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就生理学而言，棱皮龟在某种程度上更像会爬行的鲸而不是海龟。

When it comes to physiology, the leatherback turtle is, in some ways, more like a reptilian whale than a turtle.

与其他海龟相比，棱皮龟可游到寒冷的北部和南部海洋的远处，在爬行动物中，它们会用独特的方式来应对寒冷水域。

It swims farther into the cold of the northern and southern oceans than any other sea turtle, and it deals with the chilly waters in a way unique among reptiles.

温血海龟看似是一个自相矛盾的说法。

A warm-blooded turtle may seem to be a contradiction in terms.

但是，成年棱皮龟能够在仅有8摄氏度（46.4华氏度）的海水中把体温保持在25到26摄氏度（77-79华氏度）之间。

Nonetheless, an adult leatherback can maintain a body temperature of between 25 and 26°C (77–79°F) in seawater that is only 8°C (46.4°F)

要完成这一壮举就需要棱皮龟做出两种适应，既要在体内产生热量，又要防止热量散失到周边水域。

Accomplishing this feat requires adaptations both to generate heat in the turtle’s body and to keep it from escaping into the surrounding waters.

很明显，棱皮龟产生体内热量的方法与我们或者鸟类不同，并非细胞新陈代谢的副产品。

Leatherbacks apparently do not generate internal heat the way we do, or the way birds do, as a by-product of cellular metabolism.

棱皮龟或许会通过晒太阳来获得一些身体热量；其深色（近乎黑色）的体色能够帮助它吸收太阳辐射。

A leatherback may be able to pick up some body heat by basking at the surface; its dark, almost black body color may help it to absorb solar radiation.

但是，它的大部分身体热量来自于肌肉运动。

However, most of its internal heat comes from the action of its muscles.

棱皮龟通过三种不同方式来保持体温。

Leatherbacks keep their body heat in three different ways.

第一种也是最简单的方式就是体型大小。

动物体型越大，表面积与体积之比就越小；相应地，对于每盎司体质量来说，从体表流失的热量就会更少。

The bigger the animal is, the lower its surface-to-volume ratio; for every ounce of body mass, there is proportionately less surface through which heat can escape.

成年棱皮龟的体型是最大的海龟的两倍，因此它需要更长的时间来使体温变凉。

An adult leatherback is twice the size of the biggest cheloniid sea turtles and will therefore take longer to cool off.

通过庞大体积维持高体温的方式被称为巨温性。

Maintaining a high body temperature through sheer bulk is called gigantothermy.

大象、鲸、可能许多大型恐龙也是通过这一方法来保持体温的。

It works for elephants, for whales, and, perhaps, it worked for many of the larger dinosaurs.

显然，这种现象在较小程度上也适用于其它海龟。

It apparently works, in a smaller way, for some other sea turtles.

体型较大的红海龟和绿海龟能够将体温维持在高于周围水温1或2摄氏度的范围内，很可能利用的就是巨温性。

Large loggerhead and green turtles can maintain their body temperature at a degree or two above that of the surrounding water, and gigantothermy is probably the way they do it.

肌肉活动也有助于维持体温，一个活跃游动的绿海龟的体温可能比它所处水域温度高7摄氏度（12.6华氏度）。

Muscular activity helps, too, and an actively swimming green turtle may be 7°C (12.6°F) warmer than the waters it swims through.

但是，巨温性还不足以让棱皮龟在寒冷的北部水域保暖。

Gigantothermy, though, would not be enough to keep a leatherback warm in cold northern waters.

即便对于拥有厚厚一层隔热鲸脂（脂肪）的鲸来说也是不够的。

It is not enough for whales, which supplement it with a thick layer of insulating blubber (fat).

棱皮龟虽然没有鲸脂，但它们有着类似于爬行类动物的结构：厚厚的充满油的皮肤下面是一层纤维状的脂肪组织。

Leatherbacks do not have blubber, but they do have a reptilian equivalent: thick, oil-saturated skin, with a layer of fibrous, fatty tissue just beneath it.

棱皮龟的这个“保温”结构可以保护除了头和鳍状肢之外的所有部位。

Insulation protects the leatherback everywhere but on its head and flippers.

由于鳍状肢相对较薄且成叶片状，棱皮龟的这一部分身体有可能会感到寒冷。

Because the flippers are comparatively thin and blade like, they are the one part of the leatherback that is likely to become chilled.

很少有海龟可以在不损害其鳍状肢空气动力学形状的情况下做到这一点。

There is not much that the turtle can do about this without compromising the aerodynamic shape of the flipper.

问题是随着血液流经海龟的鳍状肢并流回到体内时，海龟会冒着损失足够热量从而降低中心体温的危险。

The problem is that as blood flows through the turtle’s flippers, it risks losing enough heat to lower the animal’s central body temperature when it returns.

解决方法就是降低鳍状肢的温度从而避免损耗身体其他部分的热量。

The solution is to allow the flippers to cool down without drawing heat away from the rest of the turtle’s body.

棱皮龟通过把鳍状肢底部的血管布置成逆流交换系统来实现这一点。

The leatherback accomplishes this by arranging the blood vessels in the base of its flipper into a countercurrent exchange system.

在逆流交换系统中，携带着来自鳍状肢冷却血液的血管与携带着来自身体温暖血液的血管足够靠近，这样就可以从更温暖的血管中吸收一些热量；因此，热量在到达鳍状肢之前就通过流出的血液和流入的血液完成了转移。

In a countercurrent exchange system, the blood vessels carrying cooled blood from the flippers run close enough to the blood vessels carrying warm blood from the body to pick up some heat from the warmer blood vessels; thus, the heat is transferred from the outgoing to the ingoing vessels before it reaches the flipper itself.

在老式蒸汽散热片上有着相同的结构，当水快速流过散热片时，蛇形管在其中反复地传递热量。

This is the same arrangement found in an old-fashioned steam radiator, in which the coiled pipes pass heat back and forth as water courses through them.

棱皮龟当然不是唯一拥有这种生理结构的动物；海鸥的腿部也有一个逆流交换系统。

The leatherback is certainly not the only animal with such an arrangement; gulls have a countercurrent exchange in their legs.

这就是为什么海鸥可以站在冰川上而不被冻僵。

That is why a gull can stand on an ice floe without freezing.

当然，所有这些只适用于成年棱皮龟。

All this applies, of course, only to an adult leatherback.

刚孵化的棱皮龟体型太小，即使拥有保温层和逆流交换系统，也无法保持体温。

Hatchlings are simply too small to conserve body heat, even with insulation and countercurrent exchange systems.

我们还不知道棱皮龟需要到多大年龄或者长到多大尺寸才可以从冷血动物的生活方式转变为一个温血动物的生活方式。

We do not know how old, or how large, a leatherback has to be before it can switch from a cold-blooded to a warm-blooded mode of life.

但是棱皮龟生长达到巨大体型的时间比起其他海龟生长所花费的时间要短得多。

Leatherbacks reach their immense size in a much shorter time than it takes other sea turtles to grow.

或许它们匆匆向成年过渡只是为了保暖。

Perhaps their rush to adulthood is driven by a simple need to keep warm.

The phrase “unique among” in the passage is closest in meaning to

What can be inferred about whales from paragraph 1?

The word “feat” in the passage is closest in meaning to

Paragraph 2 mentions all of the following as true about the body heat of adult leatherback turtles EXCEPT:

The word “bulk” in the passage is closest in meaning to

The word “it” in paragraph 4 refers to

According to paragraph 4, which of the following features enables the leatherback turtle to stay warm?

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

Why does the author mention “old-fashioned steam radiator” in the discussion of countercurrent exchange systems?

The phrase “courses through” in the passage is closest in meaning to

According to paragraph 6, which of the following statements is most accurate about young leatherback turtles?

Look at the four squares  that indicate where the following sentence could be added to the passage. However, these animals have additional means of staying warm.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

A Warm-Blooded Turtle When it comes to physiology, the leatherback turtle is, in some ways, more like a reptilian whale than a turtle. It swims farther into the cold of the northern and southern oceans than any other sea turtle, and it deals with the chilly waters in a way unique among reptiles. A warm-blooded turtle may seem to be a contradiction in terms. Nonetheless, an adult leatherback can maintain a body temperature of between 25 and 26°C (77–79°F) in seawater that is only 8°C (46.4°F). Accomplishing this feat requires adaptations both to generate heat in the turtle’s body and to keep it from escaping into the surrounding waters. Leatherbacks apparently do not generate internal heat the way we do, or the way birds do, as a by-product of cellular metabolism. A leatherback may be able to pick up some body heat by basking at the surface; its dark, almost black body color may help it to absorb solar radiation. However, most of its internal heat comes from the action of its muscles. Leatherbacks keep their body heat in three different ways. The first, and simplest, is size. The bigger the animal is, the lower its surface-to-volume ratio; for every ounce of body mass, there is proportionately less surface through which heat can escape. An adult leatherback is twice the size of the biggest cheloniid sea turtles and will therefore take longer to cool off. Maintaining a high body temperature through sheer bulk is called gigantothermy.  It works for elephants, for whales, and, perhaps, it worked for many of the larger dinosaurs.  It apparently works, in a smaller way, for some other sea turtles.  Large loggerhead and green turtles can maintain their body temperature at a degree or two above that of the surrounding water, and gigantothermy is probably the way they do it.  Muscular activity helps, too, and an actively swimming green turtle may be 7°C (12.6°F) warmer than the waters it swims through. Gigantothermy, though, would not be enough to keep a leatherback warm in cold northern waters. It is not enough for whales, which supplement it with a thick layer of insulating blubber (fat). Leatherbacks do not have blubber, but they do have a reptilian equivalent: thick, oil-saturated skin, with a layer of fibrous, fatty tissue just beneath it. Insulation protects the leatherback everywhere but on its head and flippers. Because the flippers are comparatively thin and blade like, they are the one part of the leatherback that is likely to become chilled. There is not much that the turtle can do about this without compromising the aerodynamic shape of the flipper. The problem is that as blood flows through the turtle’s flippers, it risks losing enough heat to lower the animal’s central body temperature when it returns. The solution is to allow the flippers to cool down without drawing heat away from the rest of the turtle’s body. The leatherback accomplishes this by arranging the blood vessels in the base of its flipper into a countercurrent exchange system. In a countercurrent exchange system, the blood vessels carrying cooled blood from the flippers run close enough to the blood vessels carrying warm blood from the body to pick up some heat from the warmer blood vessels; thus, the heat is transferred from the outgoing to the ingoing vessels before it reaches the flipper itself. This is the same arrangement found in an old-fashioned steam radiator, in which the coiled pipes pass heat back and forth as water courses through them. The leatherback is certainly not the only animal with such an arrangement; gulls have a countercurrent exchange in their legs. That is why a gull can stand on an ice floe without freezing. All this applies, of course, only to an adult leatherback. Hatchlings are simply too small to conserve body heat, even with insulation and countercurrent exchange systems. We do not know how old, or how large, a leatherback has to be before it can switch from a cold-blooded to a warm-blooded mode of life. Leatherbacks reach their immense size in a much shorter time than it takes other sea turtles to grow. Perhaps their rush to adulthood is driven by a simple need to keep warm.