General Science Questions and Answers

Answer: D

In a laser all the atoms emit light of the same frequency, amplitude and phase.

This is what stimulated emission means: a passing photon triggers an excited atom to emit a photon identical to it in every respect. The result is a beam that is monochromatic, coherent and almost perfectly parallel.

Answer: C

Lime water is a solution of calcium hydroxide, Ca(OH)₂.

It is the standard test for carbon dioxide: the gas turns it milky by forming insoluble calcium carbonate, and further gas redissolves the precipitate as the soluble bicarbonate.

Answer: B

Cocci are the smallest bacteria in shape and size - spherical cells typically about 0.5 to 1 micrometre across.

Bacilli are rod-shaped, vibrios comma-shaped and spirilla spiral, and all three are longer than a coccus is wide.

Answer: C

The visible spectrum runs from about 3900 to 7600 angstrom - 390 to 760 nanometres.

Violet is at the short-wavelength end and red at the long. Below 390 nm is ultraviolet and above 760 nm infrared, neither of which the eye detects.

Answer: D

Bauxite is the chief ore of aluminium, a mixture of hydrated aluminium oxides.

The oxide is extracted from it by the Bayer process and then reduced to the metal by electrolysis in molten cryolite. Calamine is a zinc ore, calcite calcium carbonate, and galena lead sulphide.

Answer: B

Crabs have teeth in their stomach. The gastric mill is a set of chitinous plates in the foregut that grinds food after it is swallowed.

Crustaceans have no jaws capable of chewing, so the grinding is done internally, and the mill is worked by muscles attached to the stomach wall.

Answer: B

Common salt separates soap from the solution after saponification by decreasing the soap's solubility - a process called salting out.

The sodium ions from the salt raise the concentration of sodium in the water, and the soap, being a sodium salt, is forced out of solution and floats to the top as a curd.

Answer: B

Phagocytes engulf bacteria and other foreign particles, taking them into a vesicle and digesting them with enzymes - a process called phagocytosis.

Neutrophils and macrophages are the main types. Albumin, globulin and fibrinogen are plasma proteins, not cells.

Answer: C

Chlorophyll is carried in the quantosomes, the pigment-bearing units embedded in the thylakoid membranes of the chloroplast.

Each quantosome holds about 230 chlorophyll molecules and is regarded as the physical unit of photosynthesis. Mitochondria, centrosomes and lysosomes contain no chlorophyll.

Answer: C

The ozone layer blocks ultraviolet radiation.

It absorbs essentially all UV-C and about 90 per cent of UV-B, which would otherwise cause skin cancer and cataracts and damage crops and plankton. Infrared and radio waves pass through it freely.