Reading: Summary, Note & Table Completion: IELTS Academic 9990 (IELTS Academic)

Across the salt pans and gravel plains of the Sahara, the desert ant Cataglyphis fortis forages for the bodies of insects killed by the extreme midday heat, often venturing more than a hundred metres from its nest along a winding, indirect route. Yet when a forager has found food, it does not retrace its outward path; instead it turns and walks in a single straight line directly back to a nest entrance no wider than a few millimetres, in a landscape almost entirely without visible landmarks. This remarkable feat of orientation, known as path integration, has made Cataglyphis one of the most closely studied navigators in the animal kingdom.

Path integration requires an animal to continuously track two things: the direction it has travelled and the distance covered, so that at any moment it can calculate a direct vector back to its starting point. Researchers established that the ant's sense of direction depends on a specialised region of its compound eye that detects the pattern of polarised light scattered across the sky, a pattern invisible to the human eye but which shifts predictably with the sun's position. Even under a mostly overcast sky, a small patch of blue is often enough for the ant to maintain an accurate heading.

Measuring distance proved harder to explain until a set of experiments manipulated the ants' legs directly. Foragers were captured after reaching a feeder, and their legs were either shortened using fine scissors or extended by gluing on stiff bristles, before the ants were allowed to walk home. Ants on stilts consistently overshot the nest entrance, while ants on stumps stopped short of it, in direct proportion to the change in leg length. The conclusion drawn from this work was that Cataglyphis measures distance by counting its own steps, effectively functioning as a built-in pedometer rather than relying on any external cue such as energy expended or time elapsed.

What continues to intrigue biologists is how the ant's tiny brain, containing fewer than a million neurons, integrates these two independent streams of information, compass heading and step count, into a single continuously updated vector, recalculated with every step of a foraging trip that may last less than ten minutes in total.

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The Saharan ant Cataglyphis fortis forages along an indirect route but returns to its nest via a single straight line, a navigational skill called (1) ____________________. To determine direction, the ant relies on a part of its compound eye that detects (2) ____________________ in the sky, a pattern that shifts with the sun's position. To measure distance travelled, researchers experimentally altered the ants' leg length by attaching (3) ____________________ or by shortening the legs with scissors. Ants fitted with longer legs consistently (4) ____________________ the nest entrance, showing that distance is measured by counting its own (5) ____________________ rather than through cues such as energy expended. This step-counting mechanism is often compared to a built-in (6) ____________________. Overall, the ant's brain, which contains fewer than a million neurons, must combine compass heading with step count into a single vector, recalculated throughout a foraging trip lasting under (7) ____________________.

Between 2009 and 2022, several regional water authorities in northern Europe reintroduced Eurasian beavers into upland river catchments as a low-cost method of reducing flood risk downstream. Unlike engineered flood barriers, beavers achieve this passively: by felling small trees and packing branches, mud and stones across a stream channel, a single family builds a dam that can raise the water level behind it by up to a metre, creating a pond that stores rainfall during storms and releases it slowly over the following weeks. A catchment containing a dense network of beaver dams can, according to monitoring data collected over a decade, reduce the height of a downstream flood peak by as much as sixty percent compared with an undammed stretch of the same river.

The ponds created by beaver dams bring benefits beyond flood control. Sediment and agricultural runoff carried by the stream settle in the still water behind each dam rather than being washed straight into rivers further downstream, measurably improving water clarity. The resulting wetland habitat also attracts a wider range of species; surveys of reintroduction sites recorded increases in populations of dragonflies, amphibians and wading birds within only a few years of the beavers' arrival, since the varied depths and slow-flowing margins of a beaver pond suit species that cannot tolerate a fast, uniform river channel.

Reintroduction has not been without friction. Landowners farming close to a river have occasionally objected to beavers felling mature trees or flooding low-lying pasture, and in a small number of cases dams built too near farmland have had to be partially dismantled by wildlife officers. To track the animals' movements and dam-building activity without disturbing them, most reintroduction projects now rely on a network of motion-triggered camera traps positioned along the riverbank, supplemented by occasional live-trapping to fit individual beavers with radio tags. Project managers describe the approach as a compromise: the beavers are left almost entirely to their own devices, while camera-trap footage allows researchers to intervene quickly if a dam threatens nearby property.

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A digital twin is a continuously updated virtual model of a physical structure, built from a combination of the original design data and a live stream of readings from sensors embedded in the structure itself. Unlike a static 3D drawing produced once during construction, a digital twin changes in near real time: as a bridge deck expands in summer heat or a wind-turbine blade flexes under a gust, the corresponding change appears almost instantly in the virtual model, allowing engineers to monitor a structure's condition without physically inspecting it.

The approach was first applied at scale to critical transport infrastructure. In one widely cited case, engineers fitted a century-old steel railway bridge with several hundred strain gauges and accelerometers, instruments that measure, respectively, how much a material stretches under load and how strongly a structure vibrates. Data from these sensors is fed continuously into a computer model that recalculates the stress distributed across every rivet and girder of the bridge, updating the simulation roughly once every second. Engineers responsible for the bridge reported that the digital twin allowed them to identify a developing fatigue crack in a support beam several months before it would have become visible to a human inspector during a routine walkover survey.

Building an accurate digital twin depends heavily on machine learning. Because raw sensor data is noisy and enormous in volume, engineers train pattern-recognition models on years of historical readings so that the software learns to distinguish an ordinary, harmless fluctuation, such as the bridge deck's normal thermal expansion, from an early sign of structural fatigue. Over time, the trained model becomes more accurate at flagging genuine anomalies and produces fewer false alarms, reducing the number of unnecessary physical inspections that maintenance teams must carry out.

Cost is the main obstacle to wider adoption. Retrofitting an existing structure with a dense enough sensor network can cost several million pounds, a sum that is difficult to justify for smaller or less critical assets such as a rural footbridge. For this reason, digital twin technology has so far been concentrated on the highest-value infrastructure, including major road bridges, offshore wind turbines and large dams, where the cost of an unexpected structural failure vastly exceeds the price of continuous monitoring.

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Cloud seeding is a weather modification technique that attempts to increase or redirect precipitation by dispersing substances into clouds that encourage ice crystals or water droplets to form and fall as rain or snow. The technique originated in November 1946, when the American chemist Vincent Schaefer, working at a General Electric research laboratory, discovered that dropping pellets of dry ice into a supercooled cloud caused ice crystals to form almost instantly. Schaefer tested the effect in the field by releasing dry ice from an aircraft over Mount Greylock in Massachusetts, producing a light fall of snow from a cloud that had shown no sign of precipitating on its own.

Soon afterwards, a colleague of Schaefer's, the chemist Bernard Vonnegut, discovered that silver iodide could achieve a similar effect without requiring an aircraft to fly directly into a cloud, because its crystal structure closely resembles that of ice, allowing it to be dispersed from ground-based generators or released as flares at a lower altitude. Silver iodide particles act as nuclei around which supercooled water droplets freeze, and the resulting ice crystals grow heavy enough to fall as precipitation. This discovery made large-scale seeding programmes practical and considerably cheaper to run.

Assessing how well cloud seeding actually works has proved difficult, since researchers can never observe how much rain or snow would have fallen from the same cloud without intervention; controlled trials suggest that seeding may increase precipitation from a treated cloud by around fifteen percent, though the effect varies considerably with local conditions. Despite this uncertainty, China now operates the world's largest cloud-seeding programme, reportedly using it to trigger rain over Beijing in the days before the 2008 Olympic opening ceremony so that the skies above the stadium itself would remain clear. Weather modification has also been used for military purposes: during the Vietnam War, the United States ran a classified programme, Operation Popeye, to extend the monsoon season over supply routes used by opposing forces. Public disclosure of the operation contributed to the 1977 signing of an international treaty, the ENMOD Convention, which prohibits the hostile use of weather modification techniques.

Complete the summary below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

Cloud seeding attempts to increase precipitation by dispersing substances that encourage ice crystals or water droplets to form inside clouds. The technique began in (1) ____________________, when the chemist Vincent Schaefer discovered that dropping pellets of dry ice into a cloud triggered the formation of (2) ____________________. He confirmed the effect in the field by releasing dry ice over (3) ____________________ in Massachusetts, producing snow from a cloud that had not previously been precipitating. A colleague, Bernard Vonnegut, later discovered that (4) ____________________ was equally effective and, unlike dry ice, could be released from ground-based generators. Because judging the technique's effectiveness is difficult, controlled trials indicate that seeding may raise precipitation from a treated cloud by around (5) ____________________. China reportedly used cloud seeding to trigger rain over Beijing before the 2008 Olympic (6) ____________________ so that the stadium itself would stay dry. Disclosure of a covert American military programme, (7) ____________________, which extended the monsoon season during the Vietnam War, contributed to the 1977 signing of an international treaty restricting hostile weather modification.

Yawning is one of the most recognisable involuntary human behaviours, yet it remains one of the least understood. Most people report having experienced 'contagious' yawning: the powerful urge to yawn triggered simply by seeing, hearing, or even reading about another person yawning. Laboratory studies have confirmed the effect is real and measurable, in a typical experiment, participants shown a short video of a stranger yawning repeatedly yawn themselves at roughly three times the rate of participants shown a neutral control video, such as footage of someone smiling.

Two competing explanations dominate current research. The first, the empathy hypothesis, proposes that contagious yawning is linked to an observer's capacity to recognise and share another person's internal state, since brain-imaging studies have found that watching someone yawn activates regions associated with social cognition and mirroring another's actions. Supporting this view, several studies report that susceptibility to contagious yawning is markedly reduced in young children under the age of four, an age at which the broader capacity for empathy is still developing, and is also somewhat reduced in autistic adults, a population in which social-cognitive processing can differ from the general population.

A rival explanation, the brain-cooling hypothesis, argues that yawning primarily serves to regulate the temperature of the brain rather than to communicate anything socially. According to this view, a deep yawn draws a large volume of cooler air into the mouth and increases blood flow to the face and skull, lowering brain temperature by a small but measurable amount. One frequently cited experiment found that participants holding a warm pack against their forehead yawned contagiously far more often after watching a video of yawning than participants holding a cold pack, since a brain that is already running warm has more to gain from the cooling effect a yawn provides.

Neither hypothesis has been fully confirmed, and most researchers who study the phenomenon now suspect that contagious yawning may serve both a thermoregulatory and a social function simultaneously, with the balance between the two shifting according to context, species and even the specific relationship between the yawner and the observer.

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In the 1970s, a group of researchers noticed something curious happening in a memory experiment: participants who had already read a false statement in an earlier session tended to judge that same statement as more believable the second time they encountered it, even though nothing about the statement's actual accuracy had changed. This phenomenon later became known as the illusory truth effect: the tendency for repeated exposure to a claim to increase how true that claim feels, independent of its actual truth value.

Subsequent studies confirmed that the effect does not depend on a person actually believing the statement the first time it was heard. Even statements later shown to be false, and even statements a listener had initially rejected outright, become more convincing on a second or third exposure. Psychologists explain this using a concept called processing fluency: repetition makes a sentence easier to retrieve and recognise, and the brain appears to mistake that ease of processing for a signal of accuracy, since true, familiar information is generally easier to process than unfamiliar, false information.

For decades, one assumption limited how worrying the effect seemed: researchers believed that a person's background knowledge would override it, so a claim contradicting something a person already knew with confidence would resist the fluency illusion. A widely cited 2015 study overturned this assumption. Participants were shown statements they had every reason to know were false, yet repeated exposure still nudged their truth ratings upward, even among participants who could correctly answer the true version of the same fact on a separate quiz. The researchers concluded that fluency can compete with, and sometimes override, stored knowledge rather than simply filling gaps where knowledge is absent.

The practical implications have drawn attention well beyond the laboratory. Fact-checking organisations have had to grapple with an uncomfortable corollary: merely restating a false claim in order to correct it, if done repeatedly, can itself strengthen the claim's familiarity and, paradoxically, its perceived truth. Some communication researchers now recommend that corrections lead with the accurate fact rather than repeating the myth, precisely to avoid reinforcing the fluency that makes false claims feel true.

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Researchers first identified the illusory truth effect after noticing that participants rated a false statement as more (1) ____________________ the second time they read it. The effect persists even for statements a listener had initially (2) ____________________, and it does not require that the person believed the claim on first exposure. Psychologists attribute the effect to processing fluency: repetition makes a sentence easier to (3) ____________________ and recognise, which the brain misreads as a sign of accuracy. It was long assumed that a person's (4) ____________________ would protect them from the effect, but a 2015 study found that repeated exposure still raised truth ratings even among participants who could correctly answer a separate (5) ____________________ on the true version of the fact. Communication researchers now advise that corrections should (6) ____________________ with the accurate fact rather than repeating the myth, to avoid strengthening its familiarity.

When waves approaching a coastline encounter a small island lying a short distance offshore, they do not pass it evenly. Wave energy travelling on a direct path toward the island refracts, or bends, around both ends of the obstruction, while the section of wave front travelling directly behind the island is partially blocked. This creates a comparatively calm, low-energy zone in the water immediately landward of the island, sometimes called a wave shadow, where waves arriving from either side lose much of their force and largely cancel out rather than reinforcing one another.

Because wave energy is what keeps sediment suspended and moving along a coastline, the sheltered wave shadow behaves very differently from the open water on either side of it. Sand and shingle carried by longshore drift (the gradual movement of sediment along a shore, driven by waves striking the coast at an angle) continue travelling steadily past the exposed sections of coastline, but slow down and begin to settle once they enter the calmer water directly behind the island. Over time, repeated deposits of sediment build upward and outward from the seabed, eventually forming a low ridge that breaches the surface at low tide before becoming a permanent bar of sand or shingle.

Once this ridge grows tall enough to remain exposed even at high tide, it forms a continuous strip of land joining the island to the mainland, a landform geomorphologists call a tombolo. A long-term survey near Bellhaven Point tracked one such feature over a fifteen-year period, recording that the bar widened from an initial three metres to over twenty metres as sediment supply from a nearby eroding headland increased. Researchers noted that the tombolo's orientation closely tracked the dominant wave direction recorded that year, confirming that the ridge builds directly along the axis of the wave shadow rather than at a fixed angle to the coast.

Not every offshore island develops a tombolo. Where two islands lie close together and each casts its own wave shadow that overlaps with the other, sediment can instead accumulate into a double-tailed spit rather than a single connecting bar, a variant that coastal engineers say is far less commonly documented than the classic single tombolo.

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Congestion pricing is a policy tool that charges drivers a fee for entering a specified zone, typically a city centre, during periods when traffic volume is highest. The underlying economic principle is that road space is a scarce resource typically used without a price signal, which leads drivers to overconsume it relative to what they would choose if each additional trip carried a visible cost; by attaching a fee to entry during peak hours, planners aim to shift some trips to off-peak times, public transport, or routes outside the priced zone, thereby reducing the total volume of traffic competing for the same limited road space.

The first large-scale, city-wide scheme of this kind began operating in Singapore in 1975, using paper licences displayed on a vehicle's windscreen; this later evolved into a fully electronic system that adjusts the toll amount according to real-time congestion levels rather than a flat daily rate. A more widely studied case is the zone introduced in central London in 2003, which charged a flat daily fee for any vehicle entering the zone between specified hours on weekdays. Within the first year, traffic entering the zone fell by around 15 per cent, and average traffic speeds within the zone rose measurably, reversing a decades-long trend of slowing city-centre traffic.

Revenue raised by congestion charging schemes is rarely permitted to enter a city's general budget; in London, for example, the scheme's operating rules require that net income be reinvested specifically in public transport and road infrastructure improvements, a condition intended to answer the frequent criticism that such schemes function as a disguised general tax rather than a targeted traffic-management measure. Exemptions are also a recurring design feature: emergency vehicles, and in most schemes, registered residents of the priced zone, typically pay a substantially reduced rate rather than the full charge, softening the policy's impact on those who have little practical alternative to driving within the zone.

Critics argue that congestion pricing disproportionately burdens lower-income drivers, who are less able to absorb a flat daily fee regardless of the value of their trip, while wealthier drivers experience comparatively little deterrent effect. Some cities have responded by introducing variable pricing based on a driver's income or vehicle type, though evaluating whether these adjustments meaningfully improve equity while preserving the traffic-reduction benefit remains an active area of transport-economics research.

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Peer tutoring programmes, in which pupils teach other pupils rather than relying solely on an adult instructor, have existed in various forms for centuries, but a specific variant known as cross-age tutoring, pairing an older pupil with a younger one, has attracted particular research interest over the past few decades. Unlike same-age tutoring, where partners are matched within a single class or year group, the age gap in cross-age tutoring establishes a clear and stable status difference between the two roles, which researchers argue reduces the awkwardness or rivalry that can arise when a same-age classmate is cast in an instructional role.

A frequently cited finding from studies of cross-age reading tutoring is that measurable gains are not confined to the younger pupil receiving instruction. The older tutor, who must review and explain material at a more basic level than their own current work, often shows reading-comprehension gains nearly as large as those recorded for the tutee, an outcome researchers attribute to the tutor effect: the act of preparing to teach and then explaining a concept forces a more active and organised review of material than passive re-reading would achieve on its own.

Programme design appears to matter considerably. Structured programmes, in which tutors receive explicit training in specific tutoring techniques and follow a defined script or set of materials for each session, consistently outperform informal arrangements in which older pupils are simply asked to help a younger pupil without guidance. A widely referenced meta-analysis found that structured cross-age reading programmes produced reading-age gains roughly double those of unstructured pairings over an equivalent number of weeks. Session frequency also matters: benefits plateau if sessions run less than twice a week, but show diminishing additional returns beyond three sessions weekly, suggesting a practical optimum rather than a simple more-is-better relationship.

Cost has been a major driver of adoption. Because cross-age tutoring uses existing pupils rather than additional paid staff, schools have implemented large-scale programmes at a fraction of the cost of hiring specialist reading-intervention teachers, which partly explains why the approach has spread rapidly in school systems facing budget constraints despite the additional coordination burden it places on teaching staff who must schedule and monitor the pairings.

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Cross-age tutoring pairs an older pupil with a younger one, unlike (1) ____________________ tutoring, where partners come from the same class or year group. Gains from cross-age reading tutoring are not limited to the tutee: the older tutor also shows gains attributed to what researchers term the (2) ____________________, because preparing to teach forces a more active and (3) ____________________ review of material than passive re-reading. Structured programmes give tutors explicit (4) ____________________ in specific tutoring techniques, and one meta-analysis found they produced reading-age gains roughly (5) ____________________ those of unstructured pairings. Benefits plateau if sessions run less than (6) ____________________ a week. Because the approach uses existing pupils rather than paid staff, schools have run large-scale programmes at a fraction of the cost of hiring specialist (7) ____________________ teachers.

Sociologists studying how people find jobs have long puzzled over an apparent contradiction: the people we see most often, and feel closest to, are often less useful for finding out about new opportunities than people we barely know. A landmark study addressing this question surveyed professional and technical workers who had recently changed jobs through a personal contact, asking each respondent how frequently they had been in touch with that contact before hearing about the position. Contrary to what might be expected, the majority of successful job leads came not from close friends or family, whom the researcher classified as strong ties, but from acquaintances seen only occasionally, classified as weak ties.

The explanation offered for this pattern rests on the structure of social networks rather than on any special quality of acquaintances themselves. Close friends tend to move in the same social circle as we do, meaning that the information they possess about job openings substantially overlaps with information we are likely to have encountered ourselves through other channels. Acquaintances, by contrast, typically belong to a different circle of contacts entirely, one that rarely overlaps with our own; a weak tie therefore functions as a bridge into an otherwise inaccessible pool of information, even though the relationship itself involves far less frequent contact or emotional closeness than a strong tie.

This bridging role gave rise to a broader concept the researcher termed the strength of weak ties, capturing the idea that a network's overall usefulness for spreading novel information depends heavily on how many bridging, low-frequency connections it contains, rather than on the number or intimacy of its closest relationships. Networks composed almost entirely of tightly knit strong ties, the theory predicts, become informationally isolated over time, since the same facts simply circulate repeatedly among people who already largely know them.

Later replications of the original study, conducted in different industries and countries, generally supported the basic pattern, although the size of the weak-tie advantage varied noticeably depending on how tight the local labour market was; in fields with very few employers, even weak ties struggled to surface leads that strong ties had not already found.

Complete the notes below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

Job-Search Networks. Key Findings

• Contacts are classified as either strong ties (close friends/family) or (1) ____________________ (occasional acquaintances)
• Most successful job leads came from (2) ____________________, not strong ties
• Close friends' information substantially (3) ____________________ with information we already have, because they move in the same social circle
• A weak tie acts as a (4) ____________________ into an otherwise inaccessible pool of information
• The researcher's broader concept (which says a network's usefulness for spreading novel information depends on the number of bridging, (5) ____________________ connections it contains) is called the strength of weak ties
• Networks made up mostly of strong ties risk becoming informationally (6) ____________________ over time
• Later replications found the weak-tie advantage varied depending on how (7) ____________________ the local labour market was