Science Answer the following question.

• Sericulture is the rearing of silkworms (moths) for production of silk.
• Bombyx mori is the most commonly used variety of silkworm for this purpose.
• The life cycle of silkworm consist of four stages namely egg, larva, pupa and adult.
• Thousands of eggs deposited by female moths are incubated artificially to shorten the incubation period.
• Larvae hatching out of eggs are released on mulberry plants.
• Larvae are nourished by feeding on mulberry leaves.
• After feeding for 3-4 days, larvae move to branches of mulberry plant.
• The silk thread is formed from the secretion of their salivary glands.
• Larvae spin this thread around themselves to form a cocoon. The cocoon may be spherical in nature.
• Ten days before the pupa turns into an adult, all the cocoons are transferred into boiling water.
• Due to the boiling water, the pupa dies in the cocoon and silk fibres become loose.
• These fibres are unwound, processed and reeled. Various kinds of fabric is woven from silk threads.

• Genetic engineering is the deliberate modification of the characteristics of an organism by manipulating its genetic material.
• An organism that is generated through genetic engineering is called a genetically modified organism (GMO).
• Genetic engineering is applied in many fields like research, agriculture, industrial biotechnology and medicine.
• In agriculture, genetic engineering is used in the production of cash crops, improvement in varieties of cash crops, increase in ability of plants to withstand environmental stresses.
• In medicine, genetic engineering is used for vaccine production, early diagnosis of congenital disease, organ transplant, cancer research, production of artificial skin, cartilage etc. in laboratories.

• Animal Husbandry: It is practiced for milk production and for using the cattle as help in farming operations, e.g. cows and buffaloes are raised for milk whereas bulls and male buffaloes for pulling heavy loads.
• Poultry farming: It is the rearing of egg and meat yielding chickens. Chickens raised for eggs are called layers while those raised for meat are called broilers.
• Sericulture: It is the rearing of silkworms (moths) for silk production. The silk fibres obtained are processed, reeled and then woven into fabric.

• The cells of striated muscles are long, cylindrical, multinucleate and have no branches.
• These are alternate dark and light bands on these muscles.
• As they are attached to bones, they are also called skeletal muscles.
• They move as per our will, hence they are called voluntary muscles.
• Striated muscles bring about movements of arms and legs, running, speaking etc.

• Xylem is a complex permanent tissue in plants.
• It consists of thick-walled dead cells.
• The type of cells in xylem are trachieds, vessels, xylem fibres (dead cells) and xylem parenchyma (living cells).
• Its structure is like interconnected tubes conduct water and minerals only in upward direction.

• Meristematic tissue is present in specific parts of a plant where growth takes place.
• Cells of meristematic tissue contain thick cytoplasm, a conspicuous nucleus and a thin cell wall and are compactly packed together.
• Vacuoles are usually absent in these cells and they are highly active.
• The main function of meristematic tissue is to bring about plant growth.
• According to the location, meristematic tissues are of three types: Apical meristem, intercalary meristem and lateral meristem.

• The branch of agriculture which deals with the feeding, shelter, health and breeding of domestic animals is called animal husbandry.
• It is a scientific and systematic management of livestock.
• Animal husbandry practices include:
  (a) Proper food and clean drinking water.
  (b) Proper shelter
  (c) Proper methods of breeding
  (d) Prevention and cure of disease.
• Animal husbandary practices serve as an alternative income for the farmers and help to satisfy the need of food for man.

(a) Which onion has longer roots? Why?
Answer:
The onion in jar Ahas longer roots as it continues to grow due to the presence of meristematic tissue at root tip which had dividing cells.

(b) Why did the roots of the onion in jar B stop growing?
Answer:
The roots of onion in jar B stopped growing as the meristematic tissue present in the root tips were cut off.