IELTSwithJurabek

You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2.

The story of the ocean

How humans have explored the world by boat

14A What is the ocean? Today we refer to five individual oceans: the Atlantic, Pacific, Indian, Arctic, and Southern. But in the distant past, people saw the 'ocean' as the whole mysterious mass of water surrounding the places where they lived. In fact, nothing separates the oceans from each other. There is no moment when one passes from the Atlantic to the Indian Ocean, or from the Indian Ocean to the Pacific, and in total they cover the greater part of the surface of the Earth.

15B Ocean voyages were made as long ago as 1000 BCE, when Polynesians began migrating across the Pacific, setting off into the unknown. They reached small inhabited islands using only knowledge passed from navigator to apprentice, often using songs to memorize important facts, such as where specific stars would rise and set on the horizon. From Europe, Viking sailors crossed the North Atlantic and reached North America by 1000 CE. In the Middle Ages, sea trade routes linked China to Egypt and Venice to London. Most seafarers kept close to the coastline whenever possible, however, and for many scholars, the ocean remained the subject of terror or denial. Arab geographer Al-Masudi in 957 CE recorded a common sailor's tale that at the exit from the Mediterranean Sea into the Atlantic there were giant statues, indicating that there was 'no way beyond'. The German storyteller Adam of Bremen wrote in 1076: 'Beyond Norway, which is the farthermost northern country, you will find no human habitation, nothing but ocean, terrible to look at and limitless.' Around 1290 a map was presented to Hereford Cathedral. In medieval fashion, it showed the world as consisting of the continents of Europe, Africa and Asia, which was all that was known about at the time. Even the Mediterranean was not accurately drawn. The band of oceans surrounding the great landmass was not much wider than the rivers-the oceans were simply not considered important.

16C This narrow view of the world was soon to change during the 13th-15th centuries. Venetian Marco Polo's 1298 account of his travels in the East, including a sea journey from China to the Persian Gulf, broadened the scope of knowledge. The works of the ancient Greek geographer Ptolemy, in which he had plotted the Indian Ocean, had been forgotten for many centuries, but by 1400 they were again influential in Europe. Between 1405 and 1433, the Chinese admiral Zheng He led a series of voyages into the Indian Ocean, travelling as far as the east coast of Africa. The expanding view of the world is represented in a great map made by the monk Fra Mauro in Venice around 1450. It was one of the first maps to recognize the Atlantic as an ocean. The European experience soon spread to the rest of the world. Adventurers and sailors, now sometimes backed by acquisitive kings, queens and emperors, set out in search of trade, territory and treasure. Setting out in 1498, Vasco da Gama led a Portuguese fleet around the southern tip of Africa to India. In 1519, Ferdinand Magellan, a Portuguese in the service of Spain, set off on a voyage around South America, his crew completing a circumnavigation of the globe. The age of ocean denial was over.

17D Once humans could travel over vast areas of sea, it was perhaps justifiable to use the term 'conquering the ocean.' Yet for centuries, ocean voyagers confronted discomfort and danger. Without prior knowledge or charts, sailors could never be sure what was under the surface of the sea. If bad weather came, it was often not possible to find shelter. Sicknesses, such as scurvy, killed thousands of people at sea, and accidents were commonplace. Sea travelers might run out of food or water, and it was not possible for a sailor in trouble to call for help beyond the horizon. The first ocean-going sailing ships were central to world trade and warfare and conflict, yet remained entirely at the mercy of the currents and the winds.

18E The other problem of ocean travel was the lack of navigational techniques. Observing heavenly bodies, continually measuring the ship's speed, and using the magnetic compass could at best achieve a fair degree of precision in calculating a ship's position. Sailors far out to sea often had only a vague notion of where they were, but years of technological progress, better navigational instruments and maritime experience gradually improved ocean travel. By the 19th century, scurvy was almost eliminated once it was realized it could be prevented and treated with citrus fruit, and navigation was greatly improved. As ocean-going steamships replaced sail in the second half of the century, the time spent at sea was reduced. By the 20th century, ocean travel had become reasonably safe, at least in times of peace.

19F In a sense, the ocean has not been 'conquered'. We cannot control the currents and weather, and human impact has mostly been negative. Yet we have at least developed the means to travel over vast areas, and this achievement has been the product of many centuries of adventures. Seafarers from ancient times down to the present day have faced a hard struggle against the elements, demanding endurance, skill, and ingenuity. The record of their lives includes barely credible stories of voyages into uncharted waters and survival at sea. Their experience deserves to be remembered and honored, as does the essential contribution of modern sailors to our ever-evolving history.

You should spend about 20 minutes on Questions 27-40, which are based on Reading Passage 3

Creating a Better Grapefruit

By blocking the right taste receptors, biotech researchers turn bitter into sweet

A There is a reason why grapefruit juice is served in little glasses. Most people don't want to drink more than a few ounces at a time. This is because a natural chemical compound found in grapefruit, naringin, has a bitter taste. Some people like that bitterness in small doses and believe it enhances the general flavour, but others would rather avoid it altogether. So juice packagers often select grapefruit with low naringin content, even though the compound has antioxidant properties that some nutritionists contend may help prevent many serious diseases.

B It is possible, however, to get the goodness of grapefruit without the bitter taste. In a test conducted by a biotechnology company, sets of two miniature white paper cups, labelled 304 and 305, were placed before five people seated around a conference table. Each person drank from one cup and then the other, cleansing their palates between tastes with water and a cracker. Even the smallest sip of 304 had grapefruit's unmistakeable bite. But 305 was smoother; there was the sour taste of citrus but none of the bitterness of naringin. This juice had been treated with AMP, a compound that blocks the bitterness in foods without making them less nutritious.

C Taste research is a booming business these days, with scientists delving into all five basics: sweet, bitter, sour, salty, and umami (the savory taste of protein). However, bitterness is of special interest to the food industry because it is present in so many different types of food. There are thousands of bitter-tasting compounds in nature. They defend plants by warning animals away and protect animals by letting them know when a plant may be poisonous. But the system isn't foolproof. Grapefruit and bitter green vegetables like Brussels sprouts and kale are nutritious despite - and sometimes because of - their bitter-tasting components.

D 'Humans are the only species that enjoys a bitter taste,' says Charles Zuker, a neuroscientist at the University of California School of Medicine at San Diego. 'Every other species is averse to bitter because it means bad news. But we have learned to enjoy it. We drink coffee, which is bitter, and quinine (in tonic water) too. We enjoy having that spice in our lives.' Because bitterness can be pleasant in small quantities but repellent when intense, bitter blockers like AMP could make a whole range of foods, drinks and medicines more palatable.

E People have varying capacities for tasting bitterness and the differences appear to be genetic. About 75% of people are sensitive to the taste of some well-identified bitter compounds. Those who are sensitive seem to be less likely than others to eat bitter vegetables, according to Stephen Wooding, a geneticist at the University of Utah. Some people who have an unusually high number of taste buds, and are known as 'supertasters', are especially sensitive to these compounds. Supertasters tend to shun all kinds of bitter-tasting things, including vegetables, coffee, and dark chocolate.

F The tongue is covered with taste buds. Under the microscope each one looks like an onion, consisting of 50 to 100 elongated cells running from the top of the taste buds to the bottom. At the top is a group of receptors that captures the taste molecules, known as tastants, in food and drink. The receptors function much like those for sight and smell. Once a bitter signal has been received, it is relayed via proteins known as G proteins. The G protein involved in the perception of bitterness, sweetness and umami was identified in the early 1990s by Robert Margolskee, at Mount Sinai School of Medicine in New York. The protein triggers a cascade of chemical reactions that lead to ion concentrations within the cell. Ultimately, this delivers a signal to the brain that registers as bitter.

G Once they understood the taste mechanism, scientists began to think of ways to interfere with it. They tried AMP, an organic compound found in breast milk and other substances, that is created as cells break down food. AMP has no bitterness of its own, but when put in foods, as Margolskee and his colleagues discovered, it attaches to bitter-taste receptors. As effective as it is, AMP may not be able to dampen every type of bitter taste because it probably doesn't attach to all 30 bitter-taste receptors.

H Some taste researchers believe that, in time, compounds like AMP will help make processed foods less unhealthy. Consider, for example, that a single cup of canned chicken noodle soup contains 850 milligrams of sodium chloride, or table salt - more than a third of the recommended daily allowance. The salt masks the bitterness created by the high temperatures used in the canning process, which cause sugars and amino acids to react. Part of the table salt could be replaced by another type of salt, potassium chloride, which tends to be scarce in some people's diets because of its bitter taste. But that bitter taste could be eliminated with a dose of AMP. Bitter blockers could also be used in place of sugary cherry and grape flavourings in children's cough syrups, and they could dampen the bitterness of drugs like antihistamines, antibiotics and other similar products.

I A number of foodmakers have already begun to experiment with AMP in their products, and other bitter blockers are being developed. In a few years, perhaps, after food companies have taken the bitterness from canned soup and improved the taste of medicines, they can set their sights on something more useful: a bitter blocker in a bottle that any of us can sprinkle on our Brussels sprouts or stir into our grapefruit juice.