General Science Mixed Quiz: Set 28

The correct answer is B, no external forces act on the system. The law of conservation of linear momentum follows straight from Newton's second law: the rate of change of the momentum of a system equals the net external force acting on it, so when that force is zero the total momentum stays the same in size and in direction. The forces the bodies exert on one another are internal, they come in action and reaction pairs, and they cancel out, which is why a gun and its bullet, or two carrom coins that strike each other, keep the same total momentum. Option A is wrong because gravity is itself an external force and it changes the momentum of a falling body every second. Option C is wrong because kinetic energy is lost in an inelastic collision while momentum is still conserved, so the two are separate laws. Option D is wrong because option B states the condition correctly. Exam tip: momentum is conserved in every collision, kinetic energy only in a perfectly elastic one.

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, the wire will not experience any force at all. The force on a current carrying conductor kept in a magnetic field is given by F equal to B I L sin theta, where theta is the angle between the direction of the current and the direction of the field. When the wire lies along the lines of force that angle is zero, sin theta becomes zero, and the force disappears however strong the field or the current may be. The same formula shows that the force is greatest when the wire is at right angles to the field, because sin theta is then one. Option A is wrong because the force, when there is one, never acts along the field; Fleming's left hand rule places it at right angles to both the field and the current. Option C is wrong for the same reason, as no rule gives a force pointing against the field. Option D is wrong here only because the angle is zero and no force arises at all. Exam tip: parallel means no force, perpendicular means maximum force.

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 C, 88. Johann Wolfgang Dobereiner, a German chemist, grouped elements of similar properties in sets of three that he called triads. His rule was that the atomic mass of the middle element is about the average of the other two. Here the average of 40 and 137 is 177 divided by 2, which is 88.5, so the nearest choice is 88. The triad meant is calcium, strontium and barium, whose masses are 40, 87.6 and 137. Dobereiner found only three such triads, so his scheme covered too few elements to be useful, but it was the first hint that atomic mass and properties are linked, an idea that later led to Newlands' law of octaves and to Mendeleev's periodic table. A, B and D are wrong because 35, 120 and 74 are far from the average of the two given masses. Exam tip: in a triad the middle mass is the average of the first and third.

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, ethylene. Ethylene, also called ethene, has the formula C2H4, and its two carbon atoms share two pairs of electrons, which is a carbon-carbon double bond made of one sigma and one pi bond; it is the simplest alkene. Option A is wrong because ethane, C2H6, is an alkane in which the two carbons are joined by a single bond only. Option B is wrong because methane, CH4, has just one carbon atom joined to four hydrogens by single bonds and can have no carbon-carbon bond at all. Option C is wrong because acetylene, or ethyne, C2H2, has a triple bond, three shared pairs made of one sigma and two pi bonds, not a double bond. Learn the family in order: ethane single, ethylene double and acetylene triple, and remember that the double and triple bonded compounds are unsaturated and decolourise bromine water.

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 D, decreases 1000 times. The pH is the negative logarithm of the hydrogen ion concentration, so each rise of one unit means the concentration has fallen to one tenth. A change from pH 3 to pH 6 is a rise of three units, which is ten multiplied by ten multiplied by ten, that is a thousandfold fall in hydrogen ions, and the solution becomes much less acidic. Options A and B are wrong for two reasons: a rise in pH always means fewer hydrogen ions, not more, and the change is never a simple doubling or tripling because the scale is logarithmic. Option C is wrong because a hundredfold fall would correspond to a change of only two units, say from pH 3 to pH 5. Keep in mind that the same rule works downward, so moving from pH 6 to pH 3 multiplies the hydrogen ion concentration a thousand times.

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, Potassium. A wet chemical extinguisher sprays a fine mist of a potassium salt solution — usually potassium acetate, potassium citrate or potassium carbonate — so potassium is the working element inside it. This type is built for kitchen fires of cooking oil and fat, which are put in Class F in the Indian and European scheme and Class K in the American one. It works in two ways at once: the mist cools the burning oil below the temperature at which it catches fire, and the potassium salt reacts with the hot fat to form a soapy foam layer on the surface. That reaction, called saponification, seals the oil off from oxygen so it cannot flare up again. Option A is wrong because copper is used in wiring and alloys and has no part in extinguishers. Option B is wrong because magnesium burns fiercely itself and is a fuel in metal fires, never a suppressant. Option D is wrong because phosphorus catches fire very easily and is used in matches. Exam tip: wet chemical — potassium salt, cooking-oil fires, works by saponification.

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, Cytoplasm. Bacteria are prokaryotes, so their DNA lies free in the cytoplasm instead of being packed inside a nucleus. The single circular chromosome sits in a region of the cytoplasm called the nucleoid, which has no nuclear membrane around it. Many bacteria also carry small extra rings of DNA called plasmids, which often hold genes for antibiotic resistance and are the tools used to move genes in biotechnology. Option A is wrong because a true nucleus with a membrane is found only in eukaryotes such as plants, animals and fungi; bacteria have no such organelle. Option C is wrong because the cell membrane only controls what enters and leaves the cell, although the chromosome is loosely attached to it at one point. Option D is wrong because ribosomes, of the smaller 70S type in bacteria, build proteins from the instructions in the DNA and store no genetic material themselves. Exam tip: prokaryotes have a nucleoid and 70S ribosomes; eukaryotes have a true nucleus and 80S ribosomes.

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 D, Alveoli. The alveoli are the tiny balloon-like air sacs at the ends of the smallest airways, and their thin walls are the surface where gases are exchanged. The two lungs together hold roughly 300 million alveoli, which give a surface of about 70 square metres — the size of a badminton court folded into the chest. Each alveolus has a wall one cell thick and is wrapped in blood capillaries, so oxygen passes into the blood and carbon dioxide passes out by simple diffusion, moving from higher to lower concentration without any pumping. Option A is wrong because the diaphragm is the dome of muscle below the lungs that changes the volume of the chest and drives breathing in and out; no exchange happens in it. Option B is wrong because bronchioles are the fine branching tubes that only carry air to the alveoli. Option C is wrong because the bronchi are the two large tubes running from the windpipe into each lung, again passages and not exchange surfaces. Exam tip: trachea to bronchi to bronchioles to alveoli, and only the alveoli exchange gases.

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, Pulmonary artery. The pulmonary artery is the one artery in the body that carries deoxygenated blood. It leaves the right ventricle and takes blood that has returned from the body's tissues to the lungs, where carbon dioxide is given up and fresh oxygen is picked up. This makes it the standard exception to the rule that arteries carry oxygen-rich blood away from the heart while veins bring oxygen-poor blood back. Option A is wrong because the pulmonary vein is the matching exception on the other side: it is the only vein carrying oxygenated blood, from the lungs into the left atrium. Option C is wrong because the aorta is the largest artery of the body and carries oxygenated blood from the left ventricle to every organ. Option D is wrong because capillaries are the fine exchange vessels in the tissues, holding oxygenated blood at the arterial end and deoxygenated blood at the venous end, so they cannot be named for one kind. Exam tip: pulmonary artery — deoxygenated, pulmonary vein — oxygenated; the two exceptions.

The correct answer is B, adrenaline. Adrenaline, also called epinephrine, is made by the medulla of the adrenal gland and is the body's emergency hormone; it makes the heart beat faster and stronger and narrows the small blood vessels, so blood pressure rises within seconds. That is why an injection of adrenaline is the first treatment when pressure crashes in shock or in a severe allergic reaction. The same hormone widens the air passages, raises blood sugar and gets the body ready for the fight or flight response. A is wrong because insulin, from the beta cells of the pancreas, lowers blood sugar and is used in diabetes. C is wrong because thyroxine from the thyroid controls the rate of metabolism and growth, and acts slowly over days. D is wrong because vasopressin, the antidiuretic hormone of the pituitary, chiefly saves water by making the kidney reabsorb it. Exam tip: adrenal medulla makes adrenaline, the fight or flight hormone that raises heart rate and blood pressure.

The correct answer is C, Glycogen. The carbohydrates in our food are broken down into glucose, and the glucose that the body does not need at once is stored as glycogen, a branched chain of glucose units kept mainly in the liver and the skeletal muscles. It is often called animal starch. When blood sugar falls, hormones such as glucagon and adrenaline make the liver break glycogen down and release glucose, which is why a fasting body can keep working for hours. Extra energy beyond what glycogen stores can hold is turned into fat. Option A is wrong because maltose is a double sugar formed while starch is being digested and it is not a store. Option B is wrong because glucose is the form that circulates in the blood and is used at once, not the stored form. Option D is wrong because starch is the storage carbohydrate of plants, not of animals. Exam tip: plants store starch, animals store glycogen in the liver and muscles.

The correct answer is A, Photosynthesis. Green plants give out oxygen only during photosynthesis, the process in which they use light energy to make their own food.

In photosynthesis a green leaf takes in carbon dioxide through its stomata and water through the roots, and in the presence of sunlight and chlorophyll turns them into glucose. The oxygen that comes out is a by-product, and it comes from the splitting of water molecules, not from carbon dioxide. This is the process that keeps the oxygen of the atmosphere topped up, which is why forests are called the lungs of the planet.

Option B is wrong because respiration does the opposite: it uses up oxygen and gives out carbon dioxide. Option C is wrong because transpiration is the loss of water as vapour from the leaves, not of oxygen. Option D is wrong because excretion is the removal of waste from the body and releases no oxygen.

Exam tip: photosynthesis takes in CO2 and gives out O2; respiration takes in O2 and gives out CO2.