IELTS Academic Reading Practice Test 483

The junk is the characteristic sailing vessel of the Chinese coast and of the great rivers that discharge into it, and craft of this family have been employed for at least two millennia. Individual vessels differ enormously in scale, from diminutive fishing boats operated by two or three people to oceangoing ships of several hundred tonnes displacement; the largest were capable of accommodating a thousand passengers and crew. What unites the family is a collection of structural solutions that European shipwrights reached considerably later, and which confer on the junk its unmistakable profile: a broad, elevated stern, a hull subdivided into compartments, and a rig of battened sails.

The most conspicuous element of the rig is the sail itself, which resembles a Venetian blind. Horizontal strips of bamboo, generally termed battens, are secured across a sheet of canvas or matting at intervals of approximately half a metre. These battens stiffen the fabric and maintain it in a pronounced curve, so that the sail functions in the manner of an aircraft wing and generates lift instead of merely being propelled by the wind. Because the sail is supported along its entire breadth, it can be manufactured from comparatively lightweight material without any risk of splitting. The complete rig can be lowered within seconds, and individual panels can be reefed or unfurled like a blind. Consequently the area of canvas is adjusted without requiring the crew to manipulate heavy fabric during a gale.

The masts that carry these sails are disposed in a manner quite unlike that of a European square-rigger. A junk may possess two, three or even five masts, and the mainmast, which carries the largest sail, is ordinarily positioned a little forward of the middle of the vessel. More remarkable still is that the masts are commonly unstayed: they rise vertically without the elaborate network of ropes extending to the sides that braces the mast of a Western sailing ship. This arrangement frees the deck for the stowage and handling of cargo and permits the sails to be rotated to confront the wind from any direction, a considerable advantage on a sinuous river.

At the rear, the hull ascends into a broad and elevated stern, which on the largest oceangoing junks stood several decks above the waterline and was frequently decorated with elaborate painting and carving. The configuration is not purely ornamental: a high stern raises the steering position clear of following seas and provides additional buoyancy precisely where the rudder is suspended.

That rudder constitutes the junk's most admired achievement in marine engineering. European vessels were steered by means of a paddle-like oar over the side until the twelfth century, when a rudder fixed to the sternpost was eventually adopted; Chinese shipwrights had taken that step more than a thousand years previously. Han dynasty models of boats, interred in tombs, already display a rudder hung upon the stern. The junk rudder is a substantial flat blade, frequently pierced with holes, which is lowered from the stern on ropes. Because it can be raised, it survives grounding in shallow water, and because it is suspended behind the stern it can be inspected and repaired without opening the hull.

Internally, the junk is partitioned from bow to stern by a succession of solid wooden walls termed bulkheads, each penetrated by a small doorway. These represent the ancestors of the watertight compartments that modern vessels continue to employ. Should the planking be stove in, only the compartment that has been holed admits water, and the ship remains afloat. Chinese shipwrights were constructing hulls in this fashion by the time of the Song dynasty, and travellers' accounts from the thirteenth century describe vessels possessing a dozen or more separate compartments. European shipbuilders did not embrace the principle until the nineteenth century.

The hull itself is ordinarily broad and flat-bottomed, with a shallow draught that enables a junk to penetrate a tidal creek or to rest upon a beach when the tide recedes. To resist lateral drift, certain junks lower substantial boards over the side; others employ a centreboard that descends through a slot in the bottom. The flat bottom has disadvantages in heavy weather, and oceangoing junks were frequently given a rounded or V-shaped section with a projecting keel.

For centuries these vessels conveyed the commerce of East Asia. They transported silk, porcelain and tea along the coast and across the South China Sea, and they were the ships of the Ming dynasty expeditions that reached the eastern coast of Africa in the early fifteenth century under the command of the admiral Zheng He. Chinese navigators of the Song period had already learned to employ a magnetised needle floating in a bowl of water, the ancestor of the magnetic compass, which permitted them to maintain a course out of sight of land.

The junk rig has attracted admirers far beyond China. In 1960 a British sailor, Blondie Hasler, crossed the Atlantic single-handed in a small junk-rigged boat named Jester, and the facility with which its sails could be handled from the cockpit convinced others to imitate him. Junk-rigged yachts now form a small but enthusiastic branch of the sport. Meanwhile, working junks still navigate the Pearl River and the coasts of Fujian, although many now carry outboard engines, and the skills of constructing them by hand are preserved by a diminishing number of yards.

Anyone who has watched ants on a rose bush will have seen them walking slowly along a stem, stopping now and then to touch a small green insect with their antennae. The insects are aphids, and the ants are collecting a sugary liquid called honeydew, which the aphids excrete from the rear of the abdomen. The ants drink it, carry it back to the nest and feed it to the larvae and the queen. The association is one of the most conspicuous examples of mutualism in nature, a partnership between two very different kinds of insect from which both are widely assumed to gain. The habit is far from universal, however: many ants never tend other insects at all.

Honeydew exists because of the peculiar diet of aphids. They feed on phloem sap, the fluid that carries sugars made by photosynthesis around a plant. The sap is extremely dilute in the substances an animal needs to build protein, but it is loaded with sugar, so an aphid must drink far more of it than its body requires in order to obtain enough nitrogen. The surplus is expelled as honeydew, which is rich in sugars but relatively poor in amino acids. Producing it costs the aphid water and energy, and the droplets can stick to its body and encourage mould. Handing this waste product to an ant is therefore a way of turning a disposal problem into a benefit, provided that the ant gives something in return.

The ants' behaviour is more active than simple collection. A worker will approach an aphid and drum on its back with the tips of its antennae, a movement that persuades the aphid to release a droplet. Some species go much further. They build shelters over their colonies, plastering soil and plant fragments around the stem to keep out predators, rain and direct sun; they carry aphids from a wilting leaf to a fresh shoot; and in some species they remove the wings of adults, apparently to stop the colony flying away. The black garden ant of Europe takes aphid eggs into its nest for the winter and carries the newly hatched insects out to plant roots in spring.

The advantages for the aphids are easy to demonstrate. In experiments where ants are excluded from a plant, aphid colonies are quickly attacked by ladybird adults and larvae, hoverfly larvae and lacewing larvae, all of which eat large numbers of aphids. Where ants are present, they drive these predators away, sometimes by spraying formic acid, and the colony grows faster and survives longer. Ants may also protect aphids from parasitic wasps, though here the evidence is more equivocal: some studies report lower rates of parasitism on ant-attended colonies, while others find that ants chase away the tiny hyperparasitic wasps that would otherwise attack the parasites, leaving the aphids worse off overall. The protection is real; its extent is not fixed.

The partnership is not always benign, and ants are not sentimental. When honeydew is scarce, workers may kill and eat the aphids they have been tending, and colonies have been observed to collapse after ants abandon them. Other insects exploit the arrangement. The caterpillars of many butterflies in the family Lycaenidae, and various leafhoppers and treehoppers, produce sugary secretions from special glands and are protected by ants in the same way as aphids, even though they feed on the plant in ways that damage it. Some spiders and beetles live in ant nests and steal food. From the ants' point of view, any insect that offers a sweet reward and does not resist too strongly can be treated as livestock.

How the balance of costs and benefits works out in the field is far from settled. The outcome appears to depend on the species of ant and aphid, the quality of the plant, the weather and the number of predators around. Aphids on a plant growing in nitrogen-rich soil have less need to conserve protein and may excrete more sugar, making them more valuable to ants and better protected. Ecologists therefore describe the relationship not as a fixed partnership but as a conditional one, in which each partner adjusts its behaviour to the other and to circumstances.

These details matter beyond the garden. Aphids are among the most damaging pests of arable crops, both because they weaken plants by removing sap and because many of them transmit plant viruses. If ants keep aphid numbers high and shield them from the predators that growers rely on, then an ant colony at the edge of a field can be a serious problem. Some researchers have argued that controlling ants, rather than aphids, may be the more effective strategy in certain crops, and that broad-spectrum insecticides, which kill predators but often leave ants to return, can make matters worse.

The farming of aphids by ants is thus a reminder that mutualism is not a simple exchange of favours. It is a relationship that shifts with circumstances, that can be abandoned when it stops paying, and that is exploited by outsiders. For the ants the honeydew is a dependable source of energy, often a large share of what a colony consumes; for the aphids the protection is valuable but never guaranteed. Neither partner controls the other, and neither can afford to ignore the needs of the other while the arrangement lasts.

Walk into almost any secondary school in a wealthy country and you will find commercial messages. There may be a vending machine in the corridor, a sports kit bearing a manufacturer's logo, a competition run by a bank, a screen showing advertisements in the dining hall, or a set of teaching materials produced by a company that would like pupils to think well of it. Some schools have sold the right to put a company's name on a building or a classroom. The question of whether this should be allowed is usually debated as a simple choice between protecting children and paying for their education. That framing, I shall argue, conceals the more useful questions.

Those who want advertising out of schools make several distinct points. The first is that a school is a place of compulsory attendance. A pupil cannot choose to walk out of a lesson because a company has paid to address the class. The school has, in effect, handed a captured audience to a commercial interest. The second is that pupils are not equipped to evaluate what they are shown. The third, and the strongest, is that a school that displays a brand lends it its authority. A child who sees a drinks machine in a corridor may reasonably conclude that the adults in charge approve of what it sells, which sits awkwardly beside lessons about nutrition. A fourth point concerns fairness: the schools most willing to accept money are usually those with the least of it, so the burdens of commercial life fall most heavily on the poorest pupils.

Against this, defenders of sponsorship reply that the money is real and that the choice is often not between advertising and purity but between advertising and nothing. A school that cannot afford new equipment for its science laboratories may be glad of a company's help, and refusing it on principle may hurt precisely the pupils the critics claim to protect. It is also argued that a ban would not remove commercial influence but drive it underground. Sponsored lesson plans, free online platforms and donated books all carry a message, often a subtler one than a logo on a wall, and none of them is likely to be scrutinised by a busy head teacher. Finally, children already live in a world saturated with advertising; shutting it out of school may leave them less able to recognise it, not more.

How much weight these arguments carry depends on what children actually understand, and here the research is more nuanced than either side usually admits. Studies in consumer psychology suggest that by about seven or eight most children can tell that a television commercial is trying to sell something. What develops later, through early adolescence, is an understanding of persuasive intent: the realisation that an advertisement is deliberately constructed to change what you think and want, and that its claims are therefore not disinterested.

There is a further complication that the simple arguments overlook: the terms on which commercial involvement arrives. A donated piece of equipment may come with an expectation, written into a contract or merely understood, that it will be used in a particular way, that the company's logo will remain visible, or that no rival product will be bought for several years. Exclusive agreements of this kind have been signed by school districts in the United States, where soft-drink companies have paid for the right to be the only supplier on campus. Digital services raise a related issue, because they collect information about pupils' work and behaviour, and the value of that information to a company is not always obvious to the parents who consent to it.

If the debate is to be useful, it needs to separate things that are now lumped together. The first is advertising addressed to pupils: posters, screens, branded competitions and vending machines. The second is sponsorship that buys nothing but goodwill, such as an unnamed donation to a school fund. The third is the presence of commercial products in teaching, from textbooks to online platforms, where the material has to come from somewhere. Only the first of these involves deliberately persuading children to want something, and it is the first that deserves the firmest restriction. The second is unobjectionable provided that no conditions are attached. The third requires transparency: parents and pupils should be able to see who produced a resource and why, and no company should be able to shape what is taught.

My own view is that the first category should be prohibited in schools, and that the prohibition should be a matter of national regulation rather than the private judgement of each head teacher. It is unreasonable to expect a school facing a leaking roof to weigh the interests of its pupils against a cheque, and the schools under the greatest financial pressure will always be the least able to refuse. The second category should be welcomed and, where possible, made anonymous, so that generosity is not confused with influence. The third should be visible and openly discussed in class, which is, after all, the best preparation for a life surrounded by selling. What should not happen is the present muddle, in which a school can be both a critic of consumer culture and a paid agent of it, and in which nobody is required to explain the difference.