IELTS Academic Reading Practice Test 68

The chilli pepper, a small fruit belonging to the genus Capsicum, is now so deeply woven into cuisines across Asia, Africa and Europe that it is easy to forget it was unknown outside the Americas until the end of the fifteenth century. Unlike black pepper, a spice obtained from the dried berries of an unrelated vine, chillies owe their fierce heat to a chemical called capsaicin, which is concentrated mainly in the pale membranes that hold the seeds. Botanists recognise five domesticated species, which between them include varieties as different as the mild bell pepper, the jalapeño and the intensely hot habanero.

The plant's wild ancestors grew in the tropical lowlands of South and Central America, and archaeological evidence indicates that people were using chillies in the Americas for around eight thousand years. Domestication appears to have occurred about six thousand years ago in several centres, including Mexico and the Andean region. For the Aztecs and Maya, chillies were far more than a flavouring; they were used in medicine, in tribute payments and in ritual. The Aztec word chīlli, borrowed into Spanish as chile, gave the modern English chilli its name.

When Christopher Columbus reached the Caribbean in 1492, he was searching for a western route to the spice riches of Asia. Among the unfamiliar plants he encountered were small red fruits that the indigenous people used to make their food intensely hot. Because the sensation resembled that of the costly black pepper of the Old World, the new fruits were quickly given the name pepper. Columbus carried chillies back to Spain, and within a remarkably short time they were being grown in the Iberian Peninsula. At first they were treated mainly as curiosities in European gardens, but their cheapness soon made them popular as a substitute for expensive spices.

The true global expansion of the chilli, however, was driven by Portuguese merchants and navigators. In the early sixteenth century, Portugal controlled key trading routes around Africa and into the Indian Ocean, and its ships regularly carried American plants as they moved between continents. Chillies reached the Portuguese enclave of Goa on India's west coast, and from there they spread with astonishing speed along established trade networks. The plant flourished in tropical and subtropical climates, produced abundant fruit with little care, and could be dried and stored for long periods. By the end of the sixteenth century it had arrived in Southeast Asia, China and Japan, often entering through trading ports.

The chilli did not simply add itself to existing cuisines; in many places it transformed them. Indian cooking had long relied on black pepper, ginger and other pungent ingredients, but the new arrival was cheaper and easier to grow, and it gradually became the main source of heat in many regional dishes. In Sichuan province, the chilli combined with the local Sichuan peppercorn to create the distinctive numbing and burning flavour now associated with the region. Similarly, Korean kimchi and many Thai dishes developed their characteristic fire only after chillies were introduced. In parts of Europe, however, the chilli was often regarded as a medicinal plant rather than an everyday food for several centuries.

Paprika, the bright red powder made from dried and ground chillies, became especially important in Hungary. The plant had reached Hungary through the Ottoman Empire by the early seventeenth century, and during the nineteenth century paprika developed into a symbol of Hungarian national cooking. Meanwhile, the spread of different Capsicum species and the selection of local varieties produced an extraordinary range of heat levels and flavours.

In 1912, the American pharmacist Wilbur Scoville introduced a method of measuring pungency by diluting chilli extract until its heat could no longer be detected. The resulting Scoville scale remains in use, although modern laboratories also measure capsaicin content directly. Mild bell peppers score near zero on the scale, while the hottest habaneros can exceed 300,000 units.

The biological reason for this variation lies in capsaicin's role in the plant. Capsaicin deters many mammals from eating the fruits, because mammals can damage the seeds with their chewing, while birds, which are less sensitive to its heat, can swallow the fruits and disperse the seeds unharmed. In humans, capsaicin binds to the same receptor that signals physical heat, so the brain responds as though the mouth were burning, even though no tissue damage occurs. Repeated exposure can reduce the intensity of this response, which helps explain why preferences for hot food are strongly influenced by habit and culture.

Today chillies are grown commercially on a huge scale. According to figures from the Food and Agriculture Organization, the leading producers of green chillies and peppers include China, Mexico, Turkey, Indonesia and Spain, and the annual world harvest amounts to tens of millions of tonnes. The crop is consumed fresh, dried, powdered, pickled and in countless sauces. It is the main ingredient in some of the world's most popular condiments, including harissa in North Africa, sambal in Indonesia and gochujang in Korea. The chilli has also moved beyond the kitchen; capsaicin is used in pain-relieving creams and in research on sensory receptors.

In the space of five hundred years, therefore, a group of American plants that began as a local flavouring became one of the world's most widely traded food crops. The chilli's journey is often described as one of the most successful examples of the exchange of plants and animals between the Old and New Worlds that followed the voyages of Columbus and his successors. Its ability to thrive in many climates, to survive drying and to add intense flavour cheaply ensured that it would be adopted wherever it went.

Bioluminescence is the production of light by living organisms. The phenomenon occurs in a remarkable range of creatures, including certain bacteria, fungi, jellyfish, squid, fish, insects and worms. Most bioluminescent species live in the ocean, but the most familiar examples on land are fireflies and glow-worms. The light produced by these organisms is often described as cold light because very little of its energy is wasted as heat. Despite its beauty, bioluminescence is not a single ability; it has evolved independently many times and serves a wide variety of purposes.

The light is the result of a chemical reaction. In a typical bioluminescent system, a molecule called luciferin is oxidised by an enzyme known as luciferase. The reaction usually requires oxygen and, in many cases, the energy-carrying molecule ATP. When the luciferin is oxidised, it briefly enters an excited state, and as it returns to its normal state it releases the extra energy as a photon of visible light. Different groups of organisms use different types of luciferin and luciferase, which strongly suggests that the ability evolved separately on several occasions. Some species obtain the necessary chemicals from their food, while others manufacture them internally.

Fireflies, which are actually beetles belonging to the family Lampyridae, use light mainly for courtship. Males fly in characteristic patterns, producing a series of flashes whose length, rhythm and colour vary between species. Females perched on vegetation answer with their own signals, enabling the two sexes to recognise members of their own species. In a few areas, such as the mangrove forests of Southeast Asia, thousands of male fireflies of the same species synchronise their flashes, producing waves of light along the trees. This synchrony is achieved through simple rules by which each beetle adjusts the timing of its own flash in response to the flashes of its neighbours. Some female fireflies also use light to attract and then eat the males of other species.

In the ocean, bioluminescence is far more widespread than on land. Because sunlight can penetrate only the upper layers of water, the deep ocean lies in permanent darkness, and here most animals possess the ability to produce their own light. It has been estimated that over three quarters of the animals in the ocean's midwater zone are bioluminescent. The functions are extremely varied: some animals use light to hide themselves, others to seize prey, to confuse attackers or to attract a mate. The colour of marine bioluminescent light is usually blue-green, because those wavelengths travel farthest through seawater and because most deep-sea animals have eyes that are most sensitive to that part of the spectrum.

One of the most striking displays occurs near the surface of the sea, where vast numbers of single-celled organisms called dinoflagellates sometimes produce glowing water. When these plankton are disturbed by waves, a boat or a swimmer, they emit a brief flash of blue light, creating trails and splashes of bright blue among the dark water. The flash is believed to act as a kind of alarm signal. It may startle the small animals that graze on dinoflagellates, or it may attract larger predators that feed on those grazers, thereby protecting the dinoflagellates themselves. Not all dinoflagellates are bioluminescent, but the ones that are can multiply so rapidly that their population turns an entire bay luminous.

In the dim middle depths of the ocean, many fish use light to erase their own shadow. This strategy is called counterillumination. A predator looking upward from below normally sees the dark outline of a fish against the brighter light coming down from the surface. By producing light from organs on its underside, a fish can match the intensity and colour of the light above it, making its silhouette disappear. Hatchetfish and many small midwater fish carry rows of light organs on their bellies for precisely this purpose. Some species can adjust the brightness of their ventral light as they change depth, maintaining the match over a wide range of conditions.

Bioluminescence is also used as a weapon in both attack and defence. The deep-sea anglerfish is a classic example of an animal that attracts prey with light. A modified spine on its head, tipped with a glowing bulb, dangles in front of its mouth. Small fish and crustaceans are drawn towards the light and are then engulfed. Other species produce a glowing cloud of mucus or ink to distract a predator while they escape. The vampire squid, for instance, ejects a sticky luminous slime from the tips of its arms, which can confuse an attacker for several minutes while the squid disappears into the dark.

The chemical machinery behind these displays has become an important tool in biology. In the early 1960s, researchers studying the jellyfish Aequorea victoria isolated a protein that produced a green glow when exposed to ultraviolet light. This protein, later named green fluorescent protein, or GFP, can be attached to other proteins inside living cells, allowing scientists to watch where those proteins go and when particular genes are turned on. The development of GFP as a biological marker was recognised with the Nobel Prize in Chemistry in 2008, awarded to Osamu Shimomura, Martin Chalfie and Roger Tsien. Today, bioluminescent and fluorescent markers are used in laboratories around the world to study everything from cancer cells to brain activity.

Although we tend to associate bioluminescence with spectacular flashes and glowing waves, its true significance lies in its range and adaptability. The same basic principle, a chemical reaction that turns stored energy into light, has been shaped by evolution into a host of different functions, from camouflage and courtship to attack and defence. This variety explains why bioluminescent species are found in almost every major group of organisms and in habitats ranging from forest floors to the deepest parts of the ocean.

For decades, space travel belonged to governments and a tiny group of carefully selected professionals. That began to change at the turn of the twenty-first century, when extremely wealthy individuals started buying trips beyond the atmosphere. Space tourism is now marketed as the opening of a new era, in which ordinary people will eventually travel to orbit and perhaps beyond. I should say at once that I am not convinced. The current phase of space tourism seems to me to be high-end adventure travel with little scientific value, and its social and environmental costs deserve far more scrutiny than they receive.

The first paying customer was the American businessman Dennis Tito, who in 2001 spent around eight days on the International Space Station after paying a reported twenty million dollars for the journey. His flight was arranged by an American company, Space Adventures, which had leased a seat on a Russian Soyuz spacecraft. Between 2001 and 2009, six further clients made similar trips to the station, among them Anousheh Ansari, the first woman to make a self-funded visit to space. The programme was then suspended because the available Soyuz seats were needed for professional crew members.

A different kind of space tourism emerged in 2021, when two companies began flying passengers on suborbital flights that reach the edge of space but do not enter orbit. Virgin Galactic's SpaceShipTwo and Blue Origin's New Shepard both carried their first passengers on short hops that offered only a few minutes of weightlessness before returning to Earth. Tickets for these flights have been sold for hundreds of thousands of dollars, and thousands of people are reported to have placed deposits. But a suborbital flight is little more than a brief thrill; it does not take a passenger anywhere useful.

Orbital tourism, by contrast, is far more ambitious. In September 2021, the American company SpaceX launched Inspiration4, a mission crewed entirely by private individuals, which spent three days circling the Earth inside a Crew Dragon capsule. Since then, several companies have arranged private missions to the International Space Station, where paying passengers remain for a week or more alongside professional astronauts. The price of such a trip is usually not published, but it is widely reported to be in the tens of millions of dollars. These missions sometimes include a few simple experiments, but they are primarily recreational.

Supporters of space tourism often compare it to the early days of aviation, when only the rich could afford to fly, and argue that today's expensive tickets will finance the development of reusable rockets and eventually lower prices for everyone. There is some truth in the technological part of this argument, since companies such as SpaceX have used private investment to improve the reuse of rocket stages. The analogy with aviation, however, is weak in one important respect. Early aeroplanes soon began carrying mail and passengers between distant cities, providing a practical transport service. A brief ride above the atmosphere currently offers no comparable practical value.

The scientific case is equally easy to exaggerate. Private missions carry a handful of student experiments, and some passengers monitor their own bodily responses to weightlessness, but the amount of useful data is minimal compared with what professional astronauts and automated instruments produce. If the companies were honest, they would admit that science is a secondary justification for what are essentially leisure flights. The notion that these trips are advancing human knowledge is, in my view, largely marketing.

The environmental costs are also significant. A rocket launch burns fuel at a rate that releases carbon dioxide and water vapour, but the greater concern is the soot and other particles that are deposited in the stratosphere, where they can remain for years and have a disproportionately large warming effect for the amount of fuel burned. Some propellants also produce chlorine compounds that can contribute to the destruction of ozone. At present, space tourism launches represent only a tiny fraction of all rocket activity, but that could change rapidly if the industry grows as its promoters predict.

There is also a question of fairness. Industry advertisements often speak of democratising space, yet the price of a single suborbital ticket is far beyond the annual income of most people on Earth. The high cost means that the experience is reserved for the ultra-wealthy, and it is hard to see how a market aimed at millionaires can be described as opening space to humanity. The money spent on one tourist flight could, for example, fund many scholarships or scientific research projects on the ground.

I do not wish to argue that private citizens should never go to space. The early passengers have shown admirable courage, and their flights may inspire young people to study science and engineering. If space tourism is to justify its existence, however, it must become more than an expensive thrill. It needs either to produce real scientific or technical benefits, or to find ways of reducing its environmental impact. Until then, we should treat the industry's grand promises with a healthy dose of scepticism.