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新东方优美背诵短文50篇 Unit50:CellsandTemperature

时间:2007-11-21 03:22来源:互联网 提供网友:xianging   字体: [ ]
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Cells cannot remain alive outside certain limits of temperature and much narrower limits mark the boundaries of effective functioning. Enzyme1 systems of mammals and birds are most efficient only within a narrow range around 37C;a departure of a few degrees from this value seriously impairs2 their functioning. Even though cells can survive wider fluctuations3 the integrated actions of bodily systems are impaired4. Other animals have a wider tolerance5 for changes of bodily temperature.

For centuries it has been recognized that mammals and birds differ from other animals in the way they regulate body temperature. Ways of characterizing the difference have become more accurate and meaningful over time, but popular terminology6 still reflects the old division into “warm-blooded” and “cold-blooded” species; warm-blooded included mammals and birds whereas all other creatures were considered cold-blooded. As more species were studied, it became evident that this classification was inadequate7. A fence lizard8 or a desert iguana—each cold-blooded----usually has a body temperature only a degree or two below that of humans and so is not cold. Therefore the next distinction was made between animals that maintain a constant body temperature, called home0therms, and those whose body temperature varies with their environments, called poikilotherms. But this classification also proved inadequate, because among mammals there are many that vary their body temperatures during hibernation9. Furthermore, many invertebrates10 that live in the depths of the ocean never experience change in the depths of the ocean never experience change in the chill of the deep water, and their body temperatures remain constant.


细胞与温度细胞只能在一定的温度范围内存活,而进一步保证它们有效工作的温度范围就更小了。
哺乳动物和鸟类的酶系统只能在37℃左右的很小范围内才能有效工作。与此相差仅几度的温度都会大大削弱它们的工作效率。
尽管温度变化更大时细胞仍能存活,但机体系统的整体运行能力却被削弱了。其它动物对体温的变化有更强的适应性。几个世纪以来,人们就
认识到哺乳动物和鸟类调节体温的方式与其它动物不同。随着时间的推移,人们对这种差
异的描述越来越精确和有意义,但是"暖血动物"和"冷血动物"这一古老的分类方式至今仍在大众词汇中有所反映。
暖血动物包括哺乳动物和鸟类,其它动物统统被视为冷血动物。但是对更多物种进行的研究表明这种分类显然是不适当的。美洲一种小型蜥蜴和沙漠鬣蜥同
属冷血动物,但实际上它们的体温通常只比人类的体温低1~2度,因此并不是真正的冷血。
因此又出现了恒温动物(即保持恒定体温的动物)和变温动物(即体温随外界环境的变化而改变的动物)这一区分方式。但这种分类也不恰当。
因为有不少哺乳动物在冬眠期间会改变体温,而许多生活在深海的无脊椎动物在寒冷的深海水域中体温并不变化,而是恒定的。


点击收听单词发音收听单词发音  

1 enzyme cPozF     
n.酵素,酶
参考例句:
  • Above a certain temperature,the enzyme molecule will become unfolded.超过一定温度,酶分子将会展开。
  • An enzyme that dissolves the fibrin of blood clots.能溶解血凝块中的纤维的酶。
2 impairs 866bc0da43dd90e04b6073750ff1e87c     
v.损害,削弱( impair的第三人称单数 )
参考例句:
  • Smoking impairs our health. 吸烟会损害我们的健康。 来自《简明英汉词典》
  • Almost anything that impairs liver function can cause hepatitis. 任何有损于肝功能的因素,几乎都会引起肝炎。 来自辞典例句
3 fluctuations 5ffd9bfff797526ec241b97cfb872d61     
波动,涨落,起伏( fluctuation的名词复数 )
参考例句:
  • He showed the price fluctuations in a statistical table. 他用统计表显示价格的波动。
  • There were so many unpredictable fluctuations on the Stock Exchange. 股票市场瞬息万变。
4 impaired sqtzdr     
adj.受损的;出毛病的;有(身体或智力)缺陷的v.损害,削弱( impair的过去式和过去分词 )
参考例句:
  • Much reading has impaired his vision. 大量读书损害了他的视力。 来自《现代汉英综合大词典》
  • His hearing is somewhat impaired. 他的听觉已受到一定程度的损害。 来自《现代汉英综合大词典》
5 tolerance Lnswz     
n.宽容;容忍,忍受;耐药力;公差
参考例句:
  • Tolerance is one of his strengths.宽容是他的一个优点。
  • Human beings have limited tolerance of noise.人类对噪音的忍耐力有限。
6 terminology spmwD     
n.术语;专有名词
参考例句:
  • He particularly criticized the terminology in the document.他特别批评了文件中使用的术语。
  • The article uses rather specialized musical terminology.这篇文章用了相当专业的音乐术语。
7 inadequate 2kzyk     
adj.(for,to)不充足的,不适当的
参考例句:
  • The supply is inadequate to meet the demand.供不应求。
  • She was inadequate to the demands that were made on her.她还无力满足对她提出的各项要求。
8 lizard P0Ex0     
n.蜥蜴,壁虎
参考例句:
  • A chameleon is a kind of lizard.变色龙是一种蜥蜴。
  • The lizard darted out its tongue at the insect.蜥蜴伸出舌头去吃小昆虫。
9 hibernation cdjxK     
n.冬眠
参考例句:
  • Bears wake up in the spring after a winter of hibernation.熊经过一个冬天的冬眠后在春季苏醒。
  • The tortoise spends the winter months in hibernation.乌龟在冬眠中度过寒冬季节。
10 invertebrates 7e45dc289993d00de9b9f14a70e51319     
n.无脊椎动物( invertebrate的名词复数 )
参考例句:
  • Insects and worms are all invertebrates. 昆虫和蠕虫都是无脊椎动物。 来自辞典例句
  • In the earthworm and many other invertebrates, these excretory structures are called nephridia. 在蚯蚓和许多其它无脊椎动物中,这些排泄结构称为肾管。 来自辞典例句
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