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Reading Passage 1: Carnivorous Plants
They attract insects and then eat their flesh. Is that any way for a plant to behave?
The naturalist and author of On the 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.
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.
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.’
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.
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.
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.
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.
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, it does 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.
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.
- 1
He understood why the plant (Drosera) did not respond to ______.
- 2
He demonstrated how the Venus flytrap's leaves close and then, for a short period, act like a ______.
- 3
The electric charge enters fluid-filled tunnels, causing ______ in cell membranes to open.
- 4
When water is pumped out of bladder cells, a ______ builds up inside.
- 5
Some pitcher plants are big enough to capture and eat ______.
- 6
Pitcher plants increase in size after they have digested a lot of insects.
- 7
Carnivorous plants produce light-harvesting enzymes with the nutrients they extract from animals.
- 8
Pitcher plants and Venus flytraps are more efficient at photosynthesis than plants with ordinary leaves.
- 9
Venus flytraps are better adapted to the soil of swamps and bogs than other carnivorous plants.
- 10
Carnivorous plants frequently find it difficult to photosynthesise in bogs due to a lack of sunlight.
- 11
Scientists have campaigned to reduce the amount of nitrogen that is released into the soil by agricultural practices.
- 12
A lot of exotic carnivorous plants are sold illegally.
- 13
Preventing wildfires is beneficial to the Venus flytrap.
Reading Passage 2: Movement Underwater
A Self-propelled motion is a fundamental ability in many organisms. From the beating flagella of tiny plankton keeping afloat near the ocean surface to the playful perfection of dolphins surfing the bow wave of a ship, marine creatures have adopted a huge variety of styles, speeds, and methods of movement. Each species has its own particular need for the evolutionary developments that have taken place, but the basic requirements are the same—finding food, avoiding predation, seeking a mate or a safe place to have young, or migrating to an area with more favorable conditions.
B The particular physical properties of water that most affect movement are density, viscosity (stickiness), and buoyancy. Seawater is about 800 times denser than air and nearly 100 times as viscous. Consequently, there is much more resistance to movement than on land, as anyone will know who has ever tried to wade through waist-deep water. However, with density comes much greater buoyancy, so that organisms need to spend relatively little energy to stay afloat. As they move through the ocean environment, organisms seek to make wave motion, currents, and natural turbulence work to their advantage, not to their detriment.
C Most fishes have swim bladders to help them offset the density of their bodies and so maintain neutral buoyancy with minimal effort. These small, gas-filled chambers contain specialized networks of blood vessels that can add or remove gases such as oxygen and carbon dioxide. The ability to remain indefinitely at a constant depth without expending energy is especially important for slow-moving fishes that seek food in the shallows, or for those that hunt and scavenge in kelp forests. Active swimmers, such as mackerel, skipjacks, and sharks, do not have swim bladders because they need to change depth more rapidly than they could regulate the gas content. These fishes must swim forever or they will sink.
D Many animals, especially the tiny zooplankton, have taken to a life of simply drifting near the surface, contentedly feeding on the microscopic phytoplankton and bacteria floating there. Although life among the plankton might seem easy, there is in fact a remarkable range of movement. Some tiny plankton only 1–2 mm in length actually travel long distances each day. Species that live below the level where sunlight reaches nightly swim hundreds of meters up to the surface to feed in the relative safety of darkness. At dawn, they sink back down in an effort to escape predators—a double journey equivalent to a person swimming 700 km a day.
E It has taken marine creatures millions of years of evolution to overcome the chief deterrent to motion through a dense medium such as water—that of drag resistance. Swimming efficiency has been achieved by minimizing the three types of drag created by friction, turbulence, and body form. To reduce surface friction, the body must be smooth and rounded. In addition, the scales of most fishes are coated with slime to lubricate their passage through water. To reduce the turbulent drag created as water flows around the moving shape, a rounded front end and tapered back end are required. To reduce form drag, the cross-sectional area of the body should be minimal—a pencil shape would be ideal. The combined shape, taking into account all three types of drag, is the streamlined torpedo form of a tuna, the fastest-swimming of all fishes.
F Speed is only one of three important aspects of swimming ability. Tuna, swordfish, and mackerel all specialize in fast, steady cruising, but there are many other fishes for whom sustained speed is less important, such as the barracuda. This formidable predator specializes in swift acceleration, and has a far higher success rate for its attacks than its steady-cruising cousins. The freshwater pike, which lurks in the shadows until its quarry is within striking distance and then lunges with great rapidity, achieves a remarkable 70–80 percent success rate. The third specialization is maneuverability, best demonstrated by the butterfly fishes. These have disk-shaped bodies that permit abrupt changes of track. Many fishes are generalists, being at least partly proficient in all three modes of movement.
G Almost all fishes swim by undulation. Strong W-shaped muscles along the side of the body progressively contract and relax in sequence, from head to tail and from side to side, creating a traveling horizontal wave. The body is thrown into a series of curves that press sideways and back against the water, producing a forward thrust. The narrow, elongated forms of eels and sea snakes allow easy undulation along their full length. In contrast, the more stubby and inflexible bodies of armor-plated trunkfish use only the swish of their short tail fins to move themselves through the water. Most other fishes combine elements of both methods, coordinating powerful strokes of the tail fins with subtle body undulations.
H A fish’s fins also play a vital and versatile role. The vertically oriented dorsal and ventral fins on the back and belly control sideways motion, while up-and-down motion is controlled by the pectoral and pelvic fins on the fish’s sides. Whereas the shape of the tail fin relates directly to speed—crescent-moon-shaped for fast cruising, broad and flat for acceleration—the style and arrangement of the other fins are crucial for maneuverability. Puffer fishes scull with tiny, oscillating pectoral fins, while butterfly fishes undulate their broad dorsal and ventral fins, twisting and turning with great precision through intricate coral reefs.
- 14
A strategy to avoid being attacked
- 15
How fish are able to keep afloat naturally
- 16
The physical process by which fish propel themselves ahead
- 17
A list of reasons why different creatures move from one place to another
- 18
How the medium of water both restricts and aids movement
- 19
Specialised ability: Ability to maintain the same ______ over long distances. Example fish species: Swordfish.
- 20
Specialised ability: Rapid ______. Example fish species: Barracuda.
- 21
Specialised ability: Sudden attack on prey following period of lying in wait. Example fish species: ______
- 22
Specialised ability: Rapid changes of direction. Example fish species: ______
- 23
Streamlined shape narrowing towards the rear to reduce ______ drag
- 24
Fins controlling ______ movement (vertically oriented dorsal and ventral fins)
- 25
Fins controlling ______ movement (pectoral and pelvic fins)
- 26
Fins which are important for ______ of fish
- 27
Minimal cross-sectional body area to decrease ______ drag
Reading Passage 3: Sea Change for Salinity
One of the most serious problems facing Australian farmers is an increase in the salt content in the soil. However, there are new weapons emerging in the fight against salinity.
A
Beneath the flat, impassive surface of Australia lie hidden mountains, valleys and gorges – ancient traps and channels for the deadly salt that is stealthily killing so much of the Australian landscape. The war on salt is calling forth new weapons. A suite of high technologies used by geologists to see underground and prospect for gold and minerals is now being used to pinpoint the presence of salt beneath the landscape, and to predict where it might move.
B
Unless this process is clearly understood, warns Chief of Exploration and Mining Dr Neil Phillips, the hard work now underway of planning and tree-planting on the surface may be rendered ineffective: salt can still sneak past and erupt, following one of the ancient river channels formed millions of years ago. The use of airborne electromagnetics to detect salt hidden beneath the landscape has been around for a decade, but the past two years have seen a major development in its precision and powers of detection. Like the use of radar in battles, it has the potential to turn the tide of the struggle in favour of the defence by helping to pinpoint, plot and predict the movements of the foe.
C
Angus Howell, who farms near Warrenbayne, in Southeast Australia, saw his first outbreak of salt in 1948. Over the ensuing decades the patches spread and multiplied until they consumed almost 100 hectares. By the late 1970s, Howell and his fellow farmers had decided it was time for action and established a government-funded “Landcare” group in a bid to save Australia’s farmland. But despite a mounting effort by scientists, farmers and governments, the “white death” continued to encroach. Small successes were eclipsed by larger defeats and fresh outbreaks.
D
“The technical solutions just aren’t there yet for dealing with broadacre salinity, nor are the social and economic solutions. How do you introduce the land-use changes that are needed when people still need to make a living?” Howell asks. There is no satisfactory solution yet. Part of the problem has lain in salt’s ability to mount ambushes, emerging somewhere new, sometimes unexpected and unexplained, beating plans to intercept it. Only now are scientists starting to really disclose its secret subterranean stores and passages.
E
The need for such knowledge is pressing. Salt has already afflicted six million hectares of once-productive country. At present rates, it is predicted that, by 2050, it will have sterilised a total of 17 million hectares and the waters of Australia’s Murray River will regularly exceed the World Health Organisation’s salt limits for drinking water. Defeating this assault may take centuries, not decades.
F
Electromagnetic surveys measure the electrical conductivity of soil to reveal the distribution of salt and the nature and variability of the regolith – the weathered rock and sediment that may lie above the bedrock. Magnetic surveys measure small differences in the Earth’s magnetic field, enabling scientists to probe the deep past and reconstruct ancient landscapes – rivers, basins and faults now buried under tens of metres of sediment. These features help to reveal where groundwater is stored, dictate the direction of groundwater movement, and are critical to predicting or ruling out salinity hot-spots.
G
Radiometric analysis is based on the detection of radiation emitted by elements contained in rocks and soils, allowing scientists to delineate landforms. These factors influence the mobility of salt through the soil profile and help determine where to plant particular crop species to tackle the problem. Using data from the Murray River region, scientists have revealed a network of ancient drainage systems that channelled water beneath the current land-surface. These buried channels may carry salt and sometimes run at right angles to channels on the surface. This implies that the salt could move underground in quite a different direction to what one would expect by looking at surface slope and drainage.
H
One of the biggest advances in detection, says Professor Neil Phillips, has come with the integration of different techniques such as magnetics, electromagnetics and radiometrics, and ground mapping. Individually, these technologies only gave clues to what was going on underground. Together they provide a far more revealing picture of the subsurface landscape, several hundred metres deep. Advanced airborne electromagnetics, in particular, enables scientists to take “slices” of the landscape at depths of five metres, ten metres, fifteen metres and so on, to determine where salt may be stored at depth. This is building up a four-dimensional picture of the subsurface landscape, enabling researchers to understand movements of salt in length, breadth, depth and time. From such technologies it will be possible to locate salt stores, identify how saline they are, look at man-made and natural changes to the landscape that may cause it to mobilise, and then predict where it will head to and over what time span. This in turn will give the salt warriors time to model various ways of containing or curbing the menace, see what works best and then try it out on the ground.
- 28
A prediction of the future risk of salt to water supplies.
- 29
The reason why technologies must be combined to be effective.
- 30
A reference to the recent improvements in the accuracy of airborne electromagnetics.
- 31
The organization of concerned farmers into an official body.
- 32
The estimated length of time salinity is likely to be a problem.
- 33
A summary of stages in a proposed plan of action to combat the salt problem.
- 34
The possibility that current re-vegetation practices are a waste of time.
- 35
Electromagnetic surveys
- A. can help farmers choose the best location for plants.
- B. can show the composition of the top layer of the ground.
- C. can detect how far below ground the salt is.
- D. can determine how old the salt is in a particular area.
- 36
Radiometric analysis
- 37
Airborne electromagnetics
- 38
What link does the writer make between salt and gold?
- A. They can both be found in the same locations.
- B. Both have been found to have an impact on the landscape.
- C. The same techniques can be used to find both.
- D. Neither is present in mountainous areas.
- 39
What is the 'process' referred to in Section B?
- A. the killing of vegetation by salt
- B. salt's ability to travel below ground
- C. the ability of trees to decrease salt levels
- D. the detection of salt by tracing other minerals
- 40
According to Angus Howell, one problem in the fight against salinity is that
- A. not enough farmers are concerned about the fight.
- B. farmers' requests for help have been ignored.
- C. some possible measures may cause farmers to lose income.
- D. the government has not provided farmers with sufficient financial support.
- 41
Which of the following best describes the writer's view of the salinity problem in Australia?
- A. Farmers are fighting an enemy that moves secretly and hides well.
- B. Farmers have been able to contain this enemy in a small area.
- C. Farmers have already had significant success in fighting this problem.
- D. Farmers need to form more organised groups to solve this problem.
Phiếu trả lời
Điền đáp án khi làm bài — kiểm tra kết quả ngay lập tức và lưu cục bộ, mọi câu sai sẽ vào nhật ký lỗi cùng bài học khắc phục.
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Lưu trên thiết bị này — không cần tài khoản. Đăng nhập ở trang tiến trình nếu muốn đồng bộ sang nơi khác.
Hiện đáp án
Đáp án
1. raindrops
2. stomach
3. pores
4. vacuum
5. frogs
6. TRUE
7. TRUE
8. FALSE
9. NOT GIVEN
10. FALSE
11. NOT GIVEN
12. TRUE
13. FALSE
14. D
15. C
16. G
17. A
18. B
19. speed
20. acceleration
21. freshwater pike
22. butterfly fishes
23. turbulent
24. up-and-down
25. sideways
26. maneuverability
27. form
28. E
29. H
30. B
31. C
32. E
33. H
34. B
35. B
36. A
37. C
38. C
39. B
40. C
41. A