新概念第四冊(cè)lesson69講義BacteriaBacteriaareextremelysmalllivingthings.Whilewemeasureourownsizesininchesorcentimeters,bacterial1sizeismeasuredinmicrons.Onemicronisathousandthofamillimeter:apinheadisaboutamillimeteracross.Rod-shapedbacteriaareusuallyfromtwotofourmicronslong,whileroundedonesaregenerallyonemicronindiameter.Thusifyouenlargedaroundedbacterium2athousandtimes,itwouldbejustaboutthesizeofapinhead.Anadulthumanmagnifiedbythesameamountwouldbeoveramile(1.6kilometer)tall.Evenwithanordinarymicroscope,youmustlookcloselytoseebacteria.Usingamagnificationof100times,onefindsthatbacteriaarebarelyvisibleastinyrodsordots.Onecannotmakeoutanythingoftheirstructure.Usingspecialstains,onecanseethatsomebacteriahaveattachedtothemwavy-looking“hairs”calledflagella3.Othershaveonlyoneflagellum.Theflagellarotate,pushingthebacteriathroughthewater.Manybacterialackflagellaandcannotmoveaboutbytheirownpower,whileotherscanglide4alongoversurfacesbysomelittle-understoodmechanism5.Fromthebacteriapointofview,theworldisaverydifferentplacefromwhatitistohumans.Toabacteriumwaterisasthickasmolassesistous.Bacteriaaresosmallthattheyareinfluencedbythemovementsofthechemicalmolecules6aroundthem.Bacteriaunderthemicroscope,eventhosewithnoflagella,oftenbounceaboutinthewater.Thisisbecausetheycollidewiththewatery7moleculesandarepushedthiswayandthat.Moleculesmovesorapidlythatwithinatenthofasecondthemoleculesaroundabacteriahaveallbeenreplacedbynewones;evenbacteriawithoutflagellaarethusconstantlyexposedtoachangingenvironment.細(xì)菌細(xì)菌是極其微小的生物體。我們用英寸或厘米來(lái)測(cè)量自己的大小，而測(cè)量細(xì)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(xì)菌通常有2～4微米長(zhǎng)，而圓形細(xì)菌的直徑一般只有1微米。因此，即使你把一個(gè)圓形細(xì)菌放大1000倍，它也不過(guò)一個(gè)針頭那么大?？墒侨绻岩粋€(gè)成年人放大1000倍，就會(huì)變成1英里(或1.6公里)多高。用一般的顯微鏡觀察細(xì)菌時(shí)，你必須仔細(xì)觀察才能看見(jiàn)它們。使用100倍的顯微鏡時(shí)，你會(huì)發(fā)現(xiàn)細(xì)菌不過(guò)是隱約可見(jiàn)的小細(xì)棒或小點(diǎn)點(diǎn)，而它們的結(jié)構(gòu)你卻根本看不出來(lái)。使用特殊的著色劑后，你會(huì)發(fā)現(xiàn)有的細(xì)菌上長(zhǎng)著不少波狀的"毛發(fā)"即鞭毛，而有的細(xì)菌只有一根鞭毛。鞭毛的旋轉(zhuǎn)可以推動(dòng)細(xì)菌在水中行進(jìn)。不少細(xì)菌沒(méi)有鞭毛，因而不能自己行進(jìn)。還有些細(xì)菌卻能通過(guò)某些鮮為人知的機(jī)制沿物體表面滑動(dòng)。我們所熟知的世界在細(xì)菌眼中完全是另一個(gè)樣子。對(duì)于細(xì)菌來(lái)說(shuō)，水就同糖漿之于人類(lèi)一樣稠密。細(xì)菌是如此的微小，周?chē)瘜W(xué)分子的一舉一動(dòng)都會(huì)對(duì)它們產(chǎn)生影響。在顯微鏡下，細(xì)菌，甚至包括那些沒(méi)有鞭毛的細(xì)菌，經(jīng)常在水中跳來(lái)跳去。這是因?yàn)樗鼈兣c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(xì)菌周?chē)姆肿泳蜁?huì)完全更新。因此，即使是沒(méi)有鞭毛的細(xì)菌也暴露在一個(gè)不斷變化的環(huán)境中

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1bacterial

a.細(xì)菌的參考例句：Bacterialreproductionisacceleratedinweightlessspace.在失重的空間，細(xì)菌繁殖加快了。Brainlesionscanbecausedbybacterialinfections.大腦損傷可能由細(xì)菌感染引起。2bacterium

n.(pl.)bacteria細(xì)菌參考例句：Thebacteriumpossiblygoesinthehumanbodybythemouth.細(xì)菌可能通過(guò)口進(jìn)入人體。Abacteriumisidentifiedasthecauseforhisduodenalulcer.一種細(xì)菌被斷定為造成他十二指腸潰瘍的根源。3flagella

n.鞭節(jié)，鞭毛參考例句：Therotationofflagellapushesthebacteriathroughthewater.鞭毛的旋轉(zhuǎn)可以推動(dòng)細(xì)菌在水中行進(jìn)。Manyprotoctistansaremotile,usingpseudopodia,ciliaorflagella.許多原生動(dòng)物利用偽足、纖毛或鞭毛能運(yùn)動(dòng)。4glide

n./v.溜，滑行；(時(shí)間)消逝參考例句：Westoodinsilencewatchingthesnakeglideeffortlessly.我們噤若寒蟬地站著，眼看那條蛇逍遙自在地游來(lái)游去。Sogracefulwastheballerinathatshejustseemedtoglide.那芭蕾舞女演員翩躚起舞，宛如滑翔。5mechanism

n.機(jī)械裝置；機(jī)構(gòu)，結(jié)構(gòu)參考例句：Thebonesandmusclesarepartsofthemechanismofthebody.骨骼和肌肉是人體的組成部件。Themechanismofthemachineisverycomplicated.這臺(tái)機(jī)器的結(jié)構(gòu)是非常復(fù)雜的。6molecules

分子(molecule的名詞復(fù)數(shù))參考例句：Thestructureofmoleculescanbeseenunderanelectronmicroscope.分子的結(jié)構(gòu)可在電子顯微鏡下觀察到。Insidethereactorthelargemoleculesarecrackedintosmallermolecules.在反應(yīng)堆里，大分子裂變?yōu)樾》肿印?watery

adj.有水的，水汪汪的；濕的，濕潤(rùn)的參考例句：Inhiswateryeyesthereisanexpressionofdistrust.他那含淚的眼睛流露出驚惶失措的神情。Hereyesbecamewaterybecauseofthesmoke.因?yàn)闊熝?，她的雙眼變得淚汪汪的。SleepSleet1ispartofaperson’sdailyactivitycycle.Thereareseveraldifferentstagesofsleep,andtheytoooccurincycles.Ifyouareanaveragesleeper2,yoursleepcycleisasfollows.Whenyoufistdriftoffintoslumber3,youreyeswillrollaboutabit,youtemperaturewilldropslightly,yourmuscleswillrelax,andyourbreathingwellslowandbecomequiteregular.Yourbrainwavesslowandbecomequiteregular.Yourbrainwavesslowdownabittoo,withthealpharhythmofratherfastwaves1sleep.Forthenexthalfhourorso,asyourelaxmoreandmore,youwilldriftdownthroughstage2andstage3sleep.Theloweryourstageofsleep.sloweryourbrainwaveswillbe.Thenabout40to69minutesafteryouloseconsciousnessyouwillhavereachedthedeepestsleepofall.Yourbrainwillshowthelargeslowwavesthatareknownasthedelta4rhythm.Thisisstage4sleep.Youdonotremainatthisdeepfourthstageallnightlong,butinsteadabout80minutesafteryoufallintoslumber,yourbrainactivitylevelwillincreaseagainslightly.Thedeltarhythmwilldisappear,tobereplacedbytheactivitypatternofbrainwaves.Youreyeswillbegintodart5aroundunderyourclosedeyelids6asifyouwerelookingatsomethingoccurringinfrontofyou.Thisperiodofrapideyemovementlastsforsome8to15minutesandiscalledREMsleep.ItisduringREMsleepperiod,yourbodywillsoonrelaxagain,yourbreathingwillslipgentlybackfromstage1tostage4sleep----onlytoriseonceagaintothesurfaceofnearconsciousnesssome80minuteslater.睡眠睡眠是人每天日常活動(dòng)循環(huán)的一部分。人的睡眠分幾個(gè)階段，而這些階段也是循環(huán)發(fā)生的。如果你是一個(gè)正常的睡眠者，你的睡眠循環(huán)會(huì)這樣進(jìn)行。在你開(kāi)始昏昏入睡時(shí)，你的眼睛會(huì)滾動(dòng)幾下，體溫略有下降，肌肉放松，呼吸變得緩慢而有節(jié)奏。除了開(kāi)始幾分鐘比較快的α節(jié)奏外，腦電波也稍有減緩。這被稱(chēng)為第一階段睡眠。在隨后約半小時(shí)內(nèi)，你進(jìn)一步放松，進(jìn)入第二和第三階段睡眠。睡眠越深入，腦電波就越緩慢。大約在開(kāi)始睡眠后的40到60分鐘，你將進(jìn)入沉睡狀態(tài)。這時(shí)的腦電波表現(xiàn)為巨大的緩波，被稱(chēng)為δ節(jié)奏。這就是第四階段睡眠。但你并不是整夜都保持這種沉睡狀態(tài)。入睡后約80分鐘左右，你的大腦運(yùn)動(dòng)水平會(huì)再度略有提高。δ節(jié)奏消失，并被腦電波的運(yùn)動(dòng)圖形取代。你的眼睛會(huì)在閉著的眼瞼下迅速轉(zhuǎn)動(dòng)，就好象你在看著眼前發(fā)生的什么事情。這種迅速的眼球運(yùn)動(dòng)持續(xù)約8～15分鐘，這一階段睡眠被稱(chēng)之為快速眼動(dòng)(REM)睡眠。在REM睡眠階段，你的肢體會(huì)很快再度放松，呼吸也再次放慢并變得有節(jié)奏，你會(huì)輕松地從第一階段滑入第四階段睡眠-直到大約80分鐘后重新接近清醒狀態(tài)。點(diǎn)擊收聽(tīng)單詞發(fā)音

1sleet

n.雨雪；v.下雨雪，下冰雹參考例句：Therewasagreatdealofsleetlastnight.昨夜雨夾雪下得真大。Whenwintercomes,wegetsleetandfrost.冬天來(lái)到時(shí)我們這兒會(huì)有雨夾雪和霜凍。2sleeper

n.睡眠者，臥車(chē)，臥鋪參考例句：IusuallygouptoLondononthesleeper.我一般都乘臥車(chē)去倫敦。Butfirstheexplainedthathewasaveryheavysleeper.但首先他解釋說(shuō)自己睡覺(jué)很沉。3slumber

n.睡眠，沉睡狀態(tài)參考例句：Allthepeopleinthehotelswerewrappedindeepslumber.住在各旅館里的人都已進(jìn)入夢(mèng)鄉(xiāng)。Don'twakehimfromhisslumberbecauseheneedstherest.不要把他從睡眠中喚醒，因?yàn)樗枰菹ⅰ?delta

n.（流的）角洲參考例句：HehasbeentothedeltaoftheNile.他曾去過(guò)尼羅河三角洲。TheNiledividesatitsmouthandformsadelta.尼羅河在河口分岔，形成了一個(gè)三角洲。5dart

v.猛沖，投擲；n.飛鏢，猛沖參考例句：Thechildmadeasuddendartacrosstheroad.那小孩突然沖過(guò)馬路。Markovdiedafterbeingstruckbyapoisondart.馬爾科夫身中毒鏢而亡。6eyelids

n.眼瞼(eyelid的名詞復(fù)數(shù))；眼睛也不眨一下；不露聲色；面不改色參考例句：Shewassotired,hereyelidswerebeginningtodroop.她太疲倦了，眼瞼開(kāi)始往下垂。Hereyelidsdroopedasifshewereonthevergeofsleep.她眼瞼低垂好像快要睡著的樣子。來(lái)自《簡(jiǎn)明英漢詞典》CellsandTemperatureCellscannotremainaliveoutsidecertainlimitsoftemperatureandmuchnarrowerlimitsmarktheboundariesofeffectivefunctioning.Enzyme1systemsofmammalsandbirdsaremostefficientonlywithinanarrowrangearound37C;adepartureofafewdegreesfromthisvalueseriouslyimpairs2theirfunctioning.Eventhoughcellscansurvivewiderfluctuations3theintegratedactionsofbodilysystemsareimpaired4.Otheranimalshaveawidertolerance5forchangesofbodilytemperature.Forcenturiesithasbeenrecognizedthatmammalsandbirdsdifferfromotheranimalsinthewaytheyregulatebodytemperature.Waysofcharacterizingthedifferencehavebecomemoreaccurateandmeaningfulovertime,butpopularterminology6stillreflectstheolddivisioninto“warm-blooded”and“cold-blooded”species;warm-bloodedincludedmammalsandbirdswhereasallothercreatureswereconsideredcold-blooded.Asmorespecieswerestudied,itbecameevidentthatthisclassificationwasinadequate7.Afencelizard8oradesertiguana—eachcold-blooded----usuallyhasabodytemperatureonlyadegreeortwobelowthatofhumansandsoisnotcold.Thereforethenextdistinctionwasmadebetweenanimalsthatmaintainaconstantbodytemperature,calledhome0therms,andthosewhosebodytemperaturevarieswiththeirenvironments,calledpoikilotherms.Butthisclassificationalsoprovedinadequate,becauseamongmammalstherearemanythatvarytheirbodytemperaturesduringhibernation9.Furthermore,manyinvertebrates10thatliveinthedepthsoftheoceanneverexperiencechangeinthedepthsoftheoceanneverexperiencechangeinthechillofthedeepwater,andtheirbodytemperaturesremainconstant.細(xì)胞與溫度細(xì)胞只能在一定的溫度范圍內(nèi)存活，而進(jìn)一步保證它們有效工作的溫度范圍就更小了。哺乳動(dòng)物和鳥(niǎo)類(lèi)的酶系統(tǒng)只能在37℃左右的很小范圍內(nèi)才能有效工作。與此相差僅幾度的溫度都會(huì)大大削弱它們的工作效率。盡管溫度變化更大時(shí)細(xì)胞仍能存活，但機(jī)體系統(tǒng)的整體運(yùn)行能力卻被削弱了。其它動(dòng)物對(duì)體溫的變化有更強(qiáng)的適應(yīng)性。幾個(gè)世紀(jì)以來(lái)，人們就認(rèn)識(shí)到哺乳動(dòng)物和鳥(niǎo)類(lèi)調(diào)節(jié)體溫的方式與其它動(dòng)物不同。隨著時(shí)間的推移，人們對(duì)這種差異的描述越來(lái)越精確和有意義，但是"暖血?jiǎng)游?和"冷血?jiǎng)游?這一古老的分類(lèi)方式至今仍在大眾詞匯中有所反映。暖血?jiǎng)游锇ú溉閯?dòng)物和鳥(niǎo)類(lèi)，其它動(dòng)物統(tǒng)統(tǒng)被視為冷血?jiǎng)游铩５菍?duì)更多物種進(jìn)行的研究表明這種分類(lèi)顯然是不適當(dāng)?shù)?。美洲一種小型蜥蜴和沙漠鬣蜥同屬冷血?jiǎng)游?，但?shí)際上它們的體溫通常只比人類(lèi)的體溫低1～2度，因此并不是真正的冷血。因此又出現(xiàn)了恒溫動(dòng)物(即保持恒定體溫的動(dòng)物)和變溫動(dòng)物(即體溫隨外界環(huán)境的變化而改變的動(dòng)物)這一區(qū)分方式。但這種分類(lèi)也不恰當(dāng)。因?yàn)橛胁簧俨溉閯?dòng)物在冬眠期間會(huì)改變體溫，而許多生活在深海的無(wú)脊椎動(dòng)物在寒冷的深海水域中體溫并不變化，而是恒定的。點(diǎn)擊收聽(tīng)單詞發(fā)音

1enzyme

n.酵素，酶參考例句：Aboveacertaintemperature,theenzymemoleculewillbecomeunfolded.超過(guò)一定溫度，酶分子將會(huì)展開(kāi)。Anenzymethatdissolvesthefibrinofbloodclots.能溶解血凝塊中的纖維的酶。2impairs

v.損害，削弱(impair的第三人稱(chēng)單數(shù))參考例句：Smokingimpairsourhealth.吸煙會(huì)損害我們的健康。來(lái)自《簡(jiǎn)明英漢詞典》Almostanythingthatimpairsliverfunctioncancausehepatitis.任何有損于肝功能的因素，幾乎都會(huì)引起肝炎。來(lái)自辭典例句3fluctuations

波動(dòng)，漲落，起伏(fluctuation的名詞復(fù)數(shù))參考例句：Heshowedthepricefluctuationsinastatisticaltable.他用統(tǒng)計(jì)表顯示價(jià)格的波動(dòng)。ThereweresomanyunpredictablefluctuationsontheStockExchange.股票市場(chǎng)瞬息萬(wàn)變。4impaired

adj.受損的；出毛病的；有（身體或智力）缺陷的v.損害，削弱(impair的過(guò)去式和過(guò)去分詞)參考例句：Muchreadinghasimpairedhisvision.大量讀書(shū)損害了他的視力。來(lái)自《現(xiàn)代漢英綜合大詞典》Hishearingissom