General Science Questions and Answers

Answer: A

The yeast used in bread-making, Saccharomyces cerevisiae, is a fungus - a single-celled one.

It ferments the sugars in the dough into carbon dioxide and alcohol; the gas raises the loaf and the alcohol evaporates during baking.

Answer: C

Amla, the Indian gooseberry, is among the richest natural sources of vitamin C - about 600 mg per 100 g, some twenty times that of an orange.

Its vitamin C is also unusually stable to heat and drying, because tannins in the fruit protect it from oxidation.

Answer: D

Sodium is stored under kerosene. It reacts violently with water and even with the moisture in air, so it must be kept away from both.

Kerosene works because it is a hydrocarbon that does not react with sodium and is dense enough to keep the metal covered. Sodium in air quickly forms an oxide crust and can catch fire.

Answer: B

The two strands of DNA are held together by hydrogen bonds between the paired bases - two between adenine and thymine, three between guanine and cytosine.

Each bond is weak, but there are millions along the molecule, so the double helix is stable while still coming apart strand by strand for replication.

Answer: D

Radiocarbon dating estimates the age of fossils and other once-living material - wood, bone, charcoal, cloth.

Carbon-14 has a half-life of 5,730 years, so the method works back to about 50,000 years. It cannot date rock or soil, which never contained living carbon.

Answer: C

Carbon monoxide is not a greenhouse gas. A greenhouse gas must absorb infrared radiation, which needs a molecule whose dipole moment changes as it vibrates.

Carbon monoxide absorbs very weakly and lasts only a few months in the atmosphere. Carbon dioxide, methane and water vapour are all effective greenhouse gases.

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: D

Ammonia is lighter than air. Its molar mass is 17 g/mol against the average 29 g/mol of air.

Oxygen (32), carbon dioxide (44) and chlorine (71) are all heavier, which is why carbon dioxide can be poured to smother a flame and chlorine settles in low ground.

Answer: B

The electron microscope revealed the internal structure of the cell. Using electrons instead of light, it resolves detail down to a fraction of a nanometre - a thousand times finer than a light microscope.

Mitochondria, the endoplasmic reticulum, ribosomes and the structure of membranes were all discovered with it.

Answer: A

The dark Fraunhofer lines in the solar spectrum are caused by the absorption of particular wavelengths by the sun's cooler outer layers.

The hot interior emits a continuous spectrum; atoms in the photosphere and chromosphere above absorb exactly the wavelengths they would themselves emit, leaving dark lines. Their positions identify the elements present - which is how helium was discovered.