IELTS Academic Reading Practice Test 27

For most of human history, the only concentrated sweetness available to people came from honey and ripe fruit. Today, by contrast, sugar is one of the cheapest sources of energy in the human diet. The story of how a rare and costly spice became an everyday commodity stretches across several continents and thousands of years. It is also inseparable from some of the darkest episodes in modern history, for the plantations that made sugar cheap were built on the labour of enslaved people.

Sugar cane, a tall tropical grass that stores sucrose in its stems, was probably first domesticated in New Guinea several thousand years ago. For a long time people simply chewed the raw stems to extract the sweet juice. The plant gradually spread through Southeast Asia to India, and it was there that cooks and artisans first learned to turn the juice into solid crystals, probably by the middle of the first millennium CE. The achievement left its mark on language: the Sanskrit word sharkara, which originally meant grit or gravel, is the distant ancestor of the English word 'sugar'. Even earlier, Greek writers who accompanied Alexander the Great into India in the fourth century BCE had reported, with evident astonishment, a reed that produced honey without the help of bees.

From India, knowledge of cane cultivation and sugar-making travelled to Persia, and after the Arab conquests of the seventh century it spread rapidly across the Islamic world. Arab growers established irrigated plantations in Egypt, Sicily and southern Spain. Western Europeans encountered sugar in quantity during the Crusades, and by the later Middle Ages Venice had become a major centre of the trade, importing raw sugar from the eastern Mediterranean and re-exporting it in refined form. Even so, sugar remained a luxury in medieval Europe. It was kept under lock and key, sold by apothecaries as a medicine, and used by wealthy households to create elaborate edible sculptures for their banquets.

The decisive change came when Europeans carried the crop across the Atlantic. In the fifteenth century Portuguese settlers grew cane on the island of Madeira and later on São Tomé, where they increasingly relied on the forced labour of enslaved Africans. Christopher Columbus took cane cuttings to the Caribbean on his second voyage in 1493, and in the following century Portuguese Brazil became the world's leading producer. From the middle of the seventeenth century, English and French colonies in the Caribbean, such as Barbados, Jamaica and Saint-Domingue, turned almost entirely to sugar. Millions of the Africans carried across the ocean ended their lives on sugar estates, where the death rate was so high that the enslaved population could often be maintained only by further purchases.

Making sugar from cane is a race against time, because the juice begins to ferment within hours of the stalks being cut. On a typical Caribbean estate, the cane was carried straight from the fields to a mill, where it was crushed between heavy vertical rollers turned by animals, wind or water. The juice then flowed to the boiling house and was heated in a series of copper kettles, each smaller and hotter than the last, while workers skimmed off impurities and added lime to help them separate.

When the syrup had been sufficiently concentrated, it was ladled into cooling troughs, where crystals began to form. Finally, the mixture was packed into clay pots or wooden barrels with holes in the bottom, through which a dark, sticky liquid known as molasses drained away over several weeks. The molasses was not wasted: much of it was distilled into rum.

As production expanded, prices fell and consumption soared. Historians' estimates vary considerably, but one widely quoted calculation suggests that the average person in Britain consumed about four pounds of sugar a year in 1700 and around eighteen pounds by 1800. Much of this was stirred into tea, which had by then become a national habit across all social classes. The anthropologist Sidney Mintz argued in an influential study that cheap sugar supplied the new industrial working class with quick and inexpensive calories. In little more than a century, sugar had been transformed from a rare spice into an apparent necessity.

The next transformation began in a laboratory. In 1747 the German chemist Andreas Marggraf showed that the sweet substance found in beetroot was identical to cane sugar, although the quantities he extracted were small. His student Franz Achard spent years breeding beets with a higher sugar content, and in 1801 he opened the world's first beet-sugar factory on an estate in Silesia. The industry received a powerful boost during the Napoleonic Wars, when the British naval blockade cut France off from Caribbean supplies and Napoleon actively encouraged farmers to grow beet. Because the crop thrives in temperate climates, Europe could at last produce its own sugar, and beet still accounts for roughly a fifth of global output.

Industrial technology also changed the way sugar was manufactured. In 1813 the English chemist Edward Charles Howard patented the vacuum pan, in which syrup could be boiled at a lower temperature, reducing the risk of burning and producing better crystals. In the 1840s the New Orleans-born engineer Norbert Rillieux developed a multiple-effect evaporator, in which the steam given off by one vessel was used to heat the next, greatly reducing fuel costs. Together these inventions made sugar cheaper than ever, laying the foundations of a modern diet in which, many nutrition experts now argue, it plays far too large a part.

In almost any forest, the most important relationships taking place are invisible. Beneath the leaf litter, the roots of trees are entwined with the threads of fungi, forming partnerships known as mycorrhizas, a name coined in the 1880s from the Greek words for 'fungus' and 'root'. The great majority of land plants form such associations, and the arrangement is extremely old. Fossils from the Rhynie chert in Scotland, roughly 400 million years old, show fungi living inside the tissues of some of the earliest land plants. Many biologists believe that these partnerships helped plants to colonise dry land in the first place, since the pioneers lacked true roots and depended on fungi to extract nutrients from barren ground.

The basis of the relationship is a trade. A fungus consists mostly of hyphae, tubular threads often only a few thousandths of a millimetre wide, which spread through the soil far more extensively than roots can. These threads absorb water and mineral nutrients, particularly phosphorus and nitrogen, and pass a share of them to the plant. In return, the plant supplies the fungus with sugars and, in some cases, fats manufactured through photosynthesis. The scale of this payment is considerable. A 2023 review led by the ecologist Heidi-Jayne Hawkins estimated that plants worldwide allocate the equivalent of about 13 billion tonnes of carbon dioxide each year to mycorrhizal fungi, roughly a third of annual emissions from fossil fuels, although the authors stressed that it is still unclear how long this carbon remains in the soil.

Mycorrhizas come in several forms. In arbuscular mycorrhizas, the most widespread type, the fungus penetrates the cells of the root and forms tiny branching structures inside them, where nutrients are exchanged. This type is typical of grasses, most food crops and many tropical trees. In ectomycorrhizas, which are common among pines, oaks, birches and other trees of temperate and northern forests, the fungus instead wraps the root tips in a dense sheath and grows between, rather than into, the outer cells. Many of the mushrooms that appear on the forest floor in autumn, including prized edible species such as chanterelles and porcini, are the fruiting bodies of ectomycorrhizal fungi.

Because a single fungus can colonise the roots of several plants, and a single plant can host many fungi, these partnerships can in principle link neighbouring plants together into what are called common mycorrhizal networks. In 1997 the Canadian forest ecologist Suzanne Simard and her colleagues published a study in the journal Nature that brought this idea to wide attention. They exposed paper birch and Douglas fir seedlings to carbon dioxide labelled with different isotopes of carbon, and then traced where the carbon ended up. They reported that carbon had moved between the two species, apparently through shared fungal connections, and that shaded Douglas fir seedlings received more than they gave. The finding inspired the memorable label 'wood-wide web'.

Over the following two decades the idea grew in ambition. Researchers and science writers described large, old 'mother trees' that were said to nourish their own seedlings through the network, to recognise their relatives and to send warning signals to neighbours under attack. Some of these claims drew on controlled experiments; in studies of tomato and broad bean plants grown in pots, for instance, plants connected by fungal threads appeared to activate their chemical defences when a neighbour was damaged by pests or disease. Best-selling books and documentaries spread a vivid picture of the forest as a cooperative community, and the image proved enormously appealing to the public.

In 2023, however, three researchers, Justine Karst, Melanie Jones and Jason Hoeksema, published an analysis in Nature Ecology & Evolution that questioned much of this picture. Jones had herself been one of the authors of the 1997 study. Reviewing the field research, they concluded that it had not been firmly established that such networks are widespread in forests, or that resources moving through them significantly improve the performance of seedlings. Results varied widely between studies, and many could be explained in other ways: carbon might, for example, travel between roots through the soil rather than through fungal threads. As for the idea that mature trees preferentially support their own offspring, the authors found no peer-reviewed field evidence at all. They also showed that papers in the field increasingly cited earlier work in ways that overstated what it had found.

Part of the problem is that these networks are extraordinarily difficult to study in a real forest. Fungal threads are microscopic, easily broken when the soil is disturbed, and almost impossible to follow over long distances without destroying the very connections being investigated. Genetic techniques can show that the same individual fungus is present on the roots of two trees, but not whether resources are actually flowing between them, or in which direction. Nor is a shared fungus necessarily a generous one. Some researchers point out that fungi act in their own interests and may move nutrients to wherever they receive the most carbon in return, which makes the language of altruism and family loyalty seem misplaced.

None of this means that mycorrhizas are unimportant. Their role in feeding individual trees is beyond dispute, and forestry and restoration projects increasingly take soil fungi into account, for example by planting seedlings in soil that already contains suitable species. What remains open is whether forests function as cooperative networks or as collections of individuals bound together by trade. Many ecologists now argue that settling that question will require larger and longer field experiments, and a willingness to let the evidence, rather than an appealing metaphor, lead the way.

Few environmental policies have spread as quickly, or been examined as closely, as charges on plastic shopping bags. Denmark began taxing bags in the early 1990s, Ireland introduced a levy paid directly by shoppers in 2002, and in the decades since, dozens of countries and cities have adopted either charges or outright bans. The policy appeals to governments partly because it is cheap to administer and highly visible. Yet its very success raises an awkward question: are bag charges a genuinely effective environmental measure, or a symbolic gesture that allows governments and consumers to feel virtuous while larger problems go untouched? In my view, the honest answer is that they are both, and that recognising this is essential to using them well.

The Irish case remains the best-known example. When the levy of 15 cents per bag came into force in March 2002, official estimates suggested that each person in Ireland was using around 328 plastic bags a year. By the end of that year the figure had fallen to about 21. Usage then crept back up, and in 2007 the government raised the levy to 22 cents, after which it fell once more. What makes this result striking is the trivial size of the charge relative to a typical shopping bill. Economists might reasonably have assumed that shoppers would barely notice such a sum, yet the response was far larger than any conventional estimate of price sensitivity would have predicted.

Behavioural economists have offered several explanations. A charge turns something that was previously free into a deliberate purchase, and people appear to be far more sensitive to the difference between zero and a small price than to an equivalent change between two positive prices. The charge also makes the cost visible at the very moment of decision, and it carries a clear social message about what responsible behaviour looks like. The economist Tatiana Homonoff, who observed shoppers in the Washington, DC area, found that a five-cent charge on disposable bags cut their use dramatically, whereas a five-cent reward for bringing a reusable bag had almost no effect. This asymmetry is consistent with the well-established finding that people feel losses more keenly than equivalent gains.

England provides more recent evidence. Large retailers were required to charge 5 pence for single-use carrier bags from October 2015, and in May 2021 the charge was doubled to 10 pence and extended to all shops. Government figures show that the number of such bags sold by the main supermarkets has fallen by more than 98 per cent compared with 2014, when they handed out more than seven billion. Judged on its own terms, then, the policy has been a remarkable success, and few other environmental interventions have altered everyday behaviour so quickly or so completely.

The difficulty lies in what happens next. A bag that is not used is not the same as an environmental impact that has disappeared, because shoppers switch to alternatives, and those alternatives carry costs of their own. A life-cycle assessment published by England's Environment Agency in 2011 calculated how many times various bags would need to be used to have a smaller effect on global warming than a conventional thin plastic bag. For a paper bag the figure was three uses; for a cotton bag it was 131. Because paper is heavy and cotton requires large quantities of land, water and energy to grow and process, a cotton tote that is used only a handful of times may do more harm than the plastic bags it replaced. Thicker plastic 'bags for life', meanwhile, were often bought repeatedly and treated as disposable, which partly defeated their purpose.

There is also evidence that thin plastic bags were never quite as wasteful as they appeared, because many households reused them, particularly as bin liners. When the economist Rebecca Taylor studied bag bans in California, she found that they removed about 40 million pounds of plastic carrier bags a year, but that sales of small rubbish bags rose sharply, offsetting almost 30 per cent of the reduction. The lesson is not that bag policies fail, but that their net benefit is considerably smaller than the headline figures imply.

Perhaps the most serious criticism concerns proportion. Carrier bags make up only a small fraction of the plastic that ends up in rivers and oceans, which includes vast quantities of packaging, fishing gear and countless other items, and their contribution to greenhouse gas emissions is tiny compared with that of transport, heating or diet. Critics worry that bag charges allow governments to claim environmental progress cheaply, and that consumers who have changed one conspicuous habit may feel entitled to neglect more consequential ones. Psychologists have documented this tendency, known as moral licensing, in other contexts, although whether it actually occurs as a result of bag charges has not been clearly established.

None of these objections persuades me that bag charges should be abandoned. They have reduced litter in places such as beaches, rivers and hedgerows, where thin bags caused disproportionate harm to wildlife, and they have shown that modest, well-designed price signals can change ingrained habits almost overnight. The mistake is to treat them as a solution rather than a demonstration. Their real value lies in proving that the approach works, and that lesson should now be applied where far more is at stake, from single-use packaging to the carbon emitted in producing everyday goods.