PETS背誦原文閱讀帶翻譯
Bacteria are extremely small? living things. While we? measure our? own sizes in? inches or centimeters, bacterial 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 bacterium 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 kilometers) 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 flagella. 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 glide?? along over surfaces by some little-understood mechanism.
From the bacterial 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 molecules around them. Bacteria under the microscope, even those with no flagella, often bounce about in the water. This is because they collide with the water molecules and are pushed this way and that. Molecules move so rapidly that within a tenth of a second the molecules around a bacterium have all been replaced by new ones; even bacteria without flagella are thus constantly exposed to a changing environment.
細菌細菌是極其微小的生物體。我們用英寸或厘米來(lái)測量自己的大小，而測量細菌卻 要用微米。 一微米等于千分之一毫米。 針頭直徑大約一毫米。?
棒狀細菌通常有 2～4 微米長(cháng)，而圓形細菌的直徑一般只有 1 微米。因此，即使你把一個(gè)圓形細菌放大1000 倍，它也不過(guò)一個(gè)針頭那么大。??
可是如果把一個(gè)成年人放1000倍，就會(huì )變成 1 英里(或 1.6 公里) 多高。 用一般的顯微鏡觀(guān)察細菌時(shí)，你必須仔細觀(guān)察才能看見(jiàn)它們。 使用 100 倍的顯微鏡 時(shí)，你會(huì )發(fā)現細菌不過(guò)是隱約可見(jiàn)的小細棒或小點(diǎn)點(diǎn)，而它們的結構你卻根本看不出來(lái)。 使用特殊的著(zhù)色劑后，你會(huì )發(fā)現有的`細菌上長(cháng)著(zhù)不少波狀的"毛發(fā)"即鞭毛，而有的細菌只有一 根鞭毛。? 鞭毛的旋轉可以推動(dòng)細菌在水中行進(jìn)。??
不少細菌沒(méi)有鞭毛，因而不能自己行進(jìn)。 還有些細菌卻能通過(guò)某些鮮為人知的機制沿物體表面滑動(dòng)。我們所熟知的世界在細菌眼中 完全是另一個(gè)樣子。??
對于細菌來(lái)說(shuō)，水就同糖漿之于人類(lèi)一樣稠密。細菌是如此的微小， 周?chē)瘜W(xué)分子的一舉一動(dòng)都會(huì )對它們產(chǎn)生影響。在顯微鏡下，細菌，甚至包括那些沒(méi)有鞭 毛的細菌，經(jīng)常在水中跳來(lái)跳去。這是因為它們與水分子相撞后，被彈向各個(gè)方向。分子 移動(dòng)很迅速，僅 0.1 秒之隔，一個(gè)細菌周?chē)姆肿泳蜁?huì )完全更新。因此，即使是沒(méi)有鞭毛 的細菌也暴露在一個(gè)不斷變化的環(huán)境中。
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