General Science GK Questions with Answers – Page 65

Jute is a bast or stem fibre taken from the inner bark of plants of the genus Corchorus, extracted by soaking the cut stems in water, a process called retting, and India and Bangladesh are the main producers.

Clove is the unopened flower bud of Syzygium aromaticum, picked before it blooms and dried, and it is grown in India chiefly in Kerala, Tamil Nadu and the Andaman and Nicobar Islands.

Quinine is an alkaloid extracted from the bark of trees of the genus Cinchona, native to South America and grown in India in the Nilgiris and in Darjeeling, and it was the standard treatment for malaria before synthetic drugs appeared.

Saffron is made from the stigmas of the flower of Crocus sativus, and since each flower carries only three stigmas which must be picked by hand, the spice is the most expensive in the world; in India it is grown mainly in the Kashmir valley.

2,4-dichlorophenoxyacetic acid is a synthetic auxin, and when it is sprayed in a heavy dose it throws broad-leaved dicot weeds into uncontrolled growth that kills them, while narrow-leaved cereals such as wheat and rice are far less affected, so it clears weeds from a standing crop.

Auxin made at the shoot tip moves downwards and keeps the lateral buds below it inactive, which is why a gardener who nips off the tip of a hedge plant gets a bushy growth of side branches.

Japanese rice plants attacked by this fungus grew abnormally tall and spindly, a condition called the foolish seedling or bakanae disease, and the substance responsible was isolated from the fungus and named gibberellin; gibberellic acid is the best known member of the group.

It is produced when a plant faces drought, salinity or extreme temperature; it closes the stomata so that water is not lost, for which reason it is called an antitranspirant, and it induces dormancy in seeds and buds so that growth waits for better conditions.

Ethylene is the only gaseous plant hormone, and it raises the rate of respiration in climacteric fruits such as banana, mango and tomato, so a single ripe fruit speeds up the ripening of those around it; the compound ethephon releases ethylene and is used in orchards for uniform ripening.

Pollen first reaches the stigma, then the gametes fuse, the zygote divides to form an embryo, and the embryo inside the seed grows into a seedling.

Light travels at different speeds in different media, and this change in speed at the boundary makes it bend. Light is fastest in vacuum, about 3 × 10⁸ m/s, and slower in water and glass.

Green plants use sunlight, carbon dioxide and water to make glucose, giving out oxygen as a by-product. Photosynthesis takes place mainly in the chloroplasts of leaf cells, where chlorophyll traps light energy.

Both work in neutral to alkaline conditions, in the mouth and the small intestine, and stop working in the acid of the stomach.

Filament bulbs are commonly filled with argon, often mixed with nitrogen, not helium. An inert gas in a filament bulb slows the evaporation of the hot tungsten filament.

Graphene is not a wide band-gap semiconductor; it has practically zero band gap and behaves like a semimetal.

The emf of a battery equals the power it supplies divided by the current it drives, because power P = EI.

Coal is an impure fossil fuel containing hydrogen, oxygen, nitrogen and sulphur besides carbon, so it is not a pure form of the element.

These are the signs of scurvy, the disease caused by a lack of vitamin C (ascorbic acid). Vitamin C is needed to make collagen, the protein that holds together gums, skin, blood vessels and bone.

A pearl is built up from layers of nacre, which is mostly calcium carbonate held together by a protein called conchiolin.

A body in equilibrium has no net force and no net moment on it, while neither momentum nor kinetic energy is conserved in every situation.