Biology Questions and Answers

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: B

A ringed tree dies because its roots are starved of energy.

Removing a ring of bark severs the phloem, which carries sugars down from the leaves. The roots, which cannot photosynthesise, exhaust their reserves and die, and the tree above dies with them. The xylem is untouched, so water still rises for a time.

Answer: B

The mismatched pair is Chlorella – pteridophyte. Chlorella is a single-celled green alga, not a pteridophyte.

The others are correct: Funaria is a moss and so a bryophyte, Spirogyra an alga, and Cycas a gymnosperm.

Answer: B

AIDS appears when HIV replicates rapidly in the helper T lymphocytes and destroys them.

The virus can lie latent for years while the CD4 count falls slowly. AIDS is diagnosed when the count drops below 200 per microlitre or an opportunistic infection appears - not on infection itself.

Answer: A

Cinnamon is the bark used as a condiment.

The inner bark of Cinnamomum verum is peeled, dried and curls into quills. Its flavour comes from cinnamaldehyde. Clove is a flower bud and neem is used medicinally rather than as a spice.

Answer: D

The apple has an edible fleshy thalamus.

Apple and pear are false fruits: the swollen receptacle forms the flesh and the true fruit is the papery core. In mango and tomato the flesh is the ovary wall, so those are true fruits.

Answer: C

The peanut ripens its fruit underground.

After fertilisation the stalk beneath the flower elongates and pushes the young pod into the soil, where it matures - which is why it is also called the groundnut. Potato and onion are underground stems and carrot a root, not fruits.

Answer: A

DDT reduced bird numbers because many of the eggs laid did not hatch.

DDT accumulates up the food chain, and in birds of prey it interferes with calcium deposition so the shells are too thin to bear the weight of the incubating parent. The effect nearly extinguished the peregrine and the bald eagle.

Answer: D

Common cold and AIDS are both viral.

Ringworm is fungal; typhoid, tuberculosis and bacillary dysentery are bacterial; amoebic dysentery is protozoan. Only the pairing of the common cold with AIDS gives two viral diseases.

Answer: B

The seed develops from the ovule.

After fertilisation the ovule's integuments harden into the seed coat and the zygote grows into the embryo. The ovary around it becomes the fruit.