第二篇
Putting Plants to Work
Using the power of the sun is nothing new. People have had solar-powered calculators and buildings with solar panels for decades. But plants are the real experts: They’ve been using sunlight as an energy source for billions of years. Cells in the green leaves of plants work like tiny factories to convert sunlight, carbon dioxide, and water into sugars and starches, stored energy that the plants can use. This conversion process is called photosynthesis. Unfortunately, unless you’re a plant, it’s difficult and expensive to convert sunlight into storable energy. That’s why scientists are taking a closer look at exactly how plants do it. Some scientists are trying to get plants, or biological cells that act like plants, to work as miniature photosynthetic power stations. For example, Maria Ghirardi of the National Renewable Energy Laboratory in Golden, Colo., is working with green algae. She’s trying to trick them into producing hydrogen instead of sugars when they perform photosynthesis. Once the researchers can get the algae working efficiently, the hydrogen that they produce could be used to power fuel cells in cars or to generate electricity. The algae are grown in narrow-necked glass bottles to produce hydrogen in the lab. During photosynthesis, plants normally make sugars or starches. "But under certain conditions, a lot of algae are able to use the sunlight energy not to store starch, but to make hydrogen." Ghirardi says. For example, algae will produce hydrogen in an airfree environment. It’s the oxygen in the air that prevents algae from making hydrogen most of the time. Working in an airfree environment, however, is difficult. It’s not a practical way to produce cheap energy. But Ghirardi and her colleagues have discovered that by removing a chemical called sulfate from the environment that the algae grow in, they will make hydrogen instead of sugars, even when air is present. Unfortunately, removing the sulfate also makes the algae’s cells work very slowly, and not much hydrogen is produced. Still, the researchers see this as a first step in their goal to produce hydrogen efficiently from algae. With more work, they may be able to speed the cells’ activity and produce larger quantities of hydrogen. The researchers hope that algae will one day be an easy-to-use fuel source. The organisms are cheap to get and to feed, Ghirardi says, and they can grow almost anywhere: "You can grow them in a reactor, in a pond. You can grow them in the ocean. There’s a lot of flexibility in how you can use these organisms."
A.They are the real experts in producing it.
B.They have been a source of it.
C.They have been used to produce it.
D.They have been using it for billions of years.
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The Tough Grass that Sweetens Our Lives
Sugar cane was once a wild grass that grew in New Guinea and was used by local people for roofing their houses and fencing their gardens. Gradually a different variety evolved which contained sucrose and was chewed on for its sweet taste. Over time, sugar cane became a highly valuable commercial plant, grown throughout the world. 46 Sugar became a vital ingredient in all kinds of things, from confectionery to medicine, and, as the demand for sugar grew, the industry became larger and more profitable. 47 Many crops withered and died, despite growers’ attempts to save them, and there were fears that the health of the plant would continue to deteriorate. In the 1960s, scientists working in Barbados looked for ways to make the commercial species stronger and more able to resist disease. They experimented with breeding programmes, mixing genes from the wild species of sugar cane, which tends to be tougher, with genes from the more delicate, commercial type. 48 This sugar cane is not yet ready to be sold commercially, but when this happens, it is expected to be incredibly profitable for the industry. 49 Brazil, which produces one quarter of the world’s sugar, has coordinated an international project under Professor Paulo Arrudo of the Universidade Estaudual de Campinas in Sao Paulo. Teams of experts have worked with him to discover more about which parts of the genetic structure of the plant are important for the production of sugar and its overall health. Despite all the research, however, we still do not fully understand how the genes function in sugar cane. 50 This gene is particularly exciting because it makes the plant resistant to rust, a disease which probably originated in India, but is now capable of infecting sugar cane across the world. Scientists believe they will eventually be able to grow a plant which cannot be destroyed by rust.
A.the 1980s,scientists have been analysing the mysterious of the sugar canes genetic code.
B.Unfortunately,however,the plant started to become weaker and more prone to disease.
C.The majority of the world’s sugar now comes from this particular commercial species.
D.One major gene has been identified by Dr. Angellique D’Hont and her team in Montpeller,France.
E.Eventually,a commercial plant was developed which was 5 percent sweeter than before,but also much stronger and less likely to die from disease.
F.Sugar cane is now much more vigorous and the supply of sugar is therefore more guaranteed.
He paused, waiting for her to digest the information.()
A.understand
B.withhold
C.exchange
D.contact
The contract between the two companies will expire soon.()
A.shorten
B.start
C.end
D.resume
Come out, or I’ll bust the door down.()
A.shut
B.break
C.set
D.beat
Make sure the table is securely anchored.()
A.repaired
B.cleared
C.booked
D.fixed
The police will need to keep a wary eye on this area of town.()
A.cautious
B.naked
C.blind
D.private
These animals migrate south annually in search of food.()
A.explore
B.travel
C.inhabit
D.prefer
He was tempted by the high salary offered by the company.()
A.taught
B.kept
C.changed
D.attracted
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