Human Body & Health — PPSC previous year questions

Dialysis works by diffusion. Blood flows on one side of a semipermeable membrane and dialysing fluid on the other, and waste solutes such as urea and creatinine move down their concentration gradient into the fluid. Osmosis is the movement of water alone across the membrane, not the purifying step; electrophoresis is the movement of charged particles in an electric field; absorption plays no part.

Insulin, secreted by the beta cells of the islets of Langerhans in the pancreas, lowers blood glucose by promoting its uptake into cells and its storage as glycogen. Its deficiency or ineffectiveness causes diabetes mellitus. Iodine is regulated by the thyroid hormones, iron by the liver and gut, and urea is cleared by the kidneys.

The tetanus vaccine is a toxoid: it contains the inactivated toxin of the tetanus bacterium, not the whole germ. Rabies and hepatitis A vaccines use killed (inactivated) whole viruses, and the oral polio vaccine uses live weakened (attenuated) virus.

Active immunity forms when the body's own immune system makes antibodies and memory cells against an antigen. It can arise naturally, after recovery from an infection. It can also arise artificially, from vaccination with live or killed microbes, or toxoids. Toxoids are inactivated bacterial toxins, as in tetanus and diphtheria vaccines. All three routes make the body produce its own antibodies, so the answer is 'all of these'. Passive immunity is different: the transfer of ready-made antibodies, as in antiserum or mother's milk.

A body mass index of 40 or more is classed as morbid (class III) obesity. So statement (a) is correct. The National Ambulance Service under the National Health Mission is reached by dialling 108. The free maternal/child ambulance is 102. It is not 100, which is the police number. Light bends most in the medium of highest refractive index. Water (1.33) has the lowest of the four. Glycerine and mustard oil (about 1.47) are the highest.

Alveoli are the tiny air sacs inside the lungs where oxygen passes into the blood and carbon dioxide passes out. The kidney has nephrons and the small intestine has villi.

BCG stands for Bacillus Calmette–Guérin. It is a live attenuated vaccine derived from Mycobacterium bovis, the bovine tuberculosis bacterium. Albert Calmette and Camille Guérin weakened it by sub-culturing it about 230 times between 1908 and 1921. It protects mainly against severe childhood forms of TB, such as TB meningitis. India gives it at birth under the Universal Immunisation Programme. Mycobacterium tuberculosis is the human pathogen itself. Bordetella pertussis causes whooping cough. Saccharomyces cerevisiae is baker's yeast, used to produce the hepatitis B vaccine.

About 60% of an adult's body weight is water. For a 70 kg person that is 0.6 × 70 = 42 litres.

Herd (community) immunity is indirect protection. It arises when a large proportion of a population is immune. An infected person then rarely meets a susceptible one, so chains of transmission break. Active immunity is produced by one's own immune system after infection or vaccination. Passive immunity comes from ready-made antibodies, such as mother's milk or antisera. Specific immunity is the adaptive response against a particular antigen.

Digestion begins in the mouth, where salivary amylase (ptyalin) mixes with food and starts breaking starch into maltose. Trypsin is a pancreatic enzyme acting in the small intestine, erepsin is an intestinal peptidase, and gastric juice is a secretion (containing pepsin and HCl), not a single enzyme.