General Science Mixed Quiz: Set 51

The correct answer is B, the pituitary, a pea-sized gland lodged in a bony socket at the base of the skull and attached to the hypothalamus. It is called the master gland because its secretions control other glands: thyroid stimulating hormone drives the thyroid, adrenocorticotropic hormone the adrenal cortex, and the gonadotropins the testes and ovaries, besides its own growth hormone. Option A is wrong because the thyroid is itself under the pituitary's command, and its claim to fame is being the largest endocrine gland. Option C is wrong because the pineal gland secretes melatonin and keeps the daily rhythm of sleep, a narrower task. Option D is wrong because the thymus secretes thymosin for the training of the immune cells and shrinks after puberty, so it neither controls other glands nor lasts a lifetime.

The correct answer is B, Galileo Galilei. Galileo was the first to argue that, with air resistance removed, every body falls with the same acceleration regardless of its mass. He reached this by rolling balls down inclined planes and timing them, and the idea is linked in popular accounts with his experiment from the Leaning Tower of Pisa. This overturned the older belief of Aristotle that heavier bodies fall faster. The acceleration he described is g, about 9.8 metres per second squared near the earth. A is wrong because Einstein built on this in the general theory of relativity through the equivalence principle, long afterwards. C is wrong because Edison was an inventor of the electric lamp and phonograph and did no work on falling bodies. D is wrong because Newton, born the year Galileo died, later explained why this happens through his law of gravitation. Exam tip: remember the order - Galileo found that all bodies fall alike, Newton explained the cause.

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 C, Cleaning. In electroplating the article to be coated is made the cathode, the plating metal serves as the anode, and both are dipped in an electrolyte containing a salt of that metal. When current flows, the metal ions travel to the cathode and settle on it. The coating can bond only if the surface is chemically clean, so grease, oil, rust and oxide are stripped off first by degreasing and by pickling in acid; any film left behind makes the plating peel, blister or come out patchy. Option A is wrong because buffing only brings up a shine on a surface that is already clean. Option B is wrong because soldering joins two metals with a filler alloy and has nothing to do with preparing a surface for plating. Option D is wrong because polishing smooths the surface mechanically but does not remove the oily and oxide films that spoil adhesion. Exam tip: the order is clean first, then plate, and the article is always the cathode.

The correct answer is D, 2.4. The velocity ratio of a pulley system is the distance moved by the effort divided by the distance moved by the load, so it is 12 divided by 3, that is 4. Efficiency is the mechanical advantage divided by the velocity ratio, so the mechanical advantage is 0.6 multiplied by 4, which gives 2.4. Remember that the velocity ratio depends only on how the machine is built, while the mechanical advantage also falls with friction and with the weight of the pulleys and rope; that is why no real machine reaches an efficiency of 100 per cent and the mechanical advantage is always smaller than the velocity ratio. A is wrong because 4.8 multiplies the velocity ratio by 1.2 instead of 0.6. B is wrong because 3.6 takes 60 per cent of 6, not of 4. C is wrong because 1.2 treats the velocity ratio as 2. Exam tip: efficiency equals mechanical advantage divided by velocity ratio.

The correct answer is C, Thallophyta. Litmus is a purple dye taken from lichens, and in the classification used in school science lichens are placed in Thallophyta, the group of simple plants whose body is an undifferentiated thallus with no true root, stem or leaf. Algae and fungi belong to the same group, and a lichen is in fact a partnership of an alga and a fungus living together. Litmus is a natural indicator: it stays purple in a neutral solution, turns red in acid and blue in base, and is used both as a solution and as litmus paper. Option A is wrong because gymnosperms are well developed plants with naked seeds, such as pine and cycas. Option B is wrong because pteridophytes, the ferns, are the first plants with vascular tissue. Option D is wrong because bryophytes such as moss and Marchantia are called the amphibians of the plant kingdom. Exam tip: litmus is red in acid, blue in base and purple when neutral.

The correct answer is D, Charles’s law. Charles’s law says that at constant pressure the volume of a fixed mass of gas is directly proportional to its absolute temperature, so V by T stays constant. Jacques Charles studied this in 1787, and Joseph Gay-Lussac published the quantitative form in 1802. Written as a ratio it gives V1 by T1 equals V2 by T2, with the temperature always taken in kelvin. Extending the volume-temperature graph backwards to zero volume gives absolute zero, minus 273.15 degrees Celsius, which is how the kelvin scale was fixed. A is wrong because Boyle’s law relates pressure and volume at constant temperature, with PV constant. B is wrong because Dalton’s law of partial pressures adds the pressures of the gases in a mixture. C is wrong because Avogadro’s law links equal volumes of gases to equal numbers of molecules. Exam tip: keep the three apart - Boyle for P and V, Charles for V and T, Gay-Lussac for P and T.

The correct answer is C. Ultraviolet light is a transverse wave, not a longitudinal one, so this statement is the wrong one. In an electromagnetic wave the electric and magnetic fields vibrate at right angles to each other and to the direction the wave travels, which is the definition of a transverse wave. Longitudinal waves need a material to squeeze and stretch, and sound is the standard example. Option A is correct because ultraviolet light sits in the electromagnetic spectrum between visible light and X-rays. Option B is correct because electromagnetic waves need no medium and cross empty space, which is how the Sun's ultraviolet rays reach the earth. Option D is correct because ultraviolet wavelengths run from about 400 nanometres down to 10 nanometres, shorter than violet light, and this higher energy is what burns skin and is absorbed by the ozone layer. Exam tip: all electromagnetic waves are transverse; only mechanical waves such as sound can be longitudinal.

The correct answer is D, 1 mole of Carbon will contain the same number of atoms as present in 1 mole of Helium. A mole is a count, not a weight: one mole of any element holds 6.022 into 10 to the power 23 atoms, the Avogadro number, whatever the element is. So one mole of carbon and one mole of helium each hold that many atoms. What differs is the mass, because the gram atomic mass is the mass of one mole: one mole of carbon weighs 12 grams while one mole of helium weighs 4 grams, so the carbon sample is three times heavier even though the atom count is equal. A and B are wrong because they turn the three-times ratio of masses into a ratio of atoms. C is wrong for the same reason, only in the reverse direction. Exam tip: a mole is always 6.022 into 10 to the power 23 particles; the atomic mass changes the weight, never the number.

The correct answer is C, Avogadro. The statement in the question is Avogadro's law, given by the Italian scientist Amedeo Avogadro in 1811. It says that equal volumes of all gases at the same temperature and pressure hold the same number of molecules, so the volume of a gas is directly proportional to the number of moles in it. This is why one mole of any gas occupies 22.4 litres at standard temperature and pressure, and why the number of particles in one mole, about 6.022 x 10 to the power 23, is named the Avogadro number after him. A is wrong because Charles law links the volume of a fixed mass of gas to its temperature at constant pressure. B is wrong because Boyle's law says that volume varies inversely with pressure at constant temperature. D is wrong because Gay-Lussac gave the law of combining volumes and the pressure-temperature law. Exam tip: Avogadro ties volume to the number of molecules, Boyle to pressure and Charles to temperature.

The correct answer is A, 1 and 4. Hooke's law holds only as far as the limit of proportionality, and that limit is either equal to or lower than the elastic limit, so statements 1 and 4 are the correct pair. Hooke's law says stress is proportional to strain, which is the straight part of the stress-strain graph; the point where the curve leaves the straight line is the limit of proportionality. A little beyond it the material still springs back to its original shape, and the last point at which it does so is the elastic limit. For most metals the two points lie very close together and for an ideal material they coincide. B is wrong because statement 2 extends the law past the straight part of the graph, where stress and strain are no longer proportional. C and D are wrong because statement 3 says always less, while the two limits may also be equal. Exam tip: order the four points as proportionality limit, elastic limit, yield point, ultimate stress.

The correct answer is A, Crown Gall. Crown gall is caused by the bacterium Agrobacterium tumefaciens, which enters through a wound near the base, or crown, of the stem and makes the plant grow rough tumour-like swellings there. The bacterium works by pushing a piece of its own Ti plasmid into the plant's cells and forcing them to divide, and that natural trick is why laboratories use it as a vector to carry new genes into plants. Grapevine, apple, rose, walnut and stone fruits suffer the most. Option B is wrong because mosaic diseases, such as tobacco mosaic, are caused by viruses that mottle the leaves in light and dark patches. Option C is wrong because smut of wheat, bajra and sugarcane is a fungal disease that fills the ear with black powdery spores. Option D is wrong because white blister, or white rust, of crucifers such as mustard is also fungal and raises white blisters on leaves and stems. Exam tip: bacterial — crown gall, citrus canker, bacterial blight of rice; viral — mosaic, leaf curl; fungal — smut, rust, blight.

The correct answer is C, fish farming. Pisciculture is the rearing of fish in ponds, tanks and other managed waters, the Latin word piscis meaning fish. It is a branch of aquaculture and India is one of the largest fish producers in the world; the Blue Revolution is the name given to the planned growth of fish output, and rohu, catla and mrigal are the common Indian carps raised in ponds. A is wrong because the rearing of honey bees is apiculture, which gives honey and beeswax. B is wrong because the rearing of silkworms is sericulture, in which the mulberry-fed Bombyx mori gives most of the world's silk. D is wrong because the rearing of birds is aviculture, and the keeping of fowl for eggs and meat is poultry farming. Exam tip: learn the culture words together - pisciculture fish, apiculture bees, sericulture silkworms, aviculture birds, horticulture fruits and vegetables, floriculture flowers.

The correct answer is C, Stomata. Stomata are the tiny pores on the surface of a leaf through which a plant takes in carbon dioxide and gives out oxygen and water vapour, so the exchange of gases takes place through them. Each stoma is bounded by two bean-shaped guard cells that swell to open the pore and shrink to close it, and this is how the plant controls its water loss. Most stomata lie on the lower surface of a leaf, so less water is lost to direct sunlight. Transpiration also happens largely through these pores. A is wrong because the cell membrane controls what enters and leaves a single cell, not the gas exchange of the whole plant. B is wrong because the nucleus carries the genetic material and directs the activities of the cell. D is wrong because guard cells only open and close the pore, while the exchange itself happens through the stomatal opening. Exam tip: stomata do the gas exchange and transpiration, guard cells only open and close them.

The correct answer is B, the beta cells of the islets of Langerhans in the pancreas. Insulin lowers the level of glucose in the blood by helping the cells take it in and by having the liver store it as glycogen, and a want of insulin or a failure of the body to respond to it causes diabetes mellitus. Option A is wrong because the alpha cells of the same islets make glucagon, which does the opposite and raises blood sugar; the two hormones together keep the level steady, and swapping them is the commonest error in this question. Option C is wrong because the adrenal medulla secretes adrenaline and noradrenaline; adrenaline also raises blood sugar, but it is not insulin. Option D is wrong because the thyroid follicles make thyroxine, which sets the rate of metabolism and contains iodine.

The correct answer is C, 1.6 sec. Time period is the time taken for one full oscillation, so it is the total time divided by the number of oscillations: 64 divided by 40 gives 1.6 seconds. Frequency is the reverse quantity, the number of oscillations in one second, which here is 40 divided by 64, or 0.625 hertz; period and frequency are always reciprocals of each other. For a simple pendulum the period depends only on the length of the thread and on the acceleration due to gravity, through T equal to 2 pi times the square root of L by g. It does not depend on the mass of the bob, nor, for small swings, on how wide the swing is. A pendulum about one metre long has a period of close to two seconds. A is wrong because 0.6 second would give more than 100 oscillations in 64 seconds. B and D are wrong because 6 and 16 seconds are far too long for 40 swings in just over a minute. Exam tip: time period equals total time divided by the number of oscillations.

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.

The correct answer is C, effort arm length is always less than load arm length. In a class 3 lever the effort is applied between the fulcrum and the load, so the effort always sits nearer the fulcrum and its arm is the shorter of the two. Because mechanical advantage is the effort arm divided by the load arm, a class 3 lever has a mechanical advantage below one: it needs more force than the load, but it gains speed and a longer sweep at the far end. Forceps, sugar tongs, a stapler, a fishing rod and the human forearm lifting a weight are the standard examples. A is wrong because that freedom belongs to a class 1 lever, where the fulcrum may sit anywhere between effort and load. B is wrong because the two arms are equal only in the special class 1 case of a balance. D is wrong because a longer effort arm is the mark of a class 2 lever, such as a nutcracker. Exam tip: class 1 fulcrum in the middle, class 2 load in the middle, class 3 effort in the middle.

The correct answer is B, 15 moles. The number of moles is the given mass divided by the molar mass, so 60 grams of helium divided by 4 grams per mole gives 15 moles. Helium has an atomic mass of 4, and because it is a noble gas its molecules are single atoms, so its molar mass is 4 grams and not 8. Each of those 15 moles holds 6.022 into 10 to the power 23 atoms, and at standard temperature and pressure the sample would fill about 336 litres, since one mole of any gas takes 22.4 litres. A is wrong because 12 moles uses 5 grams per mole and borrows the 12 of carbon. C is wrong because 10 moles would need a molar mass of 6, which helium does not have. D is wrong because 25 moles would need a molar mass of 2.4, the mass of no element. Exam tip: moles equal mass in grams divided by molar mass, so 4 grams of helium is exactly one mole.

The correct answer is A, goitre. Iodine is needed to make thyroxine, so when the diet is short of it the thyroid gland works harder and enlarges into a visible swelling of the neck called goitre; a severe shortage in a growing child causes cretinism and in an adult myxoedema, and iodised salt is the standard preventive. Option B is wrong because rickets, which softens and bends the bones of children, is caused by a deficiency of vitamin D and of calcium, not iodine. Option C is wrong because scurvy, with bleeding gums and slow healing, comes of a want of vitamin C, the sailor's disease cured by citrus fruit. Option D is wrong because beri-beri, with weakness of the nerves and muscles, follows a deficiency of vitamin B1 or thiamine, common where polished rice is the staple. Only goitre belongs to a mineral of the thyroid.