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Unformatted text preview: ove that of the surrounding water, and gigantothermy is probably the way they do a. Muscular activity helps, too, and an actively swimming green turtle may be T 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, oil­saturated skin, with a layer of fibrous, fatty tissue just beneath a. Insulation protects the leatherback everywhere but on its head and flippers. Because the flippers are com paratively 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 anim al'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 as 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 old­fashioned 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 warm­blooded 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. Paragraph 1 在 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. 1. The phrase unique among in the passage is closest in meaning to ○natural to ○different from all other ○quite common among ○familiar to 2. What can be inferred about whales from paragraph 1? 410 Mail@liuwenyong.com 在在在在在在 www.liuwenyong.com 在在在在在在在在在在在在在在在,在在在在在在在在在在 ○They are considered by some to be reptiles. ○Their bodies are built in a way that helps them manage extremely cold...
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