托福阅读真题第7篇RegulationofBodyTemperature

托福阅读真题第7篇RegulationofBodyTemperature
大多数动物都有可以生存的体温上限。

例如，在人类中，41摄氏度的体温会导致蛋白质功能丧失和神经系统崩溃，而42至43摄氏度的体温会导致是致命的。

鸟类的静息体温略高于哺乳动物（大约为40 至 41 摄氏度，而大多数哺乳动物为 35 至 38 摄氏度），它们无法在高于 46 至 47 摄氏度的体温下生存。

在高于 50 摄氏度的环境温度下，几乎所有动物都会死亡。

然而，在温度范围的另一端，极冷的耐受性更好。

例如，一些动物在解冻后可以冷冻并存活。

冷冻/解冻通常是危险的，因为冰晶会在细胞和破裂膜内形成。

然而，许多昆虫，如毛毛虫，少数种类的两栖动物，如林蛙，以及极少数爬行动物，如彩龟，都可以阻止其细胞中的晶体形成。

他们通过从肝脏中大量流出葡萄糖来响应皮肤表面的冰块来做到这一点。

储存在肝脏中的葡萄糖进入血液和细胞，降低它们的冰点，使细胞不会冻结成固体。

这些动物可以长时间完全冷冻 65% 或更多的身体，只有在温暖时期才解冻而不会产生有害影响。

他们通过从肝脏中大量流出葡萄糖来响应皮肤表面的冰块来做到这一点。

储存在肝脏中的葡萄糖进入血液和细胞，降低它们的冰点，使细胞不会冻结成固体。

这些动物可以长时间完全冷冻65% 或更多的身体，只有在温暖时期才解冻而不会产生有害影响。

他们通过从肝脏中大量流出葡萄糖来响应皮肤表面的冰块来做到这一点。

储存在肝脏中的葡萄糖进入血液和细胞，降低它们的冰点，使细胞不会冻结成固体。

这些动物可以长时间完全冷冻 65% 或更多的身体，只有在温暖时期才解冻而不会产生有害影响。

过去，动物被分为两类。

冷血动物需要外部热源（例如阳光）来温暖自己。

相比之下，温血动物使用内部热量来维持体温。

然而，这些术语具有误导性，因为许多冷血动物可以通过锻炼骨骼肌产生大量热量。

事实上，许多人在白天的体温至少与鸟类和哺乳动物等温血动物的体温一样温暖。

生物学家现在根据动物的热源和维持体温的能力对动物进行分类。

等温动物依靠外部热源来温暖他们的身体，而吸热动物则使用自己代
谢产生的热量来温暖自己。

恒温动物的体温保持在一个狭窄的范围内，而异温动物的体温会随着环境的变化而变化。

大多数动物分为两类。

鸟类和哺乳动物是吸热和恒温的。

而其他脊椎动物和大多数无脊椎动物是等温的和异温的。

Not all animals, however, can be neatly classified into two categories at all times.Hibernating mammals, for example, are endotherms. They are homeothermic, but during the winter their body temperature drops dramatically as their metabolism slows to conserve energy for the winter. Hibernators behave like heterotherms during the transition from fall to winter and again from winter to spring, During the winter, however, they are homeothermic except for brief periods of arousal, but at a lower body temperature than at other times of the year. Similarly, a fish swimming in deep ocean waters is an ectotherm but also homeothermic because the temperature of the water-and therefore of its body-is essentially constant. Fish that live in waters with fluctuating temperatures, by contrast are ectothermic and heterothermic.
即使是吸热恒温动物也没有真正恒定的体温，而是在一个狭窄的体温范围内，在极端气候下运动期间甚至睡眠期间都会发生轻微的升高和降低。

重要的特点是鸟类和哺乳动物可以快速调整身体保持或释放热量的机制，使体温保持相对稳定。

这提供了一个优势，即即使在环境带来极端挑战时，身体化学反应也处于最佳水平。

例如，静止的哺乳动物的新陈代谢率大约是同等大小的爬行动物的六倍。

突然醒来的哺乳动物即使在冬日也能进行激烈的活动，
Endothermy does have two major disadvantages, however. First, to produce sufficient heat by metabolic processes, endotherms must consume larger amounts of food. Small endotherms, such as shrews, must eat almost continually and may die if deprived of food for as little as a day. By contrast, many
ectotherms, such as snakes can go for weeks without eating. Second, endotherms run the risk of overheating during periods of intense activity, even in cold weather.
1.Most animals have an upper limit of body temperature at which they can survive.In humans, for example, a body temperature of 41 degrees Celsius causes loss of protein function and breakdown of the nervous system, and a body temperature of 42 to 43 degrees Celsius is fatal. Birds, which have slightly higher resting body temperatures than mammals(approximately 40 to 41 degrees Celsius compared with 35 to 38 degrees Celsius for most mammals), cannot survive at body temperatures above 46 to 47 degrees Celsius. At environmental temperatures greater than 50 degrees Celsius, nearly all animals die. At the other end of the temperature spectrum, though, extreme cold is better tolerated. Fo example, Some animals can freeze and survive after thawing. Freezing/thawing is normally dangerous because ice crystals form inside cells and rupture membranes. However, many insects, such as the woolly caterpillar, a few species of amphibian such as the wood frog, and a very small number of reptiles such as the painted turtle, can block crystal formation in their cells. They do this by responding to ice on their skin surfaces with an enormous outpouring of glucose from the liver. The glucose stored in the liver enters the blood and the cells, lowering their freezing point so that the cells do not freeze solid. These animals can have 65 percent or more of their bodies completely frozen for long periods, only to thaw during warm periods without harmful effects.。