陳蕙雅思教材 - 雅思閱讀精選 (Bacteria)

Bacteria

Bacteria are extremelysmall  living things. While we  measure our own

sizes in  inches or centimeters, bacterial size ismeasured in microns. One

micron is a thousandth ofa millimeter: a pinhead is about a millimeter

across.          Rod-shaped bacteria are usually fromtwo to four microns long,

while rounded ones aregenerally one micron in           diameter.Thus if you

enlarged a roundedbacterium a thousand times, it would  bejust about the

size  of a pinhead.         An adult humanmagnified by the same amount would be

over a mile (1.6kilometers) tall.

Even  with an  ordinary  microscope, you   must  look closely  to  see  

bacteria.  Using a magnification of 100 times, one  findsthat bacteria are

barely visible as tinyrods or dots. One cannot make out anything of their

structure. Using specialstains, one can see that some bacteria have

attached to themwavy-looking "hairs" called flagella. Others have only one

flagellum. The flagellarotate, pushing the bacteria through the water.

Many bacteria lackflagella and cannot move  about  by  their   own  

power,  while others   can  glide  along  over  surfaces by  some

little-understood    mechanism.

From the bacterial pointof view, the world is a very different place from

what it is to humans. Toa bacterium       water is as thickas  molasses is to

us. Bacteria are so smallthat they are influenced  by  the movements  of

the    chemical molecules  around  them. Bacteria  under  the microscope,

even those with noflagella, often bounce about in       thewater. This is

because they collide withthe water molecules and are pushed this way and

that. Molecules move         so rapidly that within a tenth of asecond the

molecules around abacterium have all been replaced by new ones;   even

bacteria without flagellaare thus constantly exposed to a changing

environment.

細菌細菌是極其微小的生物體。  我們用英寸或釐米來測量自己的大小，而測量細菌卻 要用微米。 一微米等於千分之一毫米。 針頭直徑大約一毫米。

棒狀細菌通常有 2～4 微米 長，而圓形細菌的直徑一般只有 1 微米。  因此，即使你把一個圓形細菌放大 1000 倍，它也 不過一個針頭那麼大。  

可是如果把一個成年人放大 1000 倍，就會變成 1 英里(或 1.6 公里) 多高。 用一般的顯微鏡觀察細菌時，你必須仔細觀察才能看見它們。 使用

100 倍的顯微鏡 時，你會發現細菌不過是隱約可見的小細棒或小點點，而它們的結構你卻根本看不出來。 使

用特殊的著色劑後，你會發現有的細菌上長著不少波狀的"毛髮"即鞭毛，而有的細菌只有一 根鞭毛。  鞭毛的旋轉可以推動細菌在水中行進。  

不少細菌沒有鞭毛，因而不能自己行進。 還有些細菌卻能通過某些鮮為人知的機制沿物體表面滑動。  我們所熟知的世界在細菌眼中 完全是另一個樣子。  

對於細菌來說，水就同糖漿之於人類一樣稠密。  細菌是如此的微小， 周圍化學分子的一舉一動都會對它們產生影響。  在顯微鏡下，細菌，甚至包括那些沒有鞭

毛的細菌，經常在水中跳來跳去。  這是因為它們與水分子相撞後，被彈向各個方向。  分子 移動很迅速，僅  0.1  

秒之隔，一個細菌周圍的分子就會完全更新。  因此，即使是沒有鞭毛 的細菌也暴露在一個不斷變化的環境中。