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新东方优美背诵短文50篇 Unit48:Bacteria

时间:2007-11-21 03:20来源:互联网 提供网友:xianging   字体: [ ]
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Bacteria are extremely small living things. While we measure our own sizes in inches or centimeters, bacterial1 size is measured in microns. One micron is a thousandth of a millimeter: a pinhead is about a millimeter across. Rod-shaped bacteria are usually from two to four microns long, while rounded ones are generally one micron in diameter. Thus if you enlarged a rounded bacterium2 a thousand times, it would be just about the size of a pinhead. An adult human magnified by the same amount would be over a mile(1.6 kilometer) tall.

Even with an ordinary microscope, you must look closely to see bacteria. Using a magnification of 100 times, one finds that bacteria are barely visible as tiny rods or dots. One cannot make out anything of their structure. Using special stains, one can see that some bacteria have attached to them wavy-looking “hairs” called flagella3. Others have only one flagellum. The flagella rotate, pushing the bacteria through the water. Many bacteria lack flagella and cannot move about by their own power, while others can glide4 along over surfaces by some little-understood mechanism5.

From the bacteria point of view, the world is a very different place from what it is to humans. To a bacterium water is as thick as molasses is to us. Bacteria are so small that they are influenced by the movements of the chemical molecules6 around them. Bacteria under the microscope, even those with no flagella, often bounce about in the water. This is because they collide with the watery7 molecules and are pushed this way and that. Molecules move so rapidly that within a tenth of a second the molecules around a bacteria have all been replaced by new ones; even bacteria without flagella are thus constantly exposed to a changing environment.


细菌细菌是极其微小的生物体。我们用英寸或厘米来测量自己的大小,而测量细菌却要用微米。一微米等于千分之一毫米。针头直径大约一毫米。
棒状细菌通常有2~4微米长,而圆形细菌的直径一般只有1微米。因此,即使你把一个圆形细菌放大1000倍,它也不过一个针头那么大。
可是如果把一个成年人放大1000倍,就会变成1英里(或1.6公里)多高。用一般的显微镜观察细菌时,你必须仔细观察才能看见它们。使用
100倍的显微镜时,你会发现细菌不过是隐约可见的小细棒或小点点,而它们的结构你却根本看不出来。使
用特殊的着色剂后,你会发现有的细菌上长着不少波状的"毛发"即鞭毛,而有的细菌只有一根鞭毛。鞭毛的旋转可以推动细菌在水中行进。
不少细菌没有鞭毛,因而不能自己行进。还有些细菌却能通过某些鲜为人知的机制沿物体表面滑动。我们所熟知的世界在细菌眼中完全是另一个样子。
对于细菌来说,水就同糖浆之于人类一样稠密。细菌是如此的微小,周围化学分子的一举一动都会对它们产生影响。在显微镜下,细菌,甚至包括那些没有鞭
毛的细菌,经常在水中跳来跳去。这是因为它们与水分子相撞后,被弹向各个方向。分子移动很迅速,仅0.1
秒之隔,一个细菌周围的分子就会完全更新。因此,即使是没有鞭毛的细菌也暴露在一个不断变化的环境中

 


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1 bacterial dy5z8q     
a.细菌的
参考例句:
  • Bacterial reproduction is accelerated in weightless space. 在失重的空间,细菌繁殖加快了。
  • Brain lesions can be caused by bacterial infections. 大脑损伤可能由细菌感染引起。
2 bacterium BN7zE     
n.(pl.)bacteria 细菌
参考例句:
  • The bacterium possibly goes in the human body by the mouth.细菌可能通过口进入人体。
  • A bacterium is identified as the cause for his duodenal ulcer.一种细菌被断定为造成他十二指肠溃疡的根源。
3 flagella ejFxm     
n.鞭节,鞭毛
参考例句:
  • The rotation of flagella pushes the bacteria through the water.鞭毛的旋转可以推动细菌在水中行进。
  • Many protoctistans are motile,using pseudopodia,cilia or flagella.许多原生动物利用伪足、纤毛或鞭毛能运动。
4 glide 2gExT     
n./v.溜,滑行;(时间)消逝
参考例句:
  • We stood in silence watching the snake glide effortlessly.我们噤若寒蝉地站着,眼看那条蛇逍遥自在地游来游去。
  • So graceful was the ballerina that she just seemed to glide.那芭蕾舞女演员翩跹起舞,宛如滑翔。
5 mechanism zCWxr     
n.机械装置;机构,结构
参考例句:
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
6 molecules 187c25e49d45ad10b2f266c1fa7a8d49     
分子( molecule的名词复数 )
参考例句:
  • The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
  • Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里,大分子裂变为小分子。
7 watery bU5zW     
adj.有水的,水汪汪的;湿的,湿润的
参考例句:
  • In his watery eyes there is an expression of distrust.他那含泪的眼睛流露出惊惶失措的神情。
  • Her eyes became watery because of the smoke.因为烟熏,她的双眼变得泪汪汪的。
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TAG标签:   新概念  背诵  短文  bacteria
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