IELTS Academic Reading Test 5

A They attract insects and then eat their flesh. Is that any way for a plant to behave? The naturalist and author of Origin of Species, Charles Darwin, was fascinated by carnivorous plants. In 1860, soon after he came across his first carnivorous plant — the sundew, Drosera — he wrote, ‘I care more about Drosera than the origin of all the species in the world.’ He spent months running experiments on the plants. He dropped flies and bits of meat on their leaves and watched them slowly fold their sticky tentacles over their prey. He thought it incredible that brushing a leaf with a single strand of human hair was enough to bring about a response. Yet sundews, he observed, ignored raindrops. To react to such a false alarm, he reasoned, would obviously be a great evil to the plant. This was no accident. This was adaptation.

B Darwin expanded his studies from sundews to other species in his book Insectivorous Plants. He was amazed at the quickness and power of the Venus flytrap. He showed that when one of its leaves snapped shut, it formed itself into a temporary ‘stomach’, secreting enzymes that could dissolve the prey. He noted that a leaf took more than a week to reopen after closing, and reasoned that the interlocking spines along the margin of the leaf allowed tiny insects to escape, saving the plant the expense of digesting an insufficient meal.

C Today, biologists using 21st-century tools to study cells and DNA are beginning to understand how these plants hunt, eat, and digest — and how these strange adaptations came about in the first place. Alexander Volkov, a plant physiologist at Oakwood University in Alabama, believes he has figured out the Venus flytrap’s secret. ‘This,’ Volkov declares, ‘is an electrical plant.’

D When an insect brushes against a hair on the leaf of a Venus flytrap, the movement sets off an electric charge. The charge builds up inside the tissue of the leaf but is not enough to stimulate the snap, which keeps the Venus flytrap from reacting to false alarms, such as raindrops. An insect, however, is likely to brush a second hair, adding enough electric charge for the leaf to close.

E Volkov’s experiments reveal that the electric charge travels down fluid-filled tunnels in a leaf, which opens up pores in cell membranes. Water rushes from the cells on the inside of the leaf to those on the outside, causing the leaf to rapidly flip in shape from convex to concave, like a soft contact lens. As the leaves flip, they snap together, trapping an insect inside.

F The bladderwort plant has an equally sophisticated way of setting its underwater trap. It pumps water out of tiny air sacs or bladders, lowering the pressure inside. When a water flea or some other small creature swims past, it bends hairs on the bladder, causing a flap to spring apart. The low pressure sucks water in, carrying the creature along with it. In one five-hundredth of a second, the flap swings shut again. The cells in the bladder then begin to pump water out again, creating a new vacuum. Many other species of carnivorous plants act like living flypaper, catching animals on sticky tentacles. Pitcher plants use yet another strategy, growing long tube-shaped leaves into which insects fall. Some of the largest have pitchers up to 30cm deep and can consume whole frogs unlucky enough to fall into them. Sophisticated chemistry helps make the pitcher a death trap.

G Nicholas Gotelli, of the University of Vermont, is trying to figure out what evolutionary forces pushed these plants towards meat. Carnivorous plants clearly benefit from eating animals; when scientists feed pitcher plants extra bugs, the plants get bigger. But the benefits of eating flesh are not the ones you might expect. Carnivorous animals, like ourselves, use the carbon in protein and the fat in meat to build muscles and store energy. Carnivorous plants, however, take nitrogen and phosphorus from the flesh in order to build light-harvesting enzymes. Eating animals, in other words, lets carnivorous plants do what all plants do: grow by taking energy directly from the sun.

H Unfortunately, they do a really bad job of it. That’s because they have to use a lot of energy to make the equipment they need to catch animals — the enzymes, the pumps, the sticky tentacles, and so on. A pitcher or a flytrap is not very good at photosynthesis because, unlike plants with ordinary leaves, they do not have flat solar panels that can absorb lots of sunlight. Gotelli suspects that only under special conditions are the benefits of being carnivorous greater than the costs. The poor soil of bogs and swamps, where many carnivorous plants grow, offers little nitrogen and phosphorus, so carnivorous plants enjoy an advantage there over ‘conventional’ plants. Also, bogs are often flooded with sunshine, so even an inefficient carnivorous plant can carry out enough photosynthesis to survive. ‘They’re stuck, and they’re making the best of it,’ says Aaron Ellison of Harvard University.

I Unfortunately, the adaptations that enable carnivorous plants to survive in harsh habitats also make them extremely sensitive to environmental changes. Chemical fertilizers used in agriculture and pollution from power plants are adding extra nitrogen to many bogs in North America. Carnivorous plants are so finely adapted to low levels of nitrogen that this extra fertilizer is overloading their systems. Humans also threaten carnivorous plants in other ways. The black market trade in exotic carnivorous plants is strong, but even if this can be prevented, carnivorous plants will continue to suffer from other dangers. Their habitat is disappearing, to be replaced by shopping centers and houses. The suppression of wildfires by government agencies allows other plants to grow quickly and outcompete the Venus flytraps. Good news, perhaps, for flies. But a loss for all who delight in the inventiveness of evolution.

A Numerous ancient civilisations collapsed or disappeared, leaving behind grand ruins reminiscent of what poet Shelley described in his sonnet Ozymandias. The term 'collapse' refers to a significant reduction in population and/or political, economic, and social complexity of a society across a wide area for an extended period.

B The awe-inspiring ruins left behind by these past societies captivate us all. As children, we marvel at them when we first discover them through pictures—vast stone structures, intricate carvings, or towering temples that defy imagination. As we grow older, many of us plan vacations to witness these remarkable sites firsthand, standing in silent reverence before the remnants of a world that once thrived. We are drawn to their magnificent and haunting beauty, as well as the enigmas they present. The grandeur of these ruins attests to the previous wealth and power of their builders, yet their sudden disappearance challenges our understanding of human resilience. These builders vanished, abandoning the remarkable structures they had painstakingly constructed. How did a once-mighty society end up collapsing, leaving behind only echoes of its former glory?

C For a long time, it has been suspected that the mysterious disappearance of many such societies was, to some extent, triggered by ecological issues—unintentional destruction of the environmental resources on which their societies relied. This suspicion of unintended ecological suicide, or ecocide, has been substantiated by discoveries made in recent decades by archaeologists, climatologists, historians, palaeontologists, and palynologists (pollen scientists). The processes through which past societies have undermined themselves by damaging their environments can be categorised into eight areas, which vary in significance from one case to another: deforestation and habitat loss, soil degradation, water management challenges, overhunting, overfishing, the impacts of invasive species on native ones, human population growth, and increased human activity.

D Historical collapses generally followed similar patterns resembling variations on a theme. These patterns often include resource depletion, environmental degradation, internal strife, or external pressures, yet the specific combination and intensity of these factors varied across civilisations. Writers are often tempted to draw analogies between the trajectory of human society and that of an individual's life, speaking of a society's birth, growth, peak, old age, and eventual demise. However, this metaphor proves inaccurate for many past societies: they experienced rapid declines after reaching their peak in terms of population and power, and these rapid declines must have come as a surprise and shock to their inhabitants. It is evident that not all past societies followed this trajectory uniformly to its conclusion: different societies collapsed to varying degrees and in somewhat distinct ways while many societies did not collapse at all. The diversity in collapse mechanisms suggests that while certain systemic vulnerabilities may be universal, their expression is deeply contingent on local conditions, cultural responses, and the interplay of multiple stressors over time.

E Currently, many individuals believe that environmental problems eclipse other global threats. These environmental problems encompass the same eight factors that contributed to past societies' downfalls, plus four new ones: human-induced climate change, the accumulation of toxic chemicals, energy shortages, and the complete utilisation of the Earth's photosynthetic capacity. However, the seriousness of these modern environmental dilemmas is vigorously debated among the scientific community. Are the perceived risks overstated or undervalued? Will contemporary technology resolve our issues, or is it producing new challenges faster than it can remedy old ones? When one resource (such as wood, oil, or ocean fish) is depleted, can we trust that new alternatives (like plastics, wind and solar energy, or farmed fish) will emerge? Isn't the rate of human population growth slowing down, suggesting we might soon reach a manageable global population?

F Questions like these highlight why the well-known collapses of past civilisations carry more significance than merely being romantic mysteries. There may be practical lessons to be learnt from these historical failures. However, there are also differences between the modern world and its problems, and those ancient societies and their problems. It would be naive to assume that studying the past will yield straightforward answers directly applicable to today's world. We have certain advantages over past societies that reduce our risks, including our powerful technology (i.e. its beneficial effects), globalisation, modern medicine, and enhanced awareness of both past and distant modern societies. At the same time, there are also factors that heighten our risks in comparison to earlier civilisations: again, our potent technology (i.e. its unintended destructive effects), globalisation (where a problem in one area can affect the entire world), the reliance of millions on modern health care for survival, and our vastly larger human population. Perhaps we can still learn from the past, but only if we carefully contemplate its lessons.

A We think of our prehistoric ancestors as people of the ice and snow, living in caves, and for many of the west European Neanderthalers that is a just picture of their life. But where there were no caves, further to the east on the Russian steppe, for example, open-air sites with some sort of constructed shelter were the only option. We now know much more about the cave sites than the open-air ones because, historically, it was the cave sites of Western Europe that were first explored by archaeologists and also because open-air sites are harder to find – many of them have disappeared under deep mud deposits or under the rising postglacial seas. Caves, moreover, aid the survival of archaeological material and can preserve the records of remote millennia.

B In south-west France, the limestone caves of the Périgord region made ideal homes for the Neanderthal people. There were good supplies of flint to hand for axes and the like, and the caves were often sited in small river valleys that offered protection against the worst of the weather. The Neanderthalers liked south-facing caves, for obvious reasons of sunshine and wind avoidance, and caves at some height above the valley floor offered refuge from floods and good game-watching vantage points. The Périgord region during the last ice age was, in fact, an exceptionally benign habitat for humans. It enjoyed a rather maritime climate with cooler summers that permitted the extension of tundra and steppe over its higher plateaux, and its year-round high levels of sunshine favoured the growth of the ground plants needed by reindeer, bison and horse. Winters were mildish for the ice age, animals never needed to migrate far from summer to winter, and men never needed to travel far from home to find abundant supplies of meat.

C In Central and Eastern Europe, where caves were unavailable, such open-air sites as have been discovered were mostly located near water – both because this was a good area to be for people and animals, and also because the sedimentation potential of lakes and stream courses has aided archaeological preservation – whereas erosion has presumably blown away sites which were out in the open. Some of the open-air sites in Germany, Central Europe and Russia have provided valuable information about Neanderthal man and his way of life. From Moldova, for example, comes evidence that has been interpreted as the remains of wind-break structures, or even a large tent: a ring, up to about 8 x 5m in size, of mainly mammoth bones enclosing a dense concentration of stone tools, animal bones and ash.

D From the west European caves more evidence of built structures is available, and some of it goes back a long way in time. In the Grotte du Lazaret, near Nice, at a date during the last ice age but one, claims for some sort of skin tent within the cave have been advanced, on the basis of arrangements of large stones out from the cave wall that might have supported timber struts for a covering of skins up to the rock face above. At Lazaret, what might be openings in the hypothesised tents seem to point away from the cave mouth, and finds of wolf and fox foot bones, without the rest of the skeletons, inside these ‘tents’ have been thought to indicate the use of animal pelts as bed coverings. The two patches of ash at Lazaret that mark ancient fires, with stone tools around them evidently made and used on the spot, are edged with small marine mollusc shells, prompting the excavator to suggest that seaweed had been used as bedding around the fires. The cave of Baume-Bonne in the Basses-Alpes region of France, another early site, boasts ten square metres of cobbles brought up from the local river and laid down, as though to take care of a puddle area in the cave, with the smoothest and roundest surfaces of the stones uppermost, and there are other similar cases.

E The ash encountered in concentrations at some sites testifies to the Neanderthal people’s use of fire: not surprising, since use of fire was, by Neanderthal times, an already ancient accomplishment of evolving humanity, and survival in the sub-arctic conditions faced by the Neanderthalers is inconceivable without control of fire. Fire gave warmth, light, heat for cooking and defence against predatory animals. A charred piece of birch from Krapina in Croatia, is thought to be the remains of a fire-making twirl stick. But Neanderthal hearths, in the sense of specially constructed places for fire, are fewer and harder to identify with certainty than the mere ash piles that are a regular feature of their sites. They seem often to have just lit a small fire (40-50cm across) on the existing ground surface of the cave, without preparation. Judging from the shallow penetration of heat effects under the ash, this fire was only of a short duration. Sometimes the fires were larger in size, up to one metre across, and quite irregular in shape. It is not always easy to decide how much additional structure some fires possessed: claims of stone circles to contain the fire run up against the fact that stones tend to litter the cave floors everywhere and those around a fire can quite accidentally look as though they were arranged in a circle.