欢迎访问Freekaoyan作文站
Cells and Temperature
欢迎访问Freekaoyan作文站

2008-01-31 01:38:58  www.zuowen1.com  第1英语作文网  
欢迎访问Freekaoyan作文站
  • 欢迎访问Freekaoyan作文站
    Cells cannot remain alive outside certain limits of temperature and much narrower limits mark the boundaries of effective functioning. Enzyme 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 impairs their functioning. Even though cells can survive wider fluctuations the integrated actions of bodily systems are impaired. Other animals have a wider tolerance 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 terminology 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 inadequate. A fence lizard 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 hibernation. Furthermore, many invertebrates 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.


    欢迎访问Freekaoyan作文站
欢迎访问Freekaoyan作文站

免责声明:本站文章均由网上收集,所有文章仅供学习参考之用,版权和著作权归原作者所有,请在24小时内删除! 如果您发现侵犯您的权益,请即时通知,本站将立即删除!

欢迎访问Freekaoyan作文站
欢迎访问Freekaoyan作文站
欢迎访问Freekaoyan作文站

附近文章

发表评论/ 全部评论

  • 验证码:
  • 验证码:
  • 匿名发表: