陳蕙雅思教材 - 雅思閱讀精選 (Cells and Temperature)

Cells and Temperature

Cells cannot remainalive  outside certain limits oftemperature, and  much

narrower limits mark theboundaries  of effectivefunctioning.  Enzyme

systems of mammals andbirds are most efficient only within a narrow range

around 37  ℃; adeparture of a few degrees from this value seriously  

impairs  their functioning.  Even  though cells  can  survive wider  

fluctuations,  the integrated  actions of bodily systems are impaired.  

Other animals have awider tolerance for changes of bodily temperature. For

centuries it has beenrecognized 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 popularterminology still reflects  the  old division  into

"warm         blooded"  and "cold      blooded"  species; warm-blooded included

mammals and birds whereasall other creatures were considered cold-blooded.

As more species werestudied, it became evident that this classification

was inadequate. A fencelizard or a

desert iguana -- eachcold-blooded -- usually has a body temperature only a

degree or two below thatof humans and so is not cold. Therefore the next

distinction was made betweenanimals that maintain a constant body

temperature, called  homeotherms, and those whose body temperaturevaries

with their environment,called poikilotherms. But this classification also

proved inadequate,because  among mammals there are many thatvary their

body temperatures  during hibernation. Furthermore, manyinvertebrates that

live in the depths of theocean never experience a change in the chill of

the deep water, and theirbody temperatures remain constant.

細胞與溫度 細胞只能在一定的溫度範圍內存活，而進一步保證它們有效工作的溫度範圍就更小了。

哺乳動物和鳥類的酶系統只能在 37℃左右的很小範圍內才能有效工作。 與此相差僅幾度的 溫度都會大大削弱它們的工作效率。  

儘管溫度變化更大時細胞仍能存活，但機體系統的整 體運行能力卻被削弱了。 其它動物對體溫的變化有更強的適應性。 幾個世紀以來，人們就

認識到哺乳動物和鳥類調節體溫的方式與其它動物不同。  隨著時間的推移，人們對這種差

異的描述越來越精確和有意義，但是"暖血動物"和"冷血動物"這一古老的分類方式至今仍在 大眾詞彙中有所反映。

暖血動物包括哺乳動物和鳥類，其它動物統統被視為冷血動物。 但 是對更多物種進行的研究表明這種分類顯然是不適當的。  美洲一種小型蜥蜴和沙漠鬣蜥同

屬冷血動物，但實際上它們的體溫通常只比人類的體溫低 1～2 度，因此並不是真正的冷血。

因此又出現了恒溫動物(即保持恒定體溫的動物)和變溫動物(即體溫隨外界環境的變化而改 變的動物)這一區分方式。  但這種分類也不恰當。  

因為有不少哺乳動物在冬眠期間會改變 體溫，而許多生活在深海的無脊椎動物在寒冷的深海水域中體溫並不變化，而是恒定的。