IELTS Academic Reading Practice Test 10

A Vertical farming — the cultivation of crops in stacked indoor environments under fully controlled conditions — has progressed from speculative idea to a meaningful, if niche, segment of food production over the past fifteen years. The basic concept is straightforward: by growing plants in racks several layers deep, with artificial lighting and precisely managed water and nutrients, a footprint of a few hundred square metres can produce yields equivalent to many hectares of conventional farmland. The intellectual roots of the idea are usually traced to the American ecologist Dickson Despommier, who began promoting the concept in the early 2000s as a response to the urbanisation of global food demand. The framing has, in many analysts' view, persuaded a generation of urban planners and food-system researchers to consider indoor cultivation as a legitimate component of future agriculture rather than a hobbyist curiosity.

B Commercial-scale operations now exist in dozens of countries, with particular concentrations in Japan, the United Kingdom, the Netherlands, the United States, and the United Arab Emirates. The crops that have proved economically viable so far are almost entirely leafy greens — lettuces, herbs, microgreens, and increasingly strawberries — which combine high market prices, short growing cycles, and low light requirements. Staple grains and root vegetables, which require either much more energy or vastly more space than vertical farms can economically provide, remain firmly in the domain of traditional agriculture. The narrow crop range has attracted critique from those who argue that vertical farming addresses only the high-margin perimeter of global food production rather than its caloric core.

C The most important enabling technology has been the light-emitting diode. Earlier indoor agriculture relied on high-pressure sodium lamps that wasted most of their energy as heat. The development of efficient LEDs tuned to plant-friendly wavelengths — primarily red and blue, which match the absorption peaks of chlorophyll — has roughly halved electricity consumption per kilogram of produce. Photoperiod control and tailored light spectra allow growers to manipulate plant morphology and flavour with a precision impossible in field conditions. The capacity to tune light recipes for specific cultivars and growth stages has transformed the practical economics of indoor cultivation over the past decade.

D The energy use of vertical farming remains its central economic challenge. A typical vertical farm uses 30 to 50 kilowatt-hours of electricity per kilogram of lettuce produced, against essentially zero for a field-grown equivalent. As long as electricity is generated primarily from fossil fuels, the carbon footprint of indoor-grown leafy greens often exceeds that of field-grown produce trucked over modest distances. The economics improve sharply where electricity is cheap and renewable, where land prices are extreme, or where extreme climates make field cultivation impractical — conditions found in cities like Singapore, Tokyo, and Dubai where vertical farming has consequently advanced fastest. The geographic concentration reflects the underlying economic logic: vertical farming flourishes where its costs are subsidised by local conditions that make conventional alternatives more expensive still.

E Water consumption is the area in which vertical farming most clearly excels. Hydroponic and aeroponic systems, which deliver nutrient-rich water directly to roots and recirculate the runoff, can reduce water use by 90 to 95 percent compared with field agriculture. Pesticide use is similarly reduced or eliminated, because the controlled environment can be sealed against insect pests. The result is a product that is essentially free of agricultural chemical residues and that requires no washing for safety — although consumers continue to wash it from habit. The combination of water efficiency and pesticide elimination is widely said to be the strongest single argument for indoor cultivation in regions where water scarcity is a dominant agricultural constraint.

F The future of the industry remains contested. Optimists project vertical farming as a major component of urban food systems by mid-century, especially in regions where climate change has made traditional agriculture unreliable. Sceptics point to repeated commercial failures — including the bankruptcy of high-profile operators in 2023 — as evidence that the model is fundamentally uneconomical at scale. A reasonable view is that vertical farming will become a permanent niche supplier of high-value perishables in wealthy urban markets, without ever replacing the traditional agriculture that produces the world's calories. The debate is, in many writers' view, less about whether the technology works than about whether its economic margins can be sustained outside the narrow niches where it currently thrives.

A The complexity of whale vocalisation has long fascinated researchers. Whales generally produce sounds in two principal modes: the elaborate songs of male humpback whales, which can last 30 minutes and propagate hundreds of kilometres through deep ocean channels; and the clicks and pulsed calls of toothed whales such as sperm whales, dolphins, and orcas, which appear to function for echolocation and social communication. Whether any of these vocalisations meet the linguistic criteria of human language remains the subject of intense debate, but the systems are unquestionably more structured than was suspected a generation ago. The reframing of whale vocalisation as a candidate communication system rather than a curiosity of natural history has, in many researchers' view, transformed how the discipline thinks about non-human cognition.

B The pioneer of whale-song research is widely held to be Roger Payne, an American biologist whose 1970 album Songs of the Humpback Whale reportedly brought the songs to public attention and contributed to the moratorium on commercial whaling adopted in 1982. Payne demonstrated that male humpbacks within a single ocean basin tend to sing essentially the same song at any given time, but that this song evolves slowly over years, with novel elements introduced and propagated through the population. The process is said to resemble cultural transmission rather than genetic inheritance — a form of horizontal learning previously thought to be largely absent from animals.

C Modern computational analyses appear to have revealed deeper structure. Songs broadly seem to be organised into a clear hierarchy: discrete units, often termed calls or notes, typically combine into phrases; phrases generally repeat to form themes; themes succeed each other in a more or less fixed order to constitute a song; and songs are repeated for hours within a singing bout. The exact functions remain widely debated, but the leading hypothesis is that song serves a combined function of male-male competition and female mate choice, analogous to bird song. The hierarchical structure has, in many analysts' view, invited comparison with the nested grammars of human language, although the parallels are described as suggestive rather than literal.

D Sperm whale clicks have been studied even more intensively in recent years. Researchers at the CETI initiative, drawing on extensive recordings from the Eastern Caribbean sperm whale population, identified that what had previously appeared to be simple repeated clicks are in fact structured into discrete patterns called codas. Each coda consists of three to twenty clicks with characteristic timing, and individual whales appear to use particular codas as identifying markers. The number of distinct coda types in the studied population is said to approach two hundred — broadly comparable in raw vocabulary size to some small human languages, although the question of whether they carry the equivalent of grammatical structure largely remains unresolved.

E Orca calls arguably provide the strongest evidence for whale cultural transmission. Different orca pods appear to have distinct call repertoires that remain stable across generations and clearly differentiate one pod from another. Calf orcas seem to learn their pod's specific calls largely from their mothers, with measurable differences in fluency between calves of different ages. When orcas from different pods occasionally socialise, individuals can be observed using calls from outside their normal repertoire — perhaps analogous to a human switching to a second language with a familiar interlocutor. The mother-to-calf transmission of pod dialect has, in many writers' view, broadly become the canonical example of stable non-human cultural inheritance.

F Machine learning has transformed the analysis of whale vocalisation. Deep neural networks trained on massive recording archives can classify call types and identify individual animals more accurately than human listeners, and may detect subtle patterns that tend to escape conventional acoustic analysis. The hope of several research groups, including those pursuing what some popular accounts have called the Doctor Dolittle problem, is that increased computational power and ever-larger acoustic datasets will eventually reveal whether and how whale vocalisations encode information. Whether such revelations are imminent or remain decades away appears to be genuinely contested within the field.

A The systems by which human societies have divided time into days, months, and years are widely held to be products of negotiation between astronomical reality and cultural convenience. The solar year — defined as the time it takes Earth to orbit the Sun — is not a whole number of days, nor is the lunar month a whole number of days, nor does any whole number of lunar months equal one solar year. Every calendar system in history has had to make compromises among these three incommensurable cycles, and the political authority needed to impose those compromises has shaped calendar history as much as astronomy has. The history of calendars is therefore, in many writers' view, broadly inseparable from the history of the political institutions that have used calendars to coordinate religion, taxation, and the agricultural year.

B The Egyptian civil calendar, generally said to have been developed by approximately 3000 BCE, was the first known calendar to fix the year at 365 days, divided into twelve months of thirty days each plus five additional days. It made no attempt to track the lunar cycle and did not include leap years, which meant the calendar drifted relative to the seasons by approximately one day every four years. Despite this drift, the system's simplicity and political durability made it influential for millennia: the modern numbered months of January through December are widely held to retain divisions inherited substantially from this original Egyptian system. The Egyptian model has been described as the first major calendar in human history to subordinate astronomical accuracy to administrative simplicity.

C The Roman calendar in its early form was regarded as something of a mess. The original Roman year was 304 days divided into ten months, with the period from December to March lacking any calendrical designation. The addition of January and February by King Numa Pompilius around 700 BCE reportedly brought the year to twelve months, but the system relied on irregular insertion of intercalary months by political appointees, and it came to be used as a tool of political manipulation. Magistrates whose terms of office were governed by the calendar regularly arranged for additional months when it suited their interests.

D Julius Caesar's calendar reform of 45 BCE is widely held to have established a 365-day year with a leap day every fourth year, producing an average year length of 365.25 days. This was considered a substantial improvement, although it remained slightly too long, since the true tropical year is approximately 365.2422 days. The Julian calendar dominated Europe for more than 1,600 years, but its small inaccuracy accumulated steadily, so that by the sixteenth century it had drifted approximately 10 days from the astronomical seasons. The accumulated drift came to threaten the calculation of religious dates, in particular the dating of Easter, in ways that eventually prompted a further reform.

E Pope Gregory XIII commissioned a reform in 1582 that produced the calendar still in worldwide use. The Gregorian calendar retained Caesar's basic structure but modified the leap-year rule: century years would not be leap years unless divisible by 400. This change produced an average year length of 365.2425 days, regarded as accurate to within about 26 seconds. The reform also removed ten days from the calendar in order to realign it with the seasons — a politically contentious move that took Protestant and Eastern Orthodox countries varying lengths of time to adopt. Britain finally accepted the Gregorian calendar in 1752; Russia not until 1918. The pattern of staggered adoption is widely said to broadly reflect the religious and political divisions of post-Reformation Europe rather than any disagreement about astronomy.

F Lunar and lunisolar calendars largely persist alongside the Gregorian system in many cultures. The Islamic calendar is regarded as purely lunar, with 12 lunar months totalling about 354 days, which means religious observances such as Ramadan tend to drift through the seasons over a 33-year cycle. The Hebrew calendar is described as lunisolar, with leap months added in seven out of every nineteen years to keep major festivals roughly aligned with the seasons. The Chinese calendar, also lunisolar, governs the dates of traditional festivals such as the Spring Festival, while everyday life in China largely runs on the Gregorian system.

G Several attempts have been made to reform the modern calendar further. Proposed perpetual calendars — in which a given date would always fall on the same day of the week — have been promoted at various times by reformers ranging from Auguste Comte in the nineteenth century to a 2012 proposal by Johns Hopkins economist Steve Hanke. None has so far been adopted, principally because the conservatism that has preserved the Gregorian system through 440 years of social change has proved more powerful than the relatively modest practical advantages that reform would offer.