考博英语强化阶段自测题-2.doc

考博英语强化阶段自测题
PART 1 PREHENSION
Passage 1
Cells cannot remain alive outside certain limits of temperature, and much narrower limits mark the boundaries of effective functioning. Enzyme (酶) systems of mammals and birds are most efficient only within a narrow range around 37ºC; 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 temperatures. Ways of characterizing the difference have e 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 (鬣蜥)—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 homo therms(同温动物), and those whose body temperature varies with their environment, called poikilot