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.
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
Paragraph 1: 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?
○They are considered by some to be reptiles.
○Their bodies are built in a way that helps them manage extremely cold temperatures.
○They are distantly related to leatherback turtles.
○They can swim farther than leatherback turtles.
Paragraph 2: 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.
3. The word “feat” in the passage is closest in meaning to
○remarkable achievement
○common transformation
○daily activity
○complex solution
4. Paragraph 2 mentions all of the following as true about the body heat of adult leatherback turtles EXCEPT:
○Their muscles produce heat for maintaining body temperature.
○Their dark bodies help trap solar radiation.
○Their cellular metabolism produces heat as a by-product.
○B(yǎng)asking at the water’s surface helps them obtain heat.
Paragraph 3: 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.
5. The word “bulk” in the passage is closest in meaning to
○strength
○effort
○activity
○mass
Paragraph 4: 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.
6. The word “it” in paragraph 4 refers to
○the problem
○blood
○the turtle
○body temperature
7. According to paragraph 4, which of the following features enables the leatherback turtle to stay warm?
○An insulating layer of blubber
○A thick, oily skin covering fatty tissue
○The aerodynamic shape of its flippers
○A well-insulated head
Paragraph 5: 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.
8. Which of the sentences below best expresses the essential information in thehighlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
○In a turtle's countercurrent exchange system, outgoing vessels lie near enough to ingoing ones that heat can be exchanged from the former to the latter before reaching the turtle's flippers.
○Within the turtle's flippers, there is a countercurrent exchange system that allows colder blood vessels to absorb heat from nearby warmer blood vessels and then return warmed blood to the turtle's body.
○In a countercurrent exchange system, a turtle can pick up body heat from being close enough to other turtles, thus raising its blood temperature as it passes them.
○When a turtle places its flippers close to its body, it is able to use its countercurrent exchange system to transfer heat from the warmer blood vessels in its body to the cooler blood vessels in its flippers.
9. Why does the author mention old-fashioned steam radiator in the discussion of countercurrent exchange systems?
○To argue that a turtle's central heating system is not as highly evolved as that of other warmblooded animals
○To provide a useful comparison with which to illustrate how a countercurrent exchange system works
○To suggest that steam radiators were modeled after the sophisticated heating system of turtles
○To establish the importance of the movement of water in countercurrent exchange systems
10. The phrase “courses through” in the passage is closest in meaning to
○rises through
○heats up in
○runs through
○collects in
Paragraph 6: 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.
11. According to paragraph 6, which of the following statements is most accurate about young leatherback turtles?
○They lack the countercurrent exchange systems that develop in adulthood.
○Their rate of growth is slower than that of other sea turtles.
○They lose heat easily even with insulation and countercurrent exchange systems.
○They switch between cold-blooded and warm-blooded modes throughout their hatchling stage.
Paragraph 3: 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.
12. 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?
13. 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.
Contrary to what we would expect of reptiles, the leatherback turtle is actually warm-blooded.
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●
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Answer Choices
○Even though they swim into cold ocean waters, leatherbacks maintain their body heat in much the same way as sea turtles in warm southern oceans do.
○The leatherback turtle uses a countercurrent exchange system in order to keep the flippers from drawing heat away from the rest of the body.
○The shape of the leatherback turtle's flippers is especially important in maintaining heat in extremely cold northern waters.
○The leatherback able to maintain body heat through sheer size.
○Leatherbacks have an insulating layer that can be considered the reptilian version of blubber.
○Young leatherbacks often do not survive to adulthood because they are not able to switch from a cold-blooded way of life to a warm-blooded one quickly enough.
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13. The leatherback turtle uses a…
The leatherback turtle is… Leatherbackshavean…
:溫血海龜
從生理學(xué)上講，棱皮龜在某些方面上更像爬行的鯨魚。跟其他海龜相比，它們能夠游入更寒冷的北部和南部海洋，并且和其他爬行類動物相比，它們在應(yīng)對寒冷水域時有其獨特的方式。
溫血海龜似乎是一個自相矛盾的術(shù)語。盡管如此，成年棱皮龜能夠在僅8攝氏度（46.4華氏度）的海水中將體溫維持在25～26攝氏度（77-79華氏度）之間。棱皮龜要做到這一點就必須調(diào)節(jié)其自身的體溫，還要防止溫度散失到周圍水域。很顯然，棱皮龜產(chǎn)生體內(nèi)熱量的方式與我們或者鳥類不同，并非細(xì)胞代謝的副產(chǎn)物。棱皮龜可能會通過曬太陽來收集身體所需的熱量。其深色近乎黑色的體色有助于吸收太陽輻射。然而，它的大部分體熱來自于肌肉運動。
棱皮龜通過三種方式保持體溫。第一種也是最簡單的方式就是體型大小。動物體型越大，表面和體積的比例越小。體重每增加一盎司，相應(yīng)的容易流失熱量的表面就越少。成年棱皮龜是最大的海龜?shù)膬杀�，因此它變涼就需要更久的時間。完全依靠龐大體積維持體溫的方法叫巨溫性。大象、鯨魚也許包括很多恐龍也是通過這種方法保持體溫的。其它海龜或多或少也存在這種現(xiàn)象。紅海龜和綠甲海龜可以維持與周圍水溫略高1攝氏度或2攝氏度或的體溫，可能就是利用的巨溫性。肌肉運動也有助于維持體溫，一個活躍游水的綠海龜體溫可能比它所游水域溫度高7攝氏度（12.6華氏度）。
然而，在寒冷的北部水域巨溫性不足讓棱皮龜保暖。同樣，對于通過厚厚的絕緣脂（脂肪）來維持體溫的鯨魚來說也是不夠的。棱皮龜沒有鯨魚那樣的脂肪，但是它們和爬行類的動物有著相似的結(jié)構(gòu)：厚且含油的皮膚，皮膚下有一層纖維，而脂肪組織就在這個纖維層下面。除了頭部和鰭，這個“絕緣”結(jié)構(gòu)可以保護它們的所有部位。因為棱皮龜?shù)啮捪鄬^薄且呈葉片狀，這一部位很有可能會被凍僵。在不損害鰭部氣動外形的情況下很少有海龜可以做到這些。問題是血液流經(jīng)海龜鰭部時，很容易損耗熱量，血液回流時便降低了動物的中心體溫。解決辦法是在身體其余部分的熱量還沒有損耗前，允許鰭部降低溫度。棱皮龜通過鰭下排列的血管流入逆流交換系統(tǒng)來實現(xiàn)這一點。
在逆流交換系統(tǒng)中，血管將鰭部冷卻的血液與身體其他部位溫?zé)岬难哼M行交換。因此，熱量在到達(dá)鰭部前就通過流入的血液和流出的血液完成了熱量轉(zhuǎn)移。人們發(fā)現(xiàn)老式蒸汽式暖氣片有著與之類似的裝置，當(dāng)水流經(jīng)這些盤繞的管子時熱量進行了交換。當(dāng)然并不只是棱皮龜有這種結(jié)構(gòu)。海鷗的腿部也有一個逆流交換系統(tǒng)，這就是為什么海鷗可以站在冰川上而不被凍結(jié)。
當(dāng)然，這些都僅適用于成年棱皮龜。剛孵化的棱皮龜太小，即使有絕緣層和逆流交換系統(tǒng)也不能保存體溫�，F(xiàn)在我們還不知道棱皮龜要達(dá)到多大年齡或者多大尺寸才能從冷血動物轉(zhuǎn)變成溫血動物。棱皮龜龐大體型的形成時間要比其它海龜短得多�？赡芩鼈兪菫榱吮Ｅ偶敝虺赡赀^渡。
