IELTS Academic Reading Practice Test 23

The discovery of penicillin is so frequently cited as a triumph of accidental observation that the more interesting aspects of its history are obscured. The story habitually begins on a September morning in 1928, when the Scottish bacteriologist Alexander Fleming returned to his cluttered laboratory at St Mary's Hospital in London after a fortnight's holiday and noticed that one of his bacterial culture plates had become contaminated with mould. Around the bluish-green colony of fungus, the colonies of Staphylococcus had been dissolved, leaving a clear ring. Fleming, then forty-seven, recognised that the mould was producing a substance capable of killing bacteria, and went on to publish his observations the following year in the British Journal of Experimental Pathology.

What is less often emphasised is that Fleming was by no means the first to notice the antibacterial properties of moulds. Folk practitioners across Europe had applied mouldy bread to wounds for centuries, and several nineteenth-century scientists, including Joseph Lister and John Tyndall, had observed similar effects in laboratory settings without recognising their full significance. Fleming's particular contribution lay not in being the first to observe the phenomenon but in undertaking systematic experiments to characterise the substance, which he initially called "mould juice" and later, more elegantly, penicillin. He identified the mould as a member of the genus Penicillium and demonstrated that its product was active against a wide range of pathogenic bacteria, while remaining harmless to laboratory animals.

Despite the apparent promise of his findings, Fleming struggled for nearly a decade to convert penicillin into a usable therapy. The mould produced its active substance in only trace quantities, and the resulting solution proved chemically unstable, losing potency within days of preparation. After a series of frustrating experiments, Fleming largely abandoned his attempts to develop penicillin as a drug, although he continued to use it occasionally as a laboratory tool for identifying bacterial species. The transformation of penicillin into the most consequential medicine of the twentieth century awaited the intervention of a different team of researchers.

That team assembled at the Sir William Dunn School of Pathology in Oxford in the late 1930s. Its leaders were the Australian pathologist Howard Florey and the German-born biochemist Ernst Chain, who had fled Berlin in 1933 after the rise of the National Socialists. Together with their younger colleague Norman Heatley, they read Fleming's neglected papers and resolved to investigate penicillin systematically. The Oxford team's breakthrough came not from a moment of insight but from sustained engineering ingenuity. Heatley devised methods of producing the mould in shallow ceramic vessels and extracting its active ingredient using a technique called countercurrent distribution, which allowed penicillin to be concentrated without destroying it.

By 1941, the team had produced enough purified penicillin to attempt the first human trial. The patient was a forty-three-year-old policeman, Albert Alexander, who had developed a severe streptococcal infection from a thorn scratch and was on the verge of death. Within twenty-four hours of receiving penicillin, his condition improved dramatically. However, the supply of the drug, painstakingly extracted from cultures grown in everything from milk bottles to bedpans, soon ran out. Florey's team even attempted to recycle the penicillin by collecting it from the patient's urine, but Alexander relapsed and died a few weeks later. The trial nevertheless demonstrated beyond doubt the extraordinary therapeutic potential of the substance.

The scaling problem fell, by historical accident, to American industry. With Britain under wartime bombardment, Florey travelled to the United States in 1941 and persuaded the Northern Regional Research Laboratory in Peoria, Illinois, to undertake the work. American researchers identified a far more productive strain of the Penicillium fungus on a mouldy cantaloupe purchased in a local market, developed deep-tank fermentation techniques that increased yields a thousandfold, and by 1944 had ramped up production in time for the Allied invasion of Normandy. Penicillin saved an estimated 12 to 15 percent of Allied wounded who would otherwise have died of infection. After the war, mass production drove the price down by approximately 99 percent within five years.

Fleming, Florey, and Chain shared the Nobel Prize in Physiology or Medicine in 1945, although public imagination has tended to focus on Fleming alone, partly because his story of accidental discovery fits a particular narrative of scientific romance. The reality, as Florey was always at pains to emphasise, was that the development of penicillin required not merely a fortunate observation but more than a decade of unglamorous chemical, biological, and engineering work. The lesson, as one historian of medicine has put it, is that scientific breakthroughs typically depend on the cumulative labour of many individuals, often working in obscurity, who together transform a curious observation into a tool capable of changing the world.

A Honey bees are extraordinary navigators. A foraging worker may travel up to ten kilometres from her hive in search of flowers, locate her nestmates returning to a small entrance hole, and convey precise information about the position of profitable nectar sources to other foragers using a coded body movement known as the waggle dance. These feats are accomplished with a brain weighing under one milligram and containing fewer than a million neurons, a fraction of the neural hardware available even to a simple vertebrate. The mechanisms underlying bee navigation have therefore attracted intense interest from biologists, ethologists, and roboticists alike, since any system capable of such performance on such limited resources offers important lessons for the design of autonomous machines.

B The pioneering investigations of honey bee behaviour were carried out by the Austrian zoologist Karl von Frisch, who began studying the species in the 1910s and continued for more than half a century. Through painstaking observation of bees in glass-walled hives, von Frisch deciphered the geometry of the waggle dance and demonstrated, in a series of landmark experiments, that bees can communicate the distance and direction of distant food sources by varying the orientation and duration of the dance. The angle of the dance relative to vertical encodes the direction of the food source relative to the sun; the duration of the central waggling phase encodes the distance. Von Frisch was awarded the Nobel Prize for this work in 1973, alongside Konrad Lorenz and Niko Tinbergen.

C For bees to communicate direction using the sun's position, they must be able to track the sun's apparent movement across the sky throughout the day. Experiments by James Gould at Princeton University in the 1980s demonstrated that bees achieve this through an internal clock combined with what biologists call a "sun ephemeris" — a learned mental model of how the sun's azimuth changes with time and latitude. Bees raised under a regime of artificial sunlight can be tricked into pointing their dance to the wrong cardinal direction, confirming that the relationship is learned during the first few days of foraging rather than genetically fixed. On overcast days, bees typically switch to using polarised light from the sky, perceived through specialised photoreceptors at the top of their compound eyes.

D While the sun compass provides a reliable directional reference, bees also need a means of estimating how far they have flown. Recent research by Mandyam Srinivasan and his colleagues at the Australian National University has shown that bees measure distance not by counting wingbeats or monitoring elapsed time, but by integrating the rate of visual flow across their compound eyes. When the team trained bees to fly through tunnels lined with patterns of varying contrast, they found that bees flying through high-contrast tunnels indicated shorter distances in their subsequent waggle dances than bees flying the same physical distance through low-contrast tunnels. The mechanism, known as optic-flow odometry, has since been mimicked in the navigation systems of several experimental flying robots.

E Beyond these basic compass and odometric systems, bees develop a remarkably detailed cognitive map of their foraging landscape. Tracking studies using harmonic radar transponders, developed by Joseph Riley and his colleagues at Rothamsted Research in the early 2000s, have shown that bees displaced from their normal foraging route can plan a novel return path home, indicating that they remember the spatial relationships between landmarks rather than merely retracing learned routes. This finding overturned an earlier consensus, dating back to insect physiologist Donald Griffin, that the navigation of bees was entirely a matter of stimulus-response associations. The cognitive sophistication implied by such map-like behaviour places bees, in this respect at least, alongside many vertebrates.

F Olfactory cues also play a substantial role in fine-scale navigation, particularly during the final approach to a flower. Honey bees can detect a wide range of plant volatiles at concentrations as low as a few parts per billion, and they associate specific scents with profitable nectar sources during early foraging trips. Karl von Frisch's later experiments showed that the same scent presented at the hive entrance significantly enhances the likelihood that recruited foragers will locate the target flower, suggesting that the waggle dance does not fully specify a destination on its own but works in concert with olfactory information carried back by the dancer.

G Magnetic field sensitivity has also been documented, although its role in everyday navigation is uncertain. Researchers at the State University of New York demonstrated in 1985 that bees deprived of their normal sun and visual cues could still orient themselves with reference to the Earth's magnetic field, possibly through magnetite crystals identified in the abdomen of foraging workers. The relative contribution of this sense to ordinary foraging trips remains a matter of active investigation, and recent work suggests it may be most important during the initial orientation flights of young bees and during long-distance migration in related species such as the European hornet.

H The implications of bee navigation research extend well beyond pure biology. Engineers at the Centre for Robotics at the University of Sheffield have built insect-inspired robots that use optic-flow odometry to navigate cluttered indoor environments, with applications ranging from disaster response to environmental monitoring. Bee-inspired algorithms are also being explored in driverless vehicles, particularly for situations in which conventional GPS is unavailable or unreliable. As the costs of climate change and habitat loss increasingly threaten wild bee populations, the urgency of understanding the cognitive ecology of these tiny insects has perhaps never been greater.

A For more than five hundred years, the heavy wheeled plough was the defining technology of English agriculture. Introduced from the continent in the early Anglo-Saxon period, sometime between the sixth and eighth centuries, it transformed the productive capacity of the kingdom's heavy clay lowlands and reshaped the social organisation of the countryside. Yet by the fourteenth century, the heavy plough was already in retreat in many regions, and by the end of the seventeenth century it had been substantially replaced across most of England by a lighter, more flexible implement of Dutch origin. Understanding its decline offers a vivid case study in how environmental, economic, and demographic forces combine to render even highly successful tools obsolete.

B The Anglo-Saxon heavy plough — known in contemporary Latin sources as the carruca — was a substantial piece of equipment. It comprised an iron coulter that cut vertically into the soil, a flat horizontal share that sliced the soil from underneath, and an angled mouldboard that turned the cut sod neatly over. Mounted on a wheeled frame to control depth and typically drawn by a team of six or eight oxen, the carruca could break the dense clay soils of the English Midlands that had proved largely impenetrable to the lighter, frameless ploughs of the late Roman period. The historian Lynn White Jr., in his influential 1962 study Medieval Technology and Social Change, argued that the heavy plough should be regarded as one of the principal motors of the rise of medieval European civilisation.

C The plough's voracious requirements for draught animals had far-reaching social consequences. Few peasant households could afford a full team of oxen on their own, and the practical solution was the open-field system of communal cultivation, in which villagers pooled their animals and ploughed long, narrow strips of land that wound through the parish landscape. The shape of these strips — typically a furlong, or roughly 220 yards, in length — was determined by the distance a team of oxen could pull the heavy plough before requiring rest. The open-field system created intense bonds of cooperation among medieval villagers, but it also produced the rigid, collectively enforced agricultural calendar that came to define the rural year.

D The early signs of trouble emerged in the fourteenth century. The Black Death of 1348-49, which killed approximately a third of the English population, dramatically reduced the rural labour force and made it difficult to assemble the large teams of oxen and human ploughmen required by the carruca. Surviving peasants increasingly demanded higher wages and individual tenancies, undermining the cooperative basis of open-field agriculture. Climate change also played a role: the onset of what climate historians call the Little Ice Age, beginning around 1300, made heavy clay soils colder and wetter, lengthening the period each year during which the plough was difficult or impossible to operate.

E A more profound challenge arose during the sixteenth and seventeenth centuries with the spread of new agricultural practices from the Low Countries. Dutch farmers, working on the soft, alluvial soils of their delta landscapes, had developed a lighter, single-handed plough — sometimes called the Brabantine plough — that required only one or two horses and could be operated by a single farmer without an attendant ploughboy. When first introduced to the eastern counties of England in the late sixteenth century, the Dutch plough met considerable resistance. Manorial courts complained that it cut too shallowly to bury weeds effectively, and many ploughmen mistrusted any implement so much lighter than the carruca.

F What ultimately rendered the heavy plough obsolete was the gradual replacement of oxen by horses. Horses, although more expensive to feed, walked roughly fifty percent faster and could be worked for longer hours each day. The widespread adoption of the horse collar, which allowed an animal to pull from its shoulders rather than its windpipe, made it possible to harness horses safely and efficiently. The agricultural reformer Walter Blith argued in his 1652 treatise The English Improver Improved that a competent farmer with a Dutch plough and two horses could cultivate as much land in a week as a traditional open-field team with eight oxen.

G The economic logic was reinforced by the political logic of enclosure. As wealthy landowners increasingly consolidated open-field strips into compact, hedged holdings, the cooperative basis of the heavy plough's continued use disappeared. By the early eighteenth century, the carruca survived only in pockets of remote upland England and parts of Wales, while across the lowlands the lighter, faster, horse-drawn plough had become standard. The transition was largely complete by the time the first iron ploughs appeared in the 1730s.

H Historians have continued to debate the broader significance of the heavy plough and its decline. Some scholars, in the tradition of Lynn White, view the carruca as a transformative technology whose impact rivalled that of any later mechanical invention. Others, including the economic historian Joan Thirsk, have argued that White overstated the case and that the heavy plough was merely one element in a wider package of medieval agricultural innovation that also included the three-field rotation system, the windmill, and improved breeds of sheep. Whatever the verdict, the story of the carruca demonstrates that the dominance of a single technology, however total it may appear in its heyday, is rarely permanent. Changes in climate, demographics, animal husbandry, and political economy can all conspire to displace even the most successful tool.