Official 18 Set 6

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
置顶

North American Wood Frog

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
What is the main purpose of the lecture?
  • A. To explain the biological advantages of a physical change that occurs in North American wood frogs

  • B. To explain why the North American wood frog’s habitat range has expanded

  • C. To describe the functioning of the circulatory system of the North American wood frog

  • D. To introduce students to an unusual phenomenon affecting North American wood frogs

显示答案 正确答案: D

我的笔记 编辑笔记

/
  • 原文
  • 译文
  • 查看听力原文

    关闭显示原文

    NARRATOR:Listen to part of a lecture in a biology class.

    FEMALE PROFESSOR:Well, it’s finally looking like spring is arriving— the last of the winter snow will be melting away in a few days.So before we close today, I thought I’d mention, uh, a biological event that’s part of the transition from winter to spring… something you can go outside and watch, if you have some patience.There's a small creature that lives in this area— you’ve probably seen it: it’s the North American wood frog…

    Now the wood frog’s not that easy to spot, since it stays pretty close to the ground, under leaves and things, and it blends in really well with its background, as you can see.But they’re worth the effort, because they do something very unusual— something you might not have even thought possible…

    OK, North American wood frog live over a very broad territory, or range they’re found all over the northeastern United States, and all through Canada and Alaska even inside the Arctic Circle.No other frog is able to live that far northBut wherever they live, once the weather starts to turn cold, and the temperatures start to drop below freezing as soon as the frog even touches an ice crystal or a bit of frozen ground well, it begins to freeze.[pause, then humorously as she notices look on student’s face]Yes, Jimmy? You look a bit taken aback…

    MALE STUDENT:Wait…you mean, it’s still alive, but it freezes? Solid?

    FEMALE PROFESSOR:Well, almost. Ice forms in all the spaces outside cells, but never within a cell.

    MALE STUDENT:But… then, how does its heart beat?

    FEMALE PROFESSOR:It doesn't.

    MALE STUDENT:But—how can it do…

    FEMALE PROFESSOR:How can it do such a thing?Well, that first touch of ice apparently triggers a biological response inside the frog, that first of all starts drawing water away from the center of its body.So the middle part of the frog, its internal organs—its heart, lungs, liver— these start getting drier and drier, while the water that’s being pulled away is forming a puddle around the organs, just underneath the skin.And then that puddle of water starts to freeze.

    OK, up to now the frog’s heart is still beating, right?Slower and slower, but…. And in those last few hours before it freezes, it distributes glucose—a blood sugar—throughout its body, its circulatory system. Sort of acts like an antifreeze…

    MALE STUDENT:A solution of antifreeze, like you put in your car in the winter?

    FEMALE PROFESSOR:[hesitantly]Well, you tell me.In frogs, the extra glucose makes it harder for the water inside the cells to freeze, so the cells stay just slightly wet— enough so that they can survive the winter.Then after that, the heart stops beating altogether.So, is that the same?

    MALE STUDENT:[laughs because he doesn’t know]I don’t really know, but uh … how long does it stay that way?

    FEMALE PROFESSOR:Well, it could be days or even months— all winter, in fact.But, um, see, the heart really doesn’t need to do any pumping now, because the blood is frozen too.

    MALE STUDENT:I just…I guess I just don’t see how it isn’t— y’know, clinically dead.

    FEMALE PROFESSOR:Well, that’s the amazing thing.And how it revives is pretty amazing too.After months without a heartbeat, springtime comes around again, the Earth starts to warm up, and suddenly one day—ping!A pulse—followed by another one, then another, until—maybe ten, twelve hours later, the animal is fully recovered.

    MALE STUDENT:And—does the, uh, thawing process have some kind of trigger as well?

    FEMALE PROFESSOR:Well, we’re not sure, actually.The peculiar thing is, even though the sun is warming the frog up on the outside, its insides thaw out first— the heart and brain and everything.But somehow, it all just happens that way every spring.

    MALE STUDENT:And after they thaw? Does it affect them? Like their life span?FEMALE PROFESSOR:Well, hmm we really don’t know a lot about how long a wood frog normally lives probably just a few years.But there’s no evidence that the freezing process affects its longevity It does have some other impacts, though.In studies we’ve found that, when it comes to reproduction, freezing diminishes the mating performance of males: after they’ve been frozen, and thawed of course, they don’t seem quite as vocal, they move slower—and they seem to have a harder time recognizing a potential mate.So if a male frog could manage not to go through this freezing cycle, he’d probably have more success at mating.

  • 旁白:听下面一段生物学的课程。

    教授:嗯,现在看来,春天终于要到来了,几天之后,最后的冬雪将会融化。所以,在我们今天结束课程之前,我想谈谈一个与冬春换季有关的生物学事例,这个事情你们如果有耐心的话,自己出门儿就能观察到。这个片区内生活着一群小动物—你们很可能已经见过了,名字叫做北美林蛙。

    现在林蛙不是特别好找,因为它们和地面贴得很近,而且藏在树叶等与它们外形相似、可以掩盖它们踪迹的隐蔽物下面。但是,它们值得你们费这番功夫,因为它们有一个非常奇妙的本领,这项本领你们想来绝对不可思议。

    好的,北美林蛙生活的地域是非常广阔的,从美国北部一直到加拿大和阿拉斯加甚至到北极圈,你们都能够看到它的身影。没有另外一种蛙类可以生活在如此遥远的北地。但不管它们到底生活在那一个地方,一旦天气变冷,气温达到冰点以下,甚至只要林蛙碰到了一小点冰渣或冻土,嗯,它马上就会被冷冻起来。你们看上去有点吃惊?

    学生:等一下,您的意思是,它是活着的,但它是冰冻、不动的?

    教授:嗯,差不多吧!在林蛙的体内,除了细胞之外的空间里,到处都是冰。

    学生:但是这样的话,它的心脏怎么跳动呢?

    教授:已经不跳了。

    学生:但是,那样它怎么…

    教授:你是想知道这是怎么一回事吗?嗯,首先,这个反应会导致体腔内脱水,林蛙接触冰这个动作触发了林蛙体内的生理反应。所以,在林蛙的中部,它的内部器官,包括心脏、肺、肝都会变得越来越干燥,当水流出的时候在器官周围形成水坑就在皮肤下面。其后,水坑开始结冰。

    好的,到了现在这一步,林蛙的心脏依旧是在跳跃,对吧?越来越慢,对的…到结冰前的几个小时里,它的体内会释放葡萄糖—一种血糖—这一血糖到全身的循环系统,这种葡萄糖似乎起到的是抗冻剂的作用。

    学生:林蛙的这种释放葡萄糖的这种做法,即像我们在冬季往车里加抗冻剂一样吗?

    教授:嗯,一会儿我讲完了你来告诉我吧!在林蛙体内,超量的葡萄糖会使得它们在冬季时细胞内部很难结冰,所以,那时细胞仅仅会湿润一些,而这个湿度恰恰是保证它们在冬季的生存的程度。等到了那时,心脏的全部机能都会停止。所以,你还觉得你的比喻恰当吗?

    学生:我真的不知道,不过,这种状态会持续多久呢?

    教授:嗯,长则几个月,甚至整个冬天,短则几天。实际上,嗯,因为心脏不需要输送血液,因为血液也是凝固的。

    学生:我想,只是这样想,我不明白,它这种状态为什么还是活着的,因为按照临床医学的经验来说,它已经死了。

    教授:嗯,那就是它的神奇所在!并且,它的解冻过程,也是令人吃惊的。在长达数月的心脏停跳期后,突然某一天,春季再次降临,地球又重新开始温暖如春。一声脉搏的颤动之后,接着又来了一个…脉搏恢复了大概 10 到 12 个小时之后,林蛙就彻底恢复了。

    学生:那么这种解冻的过程是否也有一个触发点呢?

    教授:嗯,我们目前也不清楚。我们可能会想到的是,当温暖的阳光叫醒青蛙之后,它的躯体内部包括大脑、心脏等会率先恢复。但事实上,每次春季的时候,林蛙的身体解冻是一次性到位的。

    学生:在解冻之后,这种经历会影响它的寿命吗?教授:嗯,我们现在还没有研究清楚一只林蛙正常情况下会存活多久,有可能是几年。但是没有证据表明这个过程会影响它的寿命,但这个过程对林蛙的其他方面倒有一定影响。一些研究中,我们发现到了繁殖季,有过冰冻经历的雄性林蛙交配次数会减少:在他们冰冻—解冻之后,它们鸣叫求偶的欲望并不十分强烈,它们跑动得很慢,而且寻找雌性交配对象时会有麻烦。所以,如果雄性林蛙能够设法避免进入冰冻周期的话,它交配的成功率就会大一些。

  • 官方解析
  • 网友贡献解析
  • 本题对应音频:
    1 感谢 不懂
    音频1
    解析

    题型分类:主旨题

    音频定位:So before we close today, I thought I’d mention, uh, a biological event that’s part of the transition from winter to spring…something you can go outside and watch, if you have some patience. There’s a small creature that lives in this area—you’ve probably seen it: it’s the North American wood frog…

    选项分析:So后面是重点教授想讲在冬转春时的一个生物现象关于北美wood frog,之后全部在讲wood frog神奇的过冬现象对应选项D

    标签

题目讨论

如果对题目有疑问,欢迎来提出你的问题,热心的小伙伴会帮你解答。

如何吃透这篇文章?

North American Wood Frog

0人精听过

预计练习时间:15min44s

马上精听本文

最新提问