General Science Mixed Quiz: Set 6

The correct answer is B, pascal. Pressure is force divided by area, so its unit is one newton per square metre, which is given the name pascal after Blaise Pascal. Its dimensional formula is M L⁻¹ T⁻², and atmospheric pressure at sea level is about 1.013 lakh pascals, also written as one atmosphere or about 1,013 millibars.

Option A, the newton, measures force itself and not force per unit area; this is the commonest confusion in the question. Option C, the hertz, measures frequency, that is the number of cycles per second. Option D, the tesla, measures magnetic flux density. Remember that the instrument used to measure atmospheric pressure is the barometer, and a sudden fall in its reading warns of a storm. Two other units of pressure are worth knowing: the bar, which is one lakh pascals, and the torr, the pressure of one millimetre of mercury.

The correct answer is D, Four. In diamond every carbon atom is joined to four other carbon atoms by strong covalent bonds. These bonds point towards the corners of a tetrahedron and build a rigid three-dimensional network that runs through the whole crystal. That network makes diamond the hardest natural substance, which is why it is used in cutting and drilling tools. Since all four valence electrons are used in bonding, no free electrons are left, so diamond does not conduct electricity. In graphite, the other common form of carbon, each atom bonds to only three others in flat hexagonal layers, and the spare electron lets graphite conduct. A is wrong because two bonds per carbon cannot build a solid network. B is wrong because carbon has a valency of four and cannot form five bonds. C is wrong because three bonds per atom describes graphite, not diamond. Exam tip: diamond = 4 bonds, hard, insulator; graphite = 3 bonds, soft, conductor.

The correct answer is B, violet light. Violet has the shortest wavelength in visible light, so glass slows it the most and bends it the most. White light is a mix of seven colours, remembered as VIBGYOR. The refractive index of glass is slightly different for each colour, highest for violet and lowest for red. So when white light passes through a prism, each colour bends through a different angle and the light spreads into a coloured band called a spectrum. This splitting is called dispersion, and Isaac Newton showed it with a glass prism in his experiments of 1666. A rainbow is the same dispersion happening inside raindrops. Option A is wrong because red has the longest wavelength and is bent the least, so it lies at the other end of the spectrum from violet. Option C is wrong because yellow lies in the middle of the spectrum and deviates less than violet. Option D is wrong because blue bends more than yellow but still a little less than violet. Exam tip: red deviates least and violet most; the shorter the wavelength, the bigger the bend.

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 A, 3 to 12. The d-block occupies the middle of the modern periodic table, groups 3 to 12, and its members are also called transition elements. In these elements the last electron enters a d orbital of the second-last shell, which is why they show variable valency, form coloured compounds and work as good catalysts. Iron, copper, zinc, silver, gold and mercury all belong here. The block has four series, filling the 3d, 4d, 5d and 6d orbitals, one in each of periods 4 to 7. B is wrong because groups 1 and 2 are the s-block, the alkali and alkaline earth metals. C is wrong because groups 13 to 18 form the p-block, which holds most non-metals and the noble gases. D is wrong because the d-block does not stop at group 10; zinc, cadmium and mercury in group 12 are part of it. Exam tip: s-block = groups 1 and 2, d-block = groups 3 to 12, p-block = groups 13 to 18, f-block = lanthanides and actinides placed below the table.

The correct answer is C, more than the atmospheric pressure. Air always moves from a region of higher pressure to one of lower pressure, so it flows out of the lungs only when the pressure inside them rises above that of the outside air. During expiration the diaphragm relaxes and moves up into its dome shape, and the intercostal muscles between the ribs relax, so the ribs move down and inward. This reduces the volume of the chest cavity, which raises the pressure in the lungs and pushes the air out. Inspiration is the reverse: the diaphragm contracts and flattens, the chest cavity grows, lung pressure falls below atmospheric pressure and air rushes in. Option A is wrong because when the pressures are equal no air moves; this happens for a moment between breaths. Option B is wrong because lower pressure inside the lungs draws air in, which is inspiration. Option D is wrong because contraction of the diaphragm enlarges the chest and causes inspiration, not expiration. Exam tip: inspiration means the diaphragm contracts and lung pressure falls; expiration means it relaxes and lung pressure rises.

The correct answer is C, Calcium Carbonate. Carbon dioxide reacts with lime water to form calcium carbonate, which does not dissolve, and its fine white particles make the water look milky. Lime water is a clear solution of calcium hydroxide, Ca(OH)2, and the reaction is Ca(OH)2 + CO2 → CaCO3 + H2O. This is the standard test for carbon dioxide, for example to show that the air we breathe out contains CO2. If CO2 is passed for a long time, the milkiness disappears because soluble calcium hydrogen carbonate forms. A is wrong because lime water contains no barium, so barium carbonate cannot form. B is wrong because calcium oxide (quicklime) is made by heating limestone, not by bubbling CO2. D is wrong because calcium hydrogen carbonate forms only with excess CO2, and since it dissolves in water it clears the milkiness instead of causing it. Exam tip: CO2 in lime water = milky (CaCO3); excess CO2 = clear again (Ca(HCO3)2); limestone, chalk and marble are all CaCO3.

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, Potassium. The reactivity series lists metals from the most reactive to the least reactive, and potassium heads it because it loses its single outer electron most easily. It reacts so violently with cold water that the hydrogen released catches fire, so potassium is stored under kerosene. The common order is K, Na, Ca, Mg, Al, Zn, Fe, Pb, (H), Cu, Hg, Ag, Au. A metal higher in the list pushes a lower metal out of its salt solution, which is why an iron nail kept in blue copper sulphate solution gets a brown coat of copper. Metals above hydrogen give hydrogen gas with dilute acids; those below it do not. A is wrong because copper lies below hydrogen and does not react with dilute acids. B is wrong because iron sits in the middle of the series. C is wrong because silver is near the bottom, just above gold. Exam tip: top = potassium, bottom = gold; K and Na are kept under kerosene.

The correct answer is D, Sickle cell anaemia, Haemophilia, Down syndrome. All three are genetic disorders, caused by changes in genes or chromosomes and passed on through birth, not by germs. Sickle cell anaemia is an autosomal recessive disease in which a single change in the haemoglobin gene makes red blood cells sickle-shaped. Haemophilia is a sex-linked recessive disorder carried on the X chromosome, in which blood does not clot properly; it mostly affects males, and it is called the royal disease because it spread among Queen Victoria's descendants. Down syndrome is a chromosomal disorder caused by an extra copy of chromosome 21, also called trisomy 21. Option A is wrong because AIDS is caused by the HIV virus and is not inherited through genes. Option B is wrong because AIDS and Hepatitis B are viral infections, and most cancers come from mutations acquired during life. Option C is wrong because Hepatitis B is a viral infection, even though haemophilia and colour blindness are genetic. Exam tip: genetic disorders include sickle cell anaemia, haemophilia, colour blindness, thalassaemia and Down syndrome.

The correct answer is B, Flavour enhancer. Monosodium glutamate is the sodium salt of glutamic acid, an amino acid, and it is added to soups, sauces, noodles and snacks to strengthen their savoury taste. This taste, called umami, is the fifth basic taste after sweet, sour, salty and bitter; it was identified in 1908 by the Japanese chemist Kikunae Ikeda, who first made MSG from a seaweed broth. In India MSG is widely sold as Ajinomoto, the name of the Japanese company that makes it. Option A is wrong because colour enhancers are food colours such as caramel or permitted dyes, which change how food looks, not how it tastes. Option C is wrong because preservatives such as sodium benzoate, or salt and vinegar, stop food from spoiling. Option D is wrong because emulsifiers such as lecithin help oil and water stay mixed in foods like mayonnaise and ice cream. Exam tip: MSG gives the umami flavour, sodium benzoate preserves, lecithin emulsifies.

The correct answer is A, The pressure in blood vessels exceeds outside pressure. At great heights the air is thin, so the atmospheric pressure acting on the body is much lower than at sea level. The blood inside our vessels keeps pushing outwards at nearly its usual pressure. In the nose the blood vessels are very fine and lie close to the surface, so when the pressure inside them becomes greater than the pressure outside, some of them burst and the nose bleeds. The cold, dry mountain air also makes the lining of the nose crack more easily. The same fall in air pressure is why water boils below 100 °C on mountains and food takes longer to cook. B is wrong because the pressure inside the vessels becomes more than, not less than, the outside pressure. C is wrong because equal pressures would give no push to burst the vessels. D is wrong because blood does not become thick enough at a height to cause nose bleeding. Exam tip: higher altitude, lower air pressure, so the pressure in blood vessels is relatively higher and the nose can bleed.

The correct answer is B, Dialysis. Haemodialysis uses a machine called an artificial kidney to clean the blood of a patient whose kidneys have failed. Blood is drawn from the patient, mixed with an anticoagulant such as heparin so that it does not clot, and passed through fine tubes with a semi-permeable lining that sit in a dialysing fluid. Waste products such as urea pass out through the lining into the fluid, and the cleaned blood is returned to the body through a vein. A person with complete kidney failure needs this treatment regularly, often two or three times a week, unless a kidney transplant is done. The Dutch doctor Willem Kolff built the first working artificial kidney in 1943. Option A is wrong because excretion is the body's own natural removal of wastes, which healthy kidneys perform. Option C is wrong because perspiration means sweating through the skin. Option D is wrong because expulsion only means pushing something out; it is not the name of this treatment. Exam tip: the working unit of the kidney is the nephron, and the artificial kidney process is haemodialysis, which mainly removes urea.

The correct answer is C, 1 and 3 only. The cooking temperature is set by the pressure inside the cooker, and that pressure is fixed by the weight sitting on the vent and the area of the hole under it. The boiling point of water rises with pressure. In an open pan water boils at 100°C, but when steam is trapped, pressure builds up until it can lift the weight, the whistle, off the vent. Pressure is force divided by area, so a heavier weight or a smaller hole means a higher pressure before steam escapes, and water then boils at about 120°C, which is why food cooks faster. Statement 2 is wrong because a bigger flame only makes the water boil and the whistle blow sooner; once steam escapes, the temperature stays at the boiling point for that pressure, and extra heat just makes more steam. Statements 1 and 3 are right for the reason above. So options A, B and D, which include statement 2, are wrong. Exam tip: higher pressure means a higher boiling point; the flame changes the speed, not the temperature.

The correct answer is A, Night blindness. Vitamin A, chemically retinol, is needed to make rhodopsin, the light-sensitive pigment in the rod cells of the retina that lets us see in dim light. When the vitamin is short, the eye cannot adjust to darkness, and the person cannot see properly at night or in poor light; this is night blindness (nyctalopia). If the deficiency continues, the eye becomes dry and the cornea is damaged, a condition called xerophthalmia, which can end in total blindness. Vitamin A is fat-soluble and comes from carrots, papaya, mango, green leafy vegetables, milk, eggs and fish liver oil. B is wrong because scurvy, with bleeding gums, is caused by lack of vitamin C. C is wrong because marasmus is caused by a severe shortage of both calories and protein in young children. D is wrong because kwashiorkor is a protein deficiency disease marked by a swollen belly. Exam tip: vitamin A night blindness, C scurvy, D rickets, K bleeding; marasmus and kwashiorkor are protein-energy problems, not vitamin diseases.

The correct answer is A, 20 Hz – 20000 Hz. A healthy human ear can hear sound waves with frequencies from about 20 hertz to 20,000 hertz (20 kHz); this band is called the audible range. Sounds below 20 Hz are called infrasonic, and animals such as elephants and whales use them to communicate over long distances. Sounds above 20 kHz are called ultrasonic; bats, dogs and dolphins can hear them, and ultrasound is used in medical scans, in cleaning delicate parts and in SONAR. Children under five and some animals can hear up to about 25 kHz, and the upper limit falls as people grow older. Option B is wrong because 80 to 100 Hz is only a tiny slice of the audible range. Option C is wrong because 2 lakh to 4 lakh Hz, that is 200 to 400 kHz, lies far inside the ultrasonic range. Option D is wrong because 0 to 20 Hz is the infrasonic range, which humans cannot hear. Exam tip: infrasonic below 20 Hz, audible from 20 Hz to 20 kHz, ultrasonic above 20 kHz.

The correct answer is A, Protein. The lens of the eye is made mostly of water and special proteins called crystallins, packed in a very regular order that keeps the lens clear so light can pass straight through to the retina. With age, and faster with diabetes, ultraviolet light, smoking or an injury, these proteins break down and clump together. The clumps scatter light, so the lens turns cloudy and vision becomes blurred, dim and glary. This clouding is a cataract, and it is one of the leading causes of blindness in India. It is treated by a short operation in which the cloudy lens is removed and replaced by an artificial intraocular lens. Option B is wrong because carbohydrate changes are not what clouds the lens, although high blood sugar in diabetes speeds up the protein damage. Option C is wrong because fat does not form the clear structure of the lens. Option D is wrong because the tear glands keep the eye moist and have nothing to do with the lens. Exam tip: cataract = cloudy lens from clumped proteins; glaucoma = raised pressure inside the eye.

The correct answer is C, amount of water in cells. Each stoma is surrounded by two guard cells, and the pore opens or closes as these cells gain or lose water. When water flows into the guard cells they swell and become turgid; because their inner walls are thicker than the outer walls, they curve outward and the pore between them opens. When they lose water they become flaccid, straighten and close the pore. The movement of potassium ions into and out of the guard cells drives this flow of water. Stomata are the tiny pores, mostly on the lower surface of leaves, through which plants take in carbon dioxide, give out oxygen and lose water vapour in transpiration. Option A is wrong because the position of the nucleus does not control the pore. Option B is wrong because the protein make-up of the cells does not change to open or shut the stomata. Option D is wrong because only one factor, the water content, is the cause here. Exam tip: turgid guard cells open the stoma, flaccid guard cells close it.

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 B, Pyrometer. A pyrometer measures very high temperatures, such as those of furnaces, kilns and molten metal, without touching the hot object. It works on the principle that every hot body gives off thermal radiation whose intensity and colour depend on its temperature; the instrument reads this radiation and converts it into a temperature value. Ordinary mercury thermometers stop at about 350 degrees Celsius, so steel plants, glass works and cement kilns rely on pyrometers, which can read well above 1,000 degrees Celsius. The word comes from the Greek pyro, meaning fire. A is wrong because a bolometer measures the power of incident electromagnetic radiation, such as infrared or microwaves, not furnace temperature. C is wrong because an ammeter measures electric current in amperes. D is wrong because a fluxmeter measures magnetic flux. Exam tip: pyrometer for furnace heat, thermometer for body heat, ammeter for current, fluxmeter for magnetism.