General Science Mixed Quiz: Set 33

The correct answer is D, Solids. Sound is a mechanical wave: it travels only when the particles of a medium push against their neighbours, so the closer and more tightly bound those particles are, the faster the disturbance is passed on. Particles in a solid are packed most closely and held by the strongest intermolecular forces, so sound moves through a solid quickest. Typical speeds at ordinary temperature are about 346 metres per second in air, roughly 1500 metres per second in water and about 5000 metres per second in steel, which is why a rail track carries the sound of an approaching train long before the air does. Option A is wrong because gas particles lie far apart, giving the slowest speed of the three. Option B is wrong because a vacuum has no particles at all, so sound cannot travel through it. Option C is wrong because a liquid carries sound faster than a gas but slower than a solid. Exam tip: the order is solids faster than liquids faster than gases, and sound needs a medium while light does not.

The correct answer is A, Capra aegagrus hircus. The domestic goat is treated as a subspecies of the wild goat, so its name carries three parts — the genus Capra, the species aegagrus and the subspecies hircus. It is often shortened to Capra hircus. Carl Linnaeus gave science this binomial system, in which the genus name begins with a capital letter, the species name does not, and the whole name is printed in italics or underlined when handwritten. Goats were among the first animals humans tamed, in western Asia roughly ten thousand years ago, and India keeps one of the largest goat populations in the world. Option B is wrong because Bos indicus is the humped Indian cattle, the zebu. Option C is wrong because Sus scrofa is the wild boar, the ancestor of the domestic pig. Option D is wrong because Ovis aries is the domestic sheep, the animal most often confused with the goat in such questions. Exam tip: goat Capra hircus, sheep Ovis aries, cattle Bos indicus, buffalo Bubalus bubalis.

The correct answer is B, in the downward direction. The force on a current-carrying conductor placed in a magnetic field is found with Fleming's left-hand rule. Stretch the thumb, the forefinger and the middle finger of the left hand at right angles to one another: the forefinger points along the magnetic field, which is north here, the middle finger along the current, which runs from east to west here, and the thumb then gives the direction of the force, which comes out vertically downward. The size of this force is F = BIL sin of the angle between the current and the field, and it is greatest when the two are at right angles, as they are here. This force is the principle behind the electric motor. Option A is wrong because a sideways force would need the field and the current to lie in a vertical plane. Option C is wrong because reversing either the current or the field would be needed to push the conductor upward. Option D is wrong for the same reason as option A. Exam tip: Fleming's left hand is for the motor and gives force, while Fleming's right hand is for the generator and gives induced current.

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 B, silver. Silver is an element, a pure metal with its own place in the periodic table, so it cannot be an alloy; an alloy is a homogeneous mixture of two or more metals, or of a metal with a non-metal such as carbon. Option A, solder, is an alloy of lead and tin, valued for its low melting point when joining electrical wires. Option C, bronze, is an alloy of copper and tin, the metal that gave its name to an age of human history. Option D, brass, is an alloy of copper and zinc, used for utensils, fittings and musical instruments. The trap here is German silver, which contains copper, zinc and nickel and no silver at all, so it is an alloy despite its name, while silver itself is not.

The correct answer is B, Cones. Cones are the photoreceptor cells of the retina that respond to colour in bright light. The human retina carries two kinds of photoreceptors. Cones number about six to seven million, sit densely near the centre of the retina and come in three types, sensitive to red, green and blue light; the brain mixes their signals into every shade we see. They work only when the light is good, which is why colours fade at dusk. Option A is wrong because rods are far more numerous but work in dim light and give only shades of grey, not colour. Option C is wrong because the blind spot is the point where the optic nerve leaves the eyeball and carries no photoreceptors at all. Option D is wrong because the fovea is a small pit in the retina, a place rather than a cell type, although it is packed with cones. Exam tip: rods for night and grey, cones for colour and daylight; colour blindness is a defect of the cones.

The correct answer is D, five. Hexane, C6H14, can be drawn as a straight chain of six carbons, as two chains of five carbons with a methyl branch in different positions, and as two chains of four carbons carrying branches, which gives five different structures with the same molecular formula. Option A is wrong because three is the number of isomers of pentane, C5H12, and candidates who remember the smaller member often answer with it. Option B is wrong because six is not the count for any of the first few alkanes; the next member, heptane, has nine isomers. Option C is wrong because four corresponds to no alkane in this part of the series either. The sequence worth memorising is simple: butane two, pentane three, hexane five, heptane nine.

The correct answer is C, a mechanism to reduce CO2 emission. A nuclear reactor splits heavy atoms; it burns no fuel, so it releases no carbon dioxide and needs no equipment to cut such emissions. The heat of fission is produced in the reactor core, carried away by a coolant, passed to water in a heat exchanger or steam generator, and the steam then turns a turbine coupled to a generator. Control rods of cadmium or boron absorb spare neutrons and a moderator such as heavy water slows them down so that fission continues steadily. Option A is wrong as a choice because the turbine is the part that actually converts steam energy into electricity. Option B is wrong because the heat exchanger carries heat from the radioactive coolant loop to the clean water loop. Option D is wrong because the reaction chamber, the core holding the fuel rods, is where fission happens. Exam tip: a nuclear plant emits no carbon dioxide; its waste problem is spent radioactive fuel instead.

The correct answer is B, Collenchyma. Plant tissues are first divided into meristematic tissue, whose cells keep dividing, and permanent tissue, whose cells have stopped dividing and have taken a fixed shape and job. Permanent tissue is then split into simple permanent tissue, made of only one kind of cell, and complex permanent tissue, made of more than one kind. The three simple permanent tissues are parenchyma, collenchyma and sclerenchyma. Collenchyma has cells thickened at the corners with cellulose and pectin, and it gives flexibility to young stems and leaf stalks so that they bend without breaking. Option A is wrong because apical meristem sits at the tips of roots and shoots and is meristematic, not permanent. Option C is wrong because cambium is a lateral meristem responsible for growth in girth. Option D is wrong because xylem is a complex permanent tissue built of tracheids, vessels, xylem fibres and xylem parenchyma. Exam tip: the simple permanent tissues are parenchyma, collenchyma and sclerenchyma, while xylem and phloem are complex permanent tissues.

The correct answer is D, Black. In the colour code used for fire extinguishers, a black band or label marks a carbon dioxide extinguisher. The body of the cylinder is signal red and a coloured patch near the label tells you the filling at a glance, so the right cylinder can be picked in a hurry. A carbon dioxide extinguisher works by smothering: the gas is heavier than air, so it pushes oxygen away from the fuel, and it also chills the surface as it expands out of the horn. Because it does not conduct electricity and leaves no residue, it is the choice for live electrical equipment, switchboards, laboratories and computer rooms. Option A is wrong because a red band marks a plain water extinguisher, used on wood and paper fires. Option B is wrong because blue marks dry powder, the all-purpose filling for liquid and gas fires. Option C is wrong because cream, not white, is the colour for a foam extinguisher. Exam tip: red — water, cream — foam, blue — dry powder, black — carbon dioxide, yellow — wet chemical.

The correct answer is A, To protect the lining of the stomach. The gastric glands in the stomach wall release three things: hydrochloric acid, the enzyme pepsin and mucus. The acid makes the contents strongly acidic so that pepsin can act, and the mucus coats the inner wall as a thick slippery layer so that this acid and the enzyme do not digest the stomach's own tissue. When the mucus layer breaks down the acid attacks the wall and an ulcer forms; the bacterium Helicobacter pylori is a common cause. B is wrong because fat is digested by lipase, helped by bile from the liver, mainly in the small intestine. C is wrong because germs in food are killed by the hydrochloric acid and not by mucus. D is wrong because protein is broken down by pepsin in the stomach and by trypsin further along. Exam tip: gastric juice — HCl for acid, pepsin for protein, mucus for protection of the lining.

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, Drosera. Drosera, known as the sundew, is an insect-eating plant whose leaves are covered with stalked glands tipped with a shining drop of sticky fluid. An insect that lands on it is held fast, the tentacles curl over the catch, and enzymes digest the soft parts so that the plant can absorb nitrogen. Carnivorous plants grow in marshy or sandy soils that are poor in nitrogen, and they still make their own food by photosynthesis; the insect only makes up for the missing mineral. The pitcher plant Nepenthes, the bladderwort Utricularia and the Venus flytrap trap their prey in the same way but with different leaf traps. A is wrong because Clarkia is an ordinary garden flower of the evening primrose family. C is wrong because Alyssum is a small ornamental plant of the mustard family. D is wrong because hollyhock is a tall garden plant of the mallow family. Exam tip: insect-eating plants – Drosera (sundew), Nepenthes (pitcher plant), Utricularia, Venus flytrap; they need nitrogen, not food.

The correct answer is C, Thymine. In DNA, adenine always pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three. This is called complementary base pairing, and it is why one strand of DNA can be used to copy the other. The double-helix model was proposed by James Watson and Francis Crick in 1953, using X-ray images made by Rosalind Franklin. Adenine and guanine are purines with two rings, while thymine and cytosine are pyrimidines with one ring, so each pair has the same width and the helix stays even. In RNA, thymine is replaced by uracil. Option A is wrong because guanine is a purine like adenine and pairs with cytosine. Option B is wrong because cytosine pairs with guanine through three hydrogen bonds. Option D is wrong because histone is a protein around which DNA is wound in chromosomes; it is not a base at all. Exam tip: A pairs with T by two bonds, G with C by three; RNA has U in place of T.

The correct answer is A, By microphone. A microphone is a transducer: sound waves strike a thin diaphragm, the diaphragm vibrates, and that mechanical vibration is turned into a varying electric signal. In a moving-coil microphone the diaphragm carries a small coil that moves in the field of a permanent magnet, so the changing magnetic flux induces a current by electromagnetic induction; a condenser microphone instead works by changing the capacitance between two plates. Either way the output is an electrical signal that can be amplified, recorded or transmitted. Option B is wrong because a loudspeaker does the opposite, converting an electrical signal back into sound. Option C is wrong because a sonometer is a wire-and-box apparatus used to study the frequency and the laws of vibrating strings; it converts nothing. Option D is wrong because an earphone, like a loudspeaker, turns electrical energy into sound energy. Exam tip: microphone converts sound to electrical energy, while loudspeaker and earphone convert electrical energy to sound.

The correct answer is A, a suspension is a heterogeneous mixture. In a suspension the particles of the solute are large enough to be seen and do not dissolve; they stay spread through the liquid only while it is stirred and settle to the bottom when it is left standing. Chalk powder in water, muddy river water and a shaken bottle of paint are everyday examples. Because the particles are big, a suspension scatters a beam of light, showing the Tyndall effect, and the particles can be separated by filtration. B is wrong because solids spread in a gas, such as smoke, are aerosols, a kind of colloid, not a suspension. C is wrong because the particles of a suspension are large enough to be seen with the naked eye; it is the particles of a solution that cannot be seen. D is wrong because a homogeneous mixture is a solution, which is uniform throughout. Exam tip: solution homogeneous, suspension heterogeneous and settles, colloid in between.

The correct answer is C, At room temperature, surface tension of water is less than ethyl alcohol. This is the statement that is not correct, because water has a much higher surface tension than ethyl alcohol. At about twenty degrees Celsius water measures close to seventy two dynes per centimetre while ethyl alcohol is only about twenty two, since the hydrogen bonds between water molecules pull far more strongly than the weaker forces inside alcohol. That is also why alcohol spreads out thinly on a surface while water gathers into beads. A is a correct statement, because surface tension is expressed in dynes per centimetre in the older unit system and in newtons per metre in the SI system. B is correct, because the inward pull on the surface gives a small free drop the shape with the least area for its volume, which is a sphere. D is correct, because surface tension arises from the cohesive forces among the molecules of the liquid itself. Exam tip: water is about 72 dynes per centimetre and alcohol about 22; surface tension falls as temperature rises.

The correct answer is A, 250 cm. In an astronomical telescope set for normal adjustment, the magnifying power equals the focal length of the objective divided by the focal length of the eyepiece. Here the magnification is 100 and the eyepiece is 2.5 cm, so the objective must be 100 multiplied by 2.5, that is 250 cm. This is why astronomical telescopes are long instruments: a large objective focal length with a short eyepiece focal length gives high magnification, and in normal adjustment the tube length is roughly the sum of the two focal lengths. B is wrong because an objective of 40 cm would give a magnification of only 16. C is wrong because a focal length smaller than the eyepiece would shrink the image instead of enlarging it. D is wrong because 100 cm gives a magnification of 40. Exam tip: for a telescope magnification is objective divided by eyepiece, so the objective is the longer lens.

The correct answer is D, It has no moving parts. A solar cell turns sunlight straight into electricity by the photovoltaic effect at a semiconductor junction, usually of silicon, so nothing inside it turns or slides. Having no moving parts means it needs almost no maintenance, makes no noise and lasts for decades once installed, which is why panels are used on satellites, in lighthouses and in village homes far from any grid. A single silicon cell gives about 0.5 to 0.6 volt, so cells are joined into modules and modules into panels for useful power. A is wrong because a solar cell shows no oscillatory motion; it is a static device. B is wrong because metal on the outer area describes the contacts and is not an advantage. C is wrong because having moving parts is the opposite of the cell's real strength. Exam tip: solar cell — photovoltaic effect in silicon, no moving parts, about 0.5 V per cell.

The correct answer is D, Whale. A whale is a mammal, not a fish, so it breathes with lungs and must come to the surface to take air through a blowhole on top of its head. It has no gills at any stage of its life. Whales are warm blooded, give birth to live young and feed them on milk, which is why they are grouped with dolphins and porpoises as marine mammals and not with fish; the blue whale is the largest animal known. A is wrong because an octopus draws water into its mantle cavity and passes it over gills. B is wrong because a squid, another cephalopod mollusc, also breathes through gills inside the mantle. C is wrong because a clown fish is a bony fish whose gills lie behind a bony flap called the operculum. Exam tip: whales, dolphins and porpoises are aquatic mammals — lungs and a blowhole, never gills.