General Science Mixed Quiz: Set 57

The correct answer is B, uracil. RNA carries adenine, guanine, cytosine and uracil, and the uracil occupies the place that thymine holds in DNA, pairing with adenine in the same way. Option A, thymine, is the reverse of the right answer: it is present in DNA and absent in RNA, and candidates in a hurry pick it because both words appear in the same sentence of the textbook. Option C, guanine, and option D, adenine, are purines and are present in both nucleic acids, so neither can be the answer. Two more points often asked with this one are that DNA has deoxyribose sugar where RNA has ribose, and that adenine pairs with thymine through two hydrogen bonds while guanine pairs with cytosine through three, which makes a region rich in guanine and cytosine harder to separate.

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 B, lactometer. A lactometer is a floating instrument that measures the relative density of milk. Pure milk has a density slightly greater than that of water, so adding water lowers the reading and the float sinks deeper, which is how dilution is detected. Option A, hydrometer, is the general instrument for the relative density of any liquid, and the lactometer is in fact a hydrometer graduated specially for milk; in a question that offers both, the specific instrument is the expected answer. Option C, calorimeter, is a vessel used to measure quantities of heat in experiments on specific heat capacity and latent heat. Option D, spherometer, measures the radius of curvature of a spherical surface such as a lens, using three fixed legs and a central screw. Note that a lactometer shows whether milk has been watered down, but it cannot by itself prove that milk is free of all adulterants.

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 B, 22. A human body cell has 46 chromosomes arranged in 23 pairs, of which 22 pairs are autosomes, the chromosomes that are alike in both sexes, and the remaining pair is of sex chromosomes, XX in a female and XY in a male. Option A, 21, is placed to catch the candidate who is thinking of chromosome 21 and Down syndrome. Option C, 23, is the total number of pairs including the sex pair, and it is also the number of chromosomes in a human gamete, which is haploid; it is the answer most often given by mistake. Option D, 46, is the total number of chromosomes and not a number of pairs. The habit worth building is to notice whether a question asks for chromosomes or for pairs, and whether it asks for autosomes or for all chromosomes.

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 B, fathometer. A fathometer, also called an echo sounder, sends a pulse of sound from the hull of a ship to the sea floor and times the returning echo; since the speed of sound in sea water is known, the time gives the depth. The name comes from the fathom, the old unit of six feet used for soundings. Option A, altimeter, measures height above sea level and is fitted in aircraft, where it works from the fall of atmospheric pressure with altitude. Option C, tachometer, measures the rate of rotation of a shaft in revolutions per minute and is fitted to engines and turbines. Option D, audiometer, measures the sharpness of a person's hearing across a range of frequencies. A related instrument worth remembering is the hydrophone, which detects sound under water, and sonar, which uses the same echo principle to locate submarines and shoals of fish.

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 C, chromosome 21. A person with Down syndrome carries three copies of chromosome 21 instead of two, a condition called trisomy 21, so the total chromosome number is 47 rather than 46. It arises when the pair fails to separate during gamete formation. Option A, an extra chromosome 13, and option B, an extra chromosome 18, are also trisomies, named after Patau and Edwards respectively, and are offered here because the pattern of the answer looks the same. Option D, an extra X chromosome, produces Klinefelter syndrome in a male, with 47 chromosomes written as XXY; the related condition in which a female has a single X and a total of 45 is Turner syndrome. Keep the chromosomal disorders in one list and the gene disorders such as haemophilia and sickle cell anaemia in another.

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 B, Alexander Fleming. In 1928 Fleming noticed that a mould of the genus Penicillium which had contaminated a culture plate in his London laboratory had killed the staphylococcus bacteria around it, and he named the active substance penicillin. Howard Florey and Ernst Chain later purified it and made mass production possible, and the three shared the Nobel Prize in Medicine. Option A, Louis Pasteur, established the germ theory of disease, developed pasteurisation and made vaccines for rabies and anthrax, but not penicillin. Option C, Robert Koch, identified the bacteria that cause tuberculosis, cholera and anthrax and framed the postulates that link a microbe to a disease. Option D, Edward Jenner, introduced vaccination in 1796 using cowpox material to protect against smallpox and is called the father of immunology. Papers often group these four names together, so fix one achievement firmly against each.

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 B, 1859. Darwin set out in that book the theory of evolution by natural selection, drawing on observations made during his voyage on HMS Beagle, among them the finches of the Galapagos islands whose beaks differ with their diet. Option A, 1831, is the year the Beagle sailed, and it is the near miss most often chosen. Option C, 1866, is the year Mendel published his paper on the pea, which belongs to the other half of this chapter and was not noticed until the start of the next century. Option D, 1900, is the year in which three botanists independently rediscovered Mendel's work, so it is a real date but not Darwin's. Note also that Alfred Russel Wallace arrived at natural selection independently, and that the two men's ideas were first presented together in 1858.

The correct answer is B, Class B. Fires are sorted into classes by what is burning, and a fire fed by flammable liquids such as petrol, diesel, kerosene, oil, paint or thinner is a class B fire. Such a fire is put out by smothering it with foam, carbon dioxide or dry chemical powder, which cuts off the oxygen. Water must never be thrown on burning oil, because the liquid floats on water and spreads the flames further. A is wrong because class D fires involve burning metals like magnesium, sodium and potassium, which need special dry powders. C is wrong because class C covers fires in live electrical equipment in common usage, and flammable gases under the Indian Standard. D is wrong because class A fires are the ordinary ones in solids like wood, paper and cloth, where water is the cheapest and best agent. Exam tip: A for solids, B for liquids, C for electrical or gas and D for metals.

The correct answer is A, Wilhelm Conrad Roentgen. In 1895, while working with a discharge tube, Roentgen found an unknown radiation that passed through cardboard and flesh but was stopped by bone and metal, and made a screen coated with a fluorescent salt glow. He called it the X-ray because its nature was unknown, and he received the first Nobel Prize in Physics in 1901. Option B, Henri Becquerel, discovered radioactivity the following year, in 1896, when uranium salts fogged a photographic plate kept in the dark, which is a different phenomenon from X-rays. Option C, Marie Curie, with Pierre Curie isolated polonium and radium and coined the word radioactivity, and she remains the only person to win Nobel Prizes in two different sciences. Option D, Thomas Edison, was an inventor of the electric lamp, the phonograph and the carbon microphone. Keep the years apart: X-rays in 1895 and radioactivity in 1896.

The correct answer is D, Ligament. A ligament is the connective tissue that joins one bone to another at a joint. It is very elastic and strong, and it holds the bones in place so that a joint can move without the bones slipping apart. Ligaments contain little matrix of their own and are stretched when a joint is twisted, which is what happens in a sprain. A is wrong because a tendon joins a muscle to a bone; tendons are fibrous and strong but have limited stretch, so the pull of a muscle is passed straight to the bone. B is wrong because cartilage is the smooth, flexible tissue that pads the ends of bones and shapes the nose and ear, cushioning the joint rather than tying the bones together. C is wrong because matrix is the material in which the cells of a connective tissue are embedded, not a structure by itself. Exam tip: ligament bone to bone, tendon muscle to bone.

The correct answer is B, Jean Baptiste Lamarck. He held that an organ used often becomes stronger and one left unused withers, and that characters so acquired in a lifetime are passed to the offspring, the giraffe's lengthening neck being his best known illustration. The theory is rejected because changes in body cells do not alter the DNA of the germ cells that form the next generation. Option A, Darwin, explained the same observations by natural selection acting on variation already present in a population. Option C, Hugo de Vries, proposed that evolution proceeds by sudden large mutations, working on the evening primrose. Option D, Wallace, arrived at natural selection independently of Darwin while working in the Malay archipelago. The pairing to fix is Lamarck with use and disuse, Darwin and Wallace with natural selection, and de Vries with mutation.

The correct answer is B, waves of an earthquake. A seismograph holds a heavy mass that tends to stay still while the ground and the frame of the instrument move during a tremor; the relative motion is magnified and traced as a seismogram, from which the arrival times of the primary, secondary and surface waves are read. Those arrival times at three or more stations give the location of the focus, and the amplitude gives the magnitude on the Richter scale, while intensity is described on the Mercalli scale. Option A, humidity, is measured by a hygrometer. Option C, intensity of light, is measured by a photometer or a lux meter. Option D is tested chemically and by instruments such as a turbidity meter, not by a seismograph. A connected fact asked often is that primary waves are longitudinal and travel through solids and liquids, while secondary waves are transverse and cannot pass through a liquid.

The correct answer is B, homologous organs. The same arrangement of bones, humerus, radius and ulna, carpals, metacarpals and phalanges, is used for walking in a man, for swimming in a whale, for flight in a bat and for running in a cheetah, which indicates descent from a common ancestor and is called divergent evolution. Option A, analogous organs, are the opposite case: the same function performed by structures of different origin, as in the wing of a bird and the wing of an insect, which shows convergent evolution. Option C, vestigial organs, are reduced remnants of organs that were functional in an ancestor, such as the vermiform appendix and the nictitating membrane of the human eye. Option D is not a standard category; atavism refers to the reappearance of an ancestral character in an individual, such as a human infant born with a short tail.

The correct answer is A, Jagadish Chandra Bose. Bose designed the crescograph to magnify the growth of a plant many thousand times and record it on a smoked glass plate, which allowed him to show that plants respond to light, heat, touch and other stimuli in ways that resemble responses in animals. He also did pioneering work on millimetre wave radio and founded the Bose Institute in Kolkata. Option B, Satyendra Nath Bose, is remembered in physics for Bose Einstein statistics and for the class of particles called bosons. Option C, Homi Jehangir Bhabha, founded the Tata Institute of Fundamental Research and the Indian atomic energy programme and is called the father of the Indian nuclear programme. Option D, Prafulla Chandra Ray, was a chemist who discovered mercurous nitrite and founded Bengal Chemicals, and he wrote a history of Hindu chemistry. Indian scientist questions appear in almost every general awareness paper, so keep one instrument or theory against each name.