Free IELTS Academic Practice Test

Reading Passage 1 — Gardens in the Sky

You should spend about 20 minutes on Questions 1–13, which are based on Reading Passage 1.

Gardens in the Sky

Look down on many European city centres from a tall building and you will see patches of green where you might expect grey: flat roofs covered with grasses, flowering plants and, occasionally, small trees. Green roofs are not a new idea. For centuries, farmers in Scandinavia and Iceland covered their houses with layers of turf, which kept out the rain and held in heat during long winters. What is new is the engineering. Modern green roofs are carefully designed systems in which each layer has a job, and it was in Germany, from the 1970s onwards, that much of this technology was developed and standardised.

A typical modern green roof sits on top of a waterproof membrane. Above that comes a root barrier, which stops plants from forcing their way through the waterproofing, and then a drainage layer that lets excess water run off. Next is a lightweight growing medium — usually a mixture of crushed brick, pumice or similar minerals with a small amount of organic matter — and finally the plants themselves. Ordinary garden soil is rarely used, because it becomes extremely heavy when wet and tends to compact over time.

Designers generally distinguish between two main types. Extensive green roofs have a thin growing layer, often less than 15 centimetres deep, and are planted with hardy, low-growing species such as sedums, which store water in their thick leaves. They are light, need little maintenance, and are usually not intended for people to walk on. Intensive green roofs, by contrast, have a much deeper growing layer and can support lawns, shrubs and even trees. They are essentially rooftop parks, but they require a far stronger structure beneath them, regular watering and gardening, and a considerably larger budget. Between these two extremes, some designers create so-called semi-intensive roofs, which combine features of both.

Supporters of green roofs point to a range of benefits. The most widely studied is their effect on rainwater. In a city, rain that falls on conventional roofs and roads runs off almost immediately into drains, and during heavy storms the drainage system can be overwhelmed. A green roof absorbs part of the rainfall and releases the rest slowly, which reduces the peak flow reaching the drains. Just how much water is retained depends on the depth of the growing medium, the type of plants, the season, and how wet the roof already is when the rain starts.

Green roofs also affect temperature. Dark roofing materials can become very hot in summer sunshine, and the heat they absorb contributes to the so-called urban heat island effect, in which city centres stay warmer than the surrounding countryside, particularly at night. Plants cool the air around them as water evaporates from their leaves, and the growing layer shades and insulates the building below. As a result, rooms directly under a green roof may need less air conditioning in summer, which saves energy. Researchers generally report a smaller benefit in winter, partly because a waterlogged growing layer insulates less well than a dry one.

There is an economic argument too. A waterproof membrane exposed to the weather is damaged by ultraviolet light and by the constant expansion and contraction caused by daily changes in temperature. Covered by a green roof, the membrane is shielded from both, and it is commonly expected to last considerably longer. This can partly offset the higher cost of installation. Green roofs can also provide habitat for insects and birds, although a roof planted with a single species of sedum offers far less to wildlife than one with a varied mix of native plants. Some roofs are even designed with particular species in mind, such as ground-nesting birds or rare insects.

None of this means that green roofs suit every building. Many older roofs were never designed to carry the extra weight, particularly when the growing medium is saturated after rain, and strengthening them can be expensive. In hot, dry climates, plants may need irrigation, which weakens part of the environmental case. And a poorly designed or badly maintained roof can suffer from leaks, blocked drains or unwanted weeds. Even so, a number of cities, including Toronto and Copenhagen, now require green roofs on certain types of new building, and many others offer grants or other incentives to encourage them. What began as a practical solution for farmers in cold climates has become one of the tools planners use to make crowded cities more liveable.

Reading Passage 1 — Gardens in the Sky

You should spend about 20 minutes on Questions 1–13, which are based on Reading Passage 1.

Gardens in the Sky

Look down on many European city centres from a tall building and you will see patches of green where you might expect grey: flat roofs covered with grasses, flowering plants and, occasionally, small trees. Green roofs are not a new idea. For centuries, farmers in Scandinavia and Iceland covered their houses with layers of turf, which kept out the rain and held in heat during long winters. What is new is the engineering. Modern green roofs are carefully designed systems in which each layer has a job, and it was in Germany, from the 1970s onwards, that much of this technology was developed and standardised.

A typical modern green roof sits on top of a waterproof membrane. Above that comes a root barrier, which stops plants from forcing their way through the waterproofing, and then a drainage layer that lets excess water run off. Next is a lightweight growing medium — usually a mixture of crushed brick, pumice or similar minerals with a small amount of organic matter — and finally the plants themselves. Ordinary garden soil is rarely used, because it becomes extremely heavy when wet and tends to compact over time.

Designers generally distinguish between two main types. Extensive green roofs have a thin growing layer, often less than 15 centimetres deep, and are planted with hardy, low-growing species such as sedums, which store water in their thick leaves. They are light, need little maintenance, and are usually not intended for people to walk on. Intensive green roofs, by contrast, have a much deeper growing layer and can support lawns, shrubs and even trees. They are essentially rooftop parks, but they require a far stronger structure beneath them, regular watering and gardening, and a considerably larger budget. Between these two extremes, some designers create so-called semi-intensive roofs, which combine features of both.

Supporters of green roofs point to a range of benefits. The most widely studied is their effect on rainwater. In a city, rain that falls on conventional roofs and roads runs off almost immediately into drains, and during heavy storms the drainage system can be overwhelmed. A green roof absorbs part of the rainfall and releases the rest slowly, which reduces the peak flow reaching the drains. Just how much water is retained depends on the depth of the growing medium, the type of plants, the season, and how wet the roof already is when the rain starts.

Green roofs also affect temperature. Dark roofing materials can become very hot in summer sunshine, and the heat they absorb contributes to the so-called urban heat island effect, in which city centres stay warmer than the surrounding countryside, particularly at night. Plants cool the air around them as water evaporates from their leaves, and the growing layer shades and insulates the building below. As a result, rooms directly under a green roof may need less air conditioning in summer, which saves energy. Researchers generally report a smaller benefit in winter, partly because a waterlogged growing layer insulates less well than a dry one.

There is an economic argument too. A waterproof membrane exposed to the weather is damaged by ultraviolet light and by the constant expansion and contraction caused by daily changes in temperature. Covered by a green roof, the membrane is shielded from both, and it is commonly expected to last considerably longer. This can partly offset the higher cost of installation. Green roofs can also provide habitat for insects and birds, although a roof planted with a single species of sedum offers far less to wildlife than one with a varied mix of native plants. Some roofs are even designed with particular species in mind, such as ground-nesting birds or rare insects.

None of this means that green roofs suit every building. Many older roofs were never designed to carry the extra weight, particularly when the growing medium is saturated after rain, and strengthening them can be expensive. In hot, dry climates, plants may need irrigation, which weakens part of the environmental case. And a poorly designed or badly maintained roof can suffer from leaks, blocked drains or unwanted weeds. Even so, a number of cities, including Toronto and Copenhagen, now require green roofs on certain types of new building, and many others offer grants or other incentives to encourage them. What began as a practical solution for farmers in cold climates has become one of the tools planners use to make crowded cities more liveable.

Reading Passage 2 — The Otter and the Forest

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

The Otter and the Forest

A In the 1960s, the ecologist Robert Paine carried out a simple but influential experiment on the rocky shores of Washington State. He repeatedly removed one species of predatory starfish from a stretch of shoreline and watched what happened. Mussels, which the starfish normally ate, soon took over, crowding out many of the other species that had lived there, and the variety of life on the rocks fell sharply. Paine described the starfish as a “keystone species”: like the central stone in an arch, its removal caused the structure around it to collapse. The idea that a single predator could hold an entire community together soon found one of its most famous examples a little further north, in the cold coastal waters of the North Pacific.

B Sea otters once lived along a great arc of coastline stretching from northern Japan, through Alaska, and down to Mexico. Unlike most marine mammals, they have no thick layer of blubber; instead, they rely on extremely dense fur to stay warm. That fur made them a prime target. Their pelts fetched high prices, particularly in China, and the trade drew hunters from several nations. Beginning in the eighteenth century, hunters killed them in enormous numbers, and by the early twentieth century only a few small, scattered populations remained. In 1911 an international treaty gave sea otters legal protection, and in the decades that followed, several of the surviving groups slowly began to recover.

C Sea otters eat large quantities of shellfish and other invertebrates, and among their favourite prey are sea urchins. Urchins, in turn, feed on kelp, the giant brown seaweed that forms dense underwater forests in cool coastal waters. These forests shelter young fish and provide food for a wide range of invertebrates. Where otters are present, urchins tend to be scarce and cautious, hiding in crevices and feeding mainly on pieces of kelp that break off and drift past. Where otters are absent, urchin numbers can rise sharply, and the animals move out into the open to graze on living kelp. Given enough time, they can strip an area almost bare, leaving what biologists call an “urchin barren” — a rocky seabed with little kelp and far fewer of the fish and other creatures that depend on it.

D Some of the clearest evidence for this chain of effects came from the Aleutian Islands of Alaska in the early 1970s. The ecologist James Estes and his colleagues compared the seabed around islands where otters had recovered with the seabed around islands where they were still absent. The contrast was striking. Around the first group of islands, kelp forests were thick and healthy; around the second, urchins dominated and kelp was sparse. Because the islands were otherwise similar, the difference pointed strongly to the otters themselves. The findings, published in 1974, quickly became a textbook example. Here was a real-world keystone species, and a vivid example of what ecologists call a trophic cascade: a series of knock-on effects running down a food chain from the top predator.

E The story did not end there. During the 1990s, otter numbers in parts of the Aleutians fell steeply, and the kelp declined with them. Estes and his colleagues suggested an unexpected cause. Killer whales, which had rarely been seen hunting otters before, appeared to be eating them. One possibility they raised was that the whales' usual prey, such as seals and sea lions, had become scarcer, pushing the whales towards smaller animals. This explanation has been debated, and the full picture remains uncertain, but the episode showed that a keystone species can itself be controlled by forces operating on a much larger scale.

F More recently, researchers have found that otters can shape other habitats too. In Elkhorn Slough, an estuary in California, seagrass beds have improved as otters have returned. The otters eat crabs, and crabs eat small grazing animals, such as sea slugs, that keep the seagrass healthy by feeding on the algae that grow on its blades. With fewer crabs, these grazers thrive, and the seagrass grows better. Not everyone welcomes the otters' return, however. Because they eat shellfish such as crabs, clams and sea urchins, which people also harvest, some fishing communities see them as competitors, and arguments about how far their range should be allowed to expand continue today.

Reading Passage 2 — The Otter and the Forest

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

The Otter and the Forest

A In the 1960s, the ecologist Robert Paine carried out a simple but influential experiment on the rocky shores of Washington State. He repeatedly removed one species of predatory starfish from a stretch of shoreline and watched what happened. Mussels, which the starfish normally ate, soon took over, crowding out many of the other species that had lived there, and the variety of life on the rocks fell sharply. Paine described the starfish as a “keystone species”: like the central stone in an arch, its removal caused the structure around it to collapse. The idea that a single predator could hold an entire community together soon found one of its most famous examples a little further north, in the cold coastal waters of the North Pacific.

B Sea otters once lived along a great arc of coastline stretching from northern Japan, through Alaska, and down to Mexico. Unlike most marine mammals, they have no thick layer of blubber; instead, they rely on extremely dense fur to stay warm. That fur made them a prime target. Their pelts fetched high prices, particularly in China, and the trade drew hunters from several nations. Beginning in the eighteenth century, hunters killed them in enormous numbers, and by the early twentieth century only a few small, scattered populations remained. In 1911 an international treaty gave sea otters legal protection, and in the decades that followed, several of the surviving groups slowly began to recover.

C Sea otters eat large quantities of shellfish and other invertebrates, and among their favourite prey are sea urchins. Urchins, in turn, feed on kelp, the giant brown seaweed that forms dense underwater forests in cool coastal waters. These forests shelter young fish and provide food for a wide range of invertebrates. Where otters are present, urchins tend to be scarce and cautious, hiding in crevices and feeding mainly on pieces of kelp that break off and drift past. Where otters are absent, urchin numbers can rise sharply, and the animals move out into the open to graze on living kelp. Given enough time, they can strip an area almost bare, leaving what biologists call an “urchin barren” — a rocky seabed with little kelp and far fewer of the fish and other creatures that depend on it.

D Some of the clearest evidence for this chain of effects came from the Aleutian Islands of Alaska in the early 1970s. The ecologist James Estes and his colleagues compared the seabed around islands where otters had recovered with the seabed around islands where they were still absent. The contrast was striking. Around the first group of islands, kelp forests were thick and healthy; around the second, urchins dominated and kelp was sparse. Because the islands were otherwise similar, the difference pointed strongly to the otters themselves. The findings, published in 1974, quickly became a textbook example. Here was a real-world keystone species, and a vivid example of what ecologists call a trophic cascade: a series of knock-on effects running down a food chain from the top predator.

E The story did not end there. During the 1990s, otter numbers in parts of the Aleutians fell steeply, and the kelp declined with them. Estes and his colleagues suggested an unexpected cause. Killer whales, which had rarely been seen hunting otters before, appeared to be eating them. One possibility they raised was that the whales' usual prey, such as seals and sea lions, had become scarcer, pushing the whales towards smaller animals. This explanation has been debated, and the full picture remains uncertain, but the episode showed that a keystone species can itself be controlled by forces operating on a much larger scale.

F More recently, researchers have found that otters can shape other habitats too. In Elkhorn Slough, an estuary in California, seagrass beds have improved as otters have returned. The otters eat crabs, and crabs eat small grazing animals, such as sea slugs, that keep the seagrass healthy by feeding on the algae that grow on its blades. With fewer crabs, these grazers thrive, and the seagrass grows better. Not everyone welcomes the otters' return, however. Because they eat shellfish such as crabs, clams and sea urchins, which people also harvest, some fishing communities see them as competitors, and arguments about how far their range should be allowed to expand continue today.