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TPO54托福听力lecture1听力文本
Title: Migration of Zooplankton
Listen to part of the lecture in the marine biology class.
And the sea is teaming with tiny organisms, but they don’t get as much popular attention as say, whales.
Microscopic algae just aren’t as exciting I suppose. And yet those organisms are the foundation of the bulk of the marine food chain. Without plankton which is the global term for these tiny organisms, there will be no whales.
Plankton is found both in fresh water and marine environments. Again it’s a term we use for any small organisms that float along with the current, either because they are too small or weak to swim against it, or because they don’t have any capacity at all to move by themselves.
Plants and plant-like plankton are called phytoplankton while animals and animal-like plankton are called zooplankton.
For over a century now, researchers have been trying to solve the mystery about zooplankton.
You see some species of zooplankton migrate are……um…… not the way birds do when the seasons change. But daily, in the phenomenon we call Diel vertical Migration or DVM, in the Diel Vertical Migration, sole plankton swim up near the surface of the water during the night and swim down to deeper water during the day. Depending on the species and region, this can be a round trip of between 100 and 400 meters. [1]
For a tiny microscopic organism, that’s a huge distance. Remember now, zooplankton can’t swim very well and DVM requires a lot of energy. So there must be an important benefit to these daily up-and-down commuting.[2] We’re not exactly sure what this benefit is. Though there are several compelling theories.
I’ll talk about them in a moment, but first I want to talk about what we do know or rather what we are pretty sure we know.
So researchers generally agree that the stimulus for zooplankton DVM is light. Zooplankton tend to swim away from sunlight into deeper water where the sun’s rays barely penetrate. At night, when the sun no longer illuminates shallower water, zooplankton head back toward the surface.
Now why would light cause zooplankton to expend all that energy in migrate?
One popular theory is that zooplankton are hiding during the day from visual predators, eh……those animals that hunt by sight, the darkness provides safety during the day.
Then at night after migrating upward, they have an opportunity to feed on phytoplankton that float at the surface.
Make sense, doesn’t it?
But what do we do with the data showing that many kinds of zooplankton don’t dive deep enough during the day to become invisible to predators or that others dive deeper than it’s necessary to escape hunters’ eyes. And some zooplankton are bioluminescent, which means they have special organs that light up and make them visible even at great depth. [3]
Well, despite all these, we believe predator avoidance is a possible explanation because of studies done in fresh water lakes. It turns out there is a correlation between the presence or absence of vertical migration, and the presence or absence of fish that find their prey by sight.[4]
But what are some other possible explanations?
Some researchers suggest that zooplankton migrate to avoid the sun’s ultra-violet light. That would explain why some zooplankton are found at such great depth. Visible light may not penetrate very far down, but ultra-violet light can. And we know that some zooplankton have special pigments that protect them from the damage ultra-violet light can cause.[5]
That could be why some zooplankton are able to stay closer to the surface during daylight hours.
And there is a third theory.
Although it takes a lot of energy for the zooplankton to migrate, they conserve energy while floating in deeper colder water. So while they’re not feeding, they are quietly digesting in cooler water. [6]
But remember, zooplankton consist of any number of different organisms. From microscopic worms to crab larvae to tiny fish, and they are found in a large range of marine habitats, cold water, warm water, shallow water, deep water.
So there may be different reasons for different species.[7]
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TPO54托福听力lecture1题目解析
6、What does the professor mainly discuss?
A. The importance of zooplankton in the marine food chain
B. The interdependence of two types of tiny marine organisms
C. A physical feature of zooplankton that makes them well adapted for swimming
D. A phenomenon observed in some species of zooplankton
答案：D
就是说，微生物虽然没有像鸟类那样按照季节迁徙，但是它们会有纵向迁徙，晚上的时候，微生物会游到水面，而到白天的时候，又会游到更深的水域。
解析：本题为内容主旨题，题干问教授主要讨论的问题是什么?讲座一开始给出了浮游生物的定义，并提到浮游生物每天会纵向迁徙，晚上的时候，微生物会游到水面，而到白天的时候，又会游到更深的水域，科学家正在尝试揭开这个谜团，并且后文，都是关于科学家对这个现象提出的猜想，综合全文来看，本题选D。
A选项的意思为:浮游动物在海洋食物链里的重要性，只在开头提到了一下，不是主旨，故排除;
B选项的意思为:两种微小的海洋微生物的相互联系，没提到联系，故排除;
C选项的意思为:一种让浮游动物擅长游泳的身体特点，原文未提及，故排除;
7、Why does the professor conclude that zooplankton must derive an important benefit from diel vertical migration?
A. Diel vertical migration uses up a lot of energy.
B. Diel vertical migration exposes zooplankton to predators.
C. Diel vertical migration prevents zooplankton from being able to digest phytoplankton.
D. Diel vertical migration forces zooplankton populations to live permanently in cold water.
答案：A
意思为：对于微生物来说，那是一个巨大的距离，但是浮游生物能够游得非常好，并且纵向迁移需要消耗很多的能量，所以对于浮游生物来说，每天的上下游动肯定能带来很多的好处。[a1]
解析：本题为细节题，题干问为什么教授能够得出浮游生物能够在每天的上下游动的过程中得到好处的结论?在题目出处，教授提到对于微生物来说，100-400米是一个巨大的距离，但浮游动物并不擅长游泳，并且纵向迁移需要消耗很多的能量，所以对于浮游动物来说，消耗这么多精力游动，一定是因为每天的上下游动能带来很多的好处。
B选项的意思为:昼夜的纵向迁徙会使得浮游动物在捕食者面前暴露，与原文矛盾，原文说浮游动物迁徙是为了躲避捕食者，故错误;
C选项的意思为:昼夜的纵向迁徙会阻止浮游动物去消化浮游植物，原文第三个理论提到浮游动物游动到冷水里消化吸收，所以迁徙应该是促进吸收的，故错误;
D选项的意思为:昼夜的纵向迁徙使得浮游生物的种群能够永久地生活在冷水里，原文未提及，故排除。
8、What does the professor imply about bioluminescent zooplankton?
A. Their food source is different from that of other zooplankton.
B. They probably do not rely on diel vertical migration to avoid predation
C. They migrate deeper than other zooplankton species do.
D. Most species are found in very cold water.
答案：B
解析：本题为推论题，题干问教授为什么要谈论荧光微生物?由出题点可知，教授说明有些浮游动物是发光的，这意味着它们有着特殊的器官能发光，让它们即使是在很深的海洋中也能被看见，所以它们迁移并不是为了躲避捕食者，则B正确。
A选项的意思为:它们的食物来源与其它的浮游动物不同，原文未提及，故排除;
C选项的意思为:它们比其他的浮游生物迁徙的水域更深，原文未提及，故排除;
D选项的意思为:大部分的种类在冷水区发现，原文未提及，故排除。
9、Why does the professor mention fish that live in freshwater lakes?
A. To point out that many aquatic species exhibit diel vertical migration
B. To give an example of a species of fish that feeds on bioluminescent zooplankton
C. To make a comparison between fish and zooplankton
D. To support one of the theories explaining why zooplankton migrate
答案：D
解析：本题为组织结构题，题干问教授为什么要提及淡水鱼?由出题点可知，教授提及淡水湖的鱼是为了解释浮游微生物迁徙的理论，并提供实验的支持，所以D选项正确。
A选项的意思为:为了指出许多水生物种都会纵向迁移，但是教授举实验的例子，不是为了说明这一点，故排除;
B选项的意思为:为了给出以荧光微生物为食物的物种的例子，但这并非实验的目的，故排除;
C选项的意思为:为了将鱼与浮游生物进行比较，不存在比较关系，故排除。
10、Avoiding predators is one possible explanation for why zooplankton dive so deeply in the ocean What two other explanations for this phenomenon does the professor offer?
Click on 2 answers
A. To avoid ultraviolet light
B. To avoid strong ocean currents
C. To digest in colder waters
D. To find abundant food sources
答案： A、C
解析：本题为细节题，题干问教授认为，除了避免被捕食以外，还有什么其它的解释可以用来解释为什么浮游生物要潜入那么深的海底?由出题点信息可知，第一种解释是为了避免紫外线照射，第二种解释是为了在冷水里消化吸收，则A、C项正确。
B选项的意思为:为了避免强烈的洋流，原文未提及，故排除;
D选项的意思为:为了找到充足的食物源，原文未提及，故排除。
11、What does the professor imply about the reasons for diel vertical migration in zooplankton?
A. No single explanation for all species can account for this phenomenon.
B. Researchers have not been able to propose plausible theories to explain this phenomenon.
C. All individual organisms have several reasons for migrating.
D. Researchers were able to agree on an explanation for this phenomenon after many years of investigation.
答案：A
解析：本题为推论题，题干问关于纵向迁移，教授暗指什么?由出题点可知，教授强调的是浮游动物的多样性和分布广泛性，所以，多样的浮游动物对应的纵向迁徙理由也是多样的。则A选项正确。
B选项的意思为:研究学者还不能对这个现象给出合理的解释，原文已经给出了很多合理解释，故与原文矛盾，排除;
C选项的意思为:每一个生物迁徙的理由都有好几种，错误，原文意思是每个物种都可能有各自的迁徙理由，不同物种的迁徙理由不同，故排除;
D选项的意思为:研究学者在研究很多年后，能够同意这个现象的解释，错误，研究学者已经得出结论了，很多年后显然是不对的。
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