全新版大学英语听说教程第二册 Unit14（在线收听）

2-14-A

Passage 1:

To start with, rainwater is collected in a large 3,000 gallon tank on the highest point of land on the island. The tank is so large that it measures about 12 feet in diameter. Once the tank is filled with rainwater, fish are added to the tank and are then raised in the rainwater.

Passage 2:

What are some of the similarities between the African and the Asian elephants? Well, for one thing, both animals have long noses, called trunks. An elephant sometimes uses its trunk like a third hand. Both kinds of elephants use their trunks to pick up very small objects and very large, heavy objects. They can even pick up trees with their trunks. For another thing, both the African and the Asian elephants have very large ears, although the African elephant's ears are considerably larger.

Passage 3:

Several theories have been proposed about why the dinosaurs disappeared from the face of the earth. In recent years one popular theory proposes that climatic changes caused the dinosaurs to become extinct. This climatic change theory says that millions of years ago the climate of the world gradually became colder. As the earth slowly became colder, fewer plants were able to grow. The cold weather finally resulted in a severe shortage of food for the dinosaurs. As you probably know, most of the dinosaurs were vegetarians, and they depended on plants for their food supply.

2-14-B

Why Is Biodiversity Important?

The importance of biodiversity seems obvious to us. We enjoy the beauty of biodiversity when we take a walk in the park, take a trip to the zoo or a wild area, read books or watch TV shows about strange creatures in foreign lands. Some people believe that biodiversity is important simply because it is so wonderful. Some think there are philosophical or spiritual reasons for biodiversity. But there are other reasons why it is so important.

The loss of biodiversity will change the balance of life on earth. If an ecosystem is destroyed, many species adapted to that ecosystem may very likely be destroyed as well. If that species is what scientists call "keystone", a whole ecosystem may depend on it.

Biodiversity is also important in its direct benefits to people. Plants give us the air we breathe; animals and plants supply us with the food we eat; and organisms and microorganisms clean the air, regulate floods, recycle waste, and control pests.

Biodiversity also has economic and health benefits. Both industry and agriculture depend on it for raw material and other things. And medicine is even more dependent on biodiversity. In China, more than 5,000 species of plants are used for medicinal purposes. Many species which were thought "useless" at first are found to be valuable. And this is a further threat from the loss of biodiversity.

2-14-C

How Many Species Are There?

Isn't it surprising that scientists have a better understanding of how many stars there are in the galaxy than how many species there are on Earth? Their estimates of global species diversity vary from 2 to 100 million species. Most people agree on an estimate of somewhere near 10 million and yet only 1.75 million have actually been named. Current knowledge of species diversity is limited. This problem becomes more serious because there is a lack of a central database or list of the world's species.

New species are still being discovered -- even new birds and mammals. On average, about three new species of birds are found each year, and since 1990, 10 new species of monkeys have been discovered. Other groups are still far from being completely described: an estimated 40 percent of freshwater fishes in South America have not yet been classified.

Scientists were startled in 1980 by the discovery of a huge diversity of insects in tropical forests. In one study of just 19 trees in Panama, 960 new species of beetles were discovered.

As scientists begin investigating other little-known ecosystems, like the soil and the deep sea, "surprising" discoveries of species become commonplace. There is nothing strange about this, though, since as many as a million undescribed species are believed to live in the deep sea. And one gram of a small-sized piece of land might hold 90 million bacteria and other microbes. How many species these communities contain is still anyone's guess.

2-15-A

The environment on our planet is a closed system: nothing new is ever added. Nature recycles its resources.

Today, the Earth is in trouble. Factories pour dirty water into our rivers. Many fish die and the water becomes unhealthy for people to drink. Cars and factories put poison into the air and cause plants, animals and people to get sick. People throw bottles and paper out of their car windows, and the roadside becomes covered with all sorts of wastes. Over the years, people have changed the environment, and we have pollution.

To continue to survive, we must learn how to use the Earth's resources wisely. We have to change our habits and stop dumping such enormous amounts of industrial waste into the water and air. We must cooperate with nature and learn better ways to use, not abuse, our environment.