General Science Mixed Quiz: Set 77

The correct answer is D, 1, 2 and 3. Physics recognises four fundamental forces: gravitational, electromagnetic, strong nuclear and weak nuclear, and the question lists all four.

Every other force we meet is a form of these. Friction, tension, normal reaction and the spring force all arise from electromagnetic forces between atoms. Gravity is the weakest but acts over any distance and holds planets and galaxies together. The strong nuclear force is the strongest and binds protons and neutrons in the nucleus over a very short range. The weak nuclear force causes beta decay. The electromagnetic and weak forces have been unified as the electroweak force.

A is wrong: gravity is fundamental, but so are the others.

B is wrong: it leaves out the two nuclear forces.

C is wrong: it leaves out gravitation, the first fundamental force to be described, by Newton.

Exam tip: order of strength: strong nuclear > electromagnetic > weak nuclear > gravitational.

The correct answer is C, 2 × 10⁵ A.U. One parsec equals about 2,06,265 astronomical units, which rounds to 2 × 10⁵ A.U.

An astronomical unit is the mean distance between the Earth and the Sun, about 1·5 × 10¹¹ m. A parsec is the distance at which one astronomical unit subtends an angle of one second of arc; the name comes from "parallax of one arcsecond". Since one radian holds about 2,06,265 arcseconds, a parsec is that many astronomical units, roughly 3·26 light years or 3·1 × 10¹⁶ m. Astronomers use it for distances between stars.

A is wrong: 2,000 A.U. is about a hundred times too small.

B is wrong: 20,000 A.U. is still ten times smaller than a parsec.

D is wrong: 2 × 10⁶ A.U. is ten times larger than a parsec.

Exam tip: 1 parsec ≈ 2·06 × 10⁵ A.U. ≈ 3·26 light years; order of size is A.U. < light year < parsec.

The correct answer is D, 9000 C. Charge equals current multiplied by time, and here that is 15 A × 600 s = 9000 C.

Electric current is the rate of flow of charge, I = Q/t, so Q = I × t. The SI unit of charge, the coulomb, is the charge carried by one ampere flowing for one second. The only trap in the question is the time: 10 minutes must be changed to 600 seconds before multiplying. A steady direct current makes the calculation exact, since the current does not change during the 10 minutes.

A is wrong: 1·50 C has no basis in the given figures and is far too small.

B is wrong: 150 C comes from multiplying 15 A by 10 and forgetting to convert minutes to seconds.

C is wrong: 900 C is 15 × 60, the charge for just one minute, not ten.

Exam tip: Q = I × t with t in seconds; 1 coulomb = 1 ampere × 1 second.

The correct answer is B, Concrete. Concrete is the building material made by mixing cement with coarse aggregate such as gravel, fine aggregate such as sand, and water.

The cement and water react in a process called hydration, which sets into a hard mass and binds the aggregate together. A common ratio for ordinary work is one part cement, two parts sand and four parts gravel, written as 1:2:4. Concrete is strong in compression but weak in tension, so steel bars are embedded in it to make reinforced cement concrete, the material of most modern buildings, bridges and dams.

Option A, mortar, is cement or lime with sand and water only, with no coarse aggregate, and is used to join bricks. Option C, slurry, is any thin, pourable mix of a solid in a liquid. Option D, a moderator, is the material that slows neutrons in a nuclear reactor.

Exam tip: mortar has no gravel; concrete has gravel; adding steel gives RCC.

The correct answer is C, Proteins in mammalian cells are synthesized in rough endoplasmic reticulum. The RER is studded with ribosomes, the actual sites where amino acids are joined into proteins.

Ribosomes read the message carried by mRNA and link amino acids in the right order. Those attached to the rough endoplasmic reticulum make proteins meant for membranes or for export, such as enzymes and hormones; the new chains enter the RER, fold, and then move on in vesicles. Free ribosomes in the cytoplasm make proteins used inside the cell.

A is wrong: the cell membrane only controls what enters and leaves; it has no protein-making machinery.

B is wrong: food proteins are digested into amino acids, which are absorbed and then built into the body's own proteins inside cells.

D is wrong: the Golgi apparatus modifies, packages and dispatches proteins made in the RER; it does not make them.

Exam tip: ribosome (on RER) = protein synthesis; Golgi = packaging and secretion; SER = lipid synthesis.

The correct answer is C, Infrared and microwave radiations. Both kinds of radiation carry energy that food absorbs as heat, and both are used in everyday kitchens.

Infrared radiation is the heat radiation given out by hot bodies: a grill, a toaster, an oven element or glowing coals cook the surface of food mainly by infrared rays. A microwave oven uses microwaves of about 2.45 GHz; water molecules in the food are polar, so they keep turning with the oscillating field and the friction heats the food from within. So two different bands of the spectrum are put to use in cooking.

A is wrong: infrared is used, but it leaves out the microwave oven.

B is wrong: microwaves are used, but grills and toasters cook with infrared.

D is wrong: X-rays, gamma rays and ultraviolet are harmful ionising or high-energy radiations and radio waves carry too little energy; none of them is used to cook.

Exam tip: microwave oven = about 2.45 GHz, heats water molecules; grill and toaster = infrared.

The correct answer is C, Alveoli. The alveoli are tiny air sacs at the end of the smallest airways, and oxygen and carbon dioxide pass through their walls.

Each human lung has hundreds of millions of alveoli, which together give a surface of roughly 70 square metres, about the size of a badminton court. The wall of an alveolus is only one cell thick and is wrapped in a dense net of capillaries. Oxygen diffuses from the air in the sac into the blood, and carbon dioxide diffuses the other way, to be breathed out.

A is wrong: the bronchi are the two branches of the windpipe that carry air into each lung; they only conduct air.

B is wrong: the nasal passage filters, warms and moistens the incoming air but does not exchange gases with the blood.

D is wrong: the trachea, or windpipe, is a tube held open by rings of cartilage and only carries air down to the bronchi.

Exam tip: nose → trachea → bronchi → bronchioles → alveoli, where exchange happens.

The correct answer is D, Pinctada margaritifera. Pinctada margaritifera is the black lip pearl oyster, a bivalve mollusc of the warm shallow water of the Indo-Pacific, where it fastens itself to coral reefs by strong threads. The dark rim of its shell gives the species its name, and the dark nacre inside yields the grey to black pearls sold as Tahitian pearls. In Indian waters it occurs around the Andaman and Nicobar Islands and in the Gulf of Mannar, while the related Pinctada fucata is the oyster of the old pearl fishery of the Gulf of Mannar. Option A is wrong because Aplysia dactylomela is the spotted sea hare, a sea slug. Option B is wrong because Dentalium neohexagonum is a tusk shell, a burrowing scaphopod. Option C is wrong because the name in option C belongs to a chiton, the flat mollusc with eight plates that clings to rocky shores. Exam tip: Pinctada is the pearl oyster genus, margaritifera the black lip species.

The correct answer is C, Blue. A leaf from a sunny day is full of starch made by photosynthesis, and iodine turns starch blue-black.

This is the standard school test for starch in a leaf. Boiling the leaf in water kills its cells and softens it so that the solutions can enter. Boiling it in alcohol, usually over a water bath because alcohol catches fire easily, dissolves the chlorophyll, leaving the leaf pale or nearly colourless. When iodine solution is then added, the starch stored in the leaf reacts with it and the leaf turns blue-black. A leaf kept in the dark for two days before the test shows no blue colour, proving that light is needed for photosynthesis.

A is wrong: the leaf is colourless only before iodine is added; the starch then turns it blue.

B is wrong: the green chlorophyll has already been removed by the boiling alcohol.

D is wrong: a starch-free leaf would show the brown colour of iodine, not white, and this leaf has starch.

Exam tip: iodine test: starch gives blue-black; alcohol removes chlorophyll before the test.

The correct answer is D, 2.4. The velocity ratio of a pulley system is the distance moved by the effort divided by the distance moved by the load, so it is 12 divided by 3, that is 4. Efficiency is the mechanical advantage divided by the velocity ratio, so the mechanical advantage is 0.6 multiplied by 4, which gives 2.4. Remember that the velocity ratio depends only on how the machine is built, while the mechanical advantage also falls with friction and with the weight of the pulleys and rope; that is why no real machine reaches an efficiency of 100 per cent and the mechanical advantage is always smaller than the velocity ratio. A is wrong because 4.8 multiplies the velocity ratio by 1.2 instead of 0.6. B is wrong because 3.6 takes 60 per cent of 6, not of 4. C is wrong because 1.2 treats the velocity ratio as 2. Exam tip: efficiency equals mechanical advantage divided by velocity ratio.

The correct answer is C, Echinodermata. Starfishes, sea urchins, sea cucumbers, brittle stars and sea lilies are found only in the sea, and their water vascular system, which works by taking in sea water, is one reason they never colonised fresh water or land. The phylum Ctenophora, the comb jellies, is also exclusively marine.

Option A, Annelida, includes the earthworm on land and the leech in fresh water besides marine worms such as Nereis. Option B, Mollusca, includes the land snail, the freshwater Pila and marine squids and octopuses. Option D, Platyhelminthes, includes the freshwater Planaria and parasites that live inside the bodies of land animals, such as the tapeworm. Only the echinoderms, with the comb jellies, are confined to the sea. A further mark of the phylum is that its members are radially symmetrical as adults but bilaterally symmetrical as larvae.

The correct answer is D, pinna. The pinna is the outer, visible flap of the ear, and its funnel shape collects sound from the surroundings.

Sound gathered by the pinna travels down the ear canal to the tympanic membrane, or eardrum, which starts to vibrate. These vibrations pass through the three small bones of the middle ear, the malleus, incus and stapes, to the cochlea, the coiled fluid filled part of the inner ear. There the vibrations are turned into nerve signals, and the auditory nerve carries them to the brain, where they are recognised as sound.

A is wrong: the auditory nerve carries signals to the brain but does not collect sound. B is wrong: the tympanic membrane vibrates when sound reaches it and does not gather sound itself. C is wrong: the cochlea lies deep inside the ear and changes vibrations into nerve impulses.

Exam tip: the path of sound is pinna, ear canal, eardrum, then malleus, incus and stapes, then cochlea, auditory nerve and brain.

The correct answer is C, Alexander Fleming. He noticed that a mould of the genus Penicillium growing by accident on a culture plate had stopped the growth of Staphylococcus around it, and Howard Florey and Ernst Chain later turned that observation into a usable drug, the three sharing the Nobel Prize. Option A is wrong because Louis Pasteur established the germ theory of disease, disproved spontaneous generation and developed pasteurisation and the rabies vaccine. Option B is wrong because Robert Koch identified the bacteria of anthrax and tuberculosis and framed the postulates for proving that a microbe causes a disease. Option D is wrong because Edward Jenner introduced vaccination against smallpox in 1796, long before antibiotics existed, using material from cowpox. Streptomycin, the next famous antibiotic, came from Streptomyces griseus, and remembering the pair Fleming with Penicillium and streptomycin with Streptomyces settles most questions on antibiotics.

The correct answer is A, Petiole. The petiole is the stalk that joins a leaf blade to the stem; it belongs to the leaf, not to the flower, and a leaf without one is called sessile. A typical flower is built of four whorls borne on the thalamus. The calyx is the outermost ring of sepals, which protect the bud. Inside it the corolla of petals attracts pollinators. Then comes the androecium, the male whorl, whose units are the stamens, each with an anther on a filament. At the centre is the gynoecium, the female whorl, whose unit is the pistil or carpel, made of stigma, style and ovary. Option B is wrong because the pistil is the female part of the flower. Option C is wrong because the stamen is its male part. Option D is wrong because sepals form the calyx, the flower's outermost whorl. Exam tip: the four floral whorls are calyx, corolla, androecium and gynoecium; the petiole is a part of the leaf.

The correct answer is B, Ligaments. Ligaments are bands of dense connective tissue that join one bone to another at a joint.

Ligaments are rich in tough, slightly elastic fibres, so they hold the bones of a joint together while still allowing movement. The ligaments of the knee and ankle are common examples, and a sprain is an injury in which a ligament is stretched or torn. Both ligaments and tendons are dense regular connective tissue, which is why examiners pair them.

A is wrong: tendons connect muscles to bones, not bone to bone; they are strong and almost inelastic.

C is wrong: areolar tissue is loose connective tissue found under the skin and around organs, where it fills spaces and supports.

D is wrong: cartilage covers the ends of bones at joints and forms the nose tip, ear and rings of the windpipe; it smooths surfaces but does not tie bones together.

Exam tip: Ligament links bone to bone, Tendon ties muscle to bone; think "L for links, T for tie".

The correct answer is A, Two dry surfaces. Coulomb friction, also called dry friction, is the resistance that acts when two solid surfaces touch each other with no lubricant between them. Charles-Augustin de Coulomb set out its rules: the friction force is proportional to the normal reaction, it does not depend on the apparent area of contact, and it is very nearly independent of the sliding speed. Dry friction covers both the static friction that must be beaten before motion can start and the kinetic friction that acts once sliding has begun, and the limiting static value is the larger of the two. Option B is wrong because friction between lubricated surfaces is called fluid or film friction and obeys the laws of viscosity instead. Option C is wrong because relative motion describes kinetic friction, which is only one part of Coulomb friction. Option D is wrong because the resistance between a solid and a liquid is viscous drag. Exam tip: Coulomb friction means dry friction, proportional to the normal reaction and independent of the contact area.

The correct answer is C, Passing water through a cation exchange and an anion exchange resin bed. Together the two resins take out every dissolved ion, which leaves demineralised water.

In the cation exchange resin (written RH), metal ions such as Ca2+, Mg2+ and Na+ are swapped for H+ ions. The water then passes through the anion exchange resin (written R'OH), where chloride, sulphate and bicarbonate ions are swapped for OH− ions. The H+ and OH− so released join to form water, so no salt is left. This deionised water is used in laboratories, batteries and boilers.

A is wrong: a microfiltration membrane stops suspended particles and microbes, not dissolved salts.

B is wrong: Calgon (sodium hexametaphosphate) only ties up calcium and magnesium ions; the salts stay dissolved in the water.

D is wrong: boiling removes only temporary hardness caused by bicarbonates; chlorides and sulphates remain.

Exam tip: cation resin gives H+, anion resin gives OH−; both together = demineralised (deionised) water.

The correct answer is D, Anther. The anther is the top part of the stamen, the male organ of a flower, and pollen grains form inside it.

A stamen has two parts: a thin stalk called the filament and the anther at its tip. Inside the anther are pollen sacs in which cells divide by meiosis to give pollen grains, each carrying the male gametes. When the anther matures it splits open, and wind, water or insects carry the pollen to the stigma of a flower; this transfer is called pollination.

A is wrong: the corolla is the whorl of petals, which attracts insects but produces no pollen.

B is wrong: the style is the stalk of the pistil, the female organ, through which the pollen tube grows down to the ovary.

C is wrong: the stigma is the sticky tip of the pistil that receives pollen; it does not make it.

Exam tip: stamen = filament + anther (male); pistil = stigma + style + ovary (female).

The correct answer is C, R only. On a level curve, friction alone supplies the centripetal force, so a cyclist slips when the needed force exceeds the maximum friction.

The condition for no slipping is mv²/r ≤ μmg, which gives v² ≤ μgr. Here μgr = 0.1 × 10 × 10 = 10, so the safe speed limit is √10, about 3.16 m/s. The mass cancels out, which is why identical cycles do not matter. Any rider faster than about 3.16 m/s needs more inward force than friction can give and skids outward.

A is wrong: P at 2 m/s needs v² = 4, well within the limit of 10, so P does not slip.

B is wrong: Q at 3 m/s needs v² = 9, still below 10, so Q also stays safe.

D is wrong: only R, with v² = 25, crosses the limit; P and Q are below it.

Exam tip: on a flat curve the maximum safe speed is v = √(μgr), and it does not depend on mass.

The correct answer is B, C = Cv. If pressure is proportional to temperature for a fixed amount of ideal gas, the volume must stay constant, so the process is isochoric.

For n moles of an ideal gas PV = nRT, so P/T = nR/V. If P/T equals a constant k, then V = nR/k is also constant. In a constant-volume process the gas does no work, and all the heat supplied raises its internal energy; the heat needed per mole per kelvin is by definition the molar heat capacity at constant volume, Cv. This is Gay-Lussac's (pressure) law in action.

A is wrong: Cp applies to an isobaric process, where pressure, not volume, is constant.

C is wrong: the average of Cp and Cv does not describe any of the standard processes here.

D is wrong: the heat capacity is constant and equal to Cv for an ideal gas in this process.

Exam tip: P ∝ T means isochoric (C = Cv); V ∝ T means isobaric (C = Cp); isothermal has infinite and adiabatic zero heat capacity.