Đề luyện IELTS phần Đọc số 10

【標題清單 List of Headings】 i. Scientific proof of an internal step counter ii. The role of close-range senses in home finding iii. The impact of seasonal temperature fluctuations iv. Why chemical trails are ineffective in extreme heat v. Practical applications of insect navigation in technology vi. How desert ants defend their nests from predators vii. Utilizing celestial cues to determine direction viii. The evolutionary history of desert insects ──────── [A] The salt pans of the Sahara Desert represent one of the most extreme environments on Earth. Under the intense glare of the midday sun, ground temperatures can easily exceed 50 degrees Celsius, a threshold that is fatal to almost all living creatures. Yet, this is the precise time when the desert ant (Cataglyphis fortis) emerges from its nest to search for food. Because their time window is extremely limited, speed is of the essence; any delay in finding the nest can result in lethal overheating. For most ant species, navigation is a cooperative effort relying on chemical trails. Workers find a food source and leave a path of pheromones on the ground for their nestmates to follow. However, in the searing heat of the salt pans, this strategy is entirely useless because chemical scents evaporate almost instantly on the hot sand. Consequently, these insects must forage alone, embarking on long, winding journeys in search of wind-blown insect carcasses, and then find their way back to a nest entrance that is often no larger than a tiny hole in the ground. [B] To survive these solitary excursions, the desert ant relies on a sophisticated navigation system known as path integration. This system allows the ant to continuously update its position relative to home, calculating a direct straight-line vector back to the nest at any point during its journey. To do this, the ant must know two things: its direction of travel and the distance it has covered. To determine direction, the ant utilizes a specialized sky-pointing compass. A specific part of its compound eye is highly sensitive to the polarization pattern of sunlight in the upper atmosphere. Even when the sun is blocked by light clouds, this polarized light provides a reliable compass, allowing the ant to determine its orientation with incredible precision. This sky-based orientation system acts as a constant reference point, ensuring that even if the ant turns multiple times while looking for food, it never loses track of where it is facing. [C] While tracking direction is essential, path integration also requires an accurate way to measure distance. To understand how the ants accomplish this, a researcher named Hina conducted a famous experiment. Hina hypothesized that desert ants possess an internal step counter, or pedometer. To test this, her team allowed ants to travel to a food source along a straight channel. Once at the food source, the researchers altered the leg lengths of the ants. Some had their legs lengthened with tiny plastic stilts, while others had their legs shortened to stumps. When released to return home, the ants with longer legs took longer strides and walked past their nest entrance, overshooting the target. Conversely, those with shortened legs stopped short of the nest, underestimating the distance. Crucially, after a night of adjustment, the modified ants adapted to their new leg lengths and were able to calculate the correct distance once again, proving that they measure distance by counting steps. [D] Although path integration is a powerful tool, it is not entirely perfect over long distances, as small errors in direction or step counting can accumulate. As they get closer to the nest, desert ants switch to alternative sensory strategies to pinpoint their final destination. The ants employ their keen sense of smell, detecting specific chemical odors unique to their own nest entrance. Additionally, they use visual landmark cues. They scan the immediate surroundings for recognizable features, such as specific pebbles, cracks in the soil, or sparse desert shrubs. By combining the calculation of path integration with these immediate sensory clues, the ants ensure they do not wander lost in the heat, which would lead to rapid dehydration and death. [E] The remarkable efficiency of the desert ant's navigation system has captured the interest of researchers far beyond the field of biology. Engineers and roboticists are studying these biological algorithms to design autonomous robots. Modern navigation systems, such as GPS, are highly dependent on satellite signals and consume significant amounts of power. In contrast, the desert ant navigates complex environments with a brain smaller than a pinhead and minimal energy consumption. While fully commercialized ant-inspired robots are still in development, researchers have already built prototypes that can navigate outdoor spaces successfully using only polarized light sensors and step-like distance calculations. This research demonstrates that millions of years of natural selection can offer elegant, low-power solutions to modern technological challenges.

Glaciers are often envisioned as static, silent monoliths of ice, yet they are among the most dynamic geological agents on Earth. As these massive ice sheets move slowly gravity-ward, their immense weight exerts extraordinary pressure on the underlying bedrock. This movement acts like giant sheets of sandpaper, grinding rocks into an ultra-fine powder known as "glacial flour." Unlike standard river silt, which consists of larger sand and clay particles that settle rapidly, glacial flour is composed of microscopic mineral fragments. Because these particles are so minute, they can remain suspended in water columns for extended periods. This suspension scatters light in a unique way, giving glacial lakes and fjords their distinctive, milky-turquoise appearance. The journey of glacial flour begins in subglacial channels where meltwater sweeps the fine dust from beneath the ice. This nutrient-rich slurry is carried downstream into coastal fjords and eventually out to the open ocean. Oceanographer Tomas Ekström has spent decades tracking this mineral transport in the subpolar North Atlantic. Ekström’s field observations indicate that while heavier coastal sediments drop out of suspension almost immediately, glacial flour can be transported hundreds of kilometers by ocean currents. This long-distance transport is ecologically significant because the powder is rich in bioavailable minerals, most notably iron, phosphorus, and silica. In the vast expanses of the open ocean, these specific elements are often exceptionally scarce, limiting the productivity of marine life. The ecological impact of this mineral transport is most visible in the response of phytoplankton—microscopic, single-celled organisms that form the foundation of the marine food web. Like terrestrial plants, phytoplankton require sunlight and nutrients to photosynthesize. In several regions of the world’s oceans, particularly the Southern Ocean, there is an abundance of major nutrients like nitrogen but a severe deficit of dissolved iron. This deficit creates a biological bottleneck, preventing phytoplankton from thriving. When glacial flour enters these "high-nutrient, low-chlorophyll" zones, it acts as a highly effective natural fertilizer. The sudden influx of iron and other minerals triggers rapid population explosions known as phytoplankton blooms, which can cover thousands of square kilometers and support entire marine ecosystems, from krill to apex predators. Beyond feeding marine life, these blooms play a crucial role in regulating Earth’s climate through carbon sequestration. During photosynthesis, phytoplankton absorb carbon dioxide from the atmosphere. When these organisms die, a small but significant fraction of their biomass sinks to the abyssal depths of the ocean floor, effectively locking away carbon for centuries—a mechanism referred to by oceanographers as the "biological pump." Geochemist Ingrid Vance has reconstructed ancient climate regimes by analyzing deep-sea sediment cores. Vance’s findings suggest that during the last glacial maximum, approximately 20,000 years ago, dry conditions and strong winds swept vast amounts of glacial dust across the globe into the oceans. This intense wind-borne fertilization supercharged the biological pump, drawing down atmospheric carbon dioxide levels and locking the planet into a prolonged cold state. In the modern era, the dynamics of glacial flour are shifting rapidly due to anthropogenic climate change. As global temperatures rise, polar glaciers and ice sheets are melting at an accelerated pace. In the short term, this increased melting has amplified the discharge of meltwater, flushing unprecedented volumes of glacial flour into subpolar seas. However, this surge may be temporary. Hydrological models suggest that once glaciers retreat past a critical inland threshold, meltwater streams will no longer discharge directly into the ocean. Instead, they will deposit their sediment loads in newly formed inland lakes, cutting off the marine supply of glacial nutrients and potentially destabilizing offshore fisheries that rely on the nutrient influx. Furthermore, the presence of glacial flour in coastal ecosystems is not entirely beneficial; it presents a complex ecological trade-off. While the minerals stimulate offshore productivity, the high turbidity, or cloudiness, caused by suspended particles in shallow coastal waters can be detrimental. Thick plumes of glacial flour block incoming sunlight, severely restricting the growth of kelp forests and other benthic marine plants that require light for survival. Additionally, the abrasive mineral dust can clog the delicate feeding structures of filter-feeders, such as bivalves and sponges, disrupting local food webs. As researchers continue to study these processes, it becomes increasingly clear that glacial flour is a powerful, yet sensitive, regulator of both marine biodiversity and global climate.

【配對清單 研究者】 A. Tomas B. Aisha C. Rajiv ──────── 【標題清單 List of Headings】 i. The role of symbolic exchange in prehistoric alliances ii. An administrative model of social control and its shortcomings iii. The technological shift from hollow clay envelopes to flat tablets iv. A ritualistic interpretation and the limits of speculative archaeology v. How agricultural expansion necessitated early counting devices vi. A decentralized pathway to script backed by physical distribution ──────── The transition from prehistory to history is conventionally marked by the invention of writing. In the Fertile Crescent of ancient Mesopotamia, this monumental shift did not emerge as a sudden stroke of literary genius, but rather from a humble, millennia-long reliance on small, geometric clay objects. These artifacts, known as tokens, first appeared around 8000 BCE and served as a physical recording system. A sphere might represent a specific quantity of grain, while a cylinder stood for a jar of oil. By manipulating these physical counters, early agricultural communities could keep track of their communal stores. However, the exact social dynamics that drove this system to evolve into the complex cuneiform writing of the late fourth millennium BCE remain a subject of intense academic debate. [A] The dominant narrative in twentieth-century archaeology, championed by scholars such as Tomas, positions the token system as a direct precursor to coercive state administration. According to Tomas, the proliferation of specialized tokens—incised with intricate lines and patterns—coincided with the rise of the first urban centers, such as Uruk. Tomas argues that these tokens were not mere memory aids for egalitarian farmers, but rather instruments of systemic control wielded by a nascent ruling class to register tribute, enforce taxation, and organize conscripted labor. While this administrative model elegantly explains the correlation between urban growth and record-keeping complexity, it is perhaps too eager to project modern bureaucratic structures onto the ancient past. It assumes a level of centralized authority that early Mesopotamian polities, which were still highly fluid and negotiated, likely did not possess. By viewing every clay token through the lens of state surveillance, this perspective overlooks the possibility of cooperative, non-hierarchical economic management. [B] Seeking to redress this administrative bias, Aisha offers an alternative anthropological reading, proposing that early tokens served a dual purpose that was deeply embedded in social rituals. Aisha argues that before tokens were co-opted by temple elites for tax collection, they functioned as symbolic devices within communal gift-giving networks and seasonal feasts. In this view, exchanging a clay representation of an animal was not a sterile transaction, but a highly ritualized act that cemented alliances and reinforced reciprocal social obligations between clans. While Aisha's hypothesis provides a welcome humanistic counterweight to purely economic models, it relies heavily on ethnographic analogies that are difficult to verify. The physical evidence—thousands of virtually identical clay shapes excavated from domestic refuse heaps—tends to support a more pragmatic, daily utility. Interpreting the spiritual or symbolic intentions of prehistoric actors from mute clay remains a highly speculative endeavor, and researchers must exercise caution before mapping complex ritualistic frameworks onto utilitarian tools. [C] A more compelling resolution to the mystery of how tokens evolved into script is found in the work of Rajiv, who focuses on the physical containment of these counters. Around 3400 BCE, administrators began enclosing tokens inside hollow clay spheres called bullae. To identify the contents without breaking the spheres, scribes impressed the outer surface of the wet clay with the tokens themselves before sealing them. Rajiv argues that this practice made the physical tokens redundant; eventually, scribes realized they could simply draw the shapes of the tokens directly onto flat clay tablets, giving birth to the earliest proto-cuneiform writing. Crucially, Rajiv's analysis suggests that this transition was not a top-down revolution mandated by a centralized palace elite, but a decentralized, bottom-up adaptation driven by regional trade networks. The author of this text finds Rajiv's model highly persuasive, as it is corroborated by recent excavations showing that early tablets were distributed across wide geographic areas, far beyond the immediate control of major dynastic centers. Ultimately, the journey from clay tokens to cuneiform script illustrates a profound shift in human cognitive capacity. What began as a concrete, three-dimensional representation of a physical asset became a two-dimensional abstract symbol capable of expressing not just quantities, but language itself. While debate will continue regarding the socio-political catalysts of this evolution, it is clear that the humble medium of clay did more than record transactions; it fundamentally restructured how human societies organized their shared reality.