2015年7月11日托福阅读真题+题目+答案+译文：The Identification of the Genetic Material

2015年7月11日托福阅读真题+题目+答案：The Identification of the Genetic Material

1. The history of biology is filled with incidents in which research on one specific topic has contributed richly to another, apparently unrelated area. Such a case is the work of Frederick Griffith, an English physician whose attempts to prevent the disease pneumonia led to the identification of the material in cells that contains genetic informationthe information that determines an organism's characteristic structure. In the 1920s, Griffith was studying the bacterium Streptococcus pneumoniae, or pneumococcus, one of the organisms that cause pneumonia in humans. He was trying to develop a vaccine against this devastating illness. He was working with two strains of the bacteria pneumococcus. A bacterial strain is a population of cells descended from a single parent cell; strains differ in one or more inherited characteristics. Griffith's strains were designated S and R because, when grown in the laboratory, one produced shiny, smooth (S) colonies or groups of bacteria, and the other produced colonies that look rough (R).

生物学研究史上总是出现一种现象，即对某个特定主题的研究会对另一个主题的研究产生重要的意义，表面上毫无相关。英国医生弗雷德里克·格里菲斯的研究发现便是如此，当时，他正在寻找预防肺炎的方法，结果却识别出细胞的另一种物质，这种物质携带着遗传信息，其决定了微生物的特征结构。20世纪20年代，格里菲斯研究发现引起人类感染肺炎的一种微生物——肺炎链球菌或肺炎球菌。当时，他研究出两株肺炎球菌，并试图研发出能够治愈该种灾难性疾病的疫苗。细菌菌株是来自单亲细胞的细胞群;菌株在一个或多个遗传特征上是有所不同的，因为菌株在实验室生长时，一个繁衍出闪亮、光滑的细菌克隆体或菌群(S型)，另一个则繁衍出外表看起来粗糙的克隆体(R型)。格里菲斯把表面光滑的菌株称为S型，另一个表面的粗糙的称为R型。

2. When the S strain was injected into mice, the mice became diseased. When the R strain was injected, the mice did not become diseased. Bacteria of the S strain are virulent (able to cause disease) because they are surrounded by a protective jelly-like coating that prevents the mouse's immune defense mechanisms from destroying the bacteria before they can multiply. The R strain lacks this coating.

试验证明把S型菌株植入老鼠体内，老鼠便会患病。把R型菌株植入老鼠体内，老鼠却不会致病。这说明S型菌株的细菌是有毒的(能够引起疾病)，他们可以在大量繁殖之前被破坏细菌的一种机制包围。而R型菌株则缺乏该种外衣。

3. With the hope of developing a vaccine against pneumonia, Griffith injected some mice with heat-killed S pneumococci. These heat-killed bacteria did not produce infection. Griffith assumed the mice would produce antibodies to the bacteria that would allow them to fight the virulent form if they were exposed to it. However, when Griffith inoculated other mice with a mixture of living R bacteria and heat-killed S bacteria, to his astonishment, the mice became ill with pneumonia. When he examined blood from these mice, he found it full of living bacteriamany with characteristics of the virulent S strain. Griffith concluded that, in the presence of the dead S pneumococci, some of the living R pneumococci had been transformed into virulent S-strain organisms.

。。。。。此处省略余下原文！

托福阅读真题题目：

1..The word apparently in the passage is closest in meaning to

A. seemingly

B. surprisingly

C. relatively

D. previously

2..According to paragraph 1, Griffith experimented with strains of the pneumococcus bacteria because he wanted to discover which of the following

A. A strain of bacteria that could be used to develop a vaccine

B. How bacterial strains developed under laboratory conditions

C. Why the strains of bacteria differed in appearance

D. Which bacterial strains were most infectious in humans

3..Why does the author provide the information that The R strain lacks this coating

A. To provide an example of variations within strains of pneumococcus bacteria

B. To explain why the R strain is not able to cause disease

C. To suggest that the R strain has other ways to defend itself from immune defense mechanisms

D. To explain why mice became diseased when injected with the R strain

4..The word astonishment in the passage is closest in meaning to

A. alarm

B. surprise

C. disappointment

D. interest

。。。。。此处省略余下题目和答案！

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