Biology Questions and Answers

Answer: C

The earthworm has no eyes.

Living underground it has no use for them. It detects light through photoreceptor cells scattered in the skin, densest at the front end, which is enough to make it retreat from the surface into its burrow.

Answer: B

Dicotyledonous weeds are killed by 2,4-dichlorophenoxyacetic acid, or 2,4-D.

It is a synthetic auxin that throws the plant's growth into disorder. It is selective because monocots - the cereals - metabolise it quickly, so a cereal field can be sprayed to kill the broadleaved weeds in it.

Answer: B

Plants have cellulose; animals do not.

It is the polymer of glucose that makes up the plant cell wall and gives it rigidity. Animal cells have no wall at all. Starch, protein and fat occur in both kingdoms.

Answer: A

Pollination by wind is anemophily, from the Greek anemos, wind.

Wind-pollinated flowers are small, dull and scentless, with exposed anthers, feathery stigmas and enormous quantities of light dry pollen. Grasses, cereals and most trees of the temperate forest are anemophilous.

Answer: B

Surplus red cells are stored mainly in the spleen.

It holds a reserve that contraction of its smooth muscle can release into the circulation during haemorrhage or strenuous exercise. The spleen also filters out worn-out red cells, which is why it is called the graveyard of erythrocytes.

Answer: A

Henna colours skin and hair by reacting with protein and amino acids.

Its dye, lawsone, binds to the keratin of skin and hair, which is why the colour is fast on those tissues but washes off anything else. The reaction is with the amino groups of the protein.

Answer: A

Bronchitis is a disease of the respiratory tract - inflammation of the bronchi, the airways leading to the lungs.

The lining swells and produces excess mucus, causing the persistent cough. Acute bronchitis usually follows a viral infection; the chronic form is caused chiefly by smoking.

Answer: A

Plants growing in saline water are halophytes, from the Greek halos, salt.

Mangroves are the familiar example. They exclude salt at the root, excrete it through leaf glands, or shed it in old leaves, and many have stilt roots and breathing roots for the waterlogged mud.

Answer: C

The embryo is found in the seed.

It is the young plant formed after fertilisation, consisting of the radicle, plumule and one or two cotyledons, packed with the stored food it will use until it can photosynthesise.

Answer: C

Cancer cells are damaged by radiation because they are undergoing rapid division.

DNA is most vulnerable while it is being replicated and the chromosomes separated, so dividing cells are far more radiosensitive than resting ones. It is also why radiotherapy affects hair follicles, bone marrow and gut lining - the body's other fast-dividing tissues.