General Science Questions and Answers

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.

Answer: A

The prefix iso- indicates sameness, equality or constancy, from the Greek isos, equal.

Hence isotherm (equal temperature), isobar (equal pressure), isotope (same place in the periodic table) and isomer (same formula). Mega- means large, meta- beyond or changed, and quasi- resembling.

Answer: A

Silicon is the element used to convert solar energy to electricity. A photovoltaic cell is a silicon wafer doped to make a p-n junction; light striking it frees electrons that flow as current.

Silicon is used because its band gap of 1.1 eV suits the solar spectrum well and because it is abundant and easily purified.

Answer: D

Gallium (Ga) is the metal. It is a soft, silvery element of group 13 that melts at 29.8°C - low enough to liquefy in the hand.

Sulphur and iodine are non-metals; selenium is a non-metal usually classed with the metalloids.

Answer: B

Christiaan Barnard performed the world's first human heart transplant, at Groote Schuur Hospital in Cape Town on 3 December 1967.

The patient, Louis Washkansky, lived eighteen days before dying of pneumonia. William Harvey had described the circulation of the blood three centuries earlier.

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.

Answer: C

Round bacteria are cocci (singular coccus), from the Greek for berry.

They occur in pairs as diplococci, chains as streptococci and clusters as staphylococci. Rod-shaped bacteria are bacilli, comma-shaped are vibrios and spiral are spirilla.

Answer: D

Yttrium is not an isotope of hydrogen - it is a separate element, atomic number 39.

Hydrogen has three isotopes: protium, with one proton and no neutron; deuterium, with one neutron; and tritium, with two, which is radioactive.

Answer: A

Dmitri Ivanovsky discovered viruses in 1892, showing that the agent of tobacco mosaic disease passed through a filter fine enough to hold back all bacteria.

Beijerinck repeated the work in 1898 and named it a contagious living fluid; Stanley crystallised the virus in 1935.