General Science Mixed Quiz: Set 20

The correct answer is C, Isaac Newton. Newton passed a narrow beam of sunlight through a glass prism in a darkened room and obtained a band of seven colours on the wall, which he named the spectrum. He then showed with a second prism that the colours could be recombined into white light, proving that the prism does not colour the light but only separates the colours already present in it. The order of the colours from the base of the prism is remembered as VIBGYOR.

Option A, C. V. Raman, discovered the scattering effect named after him and won the Nobel Prize in 1930. Option B, Lord Rayleigh, explained the scattering that makes the sky blue. Option D, S. Chandrasekhar, worked on the structure and evolution of stars.

The correct answer is C, a and c, that is Spirulina and Chlorella. Both are tiny algae grown in tanks and sold as protein rich food supplements, and both have been studied as food for astronauts. Spirulina is a blue green alga, really a cyanobacterium, whose dried powder is about sixty per cent protein and also carries iron and beta carotene. Chlorella is a single celled green alga that multiplies very fast in a small space and gives off oxygen as it grows, which is why space agencies have tested it in closed life support systems. Such food from microbes is called single cell protein. Option A is wrong because Spirogyra, the slippery filamentous alga of ponds, is not eaten as a supplement. Option B is wrong for the same reason, as it also carries Spirogyra. Option D is wrong because it leaves out both correct names and adds Funaria, which is a moss and not an alga at all. Exam tip: Spirulina and Chlorella give single cell protein.

The correct answer is D, 2 s. Convert the units first: 1 kilohertz is 1000 hertz and 50 centimetres is 0.5 metre. The speed is frequency multiplied by wavelength, that is 1000 multiplied by 0.5, which gives 500 metres per second. Time equals distance divided by speed, so 1000 metres divided by 500 metres per second gives 2 seconds.

Option A, 5 s, would follow from using a speed of 200 metres per second. Option B, 4 s, corresponds to a speed of 250 metres per second, which arises if the wavelength is halved by mistake. Option C, 3 s, is close to the time sound actually takes to cover a kilometre in ordinary air, about 340 metres per second, and is the trap for candidates who use the remembered speed of sound instead of the speed calculated from the data given.

The correct answer is B, tuberculosis (TB). The BCG vaccine takes its name from Albert Calmette and Camille Guerin, the two French scientists who developed it from a weakened strain of Mycobacterium bovis. In India it is given as a single dose soon after birth under the Universal Immunisation Programme, and it protects infants mainly from the severe forms of the disease, such as tuberculous meningitis and miliary tuberculosis. Tuberculosis itself is caused by the bacterium Mycobacterium tuberculosis, identified by Robert Koch in 1882, and it spreads through droplets when a patient coughs. Option A is wrong because typhoid, caused by Salmonella typhi, has its own conjugate vaccine. Option C is wrong because mumps is a viral disease covered by the MMR vaccine along with measles and rubella. Option D is wrong because plague, caused by Yersinia pestis and carried by rat fleas, needs a different vaccine. Exam tip: BCG at birth for TB, and World TB Day falls on 24 March.

The correct answer is A, Propanal. The ending 'al' marks an aldehyde, so propanal is the three-carbon aldehyde, CH3CH2CHO.

An aldehyde carries the group -CHO at the end of the carbon chain, with the carbonyl carbon attached to a hydrogen. In the naming system of organic chemistry the suffix tells the family: 'al' for an aldehyde, 'ol' for an alcohol, 'one' for a ketone, 'oic acid' for a carboxylic acid, 'ane' for an alkane, 'ene' for an alkene and 'yne' for an alkyne. Methanal and ethanal are the first two aldehydes of the series.

B is wrong: propanol ends in 'ol', so it is an alcohol with an -OH group. C is wrong: propyne ends in 'yne' and is an alkyne with a triple bond. D is wrong: propanone ends in 'one' and is a ketone, better known as acetone.

Exam tip: al for aldehyde, ol for alcohol, one for ketone, oic acid for carboxylic acid.

The correct answer is B, Papaver Somniferum. Opium is the dried latex of the opium poppy, whose botanical name is Papaver somniferum; the second word means sleep bringing. The milky latex is collected by making shallow cuts in the unripe capsule, and from it come the medicines morphine and codeine, used to control pain and cough. India grows the crop only under licence from the Narcotics Commissioner at Gwalior in Madhya Pradesh, and the licensed districts lie in Madhya Pradesh, Rajasthan and Uttar Pradesh, which is why state papers ask this question. Option A is wrong because Emblica officinalis is amla, the Indian gooseberry, rich in vitamin C. Option C is wrong because Rauvolfia serpentina is sarpagandha, the source of reserpine used for high blood pressure. Option D is wrong because Cinchona species yield quinine, the old treatment for malaria. Exam tip: opium Papaver somniferum, amla Emblica officinalis, quinine from Cinchona.

The correct answer is A, Moth. Silk comes from the cocoon spun by the caterpillar of a moth.

The common silk moth is Bombyx mori, and rearing it is called sericulture. The female lays hundreds of eggs, the larva or silkworm feeds on mulberry leaves, and when it is ready to pupate it secretes a protein thread from its salivary glands and wraps itself in a cocoon. The cocoons are treated with steam or hot water and the single long fibre is reeled off. Karnataka leads India in silk output, and India is the second largest producer after China.

Option B is wrong because goats give mohair, pashmina and cashmere, which are types of wool. Option C is wrong as sheep give wool. Option D is wrong because butterflies do not spin commercial silk cocoons; both belong to the order Lepidoptera, but only moths are reared for silk.

Exam tip: silk from the moth Bombyx mori and mulberry leaves; wool from sheep and goat.

The correct answer is A, Distillation. Distillation separates a liquid from a solution or from another liquid by boiling it and condensing the vapour, so it is used when the components differ in boiling point, as in getting pure water from salt water or separating acetone from water. It is not the method for purifying a solid mixed with solid impurities. Option B is useful because sublimation purifies a solid that turns straight into vapour on heating, such as camphor, naphthalene, iodine or ammonium chloride, leaving the non-volatile impurity behind. Option C is useful because crystallization dissolves the solid in a hot solvent and lets pure crystals form on cooling, the standard way to purify alum, copper sulphate and sugar. Option D is wrong because two of the three processes do purify solids, so they cannot all be useless. Exam tip: solids are purified by sublimation, crystallization and chromatography; distillation is for liquids.

The correct answer is D, Zygote. The fusion of a male gamete with a female gamete is called fertilisation, and the single cell it produces is the zygote. The male gamete in animals is the sperm and the female gamete is the egg or ovum. Each gamete carries half the normal number of chromosomes, so the zygote gets a full set again: in human beings 23 chromosomes come from the sperm and 23 from the egg, making 46. The zygote then divides again and again, travels down the fallopian tube and settles in the wall of the uterus. Option A is wrong because the ovum is the female gamete itself, one of the two cells that fuse, not the result. Option C is wrong because the embryo is the ball of cells formed after the zygote starts dividing. Option B is wrong because the foetus is a still later stage, when the organs have taken shape. Exam tip: remember the order gametes to zygote to embryo to foetus.

The correct answer is D, Thallophyta. Algae belong to Thallophyta, the simplest division of the plant kingdom. Their body is a thallus, which means it is not divided into root, stem and leaf, and they have no vascular tissue. Most algae live in water, make their own food by photosynthesis and reproduce by spores; Spirogyra, Ulothrix, Chara and Volvox are common examples. Option A is wrong because angiosperms are flowering plants whose seeds lie enclosed in a fruit, the most advanced group of all. Option B is wrong because pteridophytes, such as ferns, are the first plants with proper vascular tissue, though they bear no seeds. Option C is wrong because bryophytes, such as mosses and Marchantia, are called the amphibians of the plant kingdom; they stand a step above thallophytes and need water for reproduction. Exam tip: the order of the plant kingdom is Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.

The correct answer is C, Guava. Guava is the classic jam fruit because it is rich in both pectin and acid, the two things a jam needs to set into a firm gel. Jam is made by boiling fruit pulp with sugar until the mixture reaches about 68 per cent soluble solids; without enough pectin it stays syrupy and never sets. Ripe guava carries close to one per cent pectin, so guava jam sets without any added gelling agent, and its strong aroma survives the boiling. Option A, banana, has very little pectin, and its pulp darkens and turns pasty on cooking, so it goes into chips, powder and puree. Option B, pineapple, is low in pectin and high in water, which is why it is preferred for squash, juice and slices in syrup. Option D, sweet orange, is low in acid and its segments break down, so oranges are used for squash and marmalade. Exam tip: jam needs pectin plus acid — guava, apple and aonla are the standard pectin-rich fruits.

The correct answer is A, Ant. Among the four, the ant has the largest brain in proportion to its body. An ant’s brain is tiny in absolute terms, with about two hundred and fifty thousand neurons, yet it makes up roughly a sixth of the insect’s body weight, a share no vertebrate comes close to. This is a general rule of body size: as animals get smaller, the brain shrinks more slowly than the body, so small creatures carry proportionately bigger brains. Option B is wrong because an elephant has the largest brain in absolute weight on land, about five kilograms, but that is a very small fraction of a body of several tonnes. Option C is wrong because a dolphin, though highly intelligent, has a brain near one per cent of its body weight. Option D is wrong because a human brain is about 1.4 kilograms, roughly two per cent of body weight, high for a vertebrate but far below an ant’s share. Exam tip: elephant biggest brain by weight, ant biggest in proportion.

The correct answer is B, virtual, erect and of the same size. Rays reflected from a plane mirror diverge and only appear to come from a point behind the mirror, so the image cannot be caught on a screen and is virtual. It stands the same way up as the object, is exactly as large as the object and lies as far behind the mirror as the object is in front of it. It is also laterally inverted, which is why the left hand appears as the right hand and why the word AMBULANCE is painted in reverse on the front of the van so that a driver ahead reads it correctly in the mirror.

Options A and D describe real images, which a plane mirror can never form. Option C describes the image in a convex mirror, which is smaller than the object.

The correct answer is C, Two. A normal umbilical cord contains two arteries and one vein, three blood vessels in all.

The umbilical cord joins the developing foetus to the placenta. The two umbilical arteries carry deoxygenated blood, carbon dioxide and wastes from the foetus to the placenta, while the single umbilical vein brings oxygen-rich blood and nutrients from the placenta back to the foetus. This is the reverse of the usual pattern in the body, where arteries carry oxygenated blood. The vessels are cushioned by a jelly-like tissue called Wharton's jelly, and a mature cord is about 50 to 55 cm long.

A is wrong: three is the total number of vessels, not of arteries. B is wrong: one is the number of umbilical veins. D is wrong: four vessels are never present in a normal cord.

Exam tip: Umbilical cord - two arteries plus one vein; the vein is the one carrying oxygenated blood to the foetus.

The correct answer is B, the amplitude of the sound waves. Amplitude is the maximum displacement of a particle of the medium from its rest position, and the energy carried by a wave increases with the square of the amplitude. A larger amplitude therefore delivers more energy to the ear and is heard as a louder sound. Loudness is measured in decibel.

Option A, the velocity of the wave, is fixed by the medium and its temperature; a loud and a soft sound in the same room travel at exactly the same speed. Option C, frequency, decides pitch, that is whether the sound is shrill or flat, and not how loud it is; turning up the volume of a ringtone does not change its frequency. Option D combines two quantities that both govern properties other than loudness, so it is wrong for the same reasons.

The correct answer is D, gold. Calaverite is gold telluride, with the formula AuTe2.

It is one of the very few minerals in which gold occurs chemically combined rather than as the free metal, because gold is a noble metal that usually resists reaction. Calaverite was named after Calaveras County in California, where it was found in 1861, and it is an important gold ore in Kalgoorlie in Australia and in Cripple Creek in Colorado. It looks brassy yellow to silvery white and is brittle.

Option A is wrong because the common silver telluride is hessite, and silver's chief ore is argentite. Option B is wrong as zinc is mined mainly as zinc blende, a sulphide. Option C is wrong because copper comes largely from copper pyrites, malachite and cuprite.

Exam tip: link ore to metal - calaverite gold, argentite silver, zinc blende zinc, bauxite aluminium, haematite iron, cinnabar mercury.

The correct answer is C, a convex mirror. A convex mirror curves outward and spreads the light that falls on it, so it always forms a virtual, erect and diminished image, whatever the distance of the object. Because the image is smaller, a small mirror can show a very wide field of view, and the driver sees a long stretch of the road behind. The same reason puts convex mirrors at blind turnings on hill roads and in shops.

Option A, a plane mirror, would give a true sized image but a narrow field of view. Option B, a concave mirror, converges light and can form a large inverted real image of a distant object, which would be useless and dangerous in a vehicle; it is used instead for shaving, in dentistry and in headlights. Option D is not a mirror of this kind at all.

The correct answer is B, light travels much faster than sound. The flash and the clap are produced at the same instant by the same discharge. Light covers about three lakh kilometres in one second, so it reaches the observer almost immediately, while sound in air covers only about 340 metres in a second and takes roughly three seconds for each kilometre. The gap between seeing and hearing is therefore a direct measure of distance.

Option A reverses the true order and would make thunder arrive first, which never happens. Option C is wrong because equal speeds would make the flash and the clap arrive together, with no gap at all. Option D confuses brightness with speed; the flash is indeed very bright, but intensity has nothing to do with why it arrives earlier, and even a faint flash would still be seen before the sound was heard.

The correct answer is B, plus 2 dioptres. The power of a lens is the reciprocal of its focal length expressed in metres, that is P equals 1 divided by f. Fifty centimetres is 0.5 metre, and the reciprocal of 0.5 is 2, so the power is two dioptres. The lens is convex and therefore converging, so the power carries a positive sign. Power measures how strongly a lens bends light, so a short focal length means a powerful lens.

Option A takes the focal length in metres as the answer instead of its reciprocal. Option C gives the right number with the wrong sign, which would describe a concave lens. Option D uses the focal length in centimetres in the formula, which is the commonest mistake in this calculation.

The correct answer is B, longitudinal mechanical waves. In a sound wave the particles of the medium vibrate back and forth along the same line in which the wave is travelling, producing regions where they crowd together, called compressions, and regions where they spread apart, called rarefactions. Because the vibration of particles is essential, sound is a mechanical wave and needs a material medium.

Option A is wrong on both counts: sound is not electromagnetic and its particles do not vibrate at right angles to the direction of travel. Option C describes a special case; sound can travel as a transverse wave inside a solid, but ordinary sound in air, water and solids is longitudinal, and the option wrongly restricts sound to solids. Option D describes electromagnetic waves such as light, radio waves and X-rays, which do travel through a vacuum, unlike sound.