【教书匠阿伦-原创干货】托福听力生物学常考话题
为了帮助大家高效备考托福，阿伦老师为大家带来托福听力生物学常考话题整理，希望对大家托福备考有所帮助！
生物进化类文章难度较高，很可能涉及进化理论的研究方法，时序发展以及物种进化比较，可能考到理论的主要观点或者观点的对比。同时学生应该注意教授对进化理论的分析以及讲座中对内容的总结。
这里，阿伦老师就给各位同学讲解一下 TPO 21 - Biology (Snake Evolution) 关于蛇的进化。
Probably back in some previous biology course you learned that snakes evolved from lizards, and that the first snakes weren’t venomous and then along came more advanced snakes, the venomous snakes. Ok, venomous snakes are the ones that secrete poisonous substances or venom, like the snakes of the viper family or cobras. Then there is non-venomous snakes like constrictors and pythons. Another family of snakes, the colubrids, don’t really fit neatly into either category though. Colubrids, and you probably learned this too, although they are often classified as venomous snakes, they are actually generally non-venomous. They are classified as venomous snakes because they resemble them, their advanced features more than the other non-venomous snakes.
教授先提到蛇的分类，在提到一个关于蛇进化的新理论，接着讲述了一个实验是如何来证明这个理论的。
Now, what if I told you that there is a good chance that most everything I just said is wrong? Well, everything except the part about snakes evolving from lizards. See, the basic theory about snake evolution has been challenged by a recent study that revealed a whole new understanding of evolutionary relationship for reptiles, you know, which reptiles descended from which ancestors. The researchers study the proteins in the venom genes of various species of colubrids. Emm... snake venom is a mixture of proteins, some toxic, poisonous, and some not. By analyzing the DNA, the genetic material of the proteins, the researchers could focus on the toxic genes and use them to trace the evolution of snake venom, and from this, the evolution of snakes.
教授又提到Now, what if I told you that there is a good chance that most everything I just said is wrong? 可知，教授提及以前可能学过的内容是为了引出一个会 challenge 这些内容的观点。这个在托福的学术听力部分有较多的篇章都以类似的方式展开下文。
教授提及研究方法的不足就是对于有相似特征的蛇无法用相似的研究方法进行展开： The problem with this method is that characteristics that appear similar may actually have developed in quite different ways.
这一类的话题通常与人类行为有关，会涉及人类如何进行干预、人类的破坏活动，比如森林砍伐、人类威胁动物的生存，比如狩猎活动、人类通过引入新物种维护生态、或者是生态系统重建等等话题。常见的比如：一开始教授交代什么原因导致了动植物的破坏，然后人类如何可以拯救生态环境，会考到政府政策的利弊分析，教授对应政策的态度表示，或者他方(政府、生物学家等)的观点等等。
针对生态系统中的种群, 大家可以参考TPO 32 Populations in Ecosystem
Right, relationships between animal species in a given ecosystem can get pretty complex. Because in addition to predator-prey relationships, there’re other variables that affect population size.
教授回答学生的问题：在一定的生态系统中，动物互相之间的关系是很复杂的。
First I want to go over some key concepts. Let’s say there was a species that had access to plenty of food and ideal conditions. Under those circumstances, its population would increase exponentially, meaning it would increase at an ever-accelerating pace.
A rapid population growth is often followed by a sudden decline. But we do occasionally see exponential growth in nonnative species when they are transplanted into a new environment. Um…because they face little competition and have favorable growing conditions.
教授开始阐述自己的观点，即生态环境的承载容量(a carrying capacity)是会限制物种的最大数量(the maximum population size)的。There are always factors that limit population growth. This is called environmental resistance. 这些限制因素就成为：环境抵抗因素。
在动物与环境的关系这一类的话题中：主要内容包括动物的环境适应性，身体结构或者行为所相应产生的变化，在听力过程中需要注意捕捉对比信息。
Okay, so that’s how the arctic ground squirrel is able to cope in this extreme environment… Now let’s talk about your reading assignment, about reindeer… also typically found in Siberia and other far-northern regions.
教授开场在引入部分就开始讨论驯鹿，后面开始说它们的生物特征如何适应寒冷环境。
Food is very scarce in far north so reindeer herds have to cover lots of ground every day. And in the fall they might easily trek a thousand kilometers or more to get to their winter feeding site. So if you are a newborn you've got to get up to speed fast.
学生说新出生的驯鹿与成年驯鹿非常相似，出生就能站着，第二天就能迅速奔跑起来，教授回答说是的因为资源匮乏导致驯鹿需要跋涉千里寻找食物。
they can allocate less energy to heating their extremities and more energy to maintaining stable temperature in their body core where their vital organs are located. And you know I don't think it is mentioned in your textbook, but even different parts of a reindeer's legs are adapted for optimal cold weather performance. The fat in the lower part of their legs the part that gets coldest, that fat has a different chemical structure from the fat in the upper parts of the leg. So it doesn't get hard, even at temperatures down around freezing, it stays kind of gel-like, kind of oily.
保温机制，幼鹿的奔跑能力，食物来源，消化系统等等对寒冷环境的适应。教授说驯鹿的腿下半部分的脂肪结构和上半部分不一样，它们可以让驯鹿在寒冷环境下也不会冻着。
以动物为主，常考海洋生物(marine biology)、极端环境生物( in this extreme environment)等，这类讲座常见总分(总)或者直线型结构，第一类是介绍型。作者会先介绍动物的某一种特点，然后用first，second，third这样的逻辑衔接词或者其他较为明显的信号词给出几点说明，其中可能会穿插教授与学生的互动。这类行文结构层次清晰，表述逻辑强。另一种是直线型，教授先给出学术概念，之后会有较多的师生互动，但是结构可能没那么清晰。
常考动物迁徙，物种选择，冬眠，觅食，交配等，一般采用直线型的行文结构，首先教授给出某种行为的介绍，然后以特定的动物为例展开介绍，经常会考到行为背后的原因。
关于动物的巡航系统，大家可以参考：TPO 35 - Animal Navigation System
Well, for some time we’ve known that blind mole rats use some combination of two different navigation systems. Um, one system relies on their sense of time and their ability to remember underground landmarks. For example, let’s say a mole rat wants to find its way through its tunnel system back to its nest, where it sleeps. Well, it goes along then feels some hard stones or a tree root under its feet, and it basically says to itself, “OK, here’s where I took a left…” And then it might remember how long it took to get to the next turn. And so forth. The mole rat goes straight or turns based on what it remembers having sensed along the way on previous trips and the time it took between turns.
教授提到rat有2种导航方式，一种是通过tunnel system, 另一种是通过磁场来导航。
Now, the other navigation system for the mole rat relies on Earth’s magnetic field. Mole rats have the ability to sense the magnetic field and use it to orient themselves directionally. But until recently, scientists weren’t sure about the role of these two different systems.
研究者们根据blind mole rat的真实洞穴来建立模型，而“Earlier experiments have used more generic habitat, basically a wideopen circle, which was originally designed to test magnetic navigation in other animals. That design led to inconclusive results with mole rats.”通过早期和现在实验的道具对比，说明早期实验结果的不准确性，来说明标准的道具会达到更精确的效果。在第二次实验中，研究者们改变了地球磁场。
So, why two navigation systems—one for long trips and one for short trips? Well, for now we can only speculate, but we think that when mole rats rely on the first system—using underground landmarks or their sense of time—well they make small mistakes here and there. On a short trip, this doesn’t matter much…the trip is short, so they can’t make many mistakes. But on a long trip, well, there are lots of opportunities to make small mistakes…and small mistakes can add up, leaving the mole rat far from where it wants to be. So on a long trip, a magnetic navigation system is better, more useful, since Earth’s magnetic field is stable, constant, a more reliable indicator of direction.
实验结果表明：对于short trip 即较短路程，rat会以路程时间(sense of time )和路面标识(underground landmark)作为判断依据来导航；对于较长路程(long trip)，rat会以地球磁场(Earth’s magnetic field)作为判断依据来导航。
关于动物的迁徙，大家可以参考 TPO 54 - Migration of 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 their Diel Vertical Migration, zooplankton 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.
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。
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. We're not exactly sure what this benefit is. Though there are several compelling theories.
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。
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.
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。
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