General Science Mixed Quiz: Set 25

The correct answer is B, about 17 metres. The sensation of a sound persists in the human brain for roughly one tenth of a second, so a reflected sound must arrive at least that much after the original to be heard as a separate echo. In that tenth of a second sound in air covers about 34 metres, but the sound must travel to the surface and back, so the surface itself must be at least half of that away, roughly 17 metres.

Option A, 1.7 metres, is ten times too small and would give a reflection arriving in about one hundredth of a second, far too soon to be heard separately. Option C, 34 metres, is the total path length travelled by the sound rather than the distance to the wall, and is the most common error in this question. Option D, 170 metres, is ten times too large; an echo is heard well before the surface is that far away.

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 A, tungsten. Tungsten has the highest melting point of all metals, well above three thousand degrees Celsius, so a thin tungsten wire can be heated until it glows white without melting. It also has a fairly high resistivity and a low rate of evaporation at working temperature, which is why the filament lasts for hundreds of hours inside a bulb filled with an inert gas.

Option B, silver, is the best conductor of electricity of all metals, but for that very reason it would produce hardly any heat, and it melts at a temperature far too low for a filament. Option C, nichrome, is the right choice for the element of a heater or a toaster, where a red heat is wanted, but it cannot reach the white heat needed to give useful light. Option D, copper, is used for connecting wires precisely because it has a low resistance and stays cool while carrying current.

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 D, First group. The alkali metals are lithium, sodium, potassium, rubidium, caesium and francium. Each has a single electron in its outermost shell, loses it readily to form a positive ion, and therefore stands in group 1 of the modern periodic table. They are soft, highly reactive metals whose oxides and hydroxides give strongly basic, or alkaline, solutions, which is where the family name comes from. Option A is wrong because group 2 holds the alkaline earth metals, such as beryllium, magnesium and calcium, with two outermost electrons. Option B is wrong because group 18 holds the noble gases, which are inert because their outermost shells are complete. Option C is wrong because group 3 begins the d-block transition elements, starting with scandium. The safe rule for such questions is to count the outermost electrons: one places the element in group 1, two in group 2, seven in group 17 and a complete shell in group 18.

The correct answer is B, Rod-shaped. Bacteria are grouped by shape, and bacilli are the rod-shaped ones; the Latin word bacillus itself means a small rod or stick. Tuberculosis, tetanus, typhoid and anthrax are all caused by rod-shaped bacteria, and Lactobacillus, the bacterium that curdles milk into curd, belongs to the same group. The other shapes in this classification are cocci, which are spherical, spirilla, which are long and spiral, and vibrio, which are curved like a comma. A is wrong because comma-shaped bacteria are called vibrio, the best known being Vibrio cholerae, which causes cholera. C is wrong because spiral bacteria are spirilla and spirochaetes. D is wrong because spherical bacteria are cocci, such as Streptococcus. Exam tip: cocci are round, bacilli are rods, spirilla are spirals and vibrio are comma-shaped.

The correct answer is D, cells which are similar in origin, form and function. A tissue is a group of cells that come from the same source, look alike and work together at one job. The dividing of labour among tissues is what allows a large body to work well: muscle tissue contracts, nerve tissue carries messages, and blood, a fluid connective tissue, carries oxygen and food. Animals have four main kinds of tissue, epithelial, connective, muscular and nervous. Plants have meristematic tissue, whose cells keep dividing at root and shoot tips, and permanent tissue such as parenchyma, collenchyma and sclerenchyma. Several tissues working together make an organ, and organs make an organ system. A, B and C are wrong because each drops one of the three conditions; cells of one tissue must match in all three, in origin, in form and in the work they do. Exam tip: tissue, organ, organ system, organism, in that order.

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 B, Small intestine. The small intestine is the longest part of the human alimentary canal, about 6 to 7 metres in an adult, which is why it is called the longest organ of the digestive system. It has three parts, the duodenum, the jejunum and the ileum, and its inner wall is folded into millions of finger-like villi. These villi give it a huge surface area, so digestion is completed and almost all the nutrients are absorbed here. Bile from the liver and enzymes from the pancreas empty into the duodenum and break down fat, starch and protein. A is wrong because the pancreatic duct is only a narrow tube a few centimetres long. C is wrong because the large intestine is about 1.5 metres, shorter though wider, and mainly absorbs water and salts. D is wrong because the oesophagus is roughly 25 centimetres. Exam tip: small intestine about 6-7 m and longest, large intestine about 1.5 m and widest.

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 A, Urea. Human beings are ureotelic, which means the main nitrogen waste they pass out is urea. When the body breaks down extra amino acids, ammonia is produced, and ammonia is highly poisonous even in small amounts. The liver converts it into urea through the ornithine cycle, and urea is far less harmful and dissolves easily in water. The blood carries urea to the kidneys, where the nephrons filter it out, and it leaves the body in urine. B is wrong because ammonia is the chief waste of fish and other animals that live in water, where it can be washed away at once by the surrounding water. C is wrong because uric acid is the waste of birds, insects and reptiles, which need to save water, so they pass it as a near solid paste. D is wrong because ammonium chloride is not a human excretory product. Exam tip: fish ammonotelic, humans ureotelic, birds uricotelic.

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, Wild yak. Bos mutus is the scientific name of the wild yak, the long haired bovine of the high cold plateaus of Ladakh, Tibet and the Karakoram, which grazes above four thousand metres and is listed as Vulnerable on the IUCN Red List. The domestic yak is called Bos grunniens, the grunting ox, and mutus means mute, since the wild animal is far quieter. The two part naming system, with the genus first and the species second, was given by Carl Linnaeus. B is wrong because the horse is Equus caballus. C is wrong because the ox, meaning domestic cattle, is Bos taurus or Bos indicus for the humped Indian breeds. D is wrong because the Asiatic water buffalo is Bubalus bubalis. Exam tip: the genus Bos covers cattle and yak, Bos mutus wild yak and Bos grunniens domestic yak.

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 B, Abscisic acid. Abscisic acid is the one plant hormone in this list that slows growth instead of speeding it up, which is why it is often called the stress hormone of plants. It causes the closing of stomata when water is short, keeps seeds and buds dormant until conditions are right, and helps leaves and fruit fall. The other three are growth promoters. A is wrong because cytokinins encourage cell division and delay the ageing of leaves. C is wrong because gibberellins cause stems to lengthen, break seed dormancy and make some plants flower early. D is wrong because auxins make cells elongate and are the hormone behind phototropism, the bending of a shoot towards light, since auxin gathers on the shaded side. All four are chemical messengers made in one part of the plant and acting in another. Exam tip: abscisic acid alone inhibits; auxin, gibberellin and cytokinin promote growth.

The correct answer is B, sulphurous acid. Sulphur dioxide dissolves in water to give sulphurous acid, a weak acid with the formula H2SO3, by the reaction SO2 + H2O to H2SO3. Sulphur dioxide is an oxide of a non-metal, and such oxides are acidic in nature, which is why the solution turns blue litmus red. The same gas, released when coal and diesel burn, dissolves in rain water in the air and is then slowly oxidised further, so sulphur dioxide is one of the main causes of acid rain. A is wrong because sulphur trioxide is made by oxidising sulphur dioxide with more oxygen over a catalyst, not by dissolving it in water. C is wrong because sulphuric acid is formed when sulphur trioxide, and not sulphur dioxide, meets water. D is wrong because sulphur is the element itself and cannot be got back simply by dissolving its oxide. Exam tip: SO2 with water gives H2SO3; SO3 with water gives H2SO4.

The correct answer is B, the right hand thumb rule, also called Maxwell's corkscrew rule. Hold the conductor in your right hand with the thumb stretched along the direction of the conventional current; the way your fingers curl round the wire is the direction of the concentric magnetic field lines. The field is strongest close to the wire and weakens with distance.

Option A, Fleming's left hand rule, gives the direction of the force on a current-carrying conductor placed in a magnetic field, which is the principle of the electric motor, not the shape of the field around a wire. Option C, Fleming's right hand rule, gives the direction of the current induced in a conductor moved in a magnetic field, the principle of the generator. Option D, Lenz's law, states that the induced current opposes the change that produced it, which again concerns induction. Only the right hand thumb rule answers the question asked.

The correct answer is A, Fluorine. Electronegativity is the tendency of an atom to attract a shared pair of electrons towards itself. It increases from left to right across a period, as nuclear charge grows, and decreases down a group, as each new shell puts the outer electrons further from the nucleus. Fluorine stands at the top of group 17 and is the smallest halogen, so it holds a shared pair most tightly and is the most electronegative element of all, with a value of about 4.0 on the Pauling scale. Options B, C and D are wrong because bromine, iodine and chlorine all lie below fluorine in the same group, and electronegativity falls as you go down, in the order fluorine, then chlorine, then bromine, then iodine. Remember also that fluorine is the most electronegative element in the whole table, not merely among the halogens, and that caesium is among the least electronegative.

The correct answer is A, Left atrium. The left atrium is the chamber that receives oxygen-rich blood coming back from the lungs through the pulmonary veins. From there the blood passes the bicuspid or mitral valve into the left ventricle, which pumps it out through the aorta to the whole body. The right side of the heart handles the used blood: the right atrium takes oxygen-poor blood from the body through the vena cava, and the right ventricle sends it on to the lungs through the pulmonary artery. The left ventricle has the thickest wall of the four chambers because it must push blood the farthest. B is wrong because the right ventricle pumps blood to the lungs instead of receiving it from them. C is wrong because the left ventricle gets that blood next, from the left atrium, not straight from the lungs. D is wrong because the right atrium receives deoxygenated blood. Exam tip: pulmonary veins carry oxygen-rich blood to the left atrium, and the pulmonary artery is the one artery carrying oxygen-poor blood.

The correct answer is B. In Fleming's left hand rule the forefinger, the middle finger and the thumb of the left hand are held at right angles to one another: the forefinger points along the magnetic field, the middle finger along the current, and the thumb then gives the direction of the force. It is the rule behind the electric motor, which converts electrical energy into mechanical energy.

Option A describes Fleming's right hand rule, which is used for the generator, and interchanging the two rules is the single commonest mistake in this chapter. Option C is found instead by the right hand thumb rule applied to each turn of the coil, which shows that a solenoid behaves like a bar magnet. Option D is not a matter of direction in space at all: a potential difference is measured with a voltmeter and needs no hand rule. Remember the pair, left hand for the motor and right hand for the generator.