General Science Previous Year Questions (PYQ) with Answers – Page 2

The correct answer is A, Zinc, Iron, Manganese. All three are needed by plants only in very small amounts, which makes them micronutrients. Plants need macronutrients in large amounts: nitrogen, phosphorus and potassium as primary nutrients, and calcium, magnesium and sulphur as secondary ones. Micronutrients such as iron, manganese, zinc, copper, boron, molybdenum and chlorine are needed only in traces, yet a shortage of any one of them still harms the plant. For example, a lack of zinc causes khaira disease in rice, and a lack of iron makes young leaves turn yellow. B is wrong because potassium and magnesium are macronutrients, even though copper is a micronutrient. C is wrong because phosphorus and calcium are macronutrients. D is wrong because sulphur is a macronutrient and aluminium is not an essential plant nutrient at all. Exam tip: macro, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur; micro, iron, manganese, zinc, copper, boron, molybdenum and chlorine.

The correct answer is C, Only (b). Of the three, only citrus canker is caused by bacteria; rust of wheat is caused by a fungus and yellow vein mosaic of bhindi by a virus. Citrus canker produces raised, corky brown spots on the leaves, twigs and fruits of lemon, orange and other citrus plants, and it spreads through the air. Rust of wheat forms reddish-brown powdery patches on the leaves and stems, which is how it got its name. Yellow vein mosaic turns the veins of bhindi, or okra, leaves yellow, and insects carry the virus from plant to plant. NCERT's Class 8 science book gives exactly these three as its examples of bacterial, fungal and viral diseases of plants. A is wrong because yellow vein mosaic is a viral disease, not a bacterial one. B is wrong because it adds rust of wheat, which is a fungal disease. D is wrong because it adds the viral yellow vein mosaic. Exam tip: citrus canker, bacteria; rust of wheat, fungus; yellow vein mosaic of bhindi, virus.

The correct answer is B, Pulmonary vein. Veins usually carry blood low in oxygen back to the heart, but the pulmonary veins are the exception. After blood picks up oxygen in the lungs, four pulmonary veins, two from each lung, bring this oxygen-rich blood to the left atrium of the heart. From there it passes to the left ventricle, which pumps it to the whole body through the aorta. The mirror-image fact is asked just as often: the pulmonary artery is the only artery that carries deoxygenated blood, taking it from the right ventricle to the lungs. So the rule is that arteries carry blood away from the heart and veins carry it towards the heart, whatever its oxygen level. Option A is wrong because the cystic vein drains the gall bladder. Option C is wrong because the hepatic portal vein carries nutrient-rich but oxygen-poor blood from the intestines to the liver. Option D is wrong because the cardiac veins drain used blood from the heart muscle into the right atrium. Exam tip: pulmonary vein, the only vein with oxygenated blood; pulmonary artery, the only artery with deoxygenated blood.

The correct answer is B, A = 1C/s. One ampere is the current that flows when one coulomb of charge passes a point in a circuit in one second. It comes straight from the formula I = Q/t, where I is current in amperes, Q is charge in coulombs and t is time in seconds. The ampere is one of the seven SI base units and is named after the French physicist André-Marie Ampère. One coulomb is the charge of roughly 6.25 × 10¹⁸ electrons, so a current of 1 ampere means that many electrons flowing past a point every second. Turned around, the same formula gives Q = I × t, which is why a coulomb is also called an ampere-second. A is wrong because 2 coulombs per second is a current of 2 amperes, not 1. C is wrong because charge is current multiplied by time, not current divided by time. D is wrong because an ampere multiplied by 2 seconds gives 2 coulombs, not the definition of 1 ampere. Exam tip: I = Q/t, so 1 A = 1 C/s and 1 C = 1 A × 1 s.

The correct answer is C, Red blood cells. Mature red blood cells, or erythrocytes, lose their nucleus before they enter the blood. Losing the nucleus, and the mitochondria too, leaves more room for haemoglobin, the iron-rich protein that carries oxygen, and gives the cell its flexible biconcave disc shape, which lets it squeeze through narrow capillaries. With no nucleus, red blood cells cannot divide or repair themselves; they live about 120 days, are made in the red bone marrow and are broken down mainly in the spleen, often called the graveyard of red blood cells. Platelets also lack a nucleus, but they are cell fragments, not whole cells. A is wrong, because muscle cells have nuclei, and skeletal muscle fibres even have many. B is wrong, because phagocytic cells such as neutrophils and macrophages have a nucleus; a neutrophil's nucleus has several lobes. D is wrong, because the ciliated cells lining the windpipe and the oviduct are normal cells with a nucleus. Exam tip: human red blood cells have no nucleus, live 120 days, are born in bone marrow and end in the spleen.

The correct answer is C, Abscisic acid. It is the main growth inhibitor among plant hormones and works against the growth promoters. Abscisic acid, or ABA, is called the stress hormone because it helps plants survive drought, cold and salt: it makes the stomata close to save water, keeps seeds and buds dormant so they do not sprout in bad weather, and helps leaves and fruits to age and fall. So when a question asks which hormone slows or stops growth, ABA is the answer; ethylene is the other hormone linked with ageing and ripening. A is wrong, because auxins promote growth by making cells elongate, and they make shoots bend towards light. B is wrong, because cytokinins promote cell division and delay the ageing of leaves. D is wrong, because gibberellins promote stem elongation, break seed dormancy and are sprayed on grapes to increase their size. Exam tip: the growth promoters are auxin, gibberellin and cytokinin; the inhibitor is abscisic acid, the stress hormone.

The correct answer is D, Bowman's capsule. Each human kidney has about one million nephrons, and every nephron begins with a cup-shaped Bowman's capsule that encloses a knot of capillaries called the glomerulus. Blood enters the glomerulus under pressure, and water, salts, glucose, urea and other small molecules are pushed out through its walls into the capsule; this is ultrafiltration, the first step of urine formation. Proteins and blood cells are too large to pass and stay in the blood. The filtrate then flows through the tubule, where useful substances such as glucose and most of the water are reabsorbed. A, the Collecting duct, only gathers urine from many nephrons and carries it to the pelvis of the kidney. B, the Renal vein, carries filtered blood away from the kidney and is not part of a nephron. C, the Ureter, is the tube that takes urine from the kidney to the bladder. Exam tip: Bowman's capsule plus glomerulus is the Malpighian body, the filter of the nephron.

The correct answer is C, Rickets. Vitamin D helps the intestine absorb calcium and phosphorus, so without it the bones of a growing child stay soft and bend, giving bow legs, a pigeon chest and a large forehead; this disease is rickets. In adults the same deficiency causes osteomalacia, a softening of already formed bones. Vitamin D is called the sunshine vitamin because the skin makes it when sunlight falls on it; fish liver oil, egg yolk and milk are food sources. Its chemical name is calciferol. A, Beriberi, is caused by lack of vitamin B1 (thiamine) and affects the nerves and the heart. B, Scurvy, comes from lack of vitamin C (ascorbic acid) and causes bleeding gums. D, Pneumonia, is an infection of the lungs caused by bacteria or viruses, not a deficiency disease. Exam tip: remember the pairs, A night blindness, B1 beriberi, C scurvy, D rickets, K delayed clotting.

The correct answer is D, General theory of relativity. LIGO, the Laser Interferometer Gravitational-Wave Observatory in the USA, detected gravitational waves for the first time in September 2015 (announced in February 2016), and such waves were predicted by Einstein's general theory of relativity in 1916. General relativity treats gravity as the curving of space-time and says that huge accelerating masses, like two black holes spiralling into each other, send ripples through space-time at the speed of light. LIGO's two detectors at Hanford and Livingston measured a change in arm length smaller than the width of a proton. India is building a third detector, LIGO-India, at Hingoli in Maharashtra. A, String theory, has made no prediction that any experiment has yet confirmed. B, Special relativity, deals with motion at constant speed and does not include gravity. C, Quantum mechanics, describes atoms and particles, not gravitational waves. Exam tip: LIGO means gravitational waves, which means general relativity; the 2017 Physics Nobel went to Weiss, Barish and Thorne for it.

The correct answer is D, Magnesium hydroxide. Milk of magnesia is a white suspension of magnesium hydroxide, Mg(OH)2, in water, and its milky look gives it the name. It is a mild base, so it is taken as an antacid to neutralise excess hydrochloric acid in the stomach and relieve acidity; in larger doses it works as a laxative. Being only slightly soluble, it does not make the stomach strongly alkaline, which is why it is safe as a medicine. A, Magnesium bicarbonate, exists only in solution and is not used as a medicine. B, Magnesium carbonate, is used in chalk and as a drying powder for the hands in sports, and is not called milk of magnesia. C, Magnesium sulphate, is Epsom salt, used in bath salts and as a purgative. Exam tip: pair the common names: milk of magnesia is Mg(OH)2, Epsom salt is MgSO4.7H2O, milk of lime is a Ca(OH)2 suspension.

The correct answer is C, N2O. Laughing gas is nitrous oxide, N2O, a colourless gas with a faintly sweet smell that makes people giggle and feel light-headed when they breathe it in. It was first prepared by Joseph Priestley in 1772, and Humphry Davy studied its effects and gave it the popular name. Dentists and surgeons use it mixed with oxygen as a mild anaesthetic and pain-killer, and it is also the propellant in whipped-cream cans. In the laboratory it is made by gently heating ammonium nitrate. It is a greenhouse gas too, and it damages the ozone layer. A is wrong because NO is nitric oxide, a colourless gas that turns brown in air. B is wrong because N2O3 is dinitrogen trioxide, a blue liquid at low temperature. D is wrong because NO2 is nitrogen dioxide, the reddish-brown, poisonous gas seen in vehicle smoke and acid rain. Exam tip: laughing gas = nitrous oxide = N2O, discovered by Priestley, used as a dental anaesthetic.

The correct answer is B, SF6. The name itself gives the formula: 'hexa' means six, so sulphur hexafluoride has one sulphur atom joined to six fluorine atoms, SF6. The molecule is octahedral in shape, with the six fluorine atoms arranged symmetrically around the sulphur. SF6 is a colourless, odourless, non-flammable and very unreactive gas, about five times heavier than air. Because it does not conduct electricity, it is used as an insulating gas inside high-voltage circuit breakers and switchgear. It is also one of the strongest greenhouse gases known, with a global warming potential thousands of times that of carbon dioxide, and it is listed under the Kyoto Protocol. A is wrong because S2F6 would need two sulphur atoms, which the name does not say. C is wrong because SF2 is sulphur difluoride, with only two fluorine atoms. D is wrong because S6F reverses the numbers and is not a real compound. Exam tip: mono 1, di 2, tri 3, tetra 4, penta 5, hexa 6; SF6 = one sulphur, six fluorine, used in electrical switchgear.

The correct answer is C, increase in area of contact reduces pressure exerted. Pressure is the force acting on unit area, that is P equals F divided by A, so for the same force a larger area of contact means smaller pressure. The weight of the bag stays exactly the same whether the strap is thin or wide, but a wide strap spreads that weight over more of the shoulder, so the shoulder feels less pressure and the strap does not cut into the skin. The same idea explains why school bags, seat belts and the wide tyres of a tractor are made broad. A is wrong because it states the relation upside down, since pressure falls when area rises. B and D are wrong because the force is simply the weight of the load and the width of the strap cannot change it; only the pressure changes. Exam tip: P equals F divided by A, so broad straps and flat feet reduce pressure while sharp knives and pointed nails increase it.

The correct answer is D, the statement that atmospheric pressure is negligible. Atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal, which presses with roughly the weight of one kilogram on every square centimetre of our body, so it is very large and not negligible at all. We do not feel it because the pressure of the blood and other fluids inside the body pushes outward with the same force, and the two balance. A is a correct statement because pressure is force divided by area, so the same force on a smaller area gives more pressure, which is why knives are sharpened and nails are pointed. B is correct because a liquid presses in every direction, on the bottom as well as on the side walls, and the push grows with depth. C is correct because the column of air above us has weight and therefore presses on us. Exam tip: P equals force divided by area; atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal.

The correct answer is D, equal to its weight. A floating body is at rest, so the upward buoyant force must exactly balance the downward weight of the object. By Archimedes' principle the buoyant force equals the weight of the liquid displaced, so a floating object always displaces liquid weighing as much as the object itself. Here only half the volume is inside the liquid, which tells us that half the object's volume of that liquid weighs as much as the whole object, so the object's density is half the density of the liquid. How much of the body stays under the surface depends on this density ratio, not on the size of the buoyant force. A is wrong because a liquid always pushes up on a body dipped in it. B is wrong because a smaller upward force would let the object sink further. C is wrong because a larger upward force would push the object up until less of it stayed submerged. Exam tip: floating means buoyant force = weight; fraction submerged = density of body ÷ density of liquid.

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 D, Bryophytes. Moss, or Funaria, and Marchantia, a liverwort, are bryophytes, the group called the amphibians of the plant kingdom because they live on land but need water for reproduction. Bryophytes have no true roots, stems or leaves and no vascular tissue, so they stay small and grow in damp, shady places; they cling to the soil with thread-like rhizoids and their male gametes swim to the female in a film of water. Mosses help to hold soil and prevent erosion, and Sphagnum moss gives peat. Option A is wrong because algae are simple, mostly aquatic thallophytes such as Spirogyra and Chara. Option B is wrong because gymnosperms are seed plants with naked seeds, such as pine, cycas and deodar. Option C is wrong because pteridophytes, such as ferns and Selaginella, have vascular tissue but no seeds. Exam tip: thallophyta means algae, bryophyta means mosses and liverworts, pteridophyta means ferns, and the seed plants are gymnosperms and angiosperms.

The correct answer is D, Elaioplasts. Leucoplasts are the colourless plastids of plant cells, and each kind is named after what it stores. Elaioplasts are the leucoplasts that make and store oils and fats, and they are plentiful in the tapetum, the nourishing layer of cells in the anther that feeds developing pollen grains and leaves an oily coat on them. The other leucoplasts are amyloplasts, which store starch in potato tubers and cereal grains, and proteinoplasts, which store protein. Option A is wrong because gerontoplasts are chloroplasts that have aged, as in a leaf turning yellow in autumn. Option B is wrong because proteinoplasts, also called aleuroplasts, hold protein and not oil. Option C is wrong because chloroplasts are green, pigment-bearing plastids that carry out photosynthesis, so they are not leucoplasts at all. Exam tip: name the leucoplast by its store — amyloplast for starch, elaioplast for oil (elaion is Greek for oil), proteinoplast for protein.

The correct answer is B, H3O+. A hydrogen ion (H+) is just a bare proton, so it cannot stay alone in water. It at once attaches itself to a water molecule and forms the hydronium ion, H3O+. So when an acid such as hydrochloric acid dissolves in water, it really produces H3O+ ions, and these give the solution its acidic nature. Without water, acids do not show acidic behaviour, which is why dry HCl gas does not change the colour of dry blue litmus paper. Option A is wrong because HO- (OH-) is the hydroxide ion, which bases give in water. Option C is wrong because H2 is hydrogen gas, a neutral molecule, not an ion. Option D is wrong because H2SO4 is sulphuric acid itself, a compound that releases hydrogen ions in water. Exam tip: acids give H3O+ ions in water and bases give OH- ions; a solution with pH 7 is neutral, below 7 acidic and above 7 basic.

The correct answer is B, Falciparum. Plasmodium falciparum causes malignant, or cerebral, malaria, the most dangerous form of the disease. Red blood cells infected by it become sticky and block the small blood vessels of the brain and other organs, which can lead to coma and death if treatment is delayed. Malaria spreads through the bite of the female Anopheles mosquito; the parasite first multiplies in the liver and then in red blood cells, and the bursting of these cells brings the cycles of chills and high fever. Ronald Ross proved the mosquito link in 1897 while working in India and won the Nobel Prize in 1902. Option A is wrong because P. vivax causes benign tertian malaria, which can relapse from dormant stages in the liver but is rarely fatal. Option C is wrong because P. ovale causes a mild tertian malaria found mainly in Africa. Option D is wrong because P. malariae causes quartan malaria, with fever every fourth day. Exam tip: falciparum = malignant; vivax = benign but relapsing; female Anopheles = vector.