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发表于 2011-10-12 01:05:56
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TPO 15 看起来有点多，因为把文章post上了。盼回复~！
文章分别是 保温的乌龟，冰川形成，以及大灭绝
A Warm-Blooded Turtle
When itcomes to physiology, the leatherback turtle is, in some ways, more like a reptilianwhale than a turtle. It swims farther into the cold of the northern and southern oceans thanany other sea turtle, and it deals with the chilly waters in a way unique amongreptiles.
A warm-blooded turtle mayseem to be a contradiction in terms. Nonetheless,an adult leatherback can maintain a body tem perature of between 25 and 26°C (77 - 79°F) in seawaterthatis only 8°C (46.4°F). Accomplishingthis feat requires adaptations both to generateheat in the turtle' s body and to keep it from escaping into the surroundingwaters. 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 topick up some body heat by basking atthe 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 bodyheat in three different ways. The first, andsimplest, is size. The bigger the animal is, the lower as surface-to-volum e ratio; for every ounce of body mass,there is proportionately lesssurface through which heat can escape. An adult leatherback is twice the sizeof the biggest cheloniid sea turtles and will therefore take longer tocool off. Maintaining a high body temperature through sheer bulk is called gigantotherrny. 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 thesurrounding water, and gigantothermy isprobably the way they do it. Muscular activity helps, too, and an activelyswimming green turtle may be T C (12.6° F) warmer than the waters it swimsthrough.
Gigantothermy,though, would not be enough to keep a leatherback warm in cold northern waters. It is not enough forwhales, which supplement it with a thicklayer of insulating blubber (fat).
Leatherbacks do not haveblubber, but they do have a reptilian equivalent:thick, oil-saturated skin, with a layer of fibrous, fatty tissue just beneath a. Insulation protects theleatherback everywhere but on itshead and flippers. Because the flippers are com paratively thin and bladelike, they are the one part of the leatherback that is likely to become chilled. There is not much that the turtlecan do about this without compromising the aerodynamic shape of theflipper. The problem is that as blood flowsthrough the turtle's flippers, it risks losing enough heat to lower theanim al's central body temperature when (it] returns. The solution is to allowthe flippers to cool down without drawing heat away from the rest of theturtle's body. The leatherback accomplishesthis by arranging the blood vessels in the base of as flipper into a countercurrent exchange system.
In acountercurrent 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 up someheat from the warmer blood vessels; thus, the heat is transferred from theoutgoing to the ingoing vessels before it reaches the flipper itself.This isthe same arrangement found in anold-fashioned steam radiator, in whichthe coiled pipes pass heat back and forth as water courses through them . The leatherback is certainlynot 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.
Allthis applies, of course, only to an adult leatherback. Hatchlings are simply too small to conserve body heat, even withinsulation and countercurrent exchangesystems. We do not know 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 time than it takesother sea turtles to grow. Perhapstheir rush to adulthood is driven by a simple need to keep warm.
This question is worth 2 points.
Contraryto what we would expect of reptiles. the leatherbackturtle is actually warm-blooded.
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AnswerChoices
1○Even though they swim intocold ocean waters, leatherbacks maintain their body heat in much the same wayas sea turtles in warm southern oceans do.
2 The leatherback turtle usesa countercurrent exchange system in order to keep the flippers from drawingheat away from the rest of the body.
3○The shape of the leatherbackturtle's flippers is especially important in maintaining heat in extremely coldnorthern waters.
4○The leatherback turtle isable to maintain body heat through sheer size.
5○Leatherbacks have aninsulating layer that can be considered the reptilian version of blubber.
○Young leatherbacks often donot survive to adulthood because they are not able to switch from acold-blooded way of life to a warm-blooded one quickly enough
疑问：这道题答案是 2,4,5，对于第5项不明白，这个明明是说的细节啊（最后多选题的原则不是文章大意优先吗），既然是细节，为什么不选3呢？3哪里错了呢？
Glacier Formation
Parargraph5:Throughout most of Earth's history, glaciers did not exist, but at the presenttime about 10 percent of Earth's land surface is covered by glaciers.Present-day glaciers are found in Antarctica, in Greenland, and at highelevations on all the continents except Australia. In the recent past, fromabout 2.4 million to about 10,000 years ago, nearly a third of Earth's landarea was periodically covered by ice thousands of meters thick. In the muchmore distant past, other ice ages have occurred.
12. According to paragraph 5, in what way is the presenttime unusual in the history of Earth?
○There are glaciers.
○More land is covered by glaciers than at anytime in thepast.
○There is no ice age.
○No glaciers are found in Australia.
疑问：这道题答案是A，不理解，因为原文强调的是近年来的冰川比以往多，但是不是说以往没有冰川而现在有冰川，我选的是B
[url=]Mass Extinctions
Cases in which many speciesbecome extinct within a geologically short interval of time are called mass extinctions.There was one such event at the end of theCretaceous period (around 70 million years ago). There was another, evenlarger, mass extinction at the end of thePermian period (around 250 million years ago). The Permian event hasattracted much less attention than other mass extinctions because mostly unfamiliarspecies perished at that time.
The fossil record shows atleast five mass extinctions in which many families of marine organisms diedout. The rates of extinction happening today are as great as the rates duringthese mass extinctions. Many scientists have therefore concluded that a sixthgreat mass extinction is currently in progress.
What could cause such highrates of extinction? There are several hypotheses, including warming or coolingof Earth, changes in seasonal fluctuations or ocean currents, and changingpositions of the continents. Biological hypotheses include ecological changesbrought about by the evolution of cooperation between insects and floweringplants or of bottom-feeding predators in the oceans. Some of the proposedmechanisms required a very brief period during which all extinctions suddenlytook place; other mechanisms would be more likely to have taken place moregradually, over an extended period, or at different times on differentcontinents. Some hypotheses fad to account for simultaneous extinctions on landand in the seas. Each mass extinction may have had a different cause. Evidencepoints to hunting by humans and habitat destruction as the likely causes forthe current mass extinction.
American paleontologists David Raup and JohnSepkoski, who have studied extinction rates in a number of fossil groups,suggest that episodes of increased extinction have recurred periodically,approximately every 26 million years since the mid-Cretaceous period. The lateCretaceous extinction of the dinosaurs and am monoids was just one of the moredrastic in a whole series of such recurrent extinction episodes. Thepossibility that mass extinctions may recur periodically has given rise to suchhypotheses as that of a companion star with a long-period orbit deflectingother bodies from their normal orbits, making some of them fall to Earth asmeteors and causing widespread devastation upon impact.
Of the various hypothesesattempting to account for the late Cretaceous extinctions, the one that hasattracted the most attention in recent years is the asteroid-impact hypothesisfirst suggested by Luis and Walter Alvarez. According to this hypothesis, Earthcollided with an asteroid with an estimated diameter of 10 kilometers, or withseveral asteroids, the combined mass of which was comparable. The force ofcollision spewed large amounts of debris into the atmosphere, darkening theskies for several years before the finer particles settled. The reduced levelof photosynthesis led to a massive decline in plant life of all kinds, and thiscaused massive starvation first of herbivores and subsequently of carnivores.The mass extinction would have occurred very suddenly under this hypothesis.
One interesting test of theAlvarez hypothesis is based on the presence of the rare-earth element iridium(Ir). Earth' s crust contains very little of this element, but most asteroidscontain a lot more. Debris thrown into the atmosphere by an asteroid collisionwould presumably contain large amounts of iridium, and atmospheric currentswould carry this material all over the globe. A search of sedimentary depositsthat span the boundary between the Cretaceous and Tertiary periods shows thatthere is a dramatic increase in the abundance of iridium briefly and preciselyat this boundary. This iridium anomaly offers strong support for the Alvarez hypothesiseven though no asteroid itself has ever been recovered.
1. Directions: An introductory sentence for a brief summaryof the passage is provided below. Complete the summary by selecting the THREEanswer choices that express the most important ideas in the passage. Somesentences do not belong in the summary because they express ideas that are notpresented in the passage or are minor ideas in the passage. This question isworth 2 points.
There have been many attemptsto explain the causes of mass extinctions.
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AnswerChoices
1○Asteroid impacts,evolutionary developments, and changes in Earth' s climate and in the positionsof the continents have all been proposed as possible causes of massextinctions.
2○Researchers have observed26-million-year cycles in extinction rates of a number of fossil groups thatcould all be attributed to the same cause.
3○According to the Alvarezhypothesis, much of the iridium originally present on Earth was thrown into theatmosphere as a result of an asteroid impact that also caused a massextinction.
4○The unusual distribution ofiridium on Earth and the presence of craters and heat-shocked quartz arecentral to the theory that an asteroid impact caused the late Cretaceous event.
5○The collision between Earthand a large asteroid resulted in massive damage and generated enough heat tocause irreversible changes in Earth' s atmosphere.
6○There was a particularlylarge mass extinction that occurred around 250 million years ago at the end ofthe Permian period, whose cause could not be determined.
疑问：这道题答案是1,2,4，但是我选的是1,5，4，.为什么5不能入选呢？ |
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GO
楼主: wuqian0801
发表于 2011-9-1 04:45:44
，这个不缺少要点，但是when导致逻辑又不太对。一个缺因素，一个逻辑不对，怎么取舍？
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