General Science Mixed Quiz: Set 81

The correct answer is B, the crocodile. Reptiles in general have a three-chambered heart, with two atria and a ventricle that is only partly divided, so that oxygenated and deoxygenated blood mix to some extent. In crocodiles and alligators the ventricle is completely divided, giving a four-chambered heart like that of birds and mammals, which suits an animal that holds its breath while submerged.

Option A, the turtle, option C, the cobra, and option D, the chameleon, all have the usual reptilian three-chambered heart. The crocodile exception is one of the most frequently asked facts from this chapter, and it is often paired in statement questions with the other exceptions, that the platypus lays eggs although it is a mammal and that the whale is a mammal although it lives in the sea.

The correct answer is B, dust particles in the air scatter light into our eyes. A beam seen from the side is visible only because tiny particles send some of its light sideways.

Light travelling in a straight line cannot enter our eyes unless something redirects it towards us. Fine dust, smoke and water droplets in the air scatter light in all directions, so part of each sunbeam reaches an observer standing to one side. This is the Tyndall effect, the same reason a torch beam shows up in fog or sunlight looks like shafts in a dusty room or a forest. In perfectly clean air the beam would be invisible from the side.

A is wrong: reflection needs a smooth surface and sends light in one fixed direction; tiny particles scatter it everywhere.

C is wrong: refraction is bending at a boundary between two media and does not light up a beam's path.

D is wrong: scattering can partly polarise light, but polarisation is not what makes the particles visible.

Exam tip: sunbeams in a dusty room and a headlight beam in fog are both examples of the Tyndall effect.

The correct answer is B, yeast producing carbon dioxide. The yeast Saccharomyces cerevisiae ferments the sugars of the dough into ethanol and carbon dioxide, and the gas, trapped in the gluten, makes the dough rise and leaves the bread spongy; the alcohol evaporates during baking. Option A is wrong because lactic acid bacteria sour milk into curd and are what make idli and dosa batter tangy, though their gas plays a smaller part than yeast's. Option C is wrong because a virus cannot multiply except inside a living host cell and has no role in dough. Option D is wrong because protozoa are not used in baking at all. The same fermentation by yeast, carried further, yields alcoholic drinks and industrial ethanol. The gluten of wheat flour is what traps the gas, which is why bread made from wheat rises better than bread of flours poor in gluten.

The correct answer is A, The ring has higher kinetic energy. Rotational kinetic energy is ½Iω², and the ring has the larger moment of inertia.

For a thin ring about the axis through its centre and perpendicular to its plane, all the mass sits at distance R, so I = MR². For a uniform disc, much of the mass lies closer to the axis, so I = ½MR². At the same angular velocity ω, the ring has KE = ½MR²ω² while the disc has only ¼MR²ω². The ring therefore carries twice the rotational kinetic energy of the disc. The farther mass lies from the axis, the harder a body is to spin and the more energy it stores.

B is wrong: the disc has the smaller moment of inertia, so it has less energy at the same ω.

C is wrong: equal mass and radius do not mean equal moment of inertia; mass distribution matters.

D is wrong: a spinning body has rotational kinetic energy even when its centre of mass is at rest.

Exam tip: ring I = MR², disc I = ½MR², solid sphere I = ⅖MR²; rotational KE = ½Iω².

The correct answer is B, honey. The Sweet Revolution is the term used for the drive to raise honey production and beekeeping in India, supported by the National Beekeeping and Honey Mission. Option A is wrong because sugarcane and sugar do not have a colour revolution of their own in the usual list. Option C is wrong because milk is the White Revolution, associated with Operation Flood and Verghese Kurien. Option D is wrong because fruit production is called the Golden Revolution, which covers horticulture and honey in some lists, while the Yellow Revolution stands for oilseeds, the Blue for fish, the Green for food grains and the Pink for prawns or onions. These colour revolutions are asked almost every year, so learn them as one table.

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 B, the platypus, Ornithorhynchus, of Australia. It belongs to the monotremes, the only mammals that lay eggs, the other being the spiny anteater or echidna. The young hatch from the eggs and are then fed on milk from the mother's mammary glands, which is why the animal is still a mammal.

Option A, the kangaroo, Macropus, is a marsupial: its young are born very small and complete their growth in a pouch, but they are born, not hatched. Option C, the bat, Pteropus and others, is viviparous and is the only mammal capable of true flight. Option D, the whale, is also viviparous and suckles its calf under water; it is a mammal and not a fish. Only the monotremes break the rule about giving birth to young.

The correct answer is B, Ion-exchange. An ion-exchange resin or zeolite swaps the calcium and magnesium ions that cause permanent hardness for sodium or hydrogen ions.

Permanent hardness comes from the chlorides and sulphates of calcium and magnesium, which do not break down on heating. In the zeolite (permutit) process, sodium aluminium silicate takes up Ca2+ and Mg2+ and gives out Na+, which does not harden water; the exhausted zeolite is renewed by washing it with brine. Synthetic resins work the same way. Washing soda and Calgon also remove permanent hardness.

A is wrong: boiling removes only temporary hardness, by turning soluble bicarbonates into insoluble carbonates.

C is wrong: lime treatment, Clark's method, also removes only temporary (bicarbonate) hardness.

D is wrong: bubbling sulphur dioxide only makes the water acidic; it does not take out calcium or magnesium.

Exam tip: temporary hardness = bicarbonates, removed by boiling or Clark's lime; permanent = chlorides and sulphates, removed by washing soda, Calgon or ion exchange.

The correct answer is B, the bacterium Mycobacterium tuberculosis, identified by Robert Koch in 1882, which is why the organism is also called Koch's bacillus. It spreads through droplets in the air, chiefly attacks the lungs, and is treated with a long and uninterrupted course of several antibiotics. Option A is wrong because tuberculosis is bacterial; treating it as viral is the error that leads candidates to rule out antibiotics. Option C is wrong because Aspergillus causes other lung conditions in people with weak immunity and is used industrially for citric acid, but it does not cause tuberculosis. Option D is wrong because Entamoeba histolytica causes amoebic dysentery, a disease of the intestine spread by contaminated food and water. Leprosy is caused by a related species, Mycobacterium leprae.

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.

The correct answer is B, Cephalochordata. In animals such as Branchiostoma, also called Amphioxus or the lancelet, the notochord extends from the head to the tail and remains there for the whole of life, which is why the group is treated as the clearest surviving picture of the basic chordate plan.

Option A, Urochordata, includes Ascidia, Salpa and Doliolum, in which the notochord is present only in the tail of the free-swimming larva and is lost when the animal settles down, a change called retrogressive metamorphosis. Option C, Vertebrata, replaces the notochord during development with a vertebral column of cartilage or bone. Option D, Hemichordata, is now treated as a separate phylum of non-chordates and has only a short structure in the collar region, not a true notochord.

The correct answer is A, Crown Gall. Crown gall is caused by the bacterium Agrobacterium tumefaciens, which enters through a wound near the base, or crown, of the stem and makes the plant grow rough tumour-like swellings there. The bacterium works by pushing a piece of its own Ti plasmid into the plant's cells and forcing them to divide, and that natural trick is why laboratories use it as a vector to carry new genes into plants. Grapevine, apple, rose, walnut and stone fruits suffer the most. Option B is wrong because mosaic diseases, such as tobacco mosaic, are caused by viruses that mottle the leaves in light and dark patches. Option C is wrong because smut of wheat, bajra and sugarcane is a fungal disease that fills the ear with black powdery spores. Option D is wrong because white blister, or white rust, of crucifers such as mustard is also fungal and raises white blisters on leaves and stems. Exam tip: bacterial — crown gall, citrus canker, bacterial blight of rice; viral — mosaic, leaf curl; fungal — smut, rust, blight.

The correct answer is B. A virus has heredity and mutates like a living thing, yet it has no cell, no metabolism and no means of reproduction of its own; outside a host it is an inert particle that can even be crystallised, as W. M. Stanley showed with the tobacco mosaic virus in 1935, while inside a host cell it directs that cell to make copies of itself. Option A is wrong because small size alone says nothing about being alive; many bacteria are tiny and are fully living. Option C is wrong because a virus carries either DNA or RNA and never both, a favourite point of examiners. Option D is wrong because antibiotics act on bacterial structures and are useless against viruses, which are controlled by vaccines and antiviral drugs.

The correct answer is C, C-12. Relative atomic mass is measured against the carbon-12 atom, one-twelfth of whose mass is taken as the standard unit. That unit is the atomic mass unit, written u, and it is defined as exactly one-twelfth of the mass of one atom of carbon-12. So when we say the relative atomic mass of oxygen is 16 u, we mean one oxygen atom is sixteen times as heavy as one-twelfth of a carbon-12 atom. The International Union of Pure and Applied Chemistry fixed carbon-12 as the standard in 1961 because it gave the most consistent values. A is wrong because nitrogen-14 was never used as the standard. B is wrong because oxygen-16 was the older standard, replaced by carbon-12. D is wrong because C-16 is not even a known isotope of carbon used here. Exam tip: 1 u equals one-twelfth the mass of a carbon-12 atom.

The correct answer is A, the leech, Hirudinaria, an annelid that feeds on the blood of other animals. Its salivary glands secrete hirudin, an anticoagulant that keeps the host's blood flowing while the leech feeds, and the same property made leeches a part of old medical practice and a subject of modern research on blood thinners.

Option B, the earthworm, Pheretima, feeds on decaying organic matter in soil and secretes no such substance; its service is to soil fertility, which is why Darwin called earthworms the friends of the farmer. Option C, the tapeworm, Taenia, is a flatworm that absorbs digested food through its body wall in the host's intestine. Option D, the roundworm, Ascaris, is also an intestinal parasite. Only the leech is a blood feeder with an anticoagulant.

The correct answer is A, 1 and 4. Hooke's law holds only as far as the limit of proportionality, and that limit is either equal to or lower than the elastic limit, so statements 1 and 4 are the correct pair. Hooke's law says stress is proportional to strain, which is the straight part of the stress-strain graph; the point where the curve leaves the straight line is the limit of proportionality. A little beyond it the material still springs back to its original shape, and the last point at which it does so is the elastic limit. For most metals the two points lie very close together and for an ideal material they coincide. B is wrong because statement 2 extends the law past the straight part of the graph, where stress and strain are no longer proportional. C and D are wrong because statement 3 says always less, while the two limits may also be equal. Exam tip: order the four points as proportionality limit, elastic limit, yield point, ultimate stress.

The correct answer is B, 70 degrees Celsius for 15 to 30 seconds, followed by rapid chilling and storage. The short, sharp heating kills the disease-causing and most spoilage microbes while leaving the taste and most of the food value of the milk unchanged, which is exactly what boiling does not do. Option A is wrong because forty degrees is close to the temperature at which microbes grow best and would preserve nothing. Option C is wrong because a hundred degrees for ten minutes is ordinary boiling, which alters taste and destroys some vitamins. Option D is wrong because a hundred and twenty-one degrees under pressure for twenty minutes describes autoclaving, used to sterilise instruments and culture media, not milk. The method is named after Louis Pasteur.

The correct answer is D, Annelida. Annelids such as the earthworm, leech and Nereis are the first coelomates in the usual sequence: their body cavity is lined on all sides by mesoderm.

Zoologists group animals by their body cavity. Acoelomates have no cavity at all; pseudocoelomates, such as roundworms (Aschelminthes), have a cavity only partly lined by mesoderm; true coelomates have a cavity fully lined by mesoderm, which gives room for organs to grow and move. Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata and Chordata are all coelomates. In the earthworm, the fluid in this coelom also acts as a hydrostatic skeleton for burrowing.

A is wrong: Porifera, the sponges, are at the cellular level of organisation and have no true tissues or coelom.

B is wrong: Platyhelminthes, the flatworms such as tapeworm and liver fluke, are acoelomate.

C is wrong: Cnidaria such as Hydra and jellyfish are diploblastic, with only a gut cavity and no coelom.

Exam tip: acoelomate = flatworms; pseudocoelomate = roundworms; coelomate starts with Annelida.

The correct answer is A, Aspergillus niger, a fungus grown on a sugar medium to make most of the world's citric acid, which is used in soft drinks, food and medicines. Option B is wrong because Lactobacillus species produce lactic acid and are used in curd and other fermented milk products, not citric acid. Option C is wrong because Clostridium tetani is the bacterium of tetanus, an anaerobe that enters through wounds; it is a pathogen, not an industrial organism, although a related species yields butyric acid. Option D is wrong because Anabaena is a nitrogen-fixing cyanobacterium, used with the water fern Azolla as a biofertiliser in paddy fields. Other industrial pairs to remember are Saccharomyces for ethanol and Monascus purpureus for statins. Remembering a product with its organism, acid with Aspergillus, alcohol with yeast and antibiotic with Streptomyces, answers a whole set of questions on industrial microbiology.

The correct answer is A, Cell wall. Bacteria have a cell wall and human cells do not, so a drug that attacks the cell wall harms only the bacteria.

The bacterial cell wall is made of peptidoglycan, a mesh of sugars and short peptides that gives the cell its shape and stops it bursting. Penicillin blocks the enzymes that build the cross-links of this mesh. A growing bacterium then makes a weak wall, takes in water and bursts. Human cells have only a plasma membrane and no peptidoglycan, so they are left alone. Alexander Fleming discovered penicillin in 1928 from the mould Penicillium notatum.

B is wrong: human cells also have a plasma membrane, so attacking it would harm our cells too.

C is wrong: some antibiotics, such as tetracycline, act on bacterial ribosomes, but penicillin does not.

D is wrong: penicillin does not act on the bacterial chromosome or DNA.

Exam tip: penicillin, discovered by Fleming in 1928, works by blocking the bacterial cell wall.