IELTS Academic Reading Practice Test 83

Seed banks are secure facilities that store seeds under controlled conditions in order to preserve plant genetic diversity, especially in species that are useful to people. They act as an insurance policy for agriculture, holding genetic material from crop plants and their wild relatives, and they provide researchers with a ready source of material for breeding programmes. A well-managed seed bank can keep many species alive for decades, and sometimes far longer, without the expense and risk of maintaining entire plants in the field. In effect, they are libraries of genetic information that can be drawn upon when crops fail, diseases spread or habitats disappear.

The need for such collections has grown steadily as the diversity of cultivated plants has narrowed. Modern farming relies on a relatively small number of high-yielding varieties, so that many local landraces and older cultivars have fallen out of use. At the same time, wild plant populations are being lost through deforestation, urban expansion and climate change. Each lost variety may carry genes that could help future crops withstand drought, pests or disease, which is why collecting and storing seeds has become an international priority.

The basic method is straightforward, although it demands careful control. Seeds are carefully cleaned and dried to a low moisture content, usually around three to seven per cent, before being sealed in airtight containers. Most orthodox seeds tolerate this treatment and can be stored for long periods at temperatures between minus 18 and minus 20 degrees Celsius. Samples are periodically removed and germinated to check that they are still viable, and when germination rates fall, fresh seeds are produced by growing out stored material and collecting a new generation.

The best-known facility of this kind is the Svalbard Global Seed Vault, which opened in 2008 on the Norwegian island of Spitsbergen, deep inside the Arctic Circle. The vault is built about 120 metres inside a sandstone mountain, and it is designed to serve as a backup for national and regional seed banks around the world. By 2025 it held more than one million seed samples from nearly every country. Because the surrounding rock is permanently frozen, the vault is naturally cold, although mechanical cooling keeps the interior at a steady minus 18 degrees Celsius.

The Svalbard vault is deliberately located in a remote and politically stable area, and it is intended to survive disasters that would destroy ordinary genebanks. If electrical power were lost, the permafrost would help to keep the seeds frozen for years. The first withdrawal from the vault was made in 2015, when the International Center for Agricultural Research in the Dry Areas removed seeds that had been deposited from its collection in Syria, after the conflict there made it impossible to maintain its original storage site.

Another major project is the Millennium Seed Bank at Wakehurst Place in Sussex, which is managed by the Royal Botanic Gardens, Kew. Opened in 2000, it concentrates on wild plant species rather than crops and is the largest facility of its type in the world. Its underground vaults hold more than 2.4 billion seeds from about 40,000 species, with the aim of safeguarding plants from drylands and other vulnerable habitats. The seeds are cleaned and dried in a purpose-built laboratory and then stored at minus 20 degrees Celsius.

Seed banks cannot, however, preserve every plant in this way. A significant minority of species have what are known as recalcitrant seeds, which do not survive drying and are killed by the low temperatures used in conventional storage. These include oaks and many tropical species such as cocoa and rubber. Such species must be conserved as living plants in botanic gardens or in the wild, or by more expensive techniques such as cryopreservation, in which tissues are stored in liquid nitrogen.

Even for orthodox seeds, storage is not a permanent solution. Seed viability declines slowly over time, so collections must be regenerated at intervals, which requires labour, land and careful record-keeping. Funding is another concern, because the benefits of preserving a rare variety may not be felt for many years, while the costs of running a seed bank are immediate. Crop wild relatives are still underrepresented in many collections, despite their potential value to plant breeders.

Seed banking is therefore best understood not as a substitute for conserving plants in their natural environments but as a complementary measure. It provides a safety net against sudden losses and gives scientists access to genetic resources that would otherwise be scattered across the world. The challenge for the coming decades is to ensure that collections are financially sustainable, well documented and truly representative of the plants on which humanity depends.

Comets are small icy bodies left over from the formation of the solar system about 4.6 billion years ago. For most of their long orbits they remain in the cold, dark outer regions, but when one approaches the Sun, its surface ices warm and release gas and dust, producing a glowing coma and often a tail that can stretch for millions of kilometres. Because these objects are thought to contain material that has changed little since the planets formed, they are valuable targets for scientific study. Many spacecraft have now been sent to fly past, orbit, land on, or even collide with comets, and each type of encounter has added a different piece to the puzzle.

The international fleet sent to Halley's Comet in 1986 provided the first close look at a comet nucleus. The European Space Agency's Giotto spacecraft passed within about 600 kilometres of the nucleus, revealing a dark, irregular body roughly the shape of a peanut, with bright jets of gas and dust bursting from its surface. Two Soviet Vega craft and two small Japanese probes also observed the comet at different distances. The images and measurements from this 'Halley Armada' showed that comets are not simple dirty snowballs, but geologically complex and highly active objects.

To find out what lies beneath a comet's surface, NASA's Deep Impact mission took a more aggressive approach. In 2005 the spacecraft released a 370-kilogram copper impactor into the path of Comet Tempel 1. The collision, which occurred at a relative speed of about ten kilometres per second, blasted a crater into the nucleus and threw up a cloud of debris. Instruments on the flyby spacecraft analysed the ejected material, which included dust, water ice and organic compounds, giving scientists their first direct view of a comet's interior.

A different strategy was adopted by NASA's Stardust mission. In 2004 Stardust flew through the coma of Comet Wild 2 and extended a collector filled with a lightweight material called aerogel to trap dust particles. The spacecraft then returned to Earth, and in January 2006 a capsule containing the samples parachuted safely into the Utah desert. Laboratory analysis of the captured grains found the amino acid glycine, as well as a variety of other organic molecules. This was strong evidence that comets could have delivered organic building blocks to the early Earth. In addition to organic compounds, some grains contained minerals that had formed at extremely high temperatures near the young Sun, suggesting that material had been mixed across large distances in the early solar system.

The most ambitious comet mission to date has been the European Space Agency's Rosetta. Launched in 2004, Rosetta spent ten years travelling to its target, Comet 67P/Churyumov-Gerasimenko, using several flybys of Earth and Mars to adjust its course. Because solar power was too weak during the outer part of its journey, the spacecraft was placed into hibernation for more than two years. It was successfully woken in January 2014, and later that year it entered orbit around the comet, becoming the first spacecraft to do so.

Rosetta revealed that Comet 67P has a distinctive double-lobed shape, often compared to a rubber duck, with a surface covered by cliffs, pits and smooth plains. The spacecraft detected water vapour, carbon dioxide and a rich mixture of organic molecules escaping from the nucleus. In November 2014 Rosetta released a small lander named Philae. Although Philae bounced twice before settling in a shaded area, it still managed to return the first images and data from the surface of a comet. Its battery power was limited by the lack of sunlight, and contact was lost after roughly two and a half days, but much useful information had already been transmitted.

Rosetta continued to follow the comet as it moved closer to the Sun, watching its activity increase. The mission ended in September 2016 when mission controllers directed Rosetta to make a slow, controlled impact on the comet's surface. The data returned during the descent added a final set of close-up measurements. Since then, scientists have continued to analyse Rosetta's archive, and the European Space Agency, together with the Japanese space agency, is planning a future mission called Comet Interceptor, which will park itself in space and wait to visit a pristine comet entering the inner solar system for the first time. This approach will allow the mission to study a comet that has never been heated strongly by the Sun, offering a direct comparison with heavily processed comets such as Halley and 67P.

Studying comets is technically demanding because the encounters occur at high speed and often in a storm of dust particles that can damage spacecraft. Engineers therefore design spacecraft with protective shielding and plan their flight paths to minimise the time spent near the nucleus. Even so, the risk of a single high-velocity grain disabling a spacecraft is real, and missions must operate with a high degree of autonomy because radio signals take many minutes to travel between Earth and a distant comet. Nevertheless, the rewards are considerable. Comets are among the most primitive bodies in the solar system, and their ices and organic compounds may record the conditions that existed when the planets were forming. They may also hold clues to the origin of Earth's water and to the chemical ingredients from which life eventually developed.

Office plants have become an almost standard feature of modern workplaces, appearing in reception areas, open-plan floors and meeting rooms. Employers install them for a variety of reasons: to soften harsh interiors, to demonstrate environmental awareness, or simply because employees request them. At the same time, a growing industry supplies office greenery, and its marketing often makes bold claims about cleaner air, reduced stress and higher productivity. The question is how far these claims are supported by evidence rather than by wishful thinking.

The most frequently cited study is the National Aeronautics and Space Administration's Clean Air Study, published in 1989 by B. C. Wolverton. It tested a number of common houseplants in sealed chambers and found that they could remove volatile organic compounds such as benzene and formaldehyde from the air.

Those findings have been repeated in countless advertisements, but the results were obtained under laboratory conditions that bear little resemblance to a real office. A sealed chamber is, in effect, a very small room with no ventilation, whereas real offices exchange air with the outside. Later reviews have concluded that, while plants do absorb some pollutants, an extremely large number would be needed to affect indoor air quality in a typical workplace.

Where plants appear to have stronger support is in the area of psychology. Attention restoration theory, developed by the environmental psychologists Rachel and Stephen Kaplan, proposes that natural scenes give our directed attention a chance to recover from mental fatigue. Even brief views of vegetation can lower self-reported stress and improve mood, and there is evidence that patients in hospital rooms with plants require less pain medication. Indoor plants, because they provide small reminders of nature, may therefore offer similar restorative benefits to office workers.

Claims about productivity are more difficult to evaluate. Experimental studies have sometimes reported that participants working in rooms with plants perform slightly better on tasks measuring concentration or memory, but these effects are often small and the studies tend to be short. A frequently quoted field experiment in a commercial office reported a marked increase in productivity after plants were introduced; however, the workers knew they were taking part in a study, and such awareness can change behaviour on its own. Larger and longer studies have produced mixed results, with some finding fewer self-reported sick days and others finding no significant effect.

Plants also have modest physical effects on the indoor environment. Through transpiration they release water vapour, which can slightly raise humidity in dry, air-conditioned offices, and their leaves capture a small amount of airborne dust. In winter, when heating systems make indoor air dry, this may help to reduce complaints of dry eyes and sore throats. However, these effects are local and limited; a few pot plants spread across a large open-plan floor should not be expected to alter the climate of the room.

The most important limitation is that plants are not a substitute for good ventilation. The air in many offices is contaminated by emissions from furniture, carpets, printers and cleaning products, and the most effective way to reduce these pollutants is to increase the supply of fresh air. Some property managers have begun to use plants as part of a wider 'biophilic design' strategy, which combines greenery with daylight, natural materials and views of the outdoors. In such settings, plants may contribute to a more pleasant atmosphere, but they are only one element among many.

There are also practical drawbacks that are rarely mentioned in promotional material. Plants require watering, light, drainage and occasional pest control, and a neglected display can become unattractive or trigger allergies. Overwatering can lead to mould in soil, and some species produce pollen. For businesses, maintenance costs should not be ignored, especially if a large number of plants is installed. The benefits of greenery, such as they are, must be weighed against these continuing demands on staff time and budgets.

My own view is that the truth lies between the marketing claims and the sceptics. Office plants are unlikely to clean the air or dramatically increase output, but that does not make them worthless. A modest number of well-maintained plants can make a workplace feel calmer and less institutional, and for some employees that may be enough to improve satisfaction. The key is to treat greenery as a small part of good office design rather than as a solution to problems caused by poor ventilation, excessive workloads or inadequate rest areas.

Employers should therefore be cautious about spending large sums on plants in the hope of measurable returns. If the goal is better air, the first step is to improve ventilation and reduce pollutant sources. If the goal is a more comfortable workplace, plants can play a role, but they should be chosen and maintained with care. Ultimately, any small gains in productivity are likely to come as much from the message that the employer cares about the working environment as from the plants themselves.