IELTS Academic Reading Practice Test 67

Bread is one of the oldest prepared foods, but for thousands of years it was flat and hard. The loaves found in ancient Egyptian tombs, for instance, were made without leavening and would quickly have become brittle. The transformation of such simple mixtures of flour and water into the soft, airy bread eaten today was the work of a microscopic fungus.

Yeast is a single-celled organism belonging to the fungus kingdom, and the species most widely used by bakers is Saccharomyces cerevisiae, whose name means 'sugar fungus of beer'. These yeasts occur naturally on the skins of fruits and grains and in the air, so early doughs would have been inoculated without any human understanding. Evidence of breadmaking stretches back at least 14,000 years, long before agriculture was established.

When yeast cells are added to a moist flour mixture, they begin to feed on the sugars released from starch. If oxygen is scarce, as it is inside a dough, they do not use the sugars for growth in the usual way. Instead, they convert them into carbon dioxide gas and ethanol through a process known as fermentation. The carbon dioxide cannot escape easily from the mass because of the structure of the dough, and this is what makes bread rise. The ethanol evaporates later in the oven, but during fermentation it gives the dough a characteristic smell and also influences flavour. The process is the same one used in brewing, which is why bakeries and breweries long shared sources of yeast.

The discovery of leavened bread is usually credited to the Egyptians, although the details are unknown. The most likely explanation is that a flour-and-water mixture left out by accident attracted wild yeasts and lactic acid bacteria. When baked, it produced a lighter loaf than the baker had expected. Repeating the process with a little of the old dough led to the first leavened breads and, in time, to sourdough, in which yeasts and bacteria live together in a stable culture. Many other civilisations later developed their own leavened breads, but the use of sourdough remained the main method for millennia.

The scientific study of fermentation began in the nineteenth century. In the mid-1850s the French chemist Louis Pasteur demonstrated that living yeast cells, rather than a purely chemical reaction, were responsible for alcoholic fermentation. This finding opened the way to modern baking. By the end of the century, manufacturers were producing baker's yeast in compressed form on an industrial scale, and selected strains that generated carbon dioxide quickly had begun to displace the slower wild cultures of the traditional bakehouse. For the first time, bakers could buy a reliable product from a factory instead of keeping a sourdough culture alive from week to week.

Modern breadmaking begins by mixing strong wheat flour, water, yeast and salt. When the flour is wetted and kneaded, two proteins, glutenin and gliadin, combine to form gluten, a stretchy network that gives the dough its elasticity. Kneading aligns these proteins and strengthens the network, which will later trap the gas produced by the yeast. Salt is not merely a flavouring; it tightens the gluten and slows fermentation, preventing the dough from rising too rapidly before the structure is ready.

During the first rise, or bulk fermentation, the yeast converts the available sugars into carbon dioxide and ethanol. The gas inflates tiny pockets within the gluten network, sometimes doubling the volume of the dough. The rate of this process depends strongly on temperature; warm dough ferments faster, but very high temperatures kill the yeast, while refrigeration slows it almost to a stop. Bakers therefore adjust proofing times according to the season and the type of bread being made.

After the first rise, the dough is knocked back, or punched down, to expel some of the accumulated gas and to redistribute the yeast, sugars and moisture. This also evens out the temperature of the mass. The dough is then divided and shaped, and given a final proof, in which it rises again before baking. If the dough is baked without this second rise, the loaf is dense and poorly textured. Toward the end of proofing, bakers may cut the surface with a blade; these slashes allow the bread to expand in a controlled way in the oven.

In the hot oven several things happen quickly. The gas inside the dough expands, causing a final burst of rising known as oven spring. The yeast is killed when the internal temperature reaches about 60 degrees Celsius, and the alcohol produced during fermentation evaporates. The starch in the flour swells and sets, while the outside of the loaf browns through a set of chemical reactions between sugars and proteins. This crust formation gives bread much of its taste and aroma, and the process is complete when the internal temperature has risen above 90 degrees.

Industrial bakers have altered the process to suit large-scale production. Strong flours, fast-acting yeasts and enzymes may be added, along with small amounts of fats, sugar and other ingredients, to make the process quicker and more uniform. Artisan bakers, by contrast, often return to long fermentations and wild cultures, arguing that time is an essential ingredient in flavour. Whether made slowly or quickly, the basic biology remains the same: a microorganism invisible to the naked eye transforms a dense paste into one of the world's most familiar foods.

In 1997, the American biologist Janine Benyus published a book that popularised a name for an old practice: biomimicry, the deliberate imitation of nature's solutions to engineering problems. Unlike simple inspiration, biomimicry involves studying a biological mechanism closely and then transferring its principles to a human technology. Benyus argued that organisms have been testing designs for billions of years and that their successful strategies are worth copying. Her book helped turn a scattered collection of ideas into a recognised field, and the term is now used widely by engineers, architects and designers. Many of the most successful examples have come from looking closely at familiar organisms.

The most famous early example of biomimicry was discovered by accident. In 1941 the Swiss engineer George de Mestral returned from a walk and noticed that the seed cases of the burdock plant, known as burrs, were clinging firmly to his dog's coat and to his own trousers. Under a microscope he saw that each burr was covered with hundreds of tiny hooks, which caught on the loops of fabric and fur. He spent years reproducing this mechanism, and in 1955 he patented Velcro, a fastener made of two strips, one covered with stiff hooks and the other with soft loops. Today the name is used for countless versions of the hook-and-loop system.

A more recent and highly visible example comes from high-speed rail. In the 1990s, Japan's Shinkansen trains entered tunnels at such speed that the air compressed in front of them produced a loud boom at the tunnel exit. One of the engineers, Eiji Nakatsu, was also a birdwatcher. He noticed that the kingfisher dives from air into water with barely a splash, thanks to the long, flattened shape of its beak. Nakatsu modelled the nose of the train on that beak. The resulting design reduced the pressure wave, made the train quieter, and, because it was more aerodynamic, also lowered energy consumption.

Many plants also repel water in ways that engineers have copied. The leaves of the lotus plant remain clean in muddy ponds because their surface is covered with microscopic bumps. Water droplets roll across these bumps rather than spreading out, picking up dirt as they go. This self-cleaning effect, known as the lotus effect, was described by the German botanist Wilhelm Barthlott in the 1970s. It has since been applied to exterior paints, roof tiles and coatings that keep windows clear. The value of the discovery lies not in a chemical coating but in a physical structure. Commercial products based on this effect are now widely available.

Architects have also looked to animals for ways to regulate temperature. The Eastgate Centre, an office complex in Harare, Zimbabwe, was designed by architect Mick Pearce and opened in 1996. It uses a passive cooling system modelled on the mounds built by termites. A termite mound maintains a stable internal climate despite outside temperature swings because air flows through a network of passages near the surface and a central flue. The Eastgate Centre mimics this with fans that move air through hollow floors and up vertical ducts, so the building uses only a fraction of the energy of a conventionally air-conditioned block.

Fluid dynamics, too, has benefited from observations of marine animals. The humpback whale is a slow swimmer, yet it can turn in tight circles and pursue schools of fish. Biologists discovered that the leading edge of its long flippers is not smooth but has a series of rounded bumps called tubercles. These tubercles channel water over the flipper in a way that delays stalling and increases lift while reducing drag. Wind-turbine blades based on this pattern have been shown to work at lower wind speeds and to be quieter than conventional blades, and the design has also been considered for fans and even surfboard fins.

Adhesion is another area where a small structure performs a large job. The feet of geckos allow the animals to walk upside down on glass because each toe is covered with millions of microscopic hairs called setae, which end in even smaller structures. The setae are so close to the surface that weak molecular attractions, known as van der Waals forces, hold the animal in place. Unlike glue, the grip is instant, leaves no residue and works in a vacuum. Researchers have been trying for years to produce synthetic adhesives based on the same principle, with some success in the form of micro-patterned surfaces.

Perhaps the most ambitious goal of biomimicry is the imitation of spider silk. Silk produced by spiders combines strength and elasticity better than most manufactured fibres, and it is made at body temperature from ordinary proteins, without the toxic chemicals or high heat required for synthetic fibres. Because spiders cannot be farmed like silkworms, scientists have inserted silk genes into other organisms to produce the protein in bulk, and some companies are spinning fibres from these proteins. Yet Benyus has warned that biomimicry should not be used merely to continue unsustainable systems; it must also respect the constraints of the natural world. Several companies are now producing synthetic silk fibres at pilot scale.

When jet airliners entered service in the late 1950s, the communities around major airports experienced an abrupt change. Neighbourhoods accustomed to the intermittent drone of propeller aircraft were suddenly exposed to frequent and piercing engine noise. Over the following decades, engines became dramatically quieter, yet complaints have not subsided. The explanation, I would suggest, is that the problem has been transformed rather than resolved. Aircraft noise is now less a sudden loud event and more a chronic source of stress, and precisely because it is diffuse rather than dramatic, its consequences are easy to overlook.

Part of the reason the problem is overlooked lies in the way noise is measured. Regulators typically rely on averaged sound levels, expressed in decibels and weighted to reflect the sensitivity of the human ear. Such averages hide the pattern of noise, and the pattern is what matters for people near airports, because a handful of loud events at night can interrupt sleep even if the day-night average remains within accepted limits. The measure makes it easy to compare noise from different aircraft, but it does not describe the experience of residents. It is hardly surprising, then, that residents frequently regard official reassurances about average noise levels as unconvincing.

Noise from aircraft has well-known effects on health. Reviews by the World Health Organization and studies in Europe have linked long-term exposure to aircraft noise with a higher risk of high blood pressure and heart disease. Sleep disturbance is the most obvious effect, but it is not the only one. The body reacts to noise even during sleep; stress hormones are released, blood pressure rises and the quality of deep sleep goes down. Children who live under flight paths have performed worse in tests of reading and memory, and some studies have found slower cognitive development. These effects build up over many years, and they fall unevenly on people who cannot move away. Some research has even suggested a link with metabolic disorders.

Noise annoyance itself deserves attention. Surveys near airports consistently show that a large minority of residents are highly annoyed by aircraft noise, and this annoyance cannot be dismissed as merely subjective. Annoyance is influenced not only by loudness but also by trust in airport authorities, the predictability of the flight schedule and the fairness of decision-making. People accept noise more readily if they feel they have a say, and they feel more annoyance if they believe the airport is expanding without considering their health. This explains why an airport that appears to meet official noise limits can still produce strong opposition. Thus a noise level that one person accepts may be very disturbing to another.

Technology has brought real reductions in aircraft noise. Modern high-bypass turbofan engines, introduced after the 1960s, are much quieter than the turbojets they replaced. Newer aircraft such as the Airbus A350 and Boeing 787 have noise-reducing features on the airframe and landing gear, and airlines have changed the way aircraft fly, using continuous descent approaches that keep aircraft higher for longer and reduce noise on the ground. However, these gains have been partly cancelled by growth. The number of flights has risen faster than individual aircraft have become quieter, so total noise exposure around many airports has not fallen as much as engineers once hoped. These operational changes are often low-cost and have been widely used.

Policies have mostly focused on reducing the damage from noise rather than preventing it. Night flying restrictions, sound insulation for homes and financial compensation schemes all help, but they treat noise as an unavoidable side effect of an essential industry. In my view, this approach is too narrow. It allows airports to expand and then manages the damage with double glazing, rather than asking whether an extra runway is justified for the people who will live beneath its flight paths. Cost-benefit analyses usually put a monetary value on noise, but such values are unreliable because they do not capture the long-term health harm. Airport expansion is often approved before its full noise impact has been assessed.

The alternatives are not simple. Air travel supports trade, tourism and family connections, and a sudden reduction in flights would have serious economic costs. Some people propose quieter aircraft, but manufacturers cannot produce new designs quickly enough to keep up with demand. Others point to electric or hydrogen-powered aircraft, but these are unlikely to carry large numbers of passengers over long distances for many years. Yet if the social benefits of air travel are real, so are its social costs, and the people who bear the noise deserve a genuine voice in deciding how much more of it is acceptable.

A more honest noise policy would begin with a different question: not how much noise is allowed, but how much is safe. This would mean considering total night-time noise exposure, protecting schools and hospitals, and using land-use planning to keep new homes away from flight paths. It would also mean recognising that averages can hide danger and that the loudest events matter more than the quiet hours. Until policymakers stop treating aircraft noise as a minor problem, the problem will remain as persistent as the sound itself.