toefl写作范文下载之细胞与温度

　　托福(TOEFL)考试写作范文材料:Cells and Temperature 细胞与温度

　　Cells and Temperature

　　Cells cannot remain alive outside certain limits of temperature and muchnarrower limits mark the boundaries of effective functioning. Enzyme systems ofmammals and birds are most efficient only within a narrow range around 37C;adeparture of a few degrees from this value seriously impairs their functioning.Even though cells can survive wider fluctuations the integrated actions ofbodily systems are impaired. Other animals have a wider tolerance for changes ofbodily temperature.

　　For centuries it has been recognized that mammals and birds differ fromother animals in the way they regulate body temperature. Ways of characterizingthe 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 whereas allother creatures were considered cold- blooded. As more species were studied, itbecame evident that this classification was inadequate.