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发表于 2011-9-13 11:20:15
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Narrator
Listen to part of a lecture in a biology class.(提示我们这是啥课,一般我会记下来)
Professor
Ok, now(主题) I want to talk about an animal that has a fascinating set of defense mechanisms. And that’s the octopus, one of the unusual creatures that live in the sea. The octopus is prey to many species, including humans, so (主题,比开头更直接)how does it escape its predators(某种程度的重复)? Well, let me back up here a second(插入个话题). Anyone ever heard of Proteus?(这里有停顿,注意力集中)Proteus was a God in Greek mythology who could change form. He could make himself look like a lion or a stone or a tree, anything you wanted, and he could go through a whole series of changes very quickly. Well, the octopus is the real world version of Proteus. Just like Proteus, the octopus can go through all kinds of incredible transformations.(作用总是要考的) And it does this in three ways(这是下面的提纲了): by changing color, by changing its texture, and by changing its size and shape.
For me, the most fascinating transformation(方法一) is when it changes its color. It’s a normal skin color, the one it generally presents, is either red or brown or even grey, and it’s speckled with dark spots. But when it wants to blend in with its environment to hide from its enemies, it can take on the color of its immediate surroundings: the ocean floor, a rock, a piece of coral, whatever. Charles?
Student
Do we know how that works, I mean, how they change colors?(提问引出新话题,不过这里不算新,是深入探讨)
Professor
Well(回答问题), we know that the reaction that takes place is not chemical in nature. The color changes are executed by two different kinds (方式方法)of cells in the octopus’ skin, mainly by color cells on the skin’s surface call chromatophores(下定义,此句后停顿).
Chromatophores consist of tiny sacks filled with color dye. There might be a couple hundred of these color sacks per square millimeter of the octopus’ skin, and depending on the species, 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(方法一C的方式) if the muscle’s contract, then the sack expands, and you can see the colors. And by expanding different combinations of these color sacks to different degrees, the octopus can create all sorts of colors. Yes, Elizabeth?
Student
And just with various combinations of those five colors, they can recreate any color in their
environment?
Professor
Well, they can no doubt create a lot with just those five colors, but you are right, maybe they can’t mimic every color around them, so that’s where the second kind(方法一的方式二) of cell comes in. Just(方法一的第二方式) below the chromatophores is a layer of cells that reflect light from the environment, and these cells help the octopus create a precise match with the colors that surround them. The colors from the color sacks are supplemented with colors that are reflected from the environment, and that’s how they are able to mimic colors with such precision. So, that’s how octopus mimic colors(提示方法一讨论结束).
But they don’t just mimic the colors in their environment; they can also(承上启下,方法二) mimic the texture of objects in their environment. They have these little projections on their skin that allow them to resemble various textures. The projections are called papillae(停顿又来了). If the octopus wants to 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 the octopus has the ability to mimic both the color and the texture of its environment. And it’s truly amazing how well it can blend 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(重复了主题) by squirting out a cloud of ink, or something like that.
Professor
Yes. The octopus can release a cloud of ink if it feels threatened. But it doesn’t hide behind it, as is generally believed. Um, the ink cloud is ... it serves to distract a predator while the octopus makes its escape.
Um, now there’s a third way(方法三) that octopus can transform themselves to blend in with or mimic their environment, and that’s by changing their shape and size, well, at least their apparent size.
The muscular system of the octopus enables it to be very flexible to assume all sorts of shapes and postures. So it can contract into the shape of a little round stone, and sit perfectly still on the seafloor. Or it can nestle up in the middle of a plant and take the shape of one of the leaves.(例子,一般考作用,不过今天考的是用了什么例子) Even Proteus would be impressed, I think.
结构:主题--> 方法一--> 方法二-->方法三。其中,主题中有个神仙的例子,方法一中涉及两种细胞也就是两种方式, 方法二、三涉及小例子。
疑问:你这第一题是怎么错的????主题不断重复重复。。。。。
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