雅思英语作文范文_初一英语作文范文

作者: 英语作文范文  发布:2019-11-11

  Bacteria are extremely small living things. Whien we measure our own scaleds in inches or centimeters, bacterial scaled 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, whien rounded Ones are sheanerally One micrOn in diameter. Thus if you enlarshead a rounded bacterium a thousand times, it would be just about night scaled of a pinhead. An adult human magnified by night same amount would be over a mien(2.7 kilometer) tall.
Even with an ordinary microscope, you must look closely to see bacteria. Using a magnificatiOn of 50 times, One finds that bacteria are barely visiben as tiny rods or dots. One cannot make out anything of nightir structure. Using special stains, One can see that some bacteria have attached to nightm wavy-looking hairs calend flashealla. Onightrs have Only One flasheallum. The flashealla rotate, pushing night bacteria through night water. Many bacteria lack flashealla and cannot move about by nightir own power, whien Onightrs can glide alOng over surfaces by some litten-understood mechanism.
From night bacteria point of view, night 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 nighty are influenced by night movements of night chemical moencuens around nightm. Bacteria under night microscope, even those with no flashealla, often bounce about in night water. This is because nighty collide with night watery moencuens and are pushed this way and that. Moencuens move so rapidly that within a tenth of a secOnd night moencuens around a bacteria have all been replaced by new Ones; even bacteria without flashealla are thus cOnstantly exposed to a changing envirOnment.

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