You should spend about 20 minutes on Questions 1-14, which are based on Reading Passage 1 below.
Grey water
In Abu Dhabi, where fresh water sources are very limited, sustainable water management is a high priority. The region receives on average just 120 millimetres of rainfall every year but the country is seeing demand for water increase by almost 40% annually. In this situation, it is clear that Abu Dhabi needs to boost the efficiency of water use by increasing water recycling and using treated water safely. An example of how this can be done can be seen at one of Abu Dhabi's airport hotels, which is saving a quarter of its water by recycling grey water. The hotel's new grey water recycling system is reported to save 735,000 litres of water per month, or 60 litres for every one of its guests.
Every building where people live or work, such as homes, hotels, schools and offices uses two types of water, potable and non-potable. Put simply, potable water is drinking water and non-potable water is used for washing and cleaning. Non-potable water is further divided into grey and black water. Black water is waste water that has been contaminated because it has been used to carry away human waste from toilets, for example, and cannot be reused without extensive biological or chemical treatment. Grey water, however, requires less treatment prior to reuse, and although it cannot be used for drinking, as in the case of the hotel, it can help make significant savings to water usage by being used again for different purposes.
Grey water usually comes from showers, washing machines, sinks, dishwashers, and so on, and because of this it contains fats and oils from products such as soap and washing powder as well as flakes of skin and food waste. It typically makes up approximately 6% of a household's waste water but contains fewer harmful bacteria and less nitrogen than black or waste water. However, if it is recycled properly, around 70 litres of drinking water per person per day can be saved by domestic households. To separate grey water from black water, a separate water system is needed in the building because different pipes are required to keep grey water away from the contaminated water and flow it into the recycling process.
When the grey water undergoes biological cleaning, the water is collected from various sources around the house and fed into a course filter and surge tank. This serves two purposes: first of all, a valve regulates air and water flow into the surge tank so that an even flow and pressure is maintained. This is important for the filtering process to work properly and ensure an even flow of grey water through the filter. The water is then pumped into a second filtration tank, which contains natural materials. In this second tank, the water passes through different layers. The first filtration layer is made up of sand, which traps larger waste particles between the grains. Below this layer there are other layers made up of soil, finer sand and then coarse sand. Each layer traps more and more waste, thus purifying the water as it passes through. A lot of the purifying takes place in the soil layer, where microorganisms feed on the organic waste in the grey water and reproduce. Finally, the water flows through gravel or small stones to allow it to drain out of the system.
It is then pumped into a UV tank for a final mechanical treatment. In the UV tanks, ultraviolet light sterilises the water by killing any remaining microorganisms. Further filtration may also be applied after this. At this point, the water can be reused, not for drinking but for flushing toilets, or outdoor uses like washing the car or watering plants.
In contrast, the mechanical process for treating grey water is much simpler. It usually involves collecting the water from sinks, showers, etc. and passing it through a series of filters, each with a membrane that is finer than that of the previous filter. Chemicals, usually chlorine, can then be used to disinfect the water and it can also be treated with UV light.
In hot dry countries such as Abu Dhabi and in other environmentally sensitive areas, the benefits of recycling grey water are obvious. The main one is that it reduces the pressures on public water supplies. Moreover, the amount of polluted water entering rivers is reduced and the problem of poisonous blue-green algae in water reservoirs is also significantly reduced. Furthermore, grey water recycling can save on water bills in the long term.
However, grey water recycling can be expensive if it involves putting new or extra pipes into a building to move the grey water into the purification system. Furthermore, even after filtration and cleaning, the water still contains chemicals and microorganisms which limit its uses. There are few risks to human health when recycled grey water is used properly; one possible risk comes from eating fruit and vegetables that have been grown with it but the danger seems to be minimal. It is clear that commercial and domestic water use needs to be taken more seriously, and single-use water systems are hard to justify in a world of ever greater water scarcity.
You should spend about 20 minutes on Questions 15-28, which are based on Reading Passage 2 below.
Born to run
People run for many different reasons: for fun, for exercise, to raise money for charities, and so on. Over the past decades, running has become an essential part of many health routines because of the publicity about its beneficial effects. It is claimed that it is good for our heart, it reduces stress and it helps to prevent diseases like diabetes. But what if running is more than just a way of keeping fit? Perhaps we need to run because it is part of what makes us human.
Evolutionary biologists point to the physical characteristics that have made our species one of the greatest runners on Earth. Scientists like Professor Daniel Lieberman of Harvard University maintain that our ancestors' need to run long distances in hot conditions led to evolutionary adaptations, such as the ability to lose heat through our sweat; skin with relatively little hair so we cool down as we run; large powerful muscles like the gluteus maximus, which controls hip and thigh movements; the Achilles tendon, which stores and releases energy for each step or jump we make; and a short vertical neck that keeps our head stable as we run, in contrast to animals whose heads bob up and down for balance.
Professor Lieberman explains that the features of the human neck that evolved to keep the head stable when we run were vital because they gave us an evolutionary advantage. This ability enabled us to scan what is in front of us while we are running and it helped us avoid falling and tripping. It meant that apart from being foragers, who look for plants, roots and berries for food, we could also become hunters. We could now get food from animals, which is richer in protein, and Lieberman contends that this enabled the evolution of the large human brain.
All of these adaptations give humans the ability to run much further than many animals. This means they can persistence hunt. Persistence or endurance hunting gives the hunter, who may be slower than their prey over short distances, the ability to track and follow an animal over very long distances until it is exhausted, then killed. It is a strategy still used by humans today. The hunter-gatherer tribes of the Kalahari Desert will track an antelope for hours over distances of more than 30 kilometres until it is too exhausted to go further.
Our ability to run long distances also means we can run half-marathons, marathons and even ultramarathons, where people run huge distances every day for days. However, many researchers suggest that running, particularly extensive running, can have adverse effects. The list of possible injuries is long and they have been well documented, especially injuries around joints in the hips and knees. Studies of runners dating back to 1973 as well as more recent studies have found a correlation between running and osteoporosis (or weakening of the bones). Research by Melonie Burrows at the University of East London found that long distance female runners have lower bone density, a sign of osteoporosis, than women who did little exercise. Studies by James O'Keefe and others at the Mayo Foundation for Medical Education found abnormalities in the structure of the hearts of athletes who did extreme running such as ultramarathons.
Despite these findings, other studies have found that running long distances actually strengthens the parts of the knee that are impacted by running. Furthermore, where damage occurs in the knee, this is reversed six months later. It also seems that our hip joints are able to withstand or tolerate the impacts from running. It has therefore been suggested that because our bodies have evolved to run, they have also evolved to self-repair damage to joints caused by the activity, and that in fact, running makes these joints stronger in the long term.
Other studies show that running improves the condition of our hearts and lungs, and reduces blood pressure, weight and the risk of many other diseases such as diabetes and cancer. A study led by Duck-chul Lee at Iowa State University followed 55,000 adults for over 15 years and concluded that running for just 50 minutes a week increases average life expectancy by three years. The study also found that people who ran consistently had up to 50% lower risk of heart disease.
You should spend about 20 minutes on Questions 29-40, which are based on Reading Passage 3 below.
Life at the limit
What are the physical limits to life in extreme environments? Although microbes are the Earth's simplest organisms, they live in places where it is impossible for more complex life forms to survive. Some microbes are able to thrive in the water surrounding deep sea hydrothermal vents, which emit water heated up to 400°C. At the other extreme, some microbes can survive in sub-zero temperatures. In fact, marine microbes living in all regions of the ocean make up over 98% of the total organisms living in the ocean. But what exactly are the limits to survival? Can organisms live in places that lack nutrients, and how long can they survive?
The middle of the Pacific Ocean, in an area known as the South Pacific Gyre, is the place furthest from any land, and it lacks nutrients or signs of life. According to Steven D'Hondt, an oceanographer at the University of Rhode Island, it is the deadest spot in the ocean. It seemed to be the obvious place to look for limits of life on Earth, and microbes have, in fact, been found far beneath this oceanic desert. Researchers think that they have been there for at least 100 million years. The previous record for longevity was held by microbes that had survived for 15 million years but this most recent discovery exceeds that tenfold and raises some intriguing questions.
The microbes from the South Pacific Gyre were discovered by geomicrobiologist Yuki Morono of the Japan Agency for Marine-Earth Science and Technology. Morono wanted to know whether organisms are able to survive where there is very little to sustain them. He drilled 5,700 metres below the seabed and extracted clay samples. The samples were found to contain oxygen, enough to allow the microbes to live, although the clay was extremely poor in nutrients. When Morono and his team then introduced nutrients into the samples, they were absorbed by the microbes that were living in the clay. Within a few days, the microbes started to multiply and 557 days later they were still forming thriving communities.
How the organisms survived for so long is a remarkable puzzle that scientists are trying to understand. The microbes are under intense pressure from miles of mud and water above them and do not have food or sunlight. Under inhospitable conditions, some microbes can form spores, or endospores. In this inactive state, they can stay dormant in order to survive extended periods of starvation. But the Pacific microbes had not formed these spores, suggesting two different possibilities.
A microbe can either reproduce by dividing or it can conserve its energy and maintain only its most basic functions. One possibility is that in the unfavourable conditions under the South Pacific floor, the microbes could have been dividing very slowly over centuries. In this case, the microbes in Morono's study may be the descendants of microbes from an even more distant past. However, at the depth where the microbes were found, there is so little nutrition that it seems unlikely that they would have the energy to divide and multiply. In fact, it seems that the most they could do is to self-repair. But if that is the case, and the microbes are not reproducing, they must have been living at the very edge of life for millions of years. This would mean that their metabolism can slow down so much that they can survive with only the tiniest amounts of nutrients. To the researchers, it seemed almost impossible that the microbes would be able to wake up and grow but they did just that.
The study is globally important and, as Yuki Morono stated, it shows that some of the simplest living creatures in the world 'do not actually have the concept of lifespan'. Unfortunately, the research is very difficult to replicate because different areas of the seabed have different compositions and therefore different environments, so is this a unique find? Scientists have collected samples of material from the sub-seabed that are 200 million years old; could they hold even older organisms? This points to another question: at which point under the seafloor does life end and what are the conditions that limit life? These are important questions, not only for life on Earth but also for potential life on other planets. According to Bo Barker Jorgensen from Aarhus University, 'low food and energy seem not to set the ultimate limit for life on Earth'. So, could life exist on places such as Mars or Jupiter's moons? If a planet seems to be uninhabitable, perhaps life may still exist in some form beneath the extra-terrestrial surface.