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第1段

1 .<-NARRATOR:->Listen to part of a lecture in a biology class.

旁白:请听一段生物学课的节选片段。

第2段

1 .<-FEMALE PROFESSOR:->So, to review... who remembers how animals are classified, in terms of body temperature? Mike?

教授:我们先复习一下,谁还记得我们是怎么通过体温来划分动物的种类的?Mike?

第3段

1 .<-MALE STUDENT:->[hesitant] Um, endotherms and ectotherms?

学生:嗯,恒温动物和变温动物?

第4段

1 .<-FEMALE PROFESSOR:->Right. All animals are considered either endotherms or ectotherms.

教授:对的!所有的动物都可以被划分成恒温的和变温的。

第5段

1 ."Therm"...that means "heat."

“小卡”...这意味着“热”。

2 .And the main thing that distinguishes endotherms from ectotherms is the source of body heat.

还有,区分恒温动物和变温动物的主要依据之一就是体温的来源。

3 .So an endotherm- "endo" meaning "internal"-an endotherm's body heat mainly comes from inside its body.

所以一个恒温动物,恒温的意思是内部产热的,一个恒温动物的体温主要是来自身体内部。

4 .It can generate its own heat internally, with its metabolism.

它可以通过自己的新陈代谢产热。

5 .And an ectotherm- "ecto" meaning "external"- an ectotherm gets its body heat mainly from outside its own body.

而一个变温动物,变温意味着体温来自于身体外部,一个变温动物从身体之外获得热量。

6 .Meaning, from its environment. Mostly from the sun's radiation.

也就是从环境里获得,大多数是从太阳辐射获得的。

第6段

1 .So we've got endotherms- mammals and birds are the classes that fall under this category-and ectotherms-that's pretty much everything else... including reptiles, amphibians, insects...

我们再来看看恒温动物。哺乳动物和鸟类是恒温动物类别下的两种生物。变温动物就是另一类了,包括爬虫类,两栖动物类,还有昆虫......

第7段

1 .Now, body temperature is important.

所以体温很重要。

2 .And if an animal's environment gets very hot or very cold, something needs to happen in order for the animal to maintain its body temperature within its normal range.

如果动物所处的环境变得太热或者太冷,动物为了保持自己的体温在正常范围内,需要采取一些措施。

3 .In endotherms, this is mostly physiological-the body changes its rate of heat production.

在恒温动物这边,这些措施都是生理性的,它们的身体会改变产热的速率。

4 .OK, well... humans are endotherms.

好的,那么,人类就是恒温动物。

5 .What does your body automatically do when it gets really cold?

当你觉得冷的时候,你的身体会自动做什么呢?

第8段

1 .<-MALE STUDENT:->Shiver?

学生:颤抖?

第9段

1 .<-FEMALE PROFESSOR:->Right. Shivering-in fact, any muscle movement-increases metabolism, the process that produces heat and keeps your body temperature up when your surroundings get cold.

教授:对的,颤抖。实际上,任何肌肉的动作都会增加新陈代谢,新陈代谢这个过程可以产热,在周围环境变冷的时候帮助你保持体温稳定。

2 .And then there's what's known as brown fat. Like other kinds of fat, it stores triglyceride.

有一种叫做褐色脂肪的东西,就像其他的脂肪一样,储存着三碘甲状腺氨酸。

3 .But brown fat is unique because it chemically produces lots of heat even without muscle movement.

但是褐色脂肪很独特,因为它可以不需要肌肉运动也产生大量的热。

4 .That's especially beneficial for small mammals in colder climates.

这就对于寒冷环境里的小哺乳动物很有用。

第10段

1 .And when an animal gets too hot... well, have you ever seen a dog cooling off by taking short, quick breaths?

那么当一个动物很热的时候,你们见到过一只狗通过短促的呼吸来散热吗?

2 .And humans... we sweat, of course... perspire, which also gets rid of body heat.

对于我们人类,当然就是出汗了,出汗可以帮助我们散热。

3 .These are automatic physiological responses too.

这也是自动的、生理上的反应。

4 .Yes, Allie?

怎么了,Allie?

第11段

1 .<-FEMALE STUDENT:->[checking comprehension] So in endotherms, it's not really about behavior... about doing things.

学生:所以,在恒温动物身上,调节体温这件事不仅仅是关于行为的,是关于做什么事情的。

第12段

1 .<-FEMALE PROFESSOR:->Well... a human, you know, might put on a winter coat, or jump in a swimming pool.

教授:一个人类,你知道,可能会穿上冬天的大衣或者跳进游泳池的水里。

2 .Or, elephants... Elephants might splash themselves with cold water when it's warm out.

或者一头大象,可以在热爆了的时候拿凉水撒自己身上。

3 .But, for the most part, no... it's not what we endotherms do that keeps our temperatures within range.

但是对于自然界的大多数动物,这个不是一个普遍的解决办法。

4 .Unlike ectotherms.

变温动物用来把体温维持在正常范围内的手段和我们不同。

第13段

1 .<-FEMALE STUDENT:->Well, what about ectotherms? Like... frogs, they must have metabolism too...

学生:关于变温动物呢?,比如说...青蛙,它们也必须有新陈代谢。

第14段

1 .<-FEMALE PROFESSOR:->Sure they do. It's just that metabolism in ectotherms is so much lower.

教授:那是自然。只是变温动物的新陈代谢速率太低了。

2 .I mean, the metabolic rate of an endotherm-say a mouse- is at least six or seven times that of an ectotherm of a similar size, like a frog or a lizard.

我的意思是,一个恒温动物的新陈代谢速率,比如说一只老鼠的,至少是相同体型的恒温动物像青蛙或蜥蜴的六七倍。

3 .An ectotherm doesn't generate nearly as much heat internally, so its body temperature will tend to equalize with the temperature of its surroundings.

一只变温动物在内部不会产生同样多的热量,所以它们的体温一般是和环境温度持平的。

4 .And that's where behavior comes in.

这就到了动物习性发挥作用的时候了。

第15段

1 .Imagine a lizard, OK? Living in the desert. Now, a desert gets very cold at night and very hot during the day.

想象一只蜥蜴,住在沙漠里。沙漠在夜间变得很冷,在白天变得很热。

2 .So what's the lizard do to maintain its body temperature?

所以蜥蜴要怎么来维持体温呢?

3 .Well, on a cold morning, it can warm itself by going to a sunny spot and lying in the sun.

在寒冷的早晨,蜥蜴可以通过去有阳光的地方晒太阳来温暖自己。

4 .And later, if it gets too hot, it can seek out a cool place in the shade.

晒了一会儿之后,如果它觉得热了,它可以找一个树荫下的阴凉地呆着。

5 .It's by means of such behavior that an ectotherm like this lizard regulates its temperature.

通过这种行为,像这种蜥蜴一样的变温动物可以做到调节自己的体温。

第16段

1 .But you put that same lizard in a temperature-controlled chamber... and gradually drop the temperature, say, twenty degrees... and here, of course, the lizard can't go off to lie in the sun...

但是如果你把同样一只蜥蜴放在一只可控温箱子里,逐渐降温的时候,假设降个20度,当然了, 蜥蜴不能在阳光下躺着...

2 .So, what happens?

所以会发生什么呢?

第17段

1 .<-MALE STUDENT:->Well, the lizard's body temperature drops too.

学生:蜥蜴的体温也会下降。

第18段

1 .<-FEMALE PROFESSOR:->Right. And this really slows down its metabolism- which depends on temperature.

教授:对的。这就降低了它的新陈代谢速率,新陈代谢速率是基于温度的。

2 .Even that twenty-degree drop in body temperature, though... the lizard can survive that, no problem, and come out just fine when it warms up again.

即使降低了20度的气温,蜥蜴也可以活下去,当气温慢慢暖和过来时,蜥蜴还是活的很好的。

3 .Ectotherms can do that.

变温动物可以做到这一点。

第19段

1 .<-MALE STUDENT:->But an ectotherm probably wouldn't survive in a place where the temperatures got too low, right?

学生:但是一个变温动物不大可能在气温非常低的地方生存下来,对吗?

第20段

1 .<-FEMALE PROFESSOR:->[lightly affırming] Ever heard of a frog being chased by a polar bear?

教授:没听说过一只青蛙被北极熊追吧?

第21段

1 .<-MALE STUDENT:->[chuckle, understanding]No.

学生:没有。

第22段

1 .<-FEMALE PROFESSOR:->Well, there you are.

教授:这就对了。

2 .Now, a mouse in the same situation, in the same temperature chamber... it's just the opposite of the lizard.

假设现在是一只老鼠在相同的境地下,在相同的可控温箱子里,它和蜥蜴的情况相反。

3 .When the temperature goes down, the mouse's metabolism goes up.

当气温下降的时候,老鼠的新陈代谢变快了。

4 .Like any endotherm, it starts producing more heat to keep its body temperature stable.

就像是任何的恒温动物一样,它开始产更多的热量,保证体温不下降。

5 .Same as it would do outside in a field.

就像是老鼠在自然环境中所做的一样。