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1、http:/托福听力托福听力 TPO17 原文原文 Lecture 4下面就让小编来为大家介绍一下托福听力托福听力 TPO17 原文原文中 Lecture 4 的文本内容吧，大家要好好把握，这些都是非常有价值的材料，同时，大家也可以登录前程百利论坛进行 TPO 练习辅导，希望能够给准备托福听力的同学带来帮助。TPO 17 Lecture 4 BiologyProfessor：Ok, now I want to talk about an animal that has a fascinating set of defense mechanisms.And thats the octopus,
2、one of the unusual creatures that live in the sea. The octopus is prey to manyspecies, including humans, so how does it escape its predators? Well, let me back up here a second.Anyone ever heard of Proteous? Proteus was a God in Greek mythology who could change form. He couldmake himself look like a
3、 lion or a stone or a tree, anything you wanted, and he could go through a wholeseries of changes very quickly.Well, the octopus is the real world version of Proteus. Just like Proteus, theoctopus can go through all kinds of incredible transformations. And it does this in three ways: by changingcolo
4、r, by changing its texture, and by changing its size and shape. For me, the most fascinatingtransformation is when it changes its color. Its a normal skin color, the one it generally presents, is eitherred or brown or even grey, and it s speckled with dark spots. But when it wants to blend in with i
5、tsenvironment to hide from its enemies, it can take on the color of its immediate surroundings: the oceanfloor, a rock, a piece of coral, whatever. Charles?Student：Do we know how that works, I mean, how they change colors?Professor：Well, we know that the reaction that takes place is not chemical in
6、nature. The colorchanges are executed by two different kinds of cells in the octopus skin, mainly by color cells on theskins surface call chromatophoresChromatophores consist of tiny sacks filled with color dye. There mightbe a couple hundred of these color sacks per square millimeter of the octopus
7、 skin, and depending on thespecies, they can come in as many as five different colors. Each one of these sacks is controlled by muscles.If the muscles are relaxed, the sack shrinks, and all you see is a little white point. But if the musclescontract, then the sack expands, and you can see the colors
8、. And by expanding different combinationsStudent：And just with various combinations of those five colors, they can recreate any color in theirenvironment?http:/Professor：Well, they can no doubt create a lot with just those five colors, but you are right, maybethey cant mimic every color around them,
9、 so thats where the second kind of cell comes in. Just below thechromatophores is a layer of cells that reflect light from the environment, and these cells help the octopuscreate a precise match with the colors surround them. The colors from the color sacks are supplementedwith colors that are refle
10、cted from the environment, and that s how they are able to mimic colors with suchprecision. So, thats how octopus mimic colors. But they dont just mimic the colors in their environment;they can alos mimic the texture of objects in their environment. They have these little projections on theirskin th
11、at allow them to resemble various textures. The projections are called papillae6 If the octopus wantsto have a rough texture, it raises the papillae. If it wants to have a smooth texture, it flattens out the papillae,so it can acquire a smooth texture to blend in with the sandy bottom of the sea. So
12、 the octopus has theability to mimic both the color and the texture of its environment. And its truly amazing how well it canblend in with its surroundings. You can easily swim within a few feet of an octopus and never see it.Student：I read that they often hide from predators by squirting out a clou
13、d of ink, or something likethat.Professor：Yes. The octopus can release a cloud of ink if it feels threatened. But it doesnt hide behindit, as is generally believed. Um, the ink cloud is . it serves to distract a predator while the octopus makesits escape. Um, now theres a third way that octopus can
14、transform themselves to blend in withor mimictheir environment, and thats by changing their shape and size, well, at least their apparent size. Themuscular system of the octopus enables it to be very flexible to assume all sorts of shapes and postures. Soit can contract into the shape of a little ro
15、und stone, and sit perfectly still on the seafloor. Or it can nestleup7 in the middle of a plant and take the shape of one of the leaves. Even Proteus would be impressed, Ithink.教授：好的，现在我想讲一讲一种特别的动物，它有一套令人惊叹的防御机制它就是章鱼，一种生活在大海之中的不凡之物。章鱼的天敌包括人类在内的很多物种的捕食者，那么，它是怎样逃脱它的捕食者的呢?好的，我先讲些背景知识吧!有谁知道普罗透斯吗?普罗透斯来自
16、古希腊神话中的一位海神。他可以变形，使自己看上去像一头狮子或者石头、树木，你们能想到的一切，并且他能够在很短的时间之内完成变形。嗯，章鱼是真正存在的现世版的普罗透斯。和他一样，章鱼也能完成各种不可思议的变形。同时，它可以用三种方式变形：改变颜色、改变纹理、改变大小和形状。对我而言，最有趣的当属改变颜色这项了。它没有变色时的一般肤色，既可能是红的，棕色的，甚至灰色的，体表点缀有许多黑色的斑点。但是，当它试图和环境混同为一个颜色以趋避天敌时它马上就能变成周围景物的颜色：大海的、岩石的、珊瑚，什么都行。查尔斯，你有什么问题?http:/学生：我们知道这种变化的原理吗?我的意思是，章鱼是怎么做到的?教授：嗯，我们肯定都知道，章鱼变色本质上肯定不是依靠化学反应。这种颜色变化是由章鱼皮肤组织中两种不同类型的细胞完成的，主要是体表的叫做“色素体”的颜色细胞。“色素体”由许多细小的、装有染色剂的色袋构成。在章鱼皮肤表面，每一平方厘米中大概有两百个这样的色袋，它们可以组合成五种不同的
