托福TPO核心词汇之A Warm-Blooded Turtle

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新托福之TPO阅读重点单词语境记忆40

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。

托福核心单词

Physiology生理学；生理机能

原文：When it comes to physiology, the leatherback turtle is, in some ways, more like a reptilian whale than a turtle. 从生理学上讲，棱皮龟在某些方面上更像爬行的鲸鱼。

强化记忆： Physiology and anatomy are basic to medical science. 生理学和解剖学是医学的基础。

He bought a book about physiology. 他买了一本生理学方面的书。

Leatherback棱皮龟

原文：When it comes to physiology, the leatherback turtle is, in some ways, more like a reptilian whale than a turtle. 从生理学上讲，棱皮龟在某些方面上更像爬行的鲸鱼。

强化记忆：Leatherback turtles usually mate every other year. 棱皮龟通常是隔年才交配一次。

Scientists have appealed for international cooperation to protect leatherback sea turtles。科学家呼吁国际性合作来保护棱皮海龟。

Reptilian爬虫类动物

原文：When it comes to physiology, the leatherback turtle is, in some ways, more like a reptilian whale than a turtle. 从生理学上讲，棱皮龟在某些方面上更像爬行的鲸鱼。

强化记忆：The chick is ugly and almost reptilian in its appearance. 这只小鸡长得很丑，看起来几乎像个爬行动物。

The reptilian brain is much like a baby's brain. 爬行动物脑有点像婴儿的大脑。

Chilly寒冷的，可怕的

原文：It deals with the chilly waters in a way unique among reptiles. 它们在应对寒冷水域时有其独特的方式。

强化记忆： I was feeling chilly. 我感到冷得难受。

Contradiction矛盾，反驳

原文：A warm-blooded turtle may seem to be a contradiction in terms. 温血海龟似乎是一个自相矛盾的术语。