标题: TPo15阅读一道题的疑惑 [打印本页] 作者: xianggebenben 时间: 2014-12-5 17:08 标题: TPo15阅读一道题的疑惑 Tpo15 有一篇阅读6选3的题，E和F选项我不太明白，求高人指点！
原文和题目如下：
【1】When it comes to physiology, the leatherback turtle is, in some ways, more like areptilian whale than a turtle. It swims farther into the cold of the northern and southernoceans than any other sea turtle, and it deals with the chilly waters in a way unique amongreptiles.
【2】A warm-blooded turtle may seem to be a contradiction in terms. Nonetheless, an adultleatherback can maintain a body temperature of between 25 and 26°C (77-79°F) in seawaterthat is only 8°C (46.4°F). Accomplishing this feat requires adaptations both to generate heatin the turtle’s body and to keep it from escaping into the surrounding waters. Leatherbacksapparently do not generate internal heat the way we do, or the way birds do, as a by-productof cellular metabolism. A leatherback may be able to pick up some body heat by basking at thesurface; its dark, almost black body color may help it to absorb solar radiation. However, mostof its internal heat comes from the action of its muscles.
【3】Leatherbacks keep their body heat in three different ways. The first, and simplest, is size.The bigger the animalis, 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 istwice 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 forelephants, for whales, and, perhaps, it worked for many of the larger dinosaurs. It apparentlyworks, in a smaller way, for some other sea turtles. Large loggerhead and green turtles canmaintain their body temperature at a degree or two above that of the surrounding water, andgigantothermy is probably the way they do it. Muscular activity helps, too, and an activelyswimming green turtle may be 7°C (12.6°F) warmer than the waters it swims through.
【4】Gigantothermy, though, would not been ought to keep a leatherback warm in coldnorthern waters. It is not enough for whales, which supplement it with a thick layer ofinsulating blubber (fat). Leatherbacks do not have blubber, but they do have a reptilianequivalent: 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 theflippers are comparatively thin and blade-like, they are the one part of the leatherback that islikely to become chilled. There is not much that the turtle can do about this withoutcompromising the aerodynamic shape of the flipper. The problem is that as blood flows throughthe turtle’s flippers, it risks losing enough heat to lower the animal’s central body temperaturewhen it returns. The solution is to allow the flippers to cool down without drawing heat awayfrom the rest of the turtle’s body. The leatherback accomplishes this by arranging the bloodvessels in the base of its flipper into a countercurrent exchange system.
【5】In a countercurrent exchange system, the blood vessels carrying cooled blood from theflippers run close enough to the blood vessels carrying warm blood from the body to pick upsome heat from the warmer blood vessels; thus, the heat is transferred from the outgoing tothe ingoing vessels before it reaches the flipper itself. This is the same arrangement found inan old fashioned steam radiator, in which the coiled pipes pass heat back and forth as watercourses through them. The leatherback is certainly not the only animal with such anarrangement; gulls have a countercurrent exchange in their legs. That is why a gull can standon an ice floe without freezing.
【6】All this applies, of course, only to an adult leatherback. Hatchlings are simply too small toconserve body heat, even with insulation and countercurrent exchange systems. We do notknow how old, or how large, a leatherback has to be before it can switch from a cold-bloodedto a warm-blooded mode of life. Leatherbacks reach their immense size in a much shorter timethan it takes other sea turtles to grow. Perhaps their rush to adulthood is driven by a simpleneed to keep warm.
13. Directions: An introductory sentence for a brief summary of the passage isprovided below. Complete the summary by selecting the THREE answer choices thatexpress the most important ideas in the passage. Some sentences do not belong in thesummary because they express ideas that are not presented in the passage or areminor ideas in the passage. This question is worth 2 points.
Contrary to what we would expect of reptiles, the leatherback turtle is actually warm-blooded.
A.Even though they swim into cold ocean waters, leatherbacks maintain their body heat in muchthe same way as sea turtles in warm southern oceans do.
B.The leatherback turtle uses a countercurrent exchange system in order to keep the flippersfrom drawing heat away from the rest of the body.
C.The shape of the leatherback turtle's flippers is especially important in maintaining heat inextremely cold northern waters.
D.The leatherback turtle is able to maintain body heat through sheer size.
E.Leatherbacks have an insulating layer that can be considered the reptilian version ofblubber.
F.Young leatherbacks often do not survive to adulthood because they are not able to switchfrom a cold-blooded way of life to a warm-blooded one quickly enough.