2024年4月6日发(作者：u盘中毒文件夹变成exe)

2021年托福阅读真题第7篇Regulation of B…

Most animals have an upper limit of body temperature at which they can

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.

In the past, animals were classified into two categories. Cold blooded

animals require an external heat source such as sunlight to warm

themselves. By contrast, warm-blooded animals use internal heat to

maintain their body temperature. These terms are misleading, however,

because many cold-blooded animals can generate considerable heat by

exercising their skeletal muscles. Indeed, many have a body temperature

during daylight hours that is at least as warm as that of warm blooded

animals like birds and mammals.

Biologists now classify animals according to both their source of heat

and their ability to maintain body temperature. Ectotherms depend on

external heat sources to warm their bodies, while endotherms use their

own metabolically generated heat to warm themselves. Homeotherms

maintain their body temperature within a narrow range, while

heterotherrms have body temperatures that vary with the environment.

Most animals fall into two categories. Birds and mammals are endothermic

and homeothermic. while other vertebrates and most invertebrates are

ectothermic and heterothermic.

Not all animals, however, can be neatly classified into two categories at

all ating 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.

Even endothermic homeotherms do not have truly constant body

temperatures but rather a narrow range of body temperatures within which

slight increases and decreases occur in extreme climates during exercise,

or even during sleep. The important feature is that birds and mammals can

quickly adjust the body's mechanisms for retaining or releasing heat such

that body temperature remains relatively stable. This provides the

advantage that the body chemical reactions are at optimal levels even

when the environment imposes extreme challenges. The metabolic rate of

a resting mammal, for example, is roughly six times greater than that of a

comparably sized reptile. A suddenly awakened mammal is capable of

intense activity even on a winter day, but an icy-cold reptile could be at

the mercy of a predator because of the time required to warm itself and

flee.

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 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.

2.

Most animals have an upper limit of body temperature at which they can

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.

3.

In the past, animals were classified into two categories. Cold blooded

animals require an external heat source such as sunlight to warm

themselves. By contrast, warm-blooded animals use internal heat to

maintain their body temperature. These terms are misleading, however,

because many cold-blooded animals can generate considerable heat by

exercising their skeletal muscles. Indeed, many have a body

temperature during daylight hours that is at least as warm as that of

warm blooded animals like birds and mammals.

all animals, however, can be neatly classified into two categories at

all ating 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.