50. Cells and Temperature
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 iguanaeach 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.
2016届高考英语二轮语法强化训练24 动词
2016年高考英语:备考之百题精炼系列06(教师版)
2016年高考英语配套词汇检测训练:模块六《Unit 1 Laughter is good for you》(学生版) 牛津译林版
2016届高考英语二轮语法强化训练11 非谓语动词
Sharing waste food and steepest street 剩余食材再利用、最陡的街道
2016年高考英语配套词汇检测训练:模块六《Unit 2 What is happiness to you》(教师版) 牛津译林版
2016届高考英语二轮语法强化训练27 主谓一致
2016届高考英语二轮语法强化训练13 情态动词
2016届高考英语二轮语法强化训练30 省略句
2016年高考英语配套词汇检测训练:模块三《Unit 1 The world of our senses》(学生版) 牛津译林版
2016年高考英语配套词汇检测训练:模块六《Unit 3 Understanding each other》(教师版) 牛津译林版
2016年高考英语配套词汇检测训练:模块七《Unit 1 Living with Technology》(教师版) 牛津译林版
2016年高考英语配套词汇检测训练:模块二《Unit 3 Amazing people》(学生版) 牛津译林版
2016届高考英语二轮语法强化训练23 介词短语
2016届高考英语二轮语法强化训练31 反意疑问句
2016年高考英语配套词汇检测训练:模块七《Unit 3 The world on line》(教师版) 牛津译林版
2016年高考英语配套词汇检测训练:模块六《Unit 3 Understanding each other》(学生版) 牛津译林版
2016届高考英语二轮语法强化训练25 动词短语
2016届高考英语二轮语法强化训练32 情景交际
2016届高考英语二轮语法强化训练20 名词
2016年高考英语配套词汇检测训练:模块七《Unit 3 The world on line》(学生版) 牛津译林版
2016届高考英语二轮语法强化训练12 虚拟语气
2016年高考英语配套词汇检测训练:模块六《Unit 2 What is happiness to you》(学生版) 牛津译林版
2016年高考英语:备考百题精炼专题4(教师版)
2016届高考英语二轮语法强化训练17 副词
2016年高考英语配套词汇检测训练:模块七《Unit 4 Public transportation》(学生版) 牛津译林版
2016届高考英语二轮语法强化训练22 介词
2016年高考英语配套词汇检测训练:模块六《Unit 4 Helping people around the world》(学生版) 牛津译林版
2016届高考英语二轮语法强化训练15 形容词
2016届高考英语二轮语法强化训练9 非谓语动词
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