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Reading Passage 1: New Understanding of Giraffes in the Wild
Even as the tallest animals on Earth, giraffes can be easy to overlook. Despite being a favorite in zoos, until recently almost nobody studied giraffes in the wild. ‘When I first became interested in giraffes in 2008 and started looking through the scientific literature, I was really surprised to see how little had been done,’ said Megan Strauss, an animal researcher at the University of Minnesota, USA. All that is changing fast, as a growing number of researchers seek to understand the biology and complex behavior of this graceful giant in its native habitat.
Giraffes, found throughout sub-Saharan Africa, are currently classified as a single species with up to nine subspecies that differ by features like head shape and whether the fur on their legs is plain or patterned. The giraffe is not yet listed as endangered, but researchers point to evidence that in the past 15 years, the population has fallen some 40 percent.
Recent studies have allowed researchers new insights into giraffes’ social structures. Groups of female giraffes, for example, have been found to form close friendships that can last for years. ‘We’re just at the beginnings of trying to understand this kind of behavior,’ Dr Strauss said. Female giraffes can live 20 years or more, and it makes sense they might rely on each other for clues to the best feeding grounds, help with taking care of their young, or the reduction of stress, by staying in groups.
Mother giraffes have displayed signs of grief after losing their young, known as calves, to lions. Dr Strauss described one case in which a mother spent four days at the place where a lion had eaten her calf, refusing food, and often in the company of two other adult females. Giraffe calves are extremely vulnerable to predators, and though mothers will fight valiantly to keep their young alive - kicking forward and backward — half of all calves are killed in their first year of life.
Male giraffes, known as bulls, generally become more important with age, and older bulls display that dominance physically and behaviorally: as their neck muscles grow, the male’s posture becomes prouder and more vertical. Recent observations show young bulls, when left on their own, mimicking their elders: head held high and neck puffed out. But should a dominant older bull come into view, the younger males instantly try to make themselves look small and innocent.
The younger bulls have reason to fear their elders. Clashes have been witnessed between adults when each bull repeatedly ‘necks’ the other, using his massive neck to slam his head against his rival. One bull somehow survived with a broken neck.
The skin of a giraffe is mostly gray. The coat has dark patches separated by light hair, which serves as camouflage, allowing them to blend in with the light and shade patterns of the acacia trees from which they feed. Grazing giraffes are hard to see even a few meters away. Research indicates that giraffes also have excellent sight, can see in color and over great distances, which helps them to spot lions and keep track of each other. In addition, a giraffe’s extraordinary mouth has lips and tongue that can together grasp a branch and then pluck away the leaves while avoiding thorns, almost as humans would grab with their hands. Each day, a giraffe consumes about 30 kilograms of leaves, shoots and vines, all digested in its four-chambered stomach.
A giraffe can stand more than six meters tall, with its neck accounting for roughly a third of its height and its legs the same. The giraffe’s long neck is due to the length of the vertebrae, not the number of vertebrae. The growth of the neck largely takes place during early childhood, as giraffe mothers would have a difficult time giving birth to young with longer necks. The giraffe’s head and neck are held up by large muscles attached to the lower spine. Recent studies show that the greatest challenge to the giraffe’s cardiovascular system is how to both pump blood very high and retrieve it from far below. The outside of a giraffe's veins are extremely thick, to prevent blood leaking into surrounding tissue. Other adaptations in the cardiovascular system allow the giraffe to bend over for a drink of water, and then raise its head again quickly without fainting.
Researchers were also surprised to find that a giraffe does not have an unusually large heart. It is half a percent of body mass, the same as in a mouse. Moreover, the amount of blood pumped into circulation is modest, proportionally lower than it is in humans. That could help explain why giraffes rarely run for very long: enough oxygen cannot be delivered to their muscles fast enough for them to keep running. Or maybe the giraffes are worried about tripping over their own feet. This is because signals from the nerves travel at about the same speed in giraffes as in rats or other mammals. Given the greater distance they have to travel in the giraffe to reach the brain, it is possible the giraffe faces real challenges in reacting quickly to a rock beneath its hoof or a bite to its ankle.
New understanding of this wonderful animal sheds light on both its physiology and its behavior. Researchers hope to use this knowledge to increase their ability to work with preservation, as its habitat is reduced and the giraffe becomes scarcer.
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The amount of research on giraffes in their natural environment has increased lately.
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Megan Strauss disapproves of keeping giraffes in zoos.
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The number of giraffes in Africa has nearly doubled.
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Female giraffes tend to live longer than males.
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Mother giraffes sometimes use their legs to defend their young.
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Younger bulls hold their necks higher in the presence of more powerful males.
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Male giraffes have been observed fighting.
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Skin/coat provides 8……… when standing near trees
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Mouth: can be used like 9……… to get leaves
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Neck: length develops in childhood to provide an easier 10……… for mothers
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Cardiovascular system: extra strong 11……… keep blood from spilling into other tissues
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12……… normal size for such a large animal
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Nerves: slower reaction time because 13………
Reading Passage 2: Desertification
A The world's great deserts were formed by natural processes interacting over long intervals of time. During most of these times, deserts have grown and shrunk independent of human activities. Paleo deserts, large sand seas now inactive because they are stabilized by vegetation, extend well beyond the present margins of core deserts, such as the Sahara. In some regions, deserts are separated sharply from surrounding, less arid areas by mountains and other contrasting landforms that reflect basic structural differences in the regional geology. In other areas, desert fringes form a gradual transition from a dry to a more humid environment, making it more difficult to define the desert border.
B These transition zones have very fragile, delicately balanced ecosystems. Desert fringes often are a mosaic of microclimates. Small hollows support vegetation that picks up heat from the hot winds and protects the land from the prevailing winds. After rainfall the vegetated areas are distinctly cooler than the surroundings. In these marginal areas, human activity may stress the ecosystem beyond its tolerance limit, resulting in degradation of the land. By ponding the soil with their hooves, livestock compact the substrate, increase the proportion of fine material, and reduce the percolation rate of the soil, thus encouraging erosion by wind and water. Grazing and the collection of firewood reduces or eliminates plants that help to bind the soil.
C This degradation of formerly productive land - desertification - is a complex process. It involves multiple causes, and it proceeds at varying rates in different climates. Desertification may intensify a general climatic trend toward greater aridity, or it may initiate a change in local climate.
D Desertification does not occur in linear, easily mappable patterns. Deserts advance erratically, forming patches on their borders. Areas far from natural deserts can degrade quickly to barren soil, rock, or sand through poor land management. The presence of a nearly desert has no direct relationship to desertification. Unfortunately, an area undergoing desertification is brought to public attention only after the process is well underway. Often little or no data are available to indicate the previous state of the ecosystem or the rate of degradation. Scientists still question whether desertification, as a process of global change, is permanent or how and when it can be halted or reversed.
E Desertification became well known in the 1930's when part of the Great Plains in the United States turned into the "Dust Bowl" as a result of drought and poor practices in farming, although the term itself was not used until almost 1950. During the dust bowl period, millions of people were forced to abandon their farms and livelihoods. Greatly improved methods of agriculture and land and water management in the Great Plains have prevented that disaster from recurring, but desertification presently affects millions of people in almost every continent. Increased population and livestock pressure on marginal lands has accelerated desertification. In some areas, nomads moving to less arid areas disrupt the local ecosystem and increase the rate of erosion of the land. Nomads are trying to escape the desert, but because of their land-use practices, they are bringing the desert with them.
F It is a misconception that drought cause desertification. Droughts are common in arid and semiarid lands. Well-managed lands can recover from drought when the rains return. Continued land abuse during droughts, however, increases land degradation. By 1973, the drought that began in 1968 in the Sahel of West Africa and the land-use practices there had caused the deaths of more than 100,000 people and 12 million cattle, as well as the disruption of social organizations from villages to the national level.
G At the local level, individuals and governments can help to reclaim and protect their lands. In areas of sand dunes, covering the dunes with large boulders or petroleum will interrupt the wind regime near the face of the dunes and prevent the sand from moving. Sand fences are used throughout the Middle East and the United States, in the same way snow fences are used in the north. Placement of straw grids, each up to a square meter in area, will also decrease the surface wind velocity. Shrubs and trees planted within the grids are protected by the straw until they take root. In areas where some water is available for irrigation, shrubs planted on the lower one third of a dune's windward side will stabilize the dune. This vegetation decreases the wind velocity near the base of the dune and prevents much of the sand from moving.
H Oases and farmlands in windy regions can be protected by planting tree fences or grass belts. Sand that manages to pass through the grass belts can be caught in strips of trees planted as wind breaks 50 to 100 meters apart adjacent to the belts. Small plots of trees may also be scattered inside oases to stabilize the area. On a much larger scale, a "Green Wall" which will eventually stretch more than 5,700 kilometers in length, much longer than the famous Great Wall, is being planted in northeastern China to protect "sandy lands" - deserts believed to have been created by human activity.
I More efficient use of existing water resources and control of salinization are other effective tools for improving arid lands. New ways are being sought to use surface-water resources such as rain water harvesting or irrigating with seasonal runoff from adjacent highlands. Research on the reclamation of deserts also is focusing on discovering proper crop rotation to protect the fragile soil, on understanding how sand-fixing plants can be adapted to local environments, and on how grazing lands and water resources can be developed effectively without being overused.
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Desertification poses a threat to people worldwide
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It is difficult to describe the process of desertification
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Desertification may alter local climates
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People have misconceptions regarding desertification origins
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It is hard to notice desertification in its early stages
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Straw grids diminish the swiftness of the surface wind
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All desert borders are difficult to define.
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Desertification is a reversible process.
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Part of the Great Plains did not become a so-called "Dust Bowl" until almost 1950.
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Nomads cannot get away from the desert because of their current land-use methods.
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Tree fences or grass belts planted inside oases can catch sand in the wind and 24______ these areas as well. The "Green Wall" is an example.
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Water resource management and prevention of 25______ are also effective in protecting lands.
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Scientists are trying to find 26_____ to protect the vulnerable soil.
Reading Passage 3: Spider Silk 2
Scientists have succeeded in copying the silk-producing genes of the Golden Orb Weaver spider and are using them to create a synthetic material which they believe is the model for a new generation of advanced bio-materials. The new material, biosilk, which has been spun for the first time by researchers at DuPont, has an enormous range of potential uses in construction and manufacturing.
The attraction of the silk spun by the spider is a combination of great strength and enormous elasticity, which man-made fibres have been unable to replicate. On an equal-weight basis, spider silk is far stronger than steel and it is estimated that if a single strand could be made about 10m in diameter, it would be strong enough to stop a jumbo jet in flight. A third important factor is that it is extremely light. Army scientists are already looking at the possibilities of using it for lightweight, bulletproof vests and parachutes.
For some time, biochemists have been trying to synthesise the drag-line silk of the Golden Orb Weaver. The drag-line silk, which forms the radial arms of the web, is stronger than the other parts of the web and some biochemists believe a synthetic version could prove to be as important a material as nylon, which has been around for 50 years, since the discoveries of Wallace Carothers and his team ushered in the age of polymers.
To recreate the material, scientists, including Randolph Lewis at the University of Wyoming, first examined the silk-producing gland of the spider. ‘We took out the glands that produce the silk and looked at the coding for the protein material they make, which is spun into a web. We then went looking for clones with the right DNA,’ he says.
At DuPont, researchers have used both yeast and bacteria as hosts to grow the raw material, which they have spun into fibres. Robert Dorsch, DuPont’s director of biochemical development, says the globules of protein, comparable with marbles in an egg, are harvested and processed. ‘We break open the bacteria, separate out the globules of protein and use them as the raw starting material. With yeast, the gene system can be designed so that the material excretes the protein outside the yeast for better access,’ he says.
‘The bacteria and the yeast produce the same protein, equivalent to that which the spider uses in the draglines of the web. The spider mixes the protein into a water-based solution and then spins it into a solid fibre in one go. Since we are not as clever as the spider and we are not using such sophisticated organisms, we substituted man-made approaches and dissolved the protein in chemical solvents, which are then spun to push the material through small holes to form the solid fibre.’
Researchers at DuPont say they envisage many possible uses for a new biosilk material. They say that earthquake-resistant suspension bridges hung from cables of synthetic spider silk fibres may become a reality. Stronger ropes, safer seat belts, shoe soles that do not wear out so quickly and tough new clothing are among the other applications. Biochemists such as Lewis see the potential range of uses of biosilk as almost limitless. ‘It is very strong and retains elasticity: there are no man-made materials that can mimic both these properties. It is also a biological material with all the advantages that have over petrochemicals,’ he says.
At DuPont’s laboratories, Dorsch is excited by the prospect of new super-strong materials but he warns they are many years away. ‘We are at an early stage but theoretical predictions are that we will wind up with a very strong, tough material, with an ability to absorb shock, which is stronger and tougher than the man-made materials that are conventionally available to us,’ he says.
The spider is not the only creature that has aroused the interest of material scientists. They have also become envious of the natural adhesive secreted by the sea mussel. It produces a protein adhesive to attach itself to rocks. It is tedious and expensive to extract the protein from the mussel, so researchers have already produced a synthetic gene for use in surrogate bacteria.
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A comparison of the ways two materials are used to replace silk-producing glands.
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Predictions regarding the availability of the synthetic silk
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Ongoing research into other synthetic materials
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The research into the part of the spider that manufactures silk
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The possible application of the silk in civil engineering
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Synthetic gene grown in 33___ or 34___
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Synthetic gene grown in 33___ or 34___
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globules of 35___
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dissolved in 36___ solvents
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passed through 37___
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Biosilk has already replaced nylon in parachute manufacture.
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The spider produces silk of varying strengths.
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Lewis and Dorsch co-operated in the synthetic production of silk.
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. TRUE
2. NOT GIVEN
3. FALSE
4. NOT GIVEN
5. TRUE
6. FALSE
7. TRUE
8. camouflage
9. hands
10. birth
11. veins
12. heart
13. distance
14. E
15. D
16. C
17. F
18. D
19. G
20. NO
21. NOT GIVEN
22. NO
23. YES
24. stabilize
25. salinization
26. proper crop rotation
27. E
28. H
29. I
30. D
31. G
32. bacteria / yeast
33. yeast / bacteria
34. protein
35. chemical
36. holes
37. FALSE
38. TRUE
39. NOT GIVEN