Matching headings

Reading Passage 2 – Farming Upwards

A The idea sounds like science fiction: lettuces, herbs and strawberries growing in tall stacks inside a windowless warehouse, bathed in pink and blue light, without a single grain of soil. Yet over the past fifteen years, so-called vertical farms have moved from architectural drawings to commercial reality. Their supporters present them as an answer to some of the most pressing problems in agriculture, from water shortages to the long supply chains that bring food into cities. The industry's record, however, has been decidedly uneven: alongside a number of thriving operations, there have been several expensive and highly publicised failures.

B The basic technology is not complicated. In most vertical farms, plants are grown hydroponically, with their roots suspended in a solution of water and dissolved nutrients; in some, the roots hang in the air and are sprayed with a fine mist, a method known as aeroponics. Because the water is collected and recycled, operators claim that they use up to 95 per cent less than a conventional farm growing the same crop. The buildings are sealed, so pests have difficulty getting in, and pesticides are rarely needed. Light comes from LED lamps, and according to the plant scientist Professor Ines Duarte, this is where much of the sophistication lies. 'Plants don't use all colours of light equally,' she explains. 'With LEDs we can adjust the spectrum to whatever a particular species needs at each stage of its growth, which is something the sun obviously can't offer.'

C For retailers, however, the main attraction is not efficiency but freshness. A lettuce grown in a field may spend several days in lorries and warehouses before it reaches a shop, losing flavour and shelf life on the way. A vertical farm can be built on the edge of a city, or even inside it, so that produce harvested in the morning can be on supermarket shelves the same day. 'Our customers aren't paying for technology,' says Marcus Feld, who founded one of the first commercial vertical farms in northern Europe. 'They're paying for a salad that lasts a week in the fridge instead of three days.' Production is also predictable: an indoor farm is unaffected by drought, flood or an unexpected frost, and can deliver the same quantity every week of the year.

D The difficulty is energy. Sunlight is free; electricity is not. Every hour of light that a plant receives indoors has to be paid for, and so does the cooling needed to remove the heat that the lamps produce. This explains why vertical farms grow almost nothing but leafy greens, herbs and a few soft fruits. These crops grow quickly, are harvested whole and sell for a relatively high price per kilogram. Staple crops such as wheat and rice are a different matter. The agricultural economist Dr Hannah Kessler has calculated that the electricity required to produce a single loaf's worth of wheat indoors would cost many times the price of the loaf itself. 'The question for any crop is simply how much money each unit of light can earn,' she says. 'For basil, the answer is: quite a lot. For grain, it's almost nothing.'

E This arithmetic became painfully clear when energy prices rose sharply in the early 2020s. Several well-funded companies, some of which had raised hundreds of millions of dollars from investors, were forced to close farms or declare bankruptcy. In many cases, critics argued, the business plans had been based on optimistic assumptions about costs and on the belief that rapid expansion would bring economies of scale. Feld is candid about the mistakes. 'Frankly, many of us built for a world of cheap electricity,' he admits. 'When that world disappeared, the numbers stopped working.'

F Few observers now believe that vertical farming will replace conventional agriculture, but that does not mean it has no future. Some growers are combining the two approaches, using greenhouses that take advantage of natural daylight and switch on LEDs only when the sun is weak. Others are powering their farms with solar or wind energy, or using waste heat from nearby factories. Duarte believes that the technology's greatest value may lie elsewhere altogether. 'Think of research stations in Antarctica, desert cities, or one day a base on the Moon,' she says. 'Where you can't farm at all, a vertical farm doesn't have to compete with a field. It only has to work.'

Reading Passage 1 – Living Partnerships: The Hidden World of Lichens

A Walk through almost any landscape on Earth, from a city pavement to a windswept mountain summit, and you are likely to pass lichens without noticing them. They appear as grey-green crusts on rocks, leafy patches on tree bark or tiny branching tufts hanging from twigs. For centuries, naturalists classified them as a single kind of plant, and it was not until the second half of the nineteenth century that scientists began to understand that a lichen is not one organism at all, but a partnership.

B At the heart of every lichen is a fungus. Fungi cannot make their own food, and most obtain it by breaking down dead material or by living on other organisms. The lichen fungus has taken a different route: it houses a population of microscopic photosynthetic partners, either green algae or cyanobacteria, within its tissues. These partners use sunlight to produce sugars, a proportion of which pass to the fungus. In return, the fungus provides a sheltered structure that protects its partners from intense light and from drying out, and it absorbs water and minerals from rain, dust and the surface on which it grows. The body that results from this cooperation looks and behaves quite unlike either partner growing alone. Recent studies have suggested that some lichens also contain additional partners, such as yeasts, which makes the picture more complicated still.

C This arrangement allows lichens to survive in places where few other living things can. They are found on bare rock in hot deserts, on the frozen soils of Antarctica and on the exposed bark of trees in the tropics. The key to their resilience is an ability to tolerate almost complete drying out. When water is scarce, a lichen simply shuts down: its metabolism slows almost to a halt, and it can remain in this dormant state for long periods. As soon as it is moistened by rain, dew or even humid air, it resumes photosynthesis, sometimes within minutes. Experiments carried out on spacecraft have even shown that certain species can survive a period of exposure to the vacuum and radiation of space.

D The price of this toughness is extremely slow growth. Because lichens are active only when they are both wet and exposed to light, many crust-forming species expand by no more than a millimetre or two a year, and some grow far more slowly. Scientists have turned this characteristic into a practical tool. By measuring the diameter of the largest lichens on a surface such as a gravestone, a rock fall or ground left behind by a retreating glacier, and comparing it with lichens on surfaces of known age, researchers can estimate how long the surface has been exposed. The technique, known as lichenometry, has been used to date glacial deposits formed over the last few centuries, although its accuracy depends on careful calibration for each region, since growth rates vary with climate.

E Lichens are also remarkably sensitive to the quality of the air around them. Having no roots and no waxy outer layer of the kind that protects the leaves of many plants, they absorb much of what they need directly from rain and the atmosphere, and pollutants are taken in along with nutrients. Sulphur dioxide, released when coal and oil are burned, is particularly damaging to many species. In the industrial cities of nineteenth-century Europe, observers noticed that lichens were disappearing from trees and walls, and later studies linked this loss to polluted air. Today, surveys of which species are present in an area are widely used as an inexpensive way of monitoring air quality, and in several European cities some lichens have returned as levels of sulphur dioxide have fallen.

F People have found other uses for lichens too. In the Arctic, some species form a major part of the winter diet of reindeer and caribou, which dig through the snow to reach them. For centuries, lichens were also an important source of dyes: certain species were fermented to produce purple and red colours for wool, and the chemical indicator litmus, which turns red in acidic and blue in alkaline conditions, was originally obtained from lichens. In addition, lichens produce a wide range of chemical compounds, many of which are not known from any other group of organisms, and some of these are now being investigated for possible medical use.

G Despite their resilience, lichens face new pressures. Although many species have recovered from sulphur pollution, others are harmed by nitrogen compounds from traffic and intensive farming, which favour a small number of nitrogen-tolerant species at the expense of more sensitive ones. Because lichens grow so slowly, communities that are damaged may take decades to recover. Ecologists argue that these modest organisms deserve more attention, not only because of their value as indicators, but also because of the many roles they play in the ecosystems they inhabit, from beginning the slow process of turning rock into soil to providing food and nesting material for animals.

Reading Passage 2 – Second Lives Beneath the Waves

A When a ship reaches the end of its working life, it is usually towed to a breaker's yard, where it is cut up and its steel sold for scrap. A small number, however, meet a very different fate. Cleaned, stripped and then deliberately sunk, they come to rest on the seabed, where within months they begin to attract fish, corals and sponges. Artificial reefs of this kind have been created off the coasts of the United States, Australia, Malta and many other countries, and they have become popular destinations for divers. But the practice has always had its critics, and the question of whether a sunken ship is a gift to the ocean or simply a convenient way to dispose of waste has never been entirely settled.

B The idea of placing objects in the sea to attract fish is far from new. Fishermen in Japan were sinking wooden frames weighted with stones in the eighteenth century, and similar practices have been recorded in the Mediterranean. What has changed is the scale. In the second half of the twentieth century, governments began to sink not only ships but also old railway carriages, military vehicles and even concrete from demolished buildings. Some of these early projects were poorly planned: in one notorious case off the coast of Florida, around two million used car tyres were bound together and dropped into the sea in the 1970s, in the hope that they would become a reef. Instead, the bundles broke apart in storms, and loose tyres were thrown against existing natural reefs, damaging them. Clearing them up has cost millions of dollars.

C Lessons from such failures have shaped modern practice. Before a ship can be sunk today, it must be thoroughly cleaned of fuel, oil, paint containing toxic substances, and any loose material that could float away. Wiring and insulation, which may contain harmful chemicals, are removed, and openings are cut in the hull so that divers can enter and leave safely. This preparation is expensive and can take more than a year; in some cases it costs more than the value of the scrap metal the ship would otherwise have produced.

D Why do marine organisms colonise a wreck so quickly? Part of the answer is that, on much of the seabed, hard surfaces are scarce. Many coastal waters have floors of sand or mud, to which corals and sponges cannot attach themselves. A ship provides a large, stable structure rising from the seabed, with sheltered spaces of every size, from narrow gaps between metal plates to entire rooms. Small fish shelter in these spaces, and larger predators follow them. Biologist Elena Marsh, who has surveyed wrecks in the Gulf of Mexico for over a decade, has found that the number of fish around a ship can exceed that on a natural reef of similar size within five years.

E Not everyone is convinced that this represents a real benefit. A central question, raised by the fisheries scientist Tom Akers among others, is whether artificial reefs actually produce new fish or merely attract existing ones from the surrounding area. If the latter is true, a wreck may do more harm than good, because concentrating fish in one place makes them easier for fishing boats to catch. Akers argues that the answer probably varies from one species to another, and that without careful long-term monitoring it is impossible to know which effect dominates in any particular case.

F There are also concerns about what happens as a wreck ages. Steel corrodes in seawater, and while a large ship may remain structurally sound for many decades, its upper decks will eventually collapse. The engineer Rosa Lindqvist points out that the rate of corrosion depends heavily on depth and water temperature, and that ships sunk in shallow, warm waters may deteriorate much faster than their planners expected. As the structure breaks down, the habitat it provides changes too, and divers who enter older wrecks face increasing risks.

G Supporters respond that, whatever its effect on fish numbers, a well-managed artificial reef can relieve pressure on natural ones. Popular natural reefs suffer damage from the anchors and fins of large numbers of visiting divers. By offering an attractive alternative nearby, a sunken ship can draw some of these visitors away. The marine economist David Okoro has calculated that a single wreck off the coast of South Australia generates several million dollars a year in tourism, much of it for small businesses such as dive schools and guesthouses. For coastal communities, he suggests, this income may matter as much as any ecological argument.