What is the study of the production and propagation of sound waves called?

The correct answer is B, dyne-sec/cm². The poise is the CGS unit of dynamic or absolute viscosity, named after the French physician Jean Poiseuille, and one poise equals one dyne-second per square centimetre, which is the same as one gram per centimetre per second. Dynamic viscosity measures the internal friction of a fluid, the shearing stress needed for a unit rate of shear, so its unit is a stress multiplied by time. In SI the unit is the pascal-second, and one poise equals 0.1 pascal-second. Water at room temperature has a viscosity of about one centipoise, while honey is thousands of times thicker. A is wrong because dyne/cm² is a unit of stress or pressure, with no time in it. C is wrong because gram is a unit of mass, and g-sec/cm² does not reduce to the dimensions of viscosity. D is wrong because gm-cm/sec² is the dyne itself, a unit of force. Exam tip: 1 poise = 1 dyne-s/cm² = 0.1 Pa-s; water is about 1 centipoise.

The correct answer is B, Geitonogamy. Geitonogamy is pollination between two different flowers borne on the same plant. It is an odd halfway case: because the pollen has to travel from one flower to another it needs an agent such as an insect or the wind, so in working it looks like cross-pollination, yet the pollen comes from the same plant, so genetically it is self-pollination and brings no new variation. A is wrong because autogamy is pollination within the same flower, where pollen falls on the stigma of that very flower, as in pea and wheat. C is wrong because xenogamy is the transfer of pollen to the stigma of a flower on a different plant, and it is the only one of the three that brings genetically different pollen and so gives rise to variation. D is wrong because option B already names the process correctly. Exam tip: autogamy – same flower; geitonogamy – same plant, another flower; xenogamy – another plant.

The correct answer is C, Carbohydrates. The buccal cavity is the mouth, and the saliva poured into it begins the digestion of starch, a carbohydrate. Three pairs of salivary glands supply saliva, which carries the enzyme salivary amylase, also called ptyalin. It works best in a slightly alkaline medium and breaks the long starch chains into the sugar maltose, which is why a piece of bread kept in the mouth slowly tastes sweet. The teeth and tongue help by grinding the food and rolling it into a bolus. A is wrong because protein digestion begins in the stomach, where pepsin works in the acid of hydrochloric acid. B is wrong because the digestion of fat takes place chiefly in the small intestine, where bile from the liver breaks fat into small droplets and pancreatic lipase acts on them. D is wrong because starch digestion clearly does begin in the mouth. Exam tip: mouth – starch by amylase; stomach – protein by pepsin; small intestine – fat by bile and lipase.

The correct answer is C, Yeast, amoeba, bacteria. All three are unicellular, which means a single cell carries out every job of life. In a unicellular organism that one cell manages nutrition, respiration, movement and reproduction, while a multicellular body shares the work among tissues and organs. Yeast is a single-celled fungus used in baking and brewing, amoeba is a single-celled protozoan that moves and feeds with pseudopodia, and bacteria are single-celled organisms whose cells have no true nucleus. A is wrong because hydra, though a simple animal, is multicellular, with a body wall and tentacles made of many cells. B is wrong for the same reason, as sea anemone is a multicellular animal of the phylum Cnidaria, even though paramecium and bacteria are single-celled. D is wrong because only paramecium in that group is unicellular; hydra and sea anemone are both multicellular. Exam tip: unicellular – bacteria, amoeba, paramecium, yeast, chlamydomonas; multicellular – hydra, sea anemone, spirogyra.

The correct answer is C, To increase friction. The grooves cut into a sole grip the ground, so the foot does not slip while walking or running. Friction is the force that acts between two surfaces in contact and opposes motion between them. It becomes larger when the surfaces are rough, which is why the tread of a sole, the grooves of a tyre and the ridges of a bicycle handle are all made rough on purpose. A smooth sole on a wet floor has very little friction, and that is why people slip there. The same rubbing slowly wears the tread away, so an old shoe or tyre grips poorly and has to be replaced. A is wrong because a sole protects the foot by its thickness and material, not by its pattern. B is wrong because less friction would make walking unsafe; oil and ball bearings are used where friction has to be reduced. D is wrong because treading does not lengthen the life of a shoe. Exam tip: rough surface means more friction – treads, grooves and studs are all made to grip.