Biology Questions and Answers

Answer: D

Most bacteria reproduce by binary fission.

The chromosome is replicated, the two copies move apart, and the cell divides in two. It is asexual, so the daughters are genetically identical, and under good conditions a bacterium can divide every twenty minutes.

Answer: D

HIV kills the T-helper cells - the CD4 lymphocytes.

These cells coordinate the whole immune response, activating the killer cells and the antibody-producing B cells. As their number falls the defence collapses, and the patient succumbs to infections a healthy person would resist.

Answer: C

The flavour of apples is chiefly due to ethanal (acetaldehyde).

It is one of the volatile compounds released as the fruit ripens, along with esters such as ethyl butanoate. Formalin and benzaldehyde are quite different: benzaldehyde gives almonds their smell.

Answer: D

A mushroom is saprophytic.

It has no chlorophyll and cannot photosynthesise, so it secretes enzymes onto dead organic matter and absorbs the digested products. The mushroom itself is only the fruiting body; the feeding mycelium is spread through the substrate.

Answer: A

Hepatitis B has an incubation period of 30 to 180 days - commonly about 90.

The long and variable interval is why the source of infection is often impossible to trace. The virus is transmitted through blood, sexual contact and from mother to child, and is preventable by vaccine.

Answer: C

Cocoa and chocolate come from Theobroma cacao, a small tree reaching about 4 to 8 m.

Its pods grow directly from the trunk and main branches. The seeds are fermented, dried and roasted to make cocoa. It grows only within about 20 degrees of the equator.

Answer: A

The leaves are called the lungs of a plant.

They take in carbon dioxide and give out oxygen through the stomata, and the same pores admit the oxygen the plant needs for its own respiration. Their broad thin form gives the surface area the exchange requires.

Answer: C

A crop sown at the onset of the monsoon is a kharif crop.

Kharif crops are sown in June and July and harvested in September and October - rice, maize, jowar, bajra, cotton and jute. Rabi crops are sown in October and November and harvested in spring.

Answer: D

Morphine comes from the fruit coat of the opium poppy.

The unripe capsule is scored and the milky latex that oozes out is collected and dried to opium, of which morphine is the chief alkaloid. Codeine and thebaine come from the same latex.

Answer: A

The edible part of a pear is the fleshy thalamus.

Pear and apple are false fruits: the swollen receptacle, not the ovary, forms the flesh. The true fruit is the papery core in the middle enclosing the seeds.