2012年職稱英語考試衛(wèi)生類A級(jí)模擬試題及答案(4)

第三篇

'Hidden' Species May Be Surprisingly Common

Cryptic species - animals that appear identical but are genetically quite distant - may be much more widespread than previously thought. The findings could have major implications in areas ranging from biodiversity estimates and wildlife management, to our understanding of infectious diseases and evolution.

Reports of cryptic species have increased dramatically over the past two decades with the advent of relatively inexpensive DNA sequencing technology. Markus Pfenninger and Klaus Schwenk, of the Goethe-Universitat in Frankfurt1, Germany, analyzed all known data on cryptic animal species and discovered that they are found in equal proportions throughout all major branches of the animal kingdom and occur in equal numbers in all biogeographical regions.

Scientists had previously speculated that cryptic species were predominantly found in insects and reptiles, and were more likely to occur in tropical rather than temperate regions. "Species that are seemingly widespread and abundant could in reality be many different cryptic species that have low populations and are highly endangered," says Pfenninger. Until the genetic information of all species in at least one taxon is thoroughly studied, no one will know just how many cryptic species exist. "It could be as high as 30%," Pfenninger says.

"I'm extremely surprised by their results," says Alex Smith of the University of Guelph2 in Ontario3, Canada. "It's a call to arms to keep doing the broad kind of genetic studies that we are doing."

Sampling as many individuals as possible, scientists hope to complete work on all fish and birds in another 5 to 10 years. Once either of these taxonomic groups is completed, Pfenninger says researchers will able to decide how many cryptic species exist throughout the animal kingdom.

Examples of cryptic species include the African elephant. A 2001 study found the elephants were actually two genetically distinct, non-interbreeding species, the African bush elephant and the African elephant. The species are currently listed as vulnerable and threatened, respectively, by the World Conservation Union （WCU）4.

The reclassifications are more than an academic exercise. They define populations that have evolved independently of each other and whose genetic differences can have significant consequences.

In the early 1900s misidentification of mosquito species based on morphology confused attempts to control malaria in Europe. Ultimately, what was thought to be a single species was actually made up of six sibling species, only three of which transmitted the disease. "The basic unit in biology is always the species, and you have to know what you are dealing with," Pfenninger says. Much previous research is now no longer used, he says, because it is not clear what species was being studied. （428 words）

41　Which of the following about the significance of the research on cryptic species is NOT true?

A　The results of the research can help the development of many other research areas.

B　The results of the research can help the development of biodiversity estimates.

C　The results of the research can help our understanding of infectious disease evolution.

D　The results of the research can help our understanding of "survival of the fittest."

42　What was scientists' understanding of cryptic species?

A　They occurred in equal numbers in all biogeographical regions.

B　They were mostly found in insects and reptiles.

C　They were likely to be in tropical rather than temperate regions.

D　Both B and C.

43　Do scientists know how many cryptic species exist?

A　Not yet.

B　Yes, they do.

C　They will know the answer in another one or two years.

D　They will never know the answer.

44　Which of the following about the African bush elephant and the African elephant is true?

A　The WCU are interbreeding those elephants.

B　They are interbreeding species.

C　They are two genetically distant species.

D　They depend on each other for survival.

45　People were confused in their attempts to control malaria in Europe in the early 1900s, because scientists

A　identified only one mosquito species instead of six species.

B　thought only three mosquito species transmitted disease.

C　thought there was only one mosquito species.

D　did not know what species was being studied

參考答案：41. D　　42. D　　43. A　　44. C　　45. A