Night blindness results from the deficiency of

The correct answer is C, because the enzyme in saliva that acts on starch is salivary amylase, also called ptyalin, and not a lipase. Amylase breaks starch into the sugar maltose; a lipase works on fat, and saliva carries no significant lipase, so the statement pairs the right action with the wrong enzyme. Option A is a correct statement, since partly digested food leaves the stomach as chyme and enters the small intestine through the pyloric opening. Option B is correct too, because the digestion of all three major nutrients is completed in the small intestine with bile from the liver and the trypsin, amylase and lipase of pancreatic juice, and absorption follows through the villi. Option D is correct, as the oesophagus carries swallowed food from the pharynx to the stomach by peristalsis.

The correct answer is C, vitamin C. Vitamin C, chemically ascorbic acid, is needed to make collagen, the protein that holds tissues together; without it the gums swell and bleed, wounds refuse to heal and the joints ache, and the disease is called scurvy. Amla, guava, citrus fruit and tomato are rich sources, and the vitamin is destroyed by heat. Option A is wrong because a shortage of vitamin A gives night blindness and xerophthalmia, disorders of the eye. Option B is wrong because a shortage of vitamin B12 gives pernicious anaemia, a disorder of the blood. Option D is wrong because a shortage of vitamin K delays the clotting of blood, since prothrombin cannot be made in the liver without it. Scurvy was the classic disease of long sea voyages before fresh fruit was carried.

The correct answer is A, thiamine. Thiamine is vitamin B1, and its shortage causes beriberi, in which the nerves and the heart are affected, giving weakness, loss of sensation in the legs and in the wet form swelling and heart failure; the disease was common where polished rice was the staple, since polishing removes the thiamine-rich outer layer. Option B is wrong because a shortage of riboflavin, vitamin B2, gives cracks at the corners of the mouth and inflammation of the tongue. Option C is wrong because a shortage of niacin, vitamin B3, gives pellagra. Option D is wrong because ascorbic acid is vitamin C, whose deficiency gives scurvy, a disease of the gums and connective tissue. Whole grain, pulses, nuts and yeast are the usual dietary sources of thiamine.

The correct answer is D, vitamin K. Vitamin K, chemically phylloquinone, is needed by the liver to make prothrombin and other clotting factors, so a shortage of it makes bleeding last longer and can cause haemorrhage in a newborn; green leafy vegetables supply it and the bacteria of the large intestine make part of our requirement. Option A is wrong because vitamin A is concerned with vision and with the health of skin and mucous membrane. Option B is wrong because vitamin C builds collagen, and although bleeding gums occur in scurvy that is a weakness of blood vessels, not a failure of clotting. Option C is wrong because vitamin E is an antioxidant that protects cell membranes and red blood cells. Newborn babies are often given a dose of vitamin K because their gut bacteria are not yet established.

The correct answer is B, vitamin B3. Vitamin B3 is niacin, also called nicotinic acid, and its shortage gives pellagra, remembered by the three Ds of dermatitis, diarrhoea and dementia, with death as a fourth if it is untreated; the disease appeared where maize was the staple, because the niacin in maize is bound and poorly absorbed. Option A is wrong because a shortage of vitamin B1, thiamine, gives beriberi. Option C is wrong because a shortage of vitamin B6, pyridoxine, gives anaemia and in severe cases convulsions. Option D is wrong because a shortage of vitamin B9, folic acid, gives megaloblastic anaemia and, in pregnancy, defects of the neural tube in the child. Niacin can also be made in the body from the amino acid tryptophan, so a diet rich in milk protects against pellagra even when niacin itself is scarce.