共用题干
第一篇
Putting Plants to Work
Using the power of the sun is nothing new.People have had solar-powered calculators and buildings with
solar panels（太阳能电池板）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（二氧化
碳）,and water into sugars
and starche（淀粉）,stored energy that the piants can use. This conversion
process is called photosynthesis (光合作用）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 very small
photosynthesic power stations. For example, Maria Ghirardi of the National Renewable Energy Laboratory in
Golden. Cobo.,is working with green algae（水藻）.She's trying to trick them into producing hydrogen
instead of sugars when they perform photosynthesis. Once the researchers can get the algae working efficient-
ly ,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 photosynthe-
sis , plants normally make sugars or strchds. "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 hy-
drogen 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（硫酸盐）
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."
Scientists study how photosynthesis works because they want to_______________.
A: improve the efficiency of it
B: turn plant sugars to a new form of energy
C: get more sugars and starches from plants
D: make green plants a new source of energy
共用题干
第三篇
Longer Lives for Wild Elephants
Most people think of zoos as safe places for animals,where struggles such as having difficulty finding
food and avoiding predators（猛兽）don't exist. Without such problems,animals in zoos should live to a ripe
（成熟的）old age.
But that may not be true for the largest land animals on Earth.Scientists have known that elephants in
zoos often suffer from poor health.Sometimes,they even become unable to have babies.
To learn more about how captivity（圈养）affects elephants, a team of international scientists compared
the life spans of female elephants born in zoos with female elephants living outdoors in their native lands.
Zoos keep detailed records of all the animals in their care,documenting factors such as birth dates,illnes-
ses,weight and death.These records made it possible for the researchers to analyze 40 years of data on 800
African and Asian elephants in zoos across Europe.The scientists compared the life spans of the zoo-born fe-
male elephants with the life spans of thousands of wild female elephants in Africa and Asian elephants that
work in logging camps（伐木场）, over approximately the same time period.
The team found that female African elephants born in zoos lived an average of 16.9 years. Their wild
counterparts who died of natural causes lived an average of 56 years一more than three times as long. Female
Asian elephants followed a similar pattern. In zoos,they lived 18.9 years,while those in the logging camps
lived 41.7 years.
Scientists don't know yet why wild elephants seem to get on so much better than their zoo-raised coun-
terparts.Georgia Mason,a biologist at the University of Guelph in Canada who led the study,thinks stress
and obesity（肥胖症）may be to blame. Zoo elephants don't get the same kind of exercise they would in the
wild,and most are very fat. Social lives of elephants are also much different in zoos than in the wild,where
they live in large herds and family groups.
The study raises some questions about acquiring more elephants to keep in zoos.While some threatened
and endangered species living in zoos reproduce（生殖）successfully and maintain healthy populations,that
doesn't appear to be the case with elephants.
Unlike other animals in zoos,zoo-raised elephants
A:live a long life
B:give birth to many babies
C:develop poor health
D:have difficulty getting food
