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TPO 15 Lecture 4 Biology
Professor：OK. We've been talking till now about the two basic needs of a biological community – an energy source to produce organic materials, you know ah, food for the organism , and the waste recycling or breakdown of materials back into inorganic molecules, and abo ut how all this requires photosynthesis when green plants or microbes convert sunlight into energy and also requires microorganisms, bacteria, to secrete chemicals that break down or r ecycle the organic material to complete the cycle So, now we are done with this chapter of the textbook, we can just review for the weekly quiz and move on to the next chapter, right? Well, not so fast. First, I‘d like to talk about some discoveries that have challenged one of these fundamental assumptions about what you need in order to have a biological community.
And, well, there actually were quite a few surprises. I tall began in 1977 with the exploration of hydrothermal vents on the ocean floor.Hydrothermal vents are cracks in the Earth’s surface that occur, well, the ones we are taiking about here are found deep at the bottom of the ocean. And these vents on the ocean floor, they release this incredibly hot water, 3-4 times the temperature that you boil water at be cause this water has been heated deep within the Earth. Well about 30 years ago,researchers sent a deep-sea vessel to explore the ocean’s depth, about 3 kilometers down, way deep to ocean floor, No one had ever explored that far down before. Nobody expected there to be any life down there because of the conditions. First of all, sunlight doesn't rea ch that far down so it’s totally dark. There couldn’t be any plant or animal life since there's no sunlight, no source of energy to make food. If there was any life at all, it’d just be some bacter ia breaking down any dead materials that might have fallen to the bottom of the ocean . And?
Student 1：And what about the water pressure? Didn ’ t we talk before about how the deeper down into the ocean you go, the greater the pressure?
Professor：Excellent point! And not only the extreme pressure, but also the extreme temperature of the water around these vents. If the lack of sunlight didn't rule out the existence of a biological community down there then these factors certainly would, or so they thought.
Student 2：So you are telling us they did find organisms that could live under those conditions?
Professor：They did indeed, something like 300 different species
Student 1：But... but how could that be? I mean without sunlight, no energy, no no …
Protessor：What they discovered was that microorganisms, bacteria, had taken over both functions of the biological community - the recycling of waste materials and the production of energy. They were the energy source.You see, it turns out that certain microorganisms are chemosynthetic - they don't need sunlight because they take their energy from chemical reactions So, as I said, unlike green plants which are photosynthetic and their energy from sunlight, these bacteria that they found at the ocean floor,these are chemosynthetic, which means that they get their energy from chemical reactions. How does this work? As we said, these hydrothermal vents are releasing into the ocean depth this intensely hot water and here is the thing, this hot water co ntains a chemical called hydrogen sulfide, and also a gas , carbon dioxide. Now these bacteria actually combine the hydrogen sulfide with the carbon dioxide and this chemical reaction is what produces organic material which is the food for larger organisms. The researchers had n ever seen anything like it before.
Student 2：Wow! So just add a chemical to a gas, and bingo, you’ve got a food supply?
Professor：Not just t h at! W hat was even more surprising were all the large organisms that lived down there. The most distinctive of these was something called the tube worm. H ere, let me show you a picture.The tube of the tube worm is really, really long. They can be up to one and half meters long, and these tubes are attached to the ocean floor, pretty weird looking, huh? And another thing, the tube worm has no. mouth, or digestive organs. So you are asking how does it eat? Well, they have these special organs that collect the hydrogen sulfide and carbon dioxide and then transfer it to another organ, where billions of bacteria live. These bacteria that live inside the tube worms, the tube worms provide them with hydrogen sulfide and carbon dioxide. And the bacteria, well the bacteria kind of feed the tube worms through chemosynthesis, remember, that chemical reaction I described earlier.
《生物学》
教授：好了。我们一直在讲生物群体的两种基本需求----能源资源产出有机物质，你们知道的，有机物的食物，以及废物回收或者物质破坏回归无机分子，以及当绿色植物或者微生物将阳光转化为能源时，所有这些都需要光合作用，还需要微生物、细菌来分泌化学物质来分解或者再循环这些有机物质，来完成循环。那么，现在我们完成了教科书上这章的内容了，是吧?嗯，还没有这么快。首先我来讲一些发现，这些发现就挑战了够成生物群的基本需要的基本假定。而且，事情上有很多让人感到惊奇的地方。一切始于1977年的一次海底上深海热泉的探索。深海热泉是地球表面存在的裂缝，我们说的这个就是在海底的裂缝。这些海底的出口，排除及其热的水，温度比开水还要高3到4倍，因为这些水是从地球内部加热的。大概30年前，研究人员派出了一个深海船来探察海洋深度，到海洋底部大约是3千公里深，之前从里没有人到如此的深度来探索过。由于下面的这种环境，没有人想过下面会有生命。首先，阳光不能到达那么远，因此下面是漆黑一片。也不可能有任何动植物，因为那里没有阳光，没有能源来提供食物。如果有生命的话，也就是一些分解任何死去物质的细菌可能跌落直海洋底层。还有呢?
学生1：还有水压。我们之前不是讲过，越往海洋深度去，压强就越大吗?
教授：说到点子上了。而且不仅是极大的压强，还有这些出口附近水的温度。如果阳光的缺失没有使这里的生物群体消失的话，那么这些因素也会的，人们起初这么想。
学生2：那么你是在说他们在那种环境下找到有机物了?
教授：确实。找到了大概300个物种。
学生1：但是那怎么可能呢?我的意思是说没有阳光，没有能源，没有……
教授：他们找到的是有两种生物群体功能的微生物、细菌-----废物循环及能源再生。他们就是能源。你们看，原来有些微生物是化学合成的，他们不需要阳光，因为他们从化学作用中吸取能源。因此，正如我所说，和进行光合作用并从阳光中吸取能源的绿色植物不一样，这些人们在海底发现的细菌是化学合成的，意味着他们通过化学作用来获得能源。那是怎么回事呢?正如我们说的，海底热泉往海中中释放及其热的水，是这么回事，这种热水包含化学物质硫化氢和一种气体，就是二氧化碳。这些细菌实际上就是硫化氢和二氧化碳的结合体，这种化学反应就产出了有机物质，也就是更大的有机体的食物。研究人员之前从来没有看过这种现象。
学生2：哇哦。那么说往气体里放点化学位置，然后就变成了食物供应?
教授：不仅是如此。更让人吃惊的是居住在那里的大有机物。最有特点的一个叫做管虫。来，我给你们看一张照片。这管虫特别长。可能达到一米半那么长。而这些管子是连在海底呢，长的很奇怪是吧?还有一个问题。管虫没有嘴，没有消化器官。你们会问，那它怎么吃东西啊?嗯，他们有一些特殊的器官能收集硫化氢和二氧化碳并能将其转化到另一个器官，那里有亿万个细菌。这些细菌生活在管虫里面， 管虫为他们提供硫化氢和二氧化碳。而细菌呢，有点像通过化学合成的方式来为管虫提供食物，记得之前讲过的化学作用吧。
以上就是托福听力TPO15原文中Lecture 4的文本内容，希望大家能够用心体会，更多TPO文本内容小编稍后为您呈现。最后，小编祝大家在托福考试中取得好成绩！
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