Biology Questions and Answers

Answer: A

Genes are situated on chromosomes.

Each chromosome is a single long DNA molecule with its associated proteins, and a gene is a stretch of that DNA. Sutton and Boveri proposed the chromosome theory of inheritance in 1902, and Morgan proved it with Drosophila.

Answer: C

Goitre is caused by a lack of iodine.

Iodine is needed to make thyroxine; without it the thyroid enlarges as it tries to compensate, producing the swelling in the neck. In children the deficiency also stunts growth and mental development, which is why salt is iodised.

Answer: A

A colour-blind person has difficulty distinguishing green and red.

Red-green colour blindness comes from a defect in the cone pigments, and the genes lie on the X chromosome, so it is far commoner in men - about 8 per cent, against 0.5 per cent of women.

Answer: C

Man has three pairs of salivary glands: the parotid, submandibular and sublingual.

Together they secrete about 1 to 1.5 litres of saliva a day, containing the enzyme ptyalin, which begins the digestion of starch in the mouth.

Answer: A

Devouring particulate food is holozoic nutrition.

The food is ingested, digested inside the body, absorbed and the residue egested. It is how nearly all animals feed. Holophytic nutrition is photosynthesis, saprophytic is absorption from dead matter, and parasitic is taken from a living host.

Answer: A

Phycology is the study of algae, from the Greek phykos, seaweed.

Algae range from single-celled diatoms to giant kelps, are photosynthetic but lack true roots, stems and leaves, and produce a large share of the world's oxygen.

Answer: C

The mitochondrion is the powerhouse of the cell.

It carries out the Krebs cycle and the electron transport chain, producing most of the cell's ATP. Its inner membrane is deeply folded into cristae to give the enzymes room, and it has its own DNA and ribosomes.

Answer: B

Anti-snake venom is prepared at the Haffkine Institute in Mumbai.

Horses are injected with graded doses of venom and the antibodies harvested from their serum. The institute's polyvalent antivenom covers the four commonest Indian species - cobra, krait, Russell's viper and saw-scaled viper.

Answer: C

Cretinism is a disorder of the thyroid.

Deficiency of thyroxine from birth stunts both physical growth and mental development irreversibly. It is caused by iodine deficiency in the mother or by a failure of the child's own gland, and is now screened for in newborns.

Answer: C

AIDS is caused by a virus - HIV, first called HTLV-III.

It is a retrovirus: it carries RNA and copies it into DNA inside the host cell by reverse transcriptase. It infects and destroys the CD4 helper T cells, so the immune system gradually fails.