IELTS Academic Reading Practice Test 20

A The idea that plants possess intelligence has been one of the most contested propositions in modern biology. The word intelligence, ordinarily reserved for systems that learn, adapt, and respond purposefully to their environment, has traditionally been considered applicable only to animals with nervous systems. Plants, lacking neurons and brains, were until relatively recently assumed to be essentially passive organisms responding mechanically to environmental cues. Research over the past three decades has, in researchers' view, steadily eroded this view, revealing plant behaviours that meet many of the same criteria used to identify intelligence in animals. The vocabulary of plant behaviour has accordingly shifted, with terms such as signalling, decision-making, memory, and learning now widely used in the technical literature, often within careful definitions that explicitly avoid claims about plant consciousness.

B Plants are widely said to be now known to sense and respond to a wide range of environmental signals: light direction and quality, gravity, mechanical contact, neighbouring plants of the same and other species, attack by herbivores, and underground chemical signals from neighbouring root systems and soil microbes. The Italian plant physiologist Stefano Mancuso, whose work at the University of Florence has been influential in this debate, has argued that plant behaviours generally show the integration, computation, and decision-making that justify the label intelligence even though they occur without neurons. Mancuso has emphasised that intelligence in this functional sense is widely distributed throughout plant tissues rather than localised in any single organ.

C Among the most studied plant behaviours is the response to herbivore attack. When a caterpillar begins eating a tomato leaf, the plant releases volatile chemical signals that travel through the air to neighbouring leaves and even to neighbouring plants. The signals typically trigger the production of bitter or toxic compounds that deter further feeding. Some plants are widely said to release additional signals that attract predatory wasps which prey on the herbivore — what some researchers describe as a sort of biological intercom system in which a plant under attack effectively calls for help. The signals are specific: different herbivores generally produce different response profiles, suggesting plants distinguish between attackers. In ecological terms the result is widely said to be a remarkably finely-tuned set of defences that scale up or down with the specific threat being faced.

D Root systems have, in researchers' view, proved particularly intriguing. The tips of plant roots reportedly show responses to obstacles, nutrient gradients, and the chemical signatures of other roots that have been compared to simple problem-solving. Plants of the same species typically reduce root growth in the immediate vicinity of close kin, sharing resources rather than competing aggressively — behaviour that is widely said to resemble the kin-favouring behaviours documented in social animals. Different species of plant reportedly interact via underground networks of mycorrhizal fungi, exchanging nutrients and warning signals across what some researchers have memorably called the wood-wide web. The discovery of these underground networks has prompted substantial reconsideration of how forest ecosystems function as integrated communities rather than collections of independent trees.

E Critics object that calling these behaviours intelligence is, in their view, stretching the word past usefulness. Plants reportedly do not appear to plan, to have subjective experience, or to learn in ways that resemble animal cognition. Suzanne Simard, whose work on mycorrhizal communication has been particularly influential, has been criticised by some plant biologists for what they see as anthropomorphising root behaviour. The defenders of plant intelligence generally respond that intelligence is not a single thing but a spectrum of capacities, and that resistance to applying the term to plants is, in their view, itself a reflex shaped by long-standing animal-centred assumptions.

F The question of whether plant intelligence exists in some meaningful sense is, in the end, widely said to be partly semantic. What is no longer in dispute is that plants are far more capable, responsive, and communicative than the passive picture of earlier biology assumed. Whether or not the word intelligence is the right label, the practical implications for ecology, agriculture, and conservation are widely regarded as substantial — and the debate has, in researchers' view, had the secondary effect of pushing biological research toward better recognition of capacities that exist outside the animal kingdom.

A The optical telescope, first applied to astronomy by Galileo Galilei in 1609, is widely said to have transformed humanity's understanding of its place in the universe within a single generation. Before the telescope, the planets were regarded as tiny points of light, the Milky Way was thought by many to be a continuous glow, and the moon was widely assumed to be a perfect, polished sphere. Galileo's observations through a small refractor revealed mountains and craters on the moon, four satellites orbiting Jupiter, phases of Venus, and the resolution of the Milky Way into countless individual stars. His findings, published in the Sidereus Nuncius of 1610, are widely said to have provided powerful new observational support for the Copernican system at a time when the heliocentric model was still strongly contested.

B Galileo's telescopes used a convex objective and a concave eyepiece, an arrangement now called the Galilean configuration. The German astronomer Johannes Kepler proposed in 1611 a modified design using two convex lenses, which gave a wider field of view at the cost of inverting the image. Kepler's design dominated astronomical telescopes thereafter and is widely said to be the basis of nearly all subsequent refracting designs. Larger refractors with longer focal lengths produced sharper images but reached practical and optical limits — the 102-centimetre Yerkes telescope of 1897 in Wisconsin is the largest refractor ever built for science. The physical limits of refractors are widely said to follow from the sheer weight of large lenses, which can only be supported around their edges, and from the unavoidable colour-fringing that single-glass lenses introduce.

C The reflecting telescope, invented by Isaac Newton in 1668, used a curved mirror rather than a lens to focus light. Reflectors are widely said to avoid chromatic aberration, the colour-fringing effect that limits refractor performance, and allow much larger apertures to be constructed. Most large modern telescopes are reflectors of one design or another. The 5-metre Hale Telescope at Palomar Observatory in California, opened in 1948 and widely regarded as the world's largest for nearly three decades, established the segmented and active-optics designs that have made even larger telescopes possible. Subsequent improvements in mirror coatings, computer-controlled support systems, and adaptive-optics correction of atmospheric distortion are widely said to have allowed ground-based reflectors to approach the performance once thought achievable only from space.

D The development of radio astronomy from the 1930s added an entirely new dimension. Karl Jansky's 1932 discovery that radio signals reached Earth from beyond the solar system is widely said to have led to the construction of dedicated radio telescopes including the 76-metre Lovell at Jodrell Bank in 1957 and, eventually, arrays of antennas linked interferometrically to achieve angular resolution far beyond any single dish. The Very Large Array in New Mexico and the Atacama Large Millimeter Array in Chile generally illustrate the mature form of this approach, with the latter widely said to be capable of probing star and planet formation in unprecedented detail. The international 2019 first-ever direct image of a black hole, produced by combining data from radio telescopes spread across several continents, is widely cited as an iconic demonstration of what global interferometry can now achieve.

E Space-based telescopes have, in researchers' view, opened the parts of the electromagnetic spectrum that the atmosphere blocks. The Hubble Space Telescope, launched in 1990 and serviced multiple times by the Space Shuttle, is widely said to have transformed observational astronomy across visible and ultraviolet wavelengths despite an initially miscast primary mirror that required corrective optics. The James Webb Space Telescope, launched in 2021 and operating at a Lagrange point well beyond the moon, has, in researchers' view, extended sensitive infrared observation in ways that allow direct imaging of exoplanets and observation of the most distant galaxies whose light is redshifted into the infrared.

F The largest ground-based telescopes now under construction generally continue the trend toward giant segmented mirrors. The Extremely Large Telescope being built by the European Southern Observatory in Chile is widely said to have a 39-metre segmented primary; the Thirty Meter Telescope in Hawaii and the Giant Magellan Telescope in Chile reportedly complete a generational set of giant optical facilities. The technological challenge has, in researchers' view, shifted from building larger glass to engineering systems for actively shaping mirror surfaces, compensating for atmospheric distortion, and combining light from multiple telescopes interferometrically.

A Rare earth elements are widely said to be a group of seventeen metallic elements whose unusual electronic structures give them properties of central importance to modern technology. Despite the name, they are not particularly rare in the Earth's crust — cerium, for example, is said to be more abundant than copper. The elements are difficult to extract economically, however, because they reportedly occur in low concentrations and almost always together, requiring extensive chemical separation to isolate individual elements. The combination of widespread occurrence, scarce processing capacity, and concentrated production has, in researchers' view, made rare earths a recurring subject of supply-security concern. Despite repeated calls in policy circles for diversification, the geographic concentration of refining capacity has proved persistent over decades.

B Modern applications depend heavily on rare earths. Neodymium and dysprosium are widely said to be essential for the strong permanent magnets used in electric-vehicle motors, wind-turbine generators, and consumer electronics. Europium and terbium are used in fluorescent lighting and television displays. Erbium amplifies signals in fibre-optic communication. Lanthanum is used in petroleum cracking catalysts. Yttrium and cerium are used in oxygen sensors. The decarbonisation of electricity and transport will, according to many analysts, dramatically increase demand for several of these elements over the coming decades. Forecasts of demand for neodymium-dysprosium magnets in particular reportedly project a multi-fold increase by the 2040s if planned electrification trajectories are maintained across major economies.

C Production of rare earths has been overwhelmingly concentrated in China since the 1990s. At various points China is widely said to have supplied between 80 and 97 percent of global production, with substantial control over both mining and the more technically demanding separation and refining steps. The strategic implications became visible during a 2010 episode in which export restrictions on rare earths from China to Japan disrupted Japanese electronics manufacturing. Subsequent investment in alternative production has, in researchers' view, progressed unevenly: mines in California, Australia, and Vietnam have been redeveloped, and significant new projects are under way in Africa and Canada, but separation and refining capacity outside China is widely said to remain limited. The slow re-establishment of refining capacity is widely said to reflect both the long lead times of permitting and construction and the environmental costs that earlier rounds of overseas production chose to avoid.

D The environmental costs of rare-earth extraction are widely regarded as substantial. Conventional processing produces large volumes of acidic tailings, radioactive waste from thorium and uranium that often accompany the deposits, and contamination of water and soil. The Baotou mining region in northern China is widely said to have become a notorious example, with local residents suffering documented health effects from decades of inadequately regulated extraction. Improving environmental controls has, in researchers' view, been a major focus of recent investment, both in China and in newer producing countries.

E Recycling rare earths from end-of-life products has, according to many analysts, emerged as an increasingly important strategy. Permanent magnets from used wind turbines and electric vehicles, in particular, reportedly contain commercially significant quantities of neodymium and dysprosium in concentrated form. Recovery technologies including hydrometallurgical processes and direct magnet recycling have been demonstrated at pilot scale. Several startups including Hyper Solutions, Phoenix Tailings, and Geomega are widely said to have brought commercial-scale recycling operations to market in the past five years. Substitution research — finding alternative materials that achieve similar performance without rare earths — has also accelerated, although for high-performance magnets in particular, no full substitute has yet emerged.

F Deep-sea sources have, in researchers' view, attracted speculative interest. Polymetallic nodules on the Pacific seafloor and metalliferous muds in certain ocean regions are said to contain rare earths in substantial quantities, although extraction would face technical, environmental, and regulatory challenges. The International Seabed Authority is widely said to be in the process of finalising rules for commercial deep-sea mining, with the outcome likely to determine whether ocean-floor extraction proceeds. Environmental groups are campaigning for a moratorium on deep-sea mining, citing the slow recovery rates of deep-ocean ecosystems and the largely unknown consequences of disturbing sediments that have lain undisturbed for millennia.

G The economic geography of rare earths is, according to many industry analysts, bound up with the broader story of strategic minerals and the transition to clean technology. As demand grows, supply security will, in researchers' view, probably continue to drive investment in alternative production sources, in recycling, and in substitution research. The political question of whether the international supply chain returns to greater geographic diversity, or instead remains concentrated, is widely said to substantially shape both the geopolitics of strategic minerals and the cost of the clean-energy transition.