How does an ecosystem(生态系统) work? What makes the populations of different species the way they are? Why are there so many flies and so few wolves? To find an answer, scientists have built mathematical models of food webs, noting who eats whom and how much each one eats.
With such models, scientists have found out some key principles operating in food webs. Most food webs, for instance, consist of many weak links rather than a few strong ones. When a predator(掠食动物) always eats huge numbers of a single prey(猎物), the two species are strongly linked; when a predator lives on various species, they are weakly linked. Food webs may be dominated by many weak links because that arrangement is more stable over the long term. If a predator can eat several species, it can survive the extinction(灭绝) of one of them. And if a predator can move on to another species that is easier to find when a prey species becomes rare, the switch allows the original prey to recover. The weak links may thus keep species from driving one another to extinction.
Mathematical models have also revealed that food webs may be unstable, where small changes of top predators can lead to big effects throughout entire ecosystems. In the 1960s, scientists proposed that predators at the top of a food web had a surprising amount of control over the size of populations of other species—including species they did not directly attack.
And unplanned human activities have proved the idea of top-down control by top predators to be true. In the ocean, we fished for top predators such as cod on an industrial scale, while on land, we killed off large predators such as wolves. These actions have greatly affected the ecological balance.
Scientists have built an early-warning system based on mathematical models. Ideally, the system would tell us when to adapt human activities that are pushing an ecosystem toward a breakdown or would even allow us to pull an ecosystem back from the borderline. Prevention is key, scientists say, because once ecosystems pass their tipping point(临界点), it is remarkably difficult for them to return.
1.What have scientists discovered with the help of mathematical models of food webs?
A.The living habits of species in food webs.
B.The rules governing food webs of the ecosystems.
C.The approaches to studying the species in the ecosystems.
D.The differences between weak and strong links in food webs.
2.A strong link is found between two species when a predator ________.
A.has a wide food choice
B.can easily find new prey
C.sticks to one prey species
D.can quickly move to another place
3.What will happen if the populations of top predators in a food web greatly decline?
A.The prey species they directly attack will die out.
B.The species they indirectly attack will turn into top predators.
C.The living environment of other species will remain unchanged.
D.The populations of other species will experience unexpected changes.
4.What conclusion can be drawn from the examples in Paragraph 4?
A.Uncontrolled human activities greatly upset ecosystems.
B.Rapid economic development threatens animal habitats.
C.Species of commercial value dominate other species.
D.Industrial activities help keep food webs stable.
5.How does an early-warning system help us maintain the ecological balance?
A.By getting illegal practices under control.
B.By stopping us from killing large predators.
C.By bringing the broken-down ecosystems back to normal.
D.By signaling the urgent need for taking preventive action.
By the end of the century，if not sooner，the world’s oceans will be bluer and greener thanks to a warming climate，according to a new study.
At the heart of the phenomenon lie tiny marine microorganisms(海洋微生物) called phytoplankton. Because of the way light reflects off the organisms，these phytoplankton create colourful patterns at the ocean surface. Ocean colour varies from green to blue，depending on the type and concentration of phytoplankton. Climate change will fuel the growth of phytoplankton in some areas，while reducing it in other spots，leading to changes in the ocean's appearance.
Phytoplankton live at the ocean surface，where they pull carbon dioxide(二氧化碳) into the ocean while giving off oxygen. When these organisms die，they bury carbon in the deep ocean，an important process that helps to regulate the global climate. But phytoplankton are vulnerable to the ocean's warming trend. Warming changes key characteristics of the ocean and can affect phytoplankton growth，since they need not only sunlight and carbon dioxide to grow，but also nutrients.
Stephanie Dutkiewicz，a scientist in MIT's Center for Global Change Science，built a climate model that projects changes to the oceans throughout the century. In a world that warms up by 3℃，it found that multiple changes to the colour of the oceans would occur. The model projects that currently blue areas with little phytoplankton could become even bluer. But in some waters，such as those of the Arctic，a warming will make conditions riper for phytoplankton，and these areas will turn greener. “Not only are the quantities of phytoplankton in the ocean changing. ”she said，“but the type of phytoplankton is changing. ”
1.What are the first two paragraphs mainly about?
A. The various patterns at the ocean surface.
B. The cause of the changes in ocean colour.
C. The way light reflects off marine organisms.
D. The efforts to fuel the growth of phytoplankton.
2.What does the underlined word “vulnerable” in Paragraph 3 probably mean?
A. Sensitive. B. Beneficial
C. Significant D. Unnoticeable
3.What can we learn from the passage?
A. Phytoplankton play a declining role in the marine ecosystem.
B. Dutkiewicz's model aims to project phytoplankton changes
C. Phytoplankton have been used to control global climate
D. Oceans with more phytoplankton may appear greener.
4.What is the main purpose of the passage？
A. To assess the consequences of ocean colour changes
B. To analyse the composition of the ocean food chain
C. To explain the effects of climate change on oceans
D. To introduce a new method to study phytoplankton
California has lost half its big trees since the 1930s, according to a study to be published Tuesday and climate change seems to be a major factor(因素).
The number of trees larger than two feet across has declined by 50 percent on more than 46, 000 square miles of California forests, the new study finds. No area was spared or unaffected, from the foggy northern coast to the Sierra Nevada Mountains to the San Gabriels above Los Angeles. In the Sierra high country, the number of big trees has fallen by more than 55 percent; in parts of southern California the decline was nearly 75 percent.
Many factors contributed to the decline, said Patrick McIntyre, an ecologist who was the lead author of the study. Woodcutters targeted big trees. Housing development pushed into the woods. Aggressive wildfire control has left California forests crowded with small trees that compete with big trees for resources(资源).
But in comparing a study of California forests done in the 1920s and 1930s with another one between 2001 and 2010, McIntyre and his colleagues documented a widespread death of big trees that was evident even in wildlands protected from woodcutting or development.
The loss of big trees was greatest in areas where trees had suffered the greatest water shortage. The researchers figured out water stress with a computer model that calculated how much water trees were getting in comparison with how much they needed, taking into account such things as rainfall, air temperature, dampness of soil, and the timing of snowmelt(融雪).
Since the 1930s, McIntyre said, the biggest factors driving up water stress in the state have been rising temperatures, which cause trees to lose more water to the air, and earlier snowmelt, which reduces the water supply available to trees during the dry season.
1.What is the second paragraph mainly about?
A.The seriousness of big-tree loss in California.
B.The increasing variety of California big trees.
C.The distribution of big trees in California forests.
D.The influence of farming on big trees in California.
2.Which of the following is well-intentioned but may be bad for big trees?
A.Ecological studies of forests.
B.Banning woodcutting.
C.Limiting housing development.
D.Fire control measures.
3.What is a major cause of the water shortage according to McIntyre?
A.Inadequate snowmelt. B.A longer dry season.
C.A warmer climate. D.Dampness of the air.
4.What can be a suitable title for the text?
A.California’s Forests: Where Have All the Big Trees Gone?
B.Cutting of Big Trees to Be Prohibited in California Soon
C.Why Are the Big Trees Important to California Forests?
D.Patrick McIntyre: Grow More Big Trees in California
Monkeys seem to have a way with numbers.
A team of researchers trained three Rhesus monkeys to associate 26 clearly different symbols consisting of numbers and selective letters with 0-25 drops of water or juice as a reward. The researchers then tested how the monkeys combined—or added—the symbols to get the reward.
Here’s how Harvard Medical School scientist Margaret Livingstone, who led the team, described the experiment: In their cages the monkeys were provided with touch screens. On one part of the screen, a symbol would appear, and on the other side two symbols inside a circle were shown. For example, the number 7 would flash on one side of the screen and the other end would have 9 and 8. If the monkeys touched the left side of the screen they would be rewarded with seven drops of water or juice; if they went for the circle, they would be rewarded with the sum of the numbers—17 in this example.
After running hundreds of tests, the researchers noted that the monkeys would go for the higher values more than half the time, indicating that they were performing a calculation, not just memorizing the value of each combination.
When the team examined the results of the experiment more closely, they noticed that the monkeys tended to underestimate(低估) a sum compared with a single symbol when the two were close in value—sometimes choosing, for example, a 13 over the sum of 8 and 6. The underestimation was systematic: When adding two numbers, the monkeys always paid attention to the larger of the two, and then added only a fraction(小部分) of the smaller number to it.
“This indicates that there is a certain way quantity is represented in their brains, ”Dr. Livingstone says. “But in this experiment what they’re doing is paying more attention to the big number than the little one.”
1.What did the researchers do to the monkeys before testing them?
A.They fed them. B.They named them.
C.They trained them. D.They measured them.
2.How did the monkeys get their reward in the experiment?
A.By drawing a circle. B.By touching a screen.
C.By watching videos. D.By mixing two drinks.
3.What did Livingstone’s team find about the monkeys?
A.They could perform basic addition. B.They could understand simple words.
C.They could memorize numbers easily. D.They could hold their attention for long.
4.In which section of a newspaper may this text appear?
A.Entertainment. B.Health. C.Education. D.Science.
Bacteria are an annoying problem for astronauts. The microorganisms(微生物) from our bodies grow uncontrollably on surfaces of the International Space Station, so astronauts spend hours cleaning them up each week. How is NASA overcoming this very tiny big problem? It’s turning to a bunch of high school kids. But not just any kids. It is depending on NASA HUNCH high school classrooms, like the one science teachers Gene Gordon and Donna Himmelberg lead at Fairport High School in Fairport, New York.
HUNCH is designed to connect high school classrooms with NASA engineers. For the past two years, Gordon’s students have been studying ways to kill bacteria in zero gravity, and they think they’re close to a solution(解决方案). “We don’t give the students any breaks. They have to do it just like NASA engineers,” says Florence Gold, a project manager.
“There are no tests,” Gordon says. “There is no graded homework. There almost are no grades, other than ‘Are you working towards your goal?’ Basically, it’s ‘I’ve got to produce this product and then, at the end of year, present it to NASA.’ Engineers come and really do an in-person review, and...it’s not a very nice thing at times. It’s a hard business review of your product.”
Gordon says the HUNCH program has an impact(影响) on college admissions and practical life skills. “These kids are so absorbed in their studies that I just sit back. I don’t teach.” And that annoying bacteria? Gordon says his students are emailing daily with NASA engineers about the problem, readying a workable solution to test in space.
1.What do we know about the bacteria in the International Space Station?
A.They are hard to get rid of. B.They lead to air pollution.
C.They appear in different forms. D.They damage the instruments.
2.What is the purpose of the HUNCH program?
A.To strengthen teacher-student relationships.
B.To sharpen students’ communication skills.
C.To allow students to experience zero gravity.
D.To link space technology with school education.
3.What do the NASA engineers do for the students in the program?
A.Check their product. B.Guide project designs.
C.Adjust work schedules. D.Grade their homework.
4.What is the best title for the text?
A.NASA: The Home of Astronauts
B.Space: The Final Homework Frontier
C.Nature: An Outdoor Classroom
D.HUNCH: A College Admission Reform
As data and identity theft becomes more and more common, the market is growing for biometric(生物测量) technologies—like fingerprint scans—to keep others out of private e-spaces. At present, these technologies are still expensive, though.
Researchers from Georgia Tech say that they have come up with a low-cost device(装置) that gets around this problem: a smart keyboard. This smart keyboard precisely measures the cadence(节奏) with which one types and the pressure fingers apply to each key. The keyboard could offer a strong layer of security by analyzing things like the force of a user’s typing and the time between key presses. These patterns are unique to each person. Thus, the keyboard can determine people’s identities, and by extension, whether they should be given access to the computer it’s connected to—regardless of whether someone gets the password right.
It also doesn’t require a new type of technology that people aren’t already familiar with. Everybody uses a keyboard and everybody types differently.
In a study describing the technology, the researchers had 100 volunteers type the word “touch” four times using the smart keyboard. Data collected from the device could be used to recognize different participants based on how they typed, with very low error rates. The researchers say that the keyboard should be pretty straightforward to commercialize and is mostly made of inexpensive, plastic-like parts. The team hopes to make it to market in the near future.
1.Why do the researchers develop the smart keyboard?
A.To reduce pressure on keys. B.To improve accuracy in typing.
C.To replace the password system. D.To cut the cost of e-space protection.
2.What makes the invention of the smart keyboard possible?
A.Computers are much easier to operate.
B.Fingerprint scanning techniques develop fast.
C.Typing patterns vary from person to person.
D.Data security measures are guaranteed.
3.What do the researchers expect of the smart keyboard?
A.It’ll be environment-friendly. B.It’ll reach consumers soon.
C.It’ll be made of plastics. D.It’ll help speed up typing.
4.Where is this text most likely from?
A.A diary. B.A guidebook C.A novel. D.A magazine.
