Official 06 Set 3

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Nightcap Oak

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What topic related to the Nightcap Oak does the professor mainly discuss?
Click on 2 answers
  • A. factors that relate to the size of the area in which it grows

  • B. the size of its population over the last few centuries

  • C. whether anything can be done to ensure its survival

  • D. why it did not change much over the last one hundred million years

显示答案 正确答案: A B

我的笔记 编辑笔记

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

    FEMALE PROFESSOR:Ok, I have an interesting plant species to discuss with you today.Um... it's a species of a very rare tree that grows in Australia, Eidothea hardeniana, but it's better known as the Nightcap Oak.

    Now, it was discovered only very recently, just a few years ago.Um... it remained hidden for so long because it's so rare, there are only about, oh, two hundred of ‘em in existence.They grow in a rain forest, in a mountain ridge, range in the north part of New South Wales which is er... a state in Australia.So just two hundred individual trees in all.

    Now another interesting thing about the Nightcap Oak is that it is, it represents, er... a very old type, er... kind of tree that grew a hundred million years ago.Um... we found fossils that old that bear remarkable resemblance to the tree.So, it's a primitive tree, a... a living fossil you might say.It's relic from earlier times and it has survived all these years without much change.And it, it's probably a kind of tree from which other trees that grow in Australia today evolved.

    Just—just to give you an idea of what we are talking about, here's a picture of the leaves of the tree and its flowers.I don't know how well you can see the flowers. they're those little clusters sitting at the base of the leaves.

    Okay, what have we tried to find out about the tree since we've discovered it?Hum... or how, why is, is it so rare? That's one of the first questions.Um... how is it, um... how does it reproduce? This's another question. [inviting students to propose a theory]Um... maybe those two questions are actually related. [seeing hand raised] Jim?

    MALE STUDENT:Hum... I don't know, but I can imagine that, for instance, seed dispersal might be a factor.I mean if the, er... you know, if the seeds cannot really disperse in the wild area, then, you know, the tree may not colonize new areas, it can't spread from the area where it's growing.

    FEMALE PROFESSOR:Right. That's, that's actually a very good answer.Um... of course, you might think there might not be many areas where the tree could spread into, er... because, um... well, it's very specialized in terms of the habitat.But, that's not really the case here, uh... the suitable habitat, that is, the actual rain forest is much larger than the few hectares where the Nightcap Oak grows.

    Now this tree is a flowering tree as I showed you, uh uh, it—it produces a fruit, much like a plum, on the inset inside there’s a seed with a hard shell.It, it appears that the shell has to crack open or break down somewhat to allow the seed to soak up water.If the Nightcap Oak remains, if their seeds remain locked inside their shell, they will not germinate.Now actually, the seeds, er... they don't retain the power to germinate for very long, maybe two years, so there's actually quite a short window of opportunity for the seed to germinate.So the shell somehow has to be broken down before this, um... germination ability expires.And, and then there's a kind of rat that likes to feed on the seeds as well.So, given all these limitations, not many seeds that the tree produces will actually germinate.So this is a possible explanation for why the tree does not spread.It doesn't necessarily explain how it became so rare, but it explains why it doesn't increase.

    OK, so it seems to be the case that the species, this Nightcap Oak is not very good at spreading.However... it seems, though we can't be sure, that it's very good at persisting as a population.Um... we, there are some indications to suggest that the population of the Nightcap Oak has not declined over the last uh, y’know, many hundreds of years.So it's stayed quite stable; it—it’s not a remnant of some huge population that is dwindled in last few hundred years for some reason.It's not necessarily a species in retreat.Ok, so it cannot spread very well, but it's good at maintaining itself.It's rare, but it's not disappearing.

    Ok, the next thing we might want to ask about the plant like that is what chances does it have to survive into the future.Let's look at that.

  • 旁白:听一段生物课的讲座。

    教授:今天我们将要讨论一种有趣的植物品种。嗯...这是一种非常稀有的树种,它生长于澳洲,Eidothea hardeniana树,也被称为夜冠橡树。

    直到近几年才为人们发现。夜冠橡树因其罕见而隐藏了很久,目前存活个体仅有200株。它们生长在澳大利亚新南威尔士州北部山脉的热带雨林区。所以,总共个体数只有200株。

    夜冠橡树的奇特之处在于,它代表某种存活于一亿多年前的古老树种。并与迄今发现的古老化石具有惊人的相似之处。因此可以说,夜冠橡树是原始植株,也是活化石。它是历经亿年风雨存活至今,没有发生多大改变的遗迹。人们甚至可以推断,当今澳洲生长的诸多树种都是由夜冠橡树进化而来的。

    以上是关于夜冠橡树的简介,下面请同学们观看一张夜冠橡树树叶和花朵的照片。我不知道大家是否能看清楚,那些位于树叶底部的小花簇就是其花朵。

    夜冠橡树究竟有哪些谜题值得我们去探索呢?首先,为何它如此稀少?另外,夜冠橡树是如何繁殖的呢?也许这两个问题是紧密联系的。Jim你来谈谈?

    学生:嗯,我不确定,但我可以想象下,例如,种子的散播或许是影响橡树繁殖的一个因素。如果夜冠橡树的种子无法在广阔区域内散播、生长,那麽树种就无法拓展新领域,因此其繁殖也就无法突破原生地的地理范围。

    教授:回答得很好。同学们或许认为夜冠橡树能够生存的区域很稀有,因为它对生长环境的要求很独特(因此繁殖受到了限制)。但事实并非如此,适合夜冠橡树生长的热带雨林区面积广阔,远远超过其现今存活的几公顷范围。(所以,种子散播并非导致夜冠橡树极为罕有的原因。)

    请同学们思考一下,正像我给你们展示的,夜冠橡树是开花植株,能够结出像李子一样的果实,其种子外包有坚硬的外壳。只有在外壳被击破或打碎的情况下,种子才能吸收到水分。一旦种子被封闭在外壳内,那麽发芽生长就无法实现。事实上,种子不会长时间保持发芽的能力,大概只能保持两年,所以这种树的种子发芽的时间很短。因此夜冠橡树的种子必须在发芽能力到期前突破外壁。另外,当地某种鼠类也喜欢以橡树种子为食(这也对夜冠橡树的繁殖造成了威胁)。因此,由于以上原因,仅有少数夜冠橡树种子能够成功地发芽生长。这是夜冠橡树为什么无法广泛传播的一个可能的解释。这不一定能够解释夜冠橡树如何变得如此罕见的,但是至少可以解释它为什么数量无法激增。

    综上所述,夜冠橡树似乎并不是善于扩展领地积极繁殖的物种但它的确是生命力极强的物种。部分证据显示,夜冠橡树的数量在过去的数百年内都未发生明显减少,其个体数量极为稳定。因此,其个体数量极为稳定,现存的200株夜冠橡树并非数百年前丰盛繁殖之后由于某种原因衰退的剩余。它也并不处于物种衰退期。可以说,夜冠橡树繁殖力不强,但生命力强。它虽然稀少却并不面临灭绝的危险。

    那麽接下来我们将要讨论,夜冠橡树一类的植物种群在未来得以存活的几率有多大。让我们继续分析。

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    题型分析:主旨题

    原文定位

    A选项

    Hmm, I dunno, but uh I can imagine that…for instance…uh seed dispersal might be a factor I mean if the uh y’know if the seeds cannot really disperse in a wide area then you know the tree may not uh colonize new areas, it it can’t spread from the area where it’s growing.

    Right, that’s that’s actually a very good answer.


    B选项


    Uh, uh we, uh, there—there’re some indications to suggest that the population of the Nightcap Oak has not declined over the last uh, y’know, many hundreds of years.


    选项分析

    教授提到了两个问题,为什么这种树非常rare,这种树怎么繁殖,又说这两个问题是有关系的。紧接着学生可能seed dispersal可能是一个问题,教授接着这个答案讲下去,就提到了So this is a possible explanation for why the tree does not spread,对应A选项

    之后的段落,教授又说到population没有decline,对应B选项。


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