General Science Mixed Quiz: Set 80

The correct answer is D, White blood cell. Many white blood cells destroy germs by swallowing them, and that digestion needs a large number of lysosomes.

Lysosomes are small membrane-bound sacs packed with hydrolytic enzymes that break down proteins, fats, carbohydrates and nucleic acids. Phagocytic white blood cells such as neutrophils and macrophages engulf bacteria and dead cells, and lysosomes fuse with these food vacuoles to digest them. Because a cell can also be destroyed when its own lysosomes burst, they are called the 'suicide bags' of the cell.

A is wrong: a pancreatic cell is a secretory cell, rich in rough endoplasmic reticulum, Golgi bodies and enzyme granules rather than lysosomes.

B is wrong: ovarian cells that make steroid hormones are rich in smooth endoplasmic reticulum.

C is wrong: a runner's thigh muscle cell needs energy, so it is packed with mitochondria, not lysosomes.

Exam tip: lysosome = suicide bag, most abundant in phagocytic cells such as WBCs; mitochondria = powerhouse, most abundant in muscle cells.

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 D, Reaction centre in the pigment system. The reaction centre of a photosystem is a special chlorophyll a molecule, not a carotenoid.

In photosynthesis, pigments are grouped into photosystems. Chlorophyll b, carotenoids and xanthophylls act as accessory pigments: they absorb light of other wavelengths and pass the energy on. The energy finally reaches the reaction centre, chlorophyll a, called P680 in Photosystem II and P700 in Photosystem I, which gives up electrons and starts the light reaction. Carotenoids are therefore helpers, not the centre. Beta-carotene is also the source of vitamin A in our diet.

A is wrong: carotenoids do give the yellow and orange colours of autumn leaves, which show once green chlorophyll breaks down.

B is wrong: carotenoids absorb excess energy and protect chlorophyll from photo-oxidation, a real function.

C is wrong: the carotenoids lutein and zeaxanthin collect in the retina and protect the eye from harmful blue light.

Exam tip: reaction centre = chlorophyll a (P680, P700); carotenoids and chlorophyll b are accessory pigments.

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, the octopus. It belongs to the phylum Mollusca and the class Cephalopoda, so it is a relative of the squid and the cuttlefish rather than of any fish, and the common name devil fish came from its appearance and its eight arms with suckers.

Option A, the star fish, is an echinoderm, again not a fish, but it is called the sea star rather than the devil fish. Option C, the sea horse, Hippocampus, is a genuine bony fish of the class Osteichthyes, remarkable because the male carries the eggs in a brood pouch. Option D, the flying fish, Exocoetus, is also a true bony fish, which glides above the water on enlarged pectoral fins. Questions of this kind test whether a candidate separates common names from real classification.

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 A, Rhizobium. It lives in a symbiotic relationship inside the nodules on the roots of gram, pea, groundnut and other legumes, converting atmospheric nitrogen into compounds the plant can absorb while drawing its food from the plant. Option B is wrong because Nitrobacter does not fix nitrogen but carries out the second step of nitrification, oxidising nitrite to nitrate after Nitrosomonas has turned ammonia into nitrite. Option C is wrong because Pseudomonas performs denitrification, returning nitrogen from the soil to the atmosphere, the opposite of fixation. Option D is wrong because Saccharomyces is the yeast used in baking and brewing. Azotobacter fixes nitrogen while living free in the soil, and the cyanobacteria Nostoc and Anabaena do so in water. This is why pulses are sown in rotation with cereals, and why Rhizobium is sold to farmers as a biofertiliser in place of costly nitrogenous fertiliser.

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 B, sericin. The silkworm's silk gland secretes a protein called fibroin, and over it a second protein, sericin, which acts as a gum and hardens the cocoon; boiling the cocoon softens the sericin so the filament can be reeled, and removing it afterwards is called degumming, which gives silk its lustre and softness. Option A is wrong because fibroin is the fibre itself and must not be removed. Option C is wrong because chitin is the material of the insect's own exoskeleton and of fungal cell walls, not of silk. Option D is wrong because keratin is the protein of hair, wool, nails, horns and feathers; wool is keratin while silk is fibroin, a distinction examiners like to test in a single question.

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 B, 1, 2 and 4. For small swings the time period is T = 2π√(L/g), which contains the length and gravity but neither the mass nor the amplitude.

Statement 1 is correct: T grows with the square root of length, so a pendulum four times longer takes twice as long per swing. Statement 2 is correct: T falls as g rises, so a pendulum clock runs slow on a hill or on the Moon, where g is smaller. Statement 3 is wrong: the mass of the bob cancels out of the equation, so a heavy and a light bob on equal strings swing together. Statement 4 is correct: for small amplitudes the period is the same however wide the swing, which Galileo noticed and which makes pendulum clocks possible.

A is wrong: it includes statement 3 and leaves out statement 4.

C is wrong: it includes the wrong statement 3 and drops statement 1.

D is wrong: it drops statement 2, though g appears in the formula.

Exam tip: T = 2π√(L/g); independent of mass and (small) amplitude; seconds pendulum ≈ 1 m long, T = 2 s.

The correct answer is A, Goat. Capra hircus is the scientific name of the domestic goat, in which Capra is the genus and hircus the species, written in the two-word form that Carl Linnaeus gave to biology. The goat is a ruminant of the family Bovidae and is called the poor man's cow because it gives milk and meat on little feed and thrives in dry country; Rajasthan leads the states in goat population and Sirohi, Marwari, Jakhrana and Barbari are among its known breeds. B is wrong because cattle are Bos indicus, the humped Indian cattle, or Bos taurus. C is wrong because the sheep is Ovis aries. D is wrong because the Indian water buffalo is Bubalus bubalis, the animal that gives most of India's milk. Exam tip: fix the four names together, goat Capra hircus, sheep Ovis aries, cattle Bos indicus and buffalo Bubalus bubalis.

The correct answer is B, ATP. Adenosine triphosphate is the energy currency of the cell: breaking its last phosphate bond releases energy for cell work.

ATP is made mainly in the mitochondria during cellular respiration, and in the chloroplasts of green plants during photosynthesis. When a cell needs energy for muscle contraction, active transport, making proteins or sending nerve impulses, ATP is split into ADP and a phosphate, releasing about 30 kJ per mole. The ADP is then recharged to ATP using energy from food, so the same molecules are used again and again.

A is wrong: ADP, adenosine diphosphate, is the low-energy form left after ATP gives up a phosphate.

C is wrong: AMP, adenosine monophosphate, has only one phosphate and stores very little usable energy.

D is wrong: NAD is a coenzyme that carries electrons and hydrogen in respiration; it helps make ATP but is not itself the energy currency.

Exam tip: ATP is the energy currency; mitochondria, the powerhouse of the cell, produce most of it.

The correct answer is C, effort arm length is always less than load arm length. In a class 3 lever the effort is applied between the fulcrum and the load, so the effort always sits nearer the fulcrum and its arm is the shorter of the two. Because mechanical advantage is the effort arm divided by the load arm, a class 3 lever has a mechanical advantage below one: it needs more force than the load, but it gains speed and a longer sweep at the far end. Forceps, sugar tongs, a stapler, a fishing rod and the human forearm lifting a weight are the standard examples. A is wrong because that freedom belongs to a class 1 lever, where the fulcrum may sit anywhere between effort and load. B is wrong because the two arms are equal only in the special class 1 case of a balance. D is wrong because a longer effort arm is the mark of a class 2 lever, such as a nutcracker. Exam tip: class 1 fulcrum in the middle, class 2 load in the middle, class 3 effort in the middle.

The correct answer is A, length of the plant. The apical meristem at the tip of the stem and root makes new cells that increase the plant's length, so damage to it stops growth in length.

Meristems are groups of actively dividing cells. Apical meristems, at the tips of the shoot and root, bring about primary growth, that is growth in length or height. Lateral meristems, such as the vascular cambium and cork cambium, increase girth. Intercalary meristems, found at the base of the leaves and internodes of grasses, help regrow parts removed by grazing. When the shoot tip is removed, side buds grow out instead, which gardeners use to make plants bushy.

B is wrong: the colour of flowers depends on pigments such as anthocyanins, controlled by genes, not on the apical meristem.

C is wrong: leaf colour comes from chlorophyll and other pigments in mature leaf cells.

D is wrong: the taste of fruits depends on sugars, acids and other compounds stored in the fruit.

Exam tip: apical meristem gives length, lateral meristem gives thickness, intercalary meristem helps grasses regrow.

The correct answer is C, Ear. Balance is controlled by the inner ear, which holds the vestibular apparatus alongside the organ of hearing. It is made of three semicircular canals set at right angles to one another and two small sacs, the utricle and the saccule. The canals are filled with fluid; when the head turns, the fluid lags behind and bends tiny hair cells, which send the brain a signal about the direction and the speed of the movement. The utricle and the saccule report the pull of gravity and straight-line motion. This is why an inner-ear infection, or spinning round quickly, leaves a person giddy. Option A is wrong because the heart only pumps blood through the body. Option B is wrong because the liver makes bile, breaks down toxins and stores glycogen. Option D is wrong because the tongue carries the taste buds and helps in speech and swallowing. Exam tip: the cochlea of the inner ear is for hearing, and the three semicircular canals are for balance.

The correct answer is B, Malpighian tubules. These are fine blind tubules that float in the body fluid of an insect and open into the gut, where they take up nitrogenous waste and pass it out as nearly dry uric acid, so that very little water is lost. This is one reason insects survive in dry habitats.

Option A, nephridia, are the excretory organs of annelids such as the earthworm. Option C, flame cells, belong to the flatworms. Option D, green glands, also called antennal glands, are the excretory organs of crustaceans such as the prawn, so they belong to the same phylum as insects but to a different class, which makes them the most tempting wrong answer. Arthropoda is therefore a phylum with more than one excretory plan.

The correct answer is B, chitin. Fungi are eukaryotes with a true nucleus, and their wall is built of chitin, the same tough polysaccharide that forms the exoskeleton of insects and crustaceans. Option A is wrong because peptidoglycan is the bacterial wall material, and keeping the two apart, chitin for fungi and peptidoglycan for bacteria, answers a whole family of questions. Option C is wrong because cellulose is characteristic of plant cell walls, though some fungal relatives among the water moulds do contain it. Option D is wrong because protein alone forms no cell wall; proteins are present in the wall but it is the polysaccharide that gives it strength. Fungi are heterotrophic, living as saprophytes, parasites or symbionts, never making their own food. Yeast is the exception among them, a single-celled fungus, and mushrooms, moulds and the mildews are the forms a student meets most often.

The correct answer is B, Jharkhand, the leading lac producing state of India, which also explains why the country's lac research institute stands at Namkum near Ranchi. Option A is wrong, although Odisha and Chhattisgarh are also lac producing states of the same forest belt and often appear as the distractor closest to the answer. Option C is wrong because Assam is associated with muga and eri silk, not with lac. Option D is wrong because Karnataka leads in mulberry silk and in sandalwood, not in lac. Hold the three leaders together for the examination: Jharkhand for lac, Karnataka for mulberry silk and Assam for muga silk, and remember that India itself is the largest lac producer in the world. The state's forests carry both strains of the insect, Rangeeni on Palas and Ber and Kusmi on Kusum, which is what allows four crops to be harvested over two years.

The correct answer is B, an air bladder. Bony fishes of the class Osteichthyes fill or empty a gas-filled air bladder and so hover at any depth without effort. A shark, of the class Chondrichthyes, has no such bladder, and since its body is denser than sea water it sinks unless it keeps moving, using the lift from its stiff pectoral fins and the buoyancy of its large oily liver.

Option A is wrong because sharks have gills, in five to seven pairs of gill slits without an operculum. Option C is wrong because a shark has a backbone of cartilage and is a true vertebrate. Option D is wrong because all fishes, cartilaginous and bony alike, have a two-chambered heart with one atrium and one ventricle; having one is normal and is not a handicap.