英语阅读:Cells and Temperature
Cells and Temperature
细胞与温度
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 37 ℃; 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 homeotherms, and those
whose body temperature varies with their environment, 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 a
change in the chill of the deep water, and their body temperatures remain constant.
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