in summer
Answers
Answer:
1.Selective breeding involves choosing parents with particular characteristics to breed together and produce offspring with more desirable characteristics. Humans have selectively bred plants and animals for thousands of years including: crop plants with better yields.
2.Extracting raw silk starts by cultivating the silkworms on mulberry leaves. Once the worms start pupating in their cocoons, these are dissolved in boiling water in order for individual long fibres to be extracted and fed into the spinning reel.
3a)Silk containing sericin is called raw silk. The gummy substance, affording protection during processing, is usually retained until the yarn or fabric stage and is removed by boiling the silk in soap and water, leaving it soft and lustrous, with weight reduced by as much as 30 percent.Spun silk is made from short lengths obtained from damaged cocoons or broken off during processing, twisted together to make yarn
b)The protein Fibroin present in silk and the protein keratin present in the case of hair. ... This smell helps to find out the real silk. Silk does not have as strong an odor as the other animal fibres.
4The life cycle of silk moth starts when a female silk moth lays eggs. The caterpillar or larvae are hatched from the eggs of the silk moth. The silkworms feed on mulberry leaves and give rise to pupa. In the pupa stage, a weave is netted around by the silkworm to hold itself. After that it swings its head, spinning a fibre made of a protein and becomes a silk fibre. Several caterpillars form a protective layer around pupa and this covering is known as the cocoon. The silk thread (yarn) is obtained from the silk moth’s cocoon.
5a)Sorter's Disease is another name for Anthrax. It is caused by the bacteria Bacillus anthracis. Historically, anthrax was called wool sorter's disease because individuals who sorted wool of infected animals contracted the disease.
b)Workers involved in wool industry during sorting of wool sometimes get infected by a bacterium called. ... This causes a fatal blood disease called sorter? s disease. Such risks faced by workers in any occupation are known as occupational hazards.
6a)Wool yielding animals are found in the colder regions . They have thick fur coat on their body to keep them warm in cold climatic conditions. They do so by trapping the heat in their coat which helps in keeping them warm.
b)Shearing is done in summers i.e. during hot weather because sheep can survive without their protective coat of hair. Sheep are usually found in hilly and cold region. Shearing is done in summers i.e. during hot weather because sheep can survive without their protective coat of hair.