您IP所在的地区,暂不支持官方真题素材

建议使用其他功能进行听力练习

返回
小站备考
托福
托福听力
Official54听力真题

OFFICIAL54 What does the professor imply about bioluminescent zooplankton?

展开
Tip:单击查看句义;划选/双击查生词

[00:00.00]NARRATOR: Listen to part of a lecture in a marine biology class.[00:03.30]FEMALE PROFESSOR: And the sea is teeming with tiny organisms, but they don't get as much popular attention as, say, whales.
[00:10.62]Microscopic algae just aren't as exciting, I suppose, [00:14.15]and yet those organisms are the foundation of the bulk of the marine food chain. [00:18.74]Without plankton, which is the global term for these tiny organisms, there would be no whales.[00:24.22]Plankton is found both in freshwater and marine environments. [00:28.98]Again, it's a term we use for any small organisms that float along with the current, either because they're too small or weak to swim against it, or because they don't have any capacity at all to move by themselves.
[00:40.71]Plants and plantlike plankton are called phytoplankton , while animals and animal-like plankton are called zooplankton.
[00:48.49]For over a century now, researchers have been trying to solve a mystery about zooplankton.
[00:54.17]You see, some species of zooplankton migrate, er, n-n-not the way birds do when the seasons change, [01:01.72]but daily, in a phenomenon we call diel vertical migration, or DVM.[01:17.24]Depending on the species and region, this can be a round trip of between one hundred and four hundred meters.
[01:23.95]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, [01:35.21]so there must be an important benefit to this daily up and down commuting. [01:40.22]We're not exactly sure what this benefit is, [01:43.17]though there are several compelling theories.
[01:45.60]I'll talk about them in a moment, but first, I want to talk about what we do know, or rather, what we're pretty sure we know.
[01:52.10]So, researchers generally agree that the stimulus for zooplankton DVM is light.[01:58.55]Zooplankton tend to swim away from sunlight into deeper water where the Sun's rays barely penetrate. [02:04.87]At night, when the Sun no longer illuminates shallower water, zooplankton head back toward the surface.[02:11.26]Now, why would light cause zooplankton to expend all that energy and migrate?
[02:17.17]One popular theory is that zooplankton are hiding during the day from visual predators, uh, those animals that hunt by sight. The darkness provides safety during the day.
[02:28.31]Then at night, after migrating upward, they have an opportunity to feed on phytoplankton that float at the surface. [02:35.42]Makes sense, doesn't it?
[02:36.90]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 is necessary to escape hunters' eyes? [02:49.98]And that some zooplankton are bioluminescent? Which means they have special organs that light up and make them visible even at great depths.
[02:58.30]Well, despite all this, we believe predator avoidance is a possible explanation because of studies done in freshwater lakes. [03:06.34]It turns out there's a correlation between the presence or absence of vertical migration and the presence or absence of fish that find their prey by sight.[03:15.92]But what are some other possible explanations?
[03:19.16]Some researchers suggest that zooplankton migrate to avoid the Sun's ultraviolet light. [03:25.05]That would explain why some zooplankton are found at such great depths—[03:29.41]visible light may not penetrate very far down, but ultraviolet light can. [03:34.52]And we know that some zooplankton have special pigments that protect them from the damage ultraviolet light can cause.
[03:41.52]That could be why some zooplankton are able to stay closer to the surface during daylight hours.
[03:46.70]And there's a third theory.
[03:48.78]Although it takes a lot of energy for the zooplankton to migrate, they conserve energy while floating in deeper, colder water. [03:56.29]So, while they're not feeding, they're quietly digesting in cooler water.
[04:00.74]But remember, zooplankton consist of any number of different organisms, [04:05.96]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...
[04:16.67]so, there may be different reasons for different species.

3.What does the professor imply about bioluminescent zooplankton?

你的答案:
正确答案:B
题目解析:
 后才能查看题目解析,还没有账号? 马上注册
对应原文: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. 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。

学习页面

Medi

terr

anean

加强 + 政府 + 名词后缀

加强的政府——管理

原文例句

加入生词

本文生词 0

色块区域是你收藏过的生词;

查询次数越多,颜色越深哦~

显示文中生词

登录后才能收藏生词哦,现在登录注册>

本文重点词 45

文中加粗单词为本文重点词;

根据词频与核心词范围精心挑选,托福考试必掌握词汇。

显示文中重点词
学习本文词汇

文中划选/双击的生词、加粗重点词已收纳至词盒

可随时点击词盒查看哦~

只有在词句精学模式下才能开启词盒功能哦~

我知道了

词盒
收藏
笔记
我的笔记
5000
保存
反馈