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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. Rodshaped 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 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 wavylooking " 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 littleunderstood mechanism. 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 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 watery 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 Molecules move so rapidly that within a tenth of a second the molecules around a bacteria have all been replaced by new ones even bacteria without flagella are thus constantly exposed to a changing environment. |
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xì jūn shì jí qí wēi xiǎo de shēng wù tǐ. wǒ men yòng yīng cùn huò lí mǐ lái cè liáng zì jǐ de dà xiǎo, ér cè liáng xì jūn què yào yòng wēi mǐ. yī wēi mǐ děng yú qiān fēn zhī yī háo mǐ. zhēn tóu zhí jìng dà yuē yī háo mǐ. bàng zhuàng xì jūn tōng cháng yǒu 2 4 wēi mǐ zhǎng, ér yuán xíng xì jūn de zhí jìng yì bān zhǐ yǒu 1 wēi mǐ. yīn cǐ, jí shǐ nǐ bǎ yí gè yuán xíng xì jūn fàng dà 1000 bèi, tā yě bù guò yí gè zhēn tóu nà me dà. kě shì rú guǒ bǎ yí gè chéng nián rén fàng dà 1000 bèi, jiù huì biàn chéng 1 yīng lǐ huò 1. 6 gōng lǐ duō gāo. yòng yì bān de xiǎn wēi jìng guān chá xì jūn shí, nǐ bì xū zǐ xì guān chá cái néng kàn jiàn tā men. shǐ yòng 100 bèi de xiǎn wēi jìng shí, nǐ huì fā xiàn xì jūn bù guò shì yǐn yuē kě jiàn de xiǎo xì bàng huò xiǎo diǎn diǎn, ér tā men de jié gòu nǐ què gēn běn kàn bu chū lái. shǐ yòng tè shū de zhuó sè jì hòu, nǐ huì fā xiàn yǒu de xì jūn shàng zhǎng zhe bù shǎo bō zhuàng de" máo fà" jí biān máo, ér yǒu de xì jūn zhǐ yǒu yī gēn biān máo. biān máo de xuán zhuǎn kě yǐ tuī dòng xì jūn zài shuǐ zhōng xíng jìn. bù shǎo xì jūn méi yǒu biān máo, yīn ér bù néng zì jǐ xíng jìn. hái yǒu xiē xì jūn què néng tōng guò mǒu xiē xiǎn wéi rén zhī de jī zhì yán wù tǐ biǎo miàn huá dòng. wǒ men suǒ shú zhī de shì jiè zài xì jūn yǎn zhōng wán quán shì lìng yī ge yàng zi. duì yú xì jūn lái shuō, shuǐ jiù tóng táng jiāng zhī yú rén lèi yí yàng chóu mì. xì jūn shì rú cǐ de wēi xiǎo, zhōu wéi huà xué fèn zǐ de yī jǔ yī dòng dōu huì duì tā men chǎn shēng yǐng xiǎng. zài xiǎn wēi jìng xià, xì jūn, shèn zhì bāo kuò nèi xiē méi yǒu biān máo de xì jūn, jīng cháng zài shuǐ zhōng tiào lái tiào qù. zhè shì yīn wèi tā men yǔ shuǐ fèn zi xiāng zhuàng hòu, bèi dàn xiàng gè gè fāng xiàng. fèn zǐ yí dòng hěn xùn sù, jǐn 0. 1 miǎo zhī gé, yí gè xì jūn zhōu wéi de fèn zǐ jiù huì wán quán gēng xīn. yīn cǐ, jí shǐ shì méi yǒu biān máo de xì jūn yě bào lù zài yí gè bù duàn biàn huà de huán jìng zhōng. |