Official 35 Set 2

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Animal Navigation System

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What is the lecture mainly about?
  • A. The structure of the blind mole rats’ underground tunnel system

  • B. How blind mole rats find their way back to their nests

  • C. Whether some animals use Earth’s magnetic field for navigation

  • D. Whether blind mole rats have more than one navigation system

显示答案 正确答案: B

我的笔记 编辑笔记

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    Listen to part of a lecture in an animal behavior class.

    Before we leave the topic of animal navigation, let's look at one more species and how it finds its way through its environment.The species we'll look at is the blind mole rat.

    Blind mole rats are interesting in terms of navigation because they live entirely in the dark, in elaborate underground tunnel systems.So how do blind mole rats find their way around in these complicated tunnels?

    Well, for some time we've known that blind mole rats use some combination of two different navigation systems.Um, one system relies on their sense of time and their ability to remember underground landmarks.For example, let's say a mole rat wants to find its way through its tunnel system back to its nest, where it sleeps.Well, it goes along then feels some hard stones or a tree root under its feet, and it basically says to itself, "OK, here's where I took a left"And then it might remember how long it took to get to the next turn.And so forth.The mole rat goes straight or turns based on what it remembers having sensed along the way on previous trips and the time it took between turns.

    Now, the other navigation system for the mole rat relies on Earth's magnetic field.Mole rats have the ability to sense the magnetic field and use it to orient themselves directionally.But until recently, scientists weren't sure about the role of these two different systems.

    Recently, a team of researchers conducted an experiment to answer that question... do these two navigation systems play different roles?What they did was they designed a special structure that very closely resembles a blind mole rat's tunnel system... which looks like a bicycle wheel... a central hub with multiple spokes radiating outward.Now, this turned out to be quite important.Earlier experiments had used a more generic habitat- basically a wide-open circle- which was originally designed to test magnetic navigation in other animals.That design led to inconclusive results with mole rats.

    Now, with their bicycle-wheel tunnel system, the researchers were able to vary the distance that the mole rats traveled between their "nest" and their food source... by creating long routes and short routes.In each trial, the mole rats started out in their nest, went to the food source, and then had to find their way back home, back to the nest.

    To determine which navigation system they were using, the researchers tested the animals under two different conditions.First the mole rats were tested under conditions of normal magnetism... for both the trip to the food and the trip home.And under these normal conditions, they all followed their original route back home, regardless of the length of the trip to the food source.Then, in the second part of the experiment, the magnetic field was altered... but only for the trip home.A specially constructed set of magnets was used to shift the magnetic field around the habitat 90 degrees eastward.The researchers wanted to see how the mole rats responded to this shift.

    Well...it turns out that the magnetic shift had no impact on the return route of the blind mole rats after a short trip.They returned to the point where they had started from.But after a longer trip, they took a totally different route... one that led them 90 degrees east of the nest.Essentially, they got lost.This was strong evidence that blind mole rats use magnetic navigation only for longer trips.

    So, why two navigation systems- one for long trips and one for short trips?Well, for now we can only speculate, but we think that when mole rats rely on the first system- using underground landmarks or their sense of time- well they make small mistakes here and there.On a short trip, this doesn't matter much... the trip is short, so they can't make many mistakes.But on a long trip, well, there are lots of opportunities to make small mistakes and small mistakes can add up, leaving the mole rat far from where it wants to be.So on a long trip, a magnetic navigation system is better, more useful, since Earth's magnetic field is stable, constant, a more reliable indicator of direction.

  • 旁白:请听一段动物行为讲座的节选。

    教授:在我们结束动物导航的话题之前,我们再来看几个具体的例子,看看动物是怎么在环境中找路的。我们接下来要看的物种是盲眼鼹鼠。

    盲眼鼹鼠在找路方面很有意思,因为它们住在全黑的环境里——在精巧的地下洞穴通道里。所以盲眼鼹鼠要怎么在复杂的通道里找到自己的路呢?

    我们知道,盲眼鼹鼠会结合使用两种不同的导航系统。第一种系统需要依赖盲眼鼹鼠的时间感和它们记忆地下路标的能力。例如,一只盲眼鼹鼠需要通过地下管道系统回到它睡觉的地方。它先是往前走,在感到坚硬的石头或者有树根在脚下的时候,它会告诉自己,好啦,这里是我左转的地方。接下来它会记忆到下一个路口需要的时间,以此类推鼹鼠就是这样通过记忆之前在路上感知到的路标和两个转弯之间所需的时间来走直线或者转弯。

    接下来,盲眼鼹鼠的另一种导航系统是根据地球磁场定位。鼹鼠可以感知到地球的磁场,并用它来确定方向。但是直到最近,科学家才弄清楚这两种导航系统在鼹鼠找路过程中的作用。

    近来,一组科学家设计了个实验来解答这个问题,这两种导航系统起到的作用不同吗?他们的做法是设计一个高度仿真的鼹鼠地道网,它看起来像是个自行车轮子,是一个圆带有多条放射状的路线。接下来就变得很重要了。早期实验用了一个更普遍的装置,基本上是一个开放的圆形,本来是用作测试其他动物的导航的。但是这个设计导致了在鼹鼠身上得不到确定的结论。

    现在有了自行车轮地道装置,研究者可以改变鼹鼠巢穴和觅食地之间的距离,加长或者缩短。在每一个实验里,鼹鼠从自己的巢穴出发,去觅食地点,然后再找路返回巢穴。

    为了确定它们用的是哪一种导航系统,研究者们在两种不同的情景下测试了它们。第一种情景里,鼹鼠的离巢和返巢都在正常磁场下进行。在这些正常的情景下,它们离巢和返巢都是走的同样的路线,不管觅食地离巢穴有多远。然后,在实验的第二部分,磁场被改变了……但只是为了回家。一种特殊设置的磁铁会把鼹鼠巢穴周围的磁场向东偏离90度。研究者们想知道,鼹鼠是怎么应对这种改变的。

    结果是,磁场的改变并不影响盲眼鼹鼠的短途返巢。它们顺利返回了出发地。但是旅途距离加长之后,它们走了一条完全不同的路:这一条路让它们向东偏离了90度。实际上它们迷路了。这是证明盲眼鼹鼠只在长途路途中使用磁场导航的有力证据。

    所以,为什么会同时存在两种导航系统呢:一个用于长途旅行,一个用于短途旅行?现在我们只能推测,但是我们认为当鼹鼠只依赖第一种导航系统,即使用地下路标和时间感来认路时,它们偶尔是会犯错误的。在短途旅行中,这个错误是微不足道的,因为路途很短,它们也不会犯太多的错误。但是当路途变长,它们可能会犯错误的机会就变多了,小错误不断累积,最后会导致鼹鼠偏离正确路线。所以在长途旅行中,磁场导航系统更好,更实用,因为地球的磁场是稳定持续的,是一个可靠的方向指示器!

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  • 本题对应音频:
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    音频1
    解析

    题型分析:主旨题

    原文定位:

    let’s look at one more species and how it finds its way through its environment. The species we’ll look at is the blind mole rat.

    选项分析:

    原文开头处,教授直奔今日讲解lecture 的主题, 且主旨句let’s look at one more species and how it finds its way through its environment. The species we’ll look at is the blind mole rat. 直接对应选项, 故选项B正确。

    ACD 选项均提及原文部分内容。

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