Biology Questions and Answers

Answer: C

Pepsin in the acid of the stomach breaks proteins into peptones.

The acid first denatures the protein and activates pepsinogen into pepsin; pepsin then cuts the long chains into shorter fragments called proteoses and peptones. They are broken down to amino acids later, in the small intestine.

Answer: C

Deep-sea organisms are mainly detritivores.

No light reaches them, so nothing photosynthesises there; they live on the rain of dead organic matter sinking from the lit waters above, called marine snow. The exception is the vent communities, which live on chemosynthetic bacteria.

Answer: B

Pellagra is the skin disease among these, caused by a deficiency of niacin (vitamin B₃).

It is remembered by the three Ds: dermatitis, diarrhoea and dementia. The skin becomes scaly and darkly pigmented where it is exposed to sunlight.

Answer: C

Vibrio comma - now called Vibrio cholerae - causes cholera.

The comma-shaped bacterium is spread by water contaminated with faeces, and its toxin makes the intestine pour out water and salts, causing the massive diarrhoea that can kill by dehydration in hours.

Answer: C

Clove is a dried flower bud, of Syzygium aromaticum, picked before it opens.

Its aroma comes from eugenol, used in dentistry as a local anaesthetic. Cinnamon is bark, cardamom a fruit and coriander a seed.

Answer: A

Plants of dry habitats are xerophytes.

Their adaptations reduce water loss and store what they get: thick cuticles, sunken stomata, reduced or spiny leaves, swollen stems and deep or widely spread roots. Cactus, Opuntia and Acacia are examples.

Answer: C

Diabetes mellitus is caused by a lack of insulin, or by the body's failure to respond to it.

Insulin is made by the beta cells of the islets of Langerhans in the pancreas and lets cells take up glucose from the blood. Without it blood sugar rises and glucose spills into the urine.

Answer: B

The dodo is the extinct bird in question.

The tambalacoque tree of Mauritius was said to need its seeds to pass through the dodo's gut before they would germinate, so no new trees grew after the bird was hunted out in the seventeenth century. The link is disputed, but the story is the standard illustration of coextinction.

Answer: A

The placenta is formed by the union of foetal and uterine tissue.

The foetal chorionic villi interlock with the maternal endometrium, so nutrients, oxygen and waste pass between the two circulations without the blood ever mixing. It also secretes hormones that maintain the pregnancy.

Answer: C

Bones do not secrete the hormones that regulate blood calcium.

Parathormone from the parathyroid raises blood calcium and calcitonin from the thyroid lowers it; bone is the store they act on, not the source. Bones do provide muscle attachment, protect organs and make blood cells in the marrow.