General Science Questions and Answers

Answer: B

Cotton fibre is obtained from the seed. Each fibre is a single elongated cell of the seed coat, growing to two or three centimetres as the seed matures.

The fibres are packed inside the boll, which is the fruit, but the fibre itself is a seed hair - which is why cotton is classed as a seed fibre alongside kapok.

Answer: C

Yeast is a rich source of the B group of vitamins - thiamine, riboflavin, niacin, folate and B₁₂ in fortified forms.

Brewer's yeast and yeast extract are used as supplements for this reason. Yeast contains no vitamin C, which comes from fresh fruit and vegetables.

Answer: D

Lignite is called brown coal. It is the lowest rank of true coal, containing about 60–70 per cent carbon and a great deal of moisture, and it is brown rather than black.

The rank rises through bituminous coal to anthracite, which is about 90 per cent carbon. Peat is the stage below lignite and is not yet coal.

Answer: C

The study of butterflies and moths is lepidopterology, from the Greek lepis (scale) and pteron (wing) - the order Lepidoptera is named for the scales that cover the wings.

Ichthyology is the study of fish, palynology of pollen and spores, and nephrology of the kidney.

Answer: C

Micro-organisms can be seen only with a microscope. The unaided eye resolves objects down to about 0.1 mm, and most bacteria are between 0.5 and 5 micrometres - a hundred times smaller.

A hand lens magnifies only about ten times, which is far short of what is needed.

Answer: B

The Western blot is the confirmatory test for HIV. It separates viral proteins by electrophoresis and detects antibodies to specific ones, so a positive result is highly specific.

The ELISA is the screening test: it is very sensitive and cheap, but gives false positives, so every reactive ELISA is confirmed by Western blot before a diagnosis is made.

Answer: B

Immunology is the study of the immune system - the body's defences against infection, and the disorders that arise when they fail or attack the body itself.

Microbiology studies the organisms that cause infection, pathology the changes disease produces in tissue, and haematology the blood.

Answer: C

The cactus is a xerophyte - a plant adapted to survive with very little water.

Its leaves are reduced to spines to cut transpiration, the stem is swollen to store water and coated with wax, and its roots spread wide and shallow to catch what rain does fall. Hydrophytes grow in water and mesophytes in ordinary moist soil.

Answer: C

The tobacco leaf contains nicotine, an alkaloid making up about 0.6 to 3 per cent of the dry weight.

The plant produces it in the roots and stores it in the leaves as a defence against insects; in humans it is the substance that makes smoking addictive.

Answer: A

Antonie van Leeuwenhoek first observed bacteria, in 1676, using single-lens microscopes he ground himself that magnified about 200 times.

He called them animalcules. Robert Hooke had earlier named the cell, and Pasteur and Koch established two centuries later that bacteria cause disease.