Official 48 Set 5

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Symbiotic Relationship

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What is the professor mainly discussing?
  • A. Different ways that scientists use the term “symbiosis”

  • B. A specific kind of symbiotic relationship between organisms

  • C. A butterfly species that competes with another insect species

  • D. Reasons why symbiosis is considered a subtyle of mutualism

显示答案 正确答案: B

我的笔记 编辑笔记

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

    FEMALE PROFESSOR:Ok, today I'd like to spend some time going into more detail about symbiosis.Symbiosis, what is it? Anyone?

    MALE STUDENT:Urn, I thought it's when two organisms are in a relationship that they both benefit from,well, at least that's what I thought it was until I did the reading last night.Now, I am kind of confused about it, because the book used that definition to describe mutualism.Could you explain the difference?

    Good. I was hoping that someone would bring that up.Sometimes scientists working in different fields use the term “symbiosis” to mean slightly different things, and it can get confusing, for example, when “symbiosis” is used as a synonym for “mutualism.”But there are quite a few of us out there who think there should be a clearer distinction made between the two.

    Ok, where to begin... um, the original definition of symbiosis is pretty simple.It simply means “living together,” so any close relationship between two organisms of different species would be considered a symbiotic relationship, including positive and negative relationships.

    Mutualism then is a kind of symbiosis, a specific type of symbiotic relationship where both organisms benefit somehow.So, your book is correct.

    Now, I want to make it clear that, um, the positive result from being in a mutualistic relationship doesn't have to be equal for both organisms.-it's not a one-to-one ratio here.

    Is everyone with me so far?Symbiosis, general term, mutualism, a narrower or more specific kind of symbiosis. Okay.

    Now, let's take a closer look at mutualistic relationships.Um, I'll start off by describing a case of mutualism that involves a certain butterfly species found in South Africa and Australia.It's a good example of how dependence on a mutualistic relationship can vary.

    Ok, there's this butterfly family and I'll spare you the fancy Latin name because it is not important for our purposes here.Uh, I'll call them Coppers and Blues, well, because most members of this family have blue or copper colored wings.I think this is one of the most interesting cases of mutualism.These butterflies require the presence of ants to complete their life cycle,their interaction with ants is obligatory.

    So, this is what happens.A female butterfly of these Coppers and Blues will lay eggs only on vegetation where there are ants of a particular species.The butterflies can smell, well, ants leave behind pheromones, a special chemical signal.The butterfly recognizes the ants' pheromones on the plant and then the newly hatched butterflies, the caterpillars will feed on this plant after they hatch from the eggs.As the caterpillar gets a little older and find shelter under nearby rocks or stones to protect itself from predators.It's always attended or escorted by ants.And it always makes its way back to the host plant to feed,guided by the ants, the ant escort service, so to speak.

    Now, why would the ants go through all this trouble?What's their benefit? Mary?

    It's probably related to food?

    Uh-huh? You are onto something.

    Ok, ants feed on sweet stuff, right?So the caterpillar must have some kind of special access to honey or sugars, or something like that.Maybe caterpillars produce honey somehow.On second thought, um, I'm probably way off.

    You are pretty close actually.The caterpillars have a honey gland, an organ that secretes an amino acid and carbohydrate liquid.The caterpillar secretes the liquid from the honey gland, rather large quantities, enough to feed several ants.

    But what makes this relationship obligatory for the caterpillar?

    Well, if the ants don't feed regularly on the liquid from the caterpillar's honey gland, the gland overloads and gets infected.The infection will kill the caterpillar and it will never reach its final stage of development, becoming a butterfly. John?

    Ok, I just want to make sure I'm following here.The caterpillar needs the ants or it won't make it to the stage where it can become a butterfly.And the ants do this because they get an easy meal out of it, right?But the ants don't absolutely need the caterpillar for survival, 'cause they can get food from other places right?So it's still called mutualism even though it seems like the caterpillar's getting way more out of it.Oh, wait, you said they don't have to equally benefit. Never mind, sorry.

    Yes. But there is a type of mutualism where the relationship is necessary for both organisms to survive.It's called obligatory mutualism.And we'll talk about that in the next class.

  • 旁白:请听生物课上的部分内容。

    教授:今天我想花点时间更详细地讲讲共生关系(symbiosis)。共生关系是什么?有人知道吗?

    学生:我以为是两种生物处于一种双方都受益的关系中,至少在我昨天晚上看了点资料之前是这么认为的。现在我有点困惑,因为那本书上用了那个定义解释互惠共生(mutualism),你能解释一下这两个词的区别吗?

    好。我正希望有人能提出这个问题呢,有时候不同领域的科学家会使用共生关系这个术语来指代不同的东西, 有时候是挺混乱的,比如把共生关系用作互惠共生的同义词。但是也有些人认为应该对这两个词做出更明确的区分。

    该从哪开始讲呢......共生关系的原始定义非常简单。就是指生活在一起,两种不同物种的生物之间的任何亲密关系都能被认为是一种共生关系,包括积极的和消极的关系。

    而互惠共生也是一种共生关系,一种具体类型的共生关系,在这种关系中两种生物在某种程度上都有所受益。所以你看的书也没错。

    我要说清楚的是,这种共生关系中产生的积极结果对两种生物来说不一定是平等的,不是一比一的。

    大家目前都听懂了吗?共生关系是一种广义的术语,而互惠共生是一个狭义的或者更具体的共生类型。

    我们来仔细看看互利关系,我从介绍一个互惠共生的案例开始吧,这个案例与在南非和澳大利亚发现的一种蝴蝶有关。这在说明对互利关系的依赖程度有多么不同方面是个很好的例子。

    有一个族群的蝴蝶,这个蝴蝶的拉丁语名字太花哨了,我就不说了,因为这对我们现在的目的不太重要。我就叫它们蓝铜蝴蝶吧,因为大部分这种蝴蝶都有蓝色或铜色的翅膀。我觉得这是互惠共生案例中最有趣的之一,这些蝴蝶需要有蚂蚁的参与才能完成它们的生命周期,它们与蚂蚁的互动是强制性的。

    情况是这样的:雌性的蓝铜蝶只会在有一种特殊品种的蚂蚁的植物上产卵。这种蝴蝶能够闻到.....蚂蚁会留下费洛蒙,一种特殊的化学信号。蝴蝶能辨认出蚂蚁留在植物上的费洛蒙,然后新孵出的蝴蝶幼虫,也就是毛毛虫孵化后会以这株植物为食。毛毛虫稍微长大一点后会在附近的岩石下找到庇护所,以保护自己不被捕食者吃掉,它通常会由蚂蚁照顾或护送。而且它会回到寄主植物上进食,通常是蚂蚁带路,可以说是蚂蚁的护送服务。

    那么,蚂蚁为什么要给自己找这么多麻烦呢?它们能得到什么好处呢?Mary,你来说?

    也许和食物有关?

    哦?你发现了一些什么。

    蚂蚁以一些甜的东西为食,对吧?所以毛毛虫一定有某种特殊的方法能弄到花蜜或糖分之类的。也许毛毛虫能制造出蜜,我仔细想了想这错得太离谱了。

    你已经很接近了,事实上,毛毛虫有一个蜜腺,一种能分泌氨基酸和液态糖的器官。毛毛虫从蜜腺中分泌出大量液体,足够喂饱好几只蚂蚁。

    但是这种关系对毛毛虫来说为什么是强制性的呢?

    如果蚂蚁不定期吃掉毛毛虫从蜜腺中分泌出的液体,蜜腺就会负荷过重,受到感染。这种感染对毛毛虫来说是致命的,它永远也无法成长到进化的最后阶段变成一只蝴蝶了,John,请说?

    我只是想确认一下我听懂了,毛毛虫需要蚂蚁,否则就活不到进化成蝴蝶的阶段了。而蚂蚁这么做是因为它们能从中获得白吃的午餐,对吗?但是蚂蚁不是绝对需要毛毛虫才能生存啊,因为它们能从其他地方弄到食物,不是吗?所以这种关系仍被称为互惠共生,即使看起来毛毛虫获得的利益比较多。啊,等一下,你说过它们得到的不一定是同等的好处,不好意思,忘记我说过的话吧。

    是的,但是有一种类型的互惠共生关系对两种生物来说都是生存必需的。它叫做义务性共生,我们下节课再讲。

  • 官方解析
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  • 本题对应音频:
    1 感谢 不懂
    音频1
    解析
    题型分类: 主旨题
    选项分析:全文首先介绍互惠关系是共生关系的一种,再举例蝴蝶毛虫和蚂蚁来说明某种互惠关系,最后再介绍这种互惠关系中的两种生物体受益程度并不相等,说明全文在讨论互惠关系,一种共生关系,对应选项B。

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