IELTS Academic Reading Practice Test 35

For centuries before photography existed, artists made use of a device called the camera obscura. In its simplest form it was a darkened room or box with a small opening, through which light entered to project an upside-down image of the outside world onto the opposite wall. By the eighteenth century portable versions fitted with lenses were widely used as an aid to drawing, since an artist could trace the projected outlines onto paper.

What nobody could do was make the image permanent. It had long been known that certain silver compounds darken when exposed to light, and around 1800 the Englishman Thomas Wedgwood succeeded in producing faint images on paper treated with silver nitrate. He could not, however, stop the process: when his pictures were viewed in daylight, the rest of the paper darkened too, and the images disappeared.

The first lasting image made with a camera was produced by a French inventor, Nicéphore Niépce. Rather than silver, Niépce used bitumen of Judea, a natural form of asphalt that hardens when exposed to light. He coated a pewter plate with the bitumen, placed it in a camera aimed through an upstairs window of his country house, and left it exposed. Afterwards, the parts that had not hardened were washed away with a solvent, leaving a crude image of buildings and rooftops. This picture, usually dated to 1826 or 1827, is the oldest surviving photograph taken with a camera. Its exposure is traditionally estimated at around eight hours, though some researchers who have recreated Niépce's methods believe it may have lasted several days.

In 1829 Niépce formed a partnership with Louis Daguerre, a Parisian painter who had become famous as the creator of the Diorama, a theatrical display of huge illuminated paintings. Niépce died in 1833, but Daguerre continued the work and made a crucial discovery. He found that a plate of silver-plated copper, made sensitive to light by exposure to iodine vapour, recorded an invisible image after a comparatively short exposure, and that this hidden image could then be made visible, or developed, using mercury vapour. This reduced exposure times from many hours to a matter of minutes. The image was then fixed in a solution of common salt, and later in a chemical recommended by the English scientist John Herschel, which proved far more effective.

Daguerre's process was announced in Paris in January 1839, and later that year the French government acquired the rights to it, granting Daguerre a pension for life and presenting the details to the public. The daguerreotype caused a sensation. Its images were astonishingly detailed, recording individual bricks and leaves with a precision no painter could match. They had drawbacks, however. The mirror-like surface had to be held at an angle to be seen properly, and each plate was unique: there was no way to make copies. Early exposures were also too long for portraits, but improvements in lenses and chemistry soon reduced them, and by the early 1840s portrait studios were opening in cities across Europe and North America.

Across the Channel, the English scholar William Henry Fox Talbot had been working independently along quite different lines. Talbot used ordinary writing paper soaked in salt and silver nitrate, and in 1835 he made a small image of a latticed window in his home, Lacock Abbey, which is the oldest surviving photographic negative. On paper, light areas of the scene appeared dark and dark areas light. Talbot realised that by placing this negative over a second sheet of sensitive paper and exposing it to light, he could produce a positive print, and that he could repeat the process as many times as he wished. In 1840 he too discovered how to develop a latent image, and he patented his improved process, the calotype, the following year.

The calotype's images were softer than daguerreotypes, because the fibres of the paper blurred fine detail, and Talbot's patents discouraged many potential users. Yet the principle of the negative, from which many identical prints could be made, would shape photography for the next century and a half. Between 1844 and 1846 Talbot published The Pencil of Nature, the first commercially published book to be illustrated with photographs.

The two approaches were effectively combined in 1851, when another Englishman, Frederick Scott Archer, published a process in which glass plates were coated with collodion, a sticky solution in which light-sensitive chemicals could be held. Glass produced negatives as sharp as a daguerreotype, while still allowing unlimited prints, and exposures fell to a few seconds. The plates, however, had to be coated, exposed and developed while still wet, so photographers working away from a studio needed to carry portable darkrooms in the form of tents or horse-drawn vans. Archer chose not to patent his invention, and it dominated photography for some thirty years, although he himself earned almost nothing from it.

The final step towards popular photography came with factory-made dry plates and, eventually, flexible film. In 1888 the American businessman George Eastman introduced the Kodak camera, which was sold already loaded with a roll of film long enough for a hundred pictures. When the film was finished, the owner sent the entire camera back to the company, which developed and printed the photographs and returned the camera reloaded. The advertising slogan 'You press the button, we do the rest' summed up the change: photography had become something that anyone could do.

Hummingbirds, a family of around 360 species found only in the Americas, range from Alaska to Tierra del Fuego. They include the smallest bird in the world, the bee hummingbird of Cuba, which weighs about two grams. Small size brings particular challenges. Because a tiny body has a large surface area relative to its volume, it loses heat rapidly to its surroundings, and it can store only small reserves of energy. Hummingbirds compound this problem with a way of feeding that is extraordinarily costly: they hover in front of flowers while drinking nectar. As a result, they have the highest metabolic rate, relative to body mass, of any vertebrate animal. Their feathers also slow heat loss, and the birds can fluff them out to adjust insulation, but staying warm still consumes a large share of their daily energy.

Hovering demands remarkable anatomy. A hummingbird's wings rotate freely at the shoulder, allowing the bird to turn them over on the backstroke, and they beat dozens of times a second. The flight muscles make up roughly a quarter of the bird's body mass. For many years it was assumed that hummingbirds produced lift equally on the downstroke and the upstroke, much as hovering insects do. In 2005, however, researchers who used a laser-based technique to observe the movement of air around rufous hummingbirds hovering at a feeder reported in Nature that about three-quarters of the lift came from the downstroke and only a quarter from the upstroke. Hummingbirds, in other words, hover in a manner that is part bird and part insect. The wrist joint is highly flexible, and the wing is made mainly of elongated hand bones, allowing each feather to twist precisely as the wing reverses direction.

Powering this activity requires a circulatory system to match. Relative to its size, a hummingbird's heart is very large, and during intense activity it may beat around 1,200 times a minute. The birds also breathe very rapidly, and their flight muscles are packed with mitochondria, the structures within cells that convert fuel into usable energy. Oxygen and fuel must be delivered to these muscles at rates that would be impossible for most other animals. In addition, the density of capillaries around flight muscles is extremely high, so oxygen reaches the working tissue quickly, and specialised air sacs make breathing efficient even during the fastest wingbeats.

The fuel itself comes largely from nectar, a solution of sugars, although hummingbirds also catch small insects and spiders, which supply the protein that nectar lacks. A hummingbird may drink a large proportion of its own weight in nectar each day. Research by Kenneth Welch and Chris Chen at the University of Toronto Scarborough showed how quickly this sugar is put to use. By feeding hummingbirds sugar solutions and analysing the carbon dioxide in their breath, they found that hovering birds powered most of their activity with sugar they had consumed only shortly before. The birds burned fructose as readily as glucose, an ability that is unusual among vertebrates. Because sugar is used so quickly, hummingbirds must refuel frequently, and their daily foraging often follows a repeated circuit from flower to flower.

Living so close to the limit creates a serious problem at night, when hummingbirds cannot feed. To avoid exhausting their reserves before morning, many species enter torpor, a state in which body temperature and metabolic rate fall dramatically and the heart may slow to only a few dozen beats a minute. A study published in 2020 measured the body temperatures of hummingbirds in the Andes of Peru during cold nights and found that one bird, a black metaltail, cooled to just over three degrees Celsius, the lowest body temperature recorded in any bird or non-hibernating mammal. Torpor saves a great deal of energy, but it carries risks: a bird in this state cannot respond quickly to predators and needs time to warm up before it can fly. Arousal from torpor is gradual: the bird shivers to raise its temperature and may take several minutes before it can fly normally.

Even more surprising is the fact that some hummingbirds migrate long distances. The ruby-throated hummingbird, which breeds in eastern North America and weighs about three grams, spends the winter in Central America. Many individuals are thought to cross the Gulf of Mexico in a single non-stop flight of around 800 kilometres. To prepare, they feed intensively and may almost double their body mass by storing fat, which is a more concentrated source of energy than sugar. Exactly how many birds take the direct route over the sea, rather than following the coast, has not yet been firmly established. Fat is stored under the skin and in the abdomen, and a bird preparing for migration may gain more than a gram of fat in a week; a delayed weather front can therefore be fatal if a bird runs out of fuel over water.

Hummingbirds have become valuable subjects for scientists studying the limits of animal physiology. Their ability to process and burn sugar at such high rates, without apparent harm, interests researchers investigating how bodies manage energy. Their dependence on flowers also makes them vulnerable. As the climate changes, the timing of flowering and of migration may shift at different rates, and a bird that arrives after the flowers it relies on have bloomed could struggle to find enough food. Researchers now monitor flowering times and arrival dates for signs of mismatch, and these data are beginning to guide conservation plans for species at greatest risk.

The scale of food waste is difficult to comprehend. According to the United Nations Environment Programme's Food Waste Index Report, published in 2024, about 1.05 billion tonnes of food were wasted in 2022 by households, restaurants and shops, roughly a fifth of all the food available to consumers. Further quantities are lost earlier, on farms, in storage and during transport.

Because growing, processing and transporting food all consume energy, land and water, food loss and waste together are estimated to account for between eight and ten per cent of global greenhouse gas emissions. These figures are often set beside the fact that hundreds of millions of people do not have enough to eat. The comparison is understandable, but in my view it obscures more than it reveals.

Food that is thrown away in a wealthy city cannot simply be redirected to people suffering from hunger elsewhere. Hunger is primarily a consequence of poverty, conflict and the failure of systems that distribute food, not of a global shortage. Reducing waste in rich countries is therefore valuable mainly because it would save money, protect the environment and reduce the pressure on land, not because it would directly feed the hungry. Recognising this matters, because policies designed around a misleading picture are unlikely to succeed. For example, food discarded in Europe cannot easily be sent to regions where harvests have failed, because many products are perishable and transport itself would generate emissions.

It is also important to be clear about where the waste occurs. The UNEP report attributed around sixty per cent of the total to households, with restaurants and other food services responsible for about twenty-eight per cent and retailers for the remaining twelve per cent. The average person wastes about 79 kilograms of food at home each year. Perhaps the most striking finding was that household food waste was not confined to rich countries: average levels differed surprisingly little between high-income countries and much poorer ones. Waste in the home is not simply a symptom of affluence.

Households waste food for many reasons, including buying more than they need, poor storage and uncertain planning. One problem that is relatively easy to solve is confusion over date labels. In many countries a 'use by' date indicates when food may become unsafe to eat, whereas a 'best before' date refers only to quality, yet many people treat the two as if they meant the same thing and discard food that is perfectly safe. Several British supermarkets have recently removed 'best before' dates from many fresh fruits and vegetables, encouraging customers to judge for themselves whether produce is still good to eat.

Retailers deserve more attention than their modest share of the total suggests. Although shops themselves throw away relatively little, their practices influence waste at other stages. Strict cosmetic standards can lead farmers to discard fruit and vegetables that are perfectly edible but misshapen or the wrong size, and promotions offering extra quantities at a discount encourage customers to buy more than they can use. Waste that appears in household bins may, in part, have been created at the checkout. In some countries, researchers have found that a large share of farm produce never reaches shops for this reason, although estimates vary considerably from crop to crop.

Governments have experimented with different responses. In 2016 France passed a law prohibiting supermarkets of 400 square metres or more from destroying unsold food that is still fit to eat, and requiring them to arrange donations with charities. Donations to food banks rose considerably in the following years. South Korea has taken a different approach. Since 2013 households throughout the country have paid for the disposal of food waste according to its weight or volume, and in some apartment buildings residents use bins that automatically weigh each deposit and charge it to the household's account. The country now recycles the overwhelming majority of its food waste, much of it into animal feed, compost and energy.

Both policies have merits, but neither addresses the problem at its root. Redistribution and recycling are better than sending food to landfill, where it decomposes and releases methane, yet the most environmentally beneficial option is to avoid producing surplus food in the first place. Every tonne of food that is recycled has still consumed the land, water and energy needed to grow and transport it. Specialists accordingly describe a hierarchy of responses, with prevention at the top, followed by redistribution to people, use as animal feed, recycling, and finally disposal.

The international community has committed itself, under the Sustainable Development Goals, to halving food waste per person at the retail and consumer levels by 2030. Meeting that target will require more than public appeals to clean our plates. It will demand reliable measurement, which many countries still lack, clearer labelling, an end to retail practices that encourage over-buying and price signals that reflect the true cost of disposal. Above all, it requires us to treat food waste not as a matter of individual guilt, but as a feature of the way our food systems are designed. Success will also depend on changing habits in millions of kitchens, schools and workplaces, a task that is slower than passing any single law.