Organisms and their Environment
IGCSE Biology Topic 19 8:11 English narration · English + 中文 subtitles burned in
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An African savanna.
非洲的稀树草原。
A coral reef.
一片珊瑚礁。
They look nothing alike, but they run on the same rule.
它们看起来毫不相像，却遵循同样的规律。
Every living thing here is joined to the others by feeding.
这里的每一种生物都通过取食与其他生物相连。
Energy arrives from the Sun and leaks away as heat.
能量来自太阳，并以热的形式散失。
Here is the plan.
这是我们的计划。
Energy flow and food chains.
能量流动和食物链。
Food webs and feeding roles.
食物网和取食角色。
Pyramids, and why so little energy passes up.
金字塔，以及为什么向上传递的能量这么少。
The carbon and nitrogen cycles.
碳循环和氮循环。
And populations.
还有种群。
The Sun is the main source of energy for almost all life.
太阳是几乎所有生命的主要能量来源。
Plants catch light energy and store it as chemical energy in food.
植物捕获光能，把它以化学能的形式储存在食物里。
Feeding passes that chemical energy along the chain.
取食把这些化学能沿着食物链传下去。
At every step some is lost to the environment as heat, from respiration.
每一步都有一部分能量以热的形式散失到环境中， 来自呼吸作用。
So energy flows one way: in as light, out as heat, never recycled.
所以能量单向流动：以光进来，以热出去，从不被循环利用。
A food chain shows the transfer of energy from one organism to the next, always beginning with a producer.
食物链表示能量从一种生物传到下一种生物，而且总是从生产者开始。
Grass, eaten by a rabbit; the rabbit eaten by a fox.
草被兔子吃掉，兔子又被狐狸吃掉。
Every arrow points from the organism that is eaten to the one that eats it; it shows which way energy flows.
现在看箭头。 每个箭头都从被吃的生物指向吃它的生物——它表示能量流动的方向。
Name each by position: producer, primary, secondary, tertiary and quaternary consumers.
再按位置命名：生产者、初级、次级、三级和四级消费者。
Five words, precisely.
五个词，要准确。
A producer makes its own organic nutrients, using energy from sunlight, in photosynthesis.
生产者自己制造有机营养物质，利用阳光的能量，通过光合作用完成。
A consumer gets its energy by feeding on other organisms.
消费者通过取食其他生物获得能量。
A herbivore is an animal that eats plants.
食草动物是吃植物的动物。
A carnivore is an animal that eats other animals.
食肉动物是吃其他动物的动物。
And a decomposer gets its energy from dead or waste material.
分解者从死亡的或废弃的有机物中获得能量。
For the producer, you need both halves: organic nutrients, and energy from sunlight.
写生产者时，两半都要写到：有机营养物质，和来自阳光的能量。
Join chains together and you get a food web: a network of interconnected food chains.
把食物链连在一起，就得到一个食物网：许多相互连接的食物链组成的网络。
Grass feeds the rabbit and the insect.
草养活兔子和昆虫。
Clover feeds the insect and the mouse.
三叶草养活昆虫和老鼠。
The fox eats the rabbit and the mouse; the bird eats the insect and the mouse.
狐狸吃兔子和老鼠；鸟吃昆虫和老鼠。
Start at a producer and follow one arrow at a time.
从生产者开始，一次跟着一个箭头走。
Notice the mouse: one species can sit in several chains.
注意这只老鼠：同一个物种可以出现在好几条食物链里。
Draw that chain as a stack: an ecological pyramid.
把这条食物链画成一层层的堆叠：这就是生态金字塔。
Each layer is a trophic level — the position of an organism in a food chain.
每一层是一个营养级——生物在食物链中的位置。
Producers at the wide base, then primary and secondary consumers, then a top carnivore.
生产者在宽阔的底部，然后是初级和次级消费者，顶端是顶级肉食动物。
The layers shrink as you climb, because only about ten percent of the energy passes up.
越往上层越小，因为只有大约百分之十的能量向上传递。
The orange arrows show the rest leaving as heat.
橙色的箭头显示其余的能量以热的形式离开。
Watch the same idea in numbers.
用数字来看同样的道理。
The producers hold ten thousand units of energy.
生产者拥有一万个单位的能量。
Only a tenth reaches the primary consumers: one thousand.
只有十分之一到达初级消费者：一千。
A tenth again reaches the secondary consumers: one hundred.
再取十分之一到达次级消费者：一百。
The top consumers are left with ten.
顶级消费者只剩下十。
About ninety percent is lost at every step, mostly as heat.
每一步大约有百分之九十损失掉，主要以热的形式。
Three kinds of pyramid; the exam compares them.
金字塔有三种；考试会让你比较它们。
A pyramid of numbers simply counts the organisms, so the shape can come out wrong: one oak tree feeds hundreds of insects.
数量金字塔只是数生物的个数， 所以形状可能出错：一棵橡树能养活成百上千只昆虫。
A pyramid of biomass shows the total mass at each level, so organism size no longer matters.
生物量金字塔显示每一层的总质量，所以生物体的大小就不再重要。
Best of all is the pyramid of energy.
最好的是能量金字塔。
It shows the energy transfer accurately, it lets you compare different ecosystems, and it is not upset by different life spans.
它准确地显示能量的传递，能让你比较不同的生态系统， 而且不受寿命长短的影响。
Here is a classic exam question: why does a food chain rarely have more than four or five links?
这是一道经典考题：为什么一条食物链很少超过四到五个环节？
Where does the other ninety percent go?
另外那百分之九十去哪了？
Most is lost as heat, from respiration.
大部分以热的形式散失，来自呼吸作用。
Some leaves in faeces and urine.
一部分随粪便和尿液离开。
And some parts are never eaten at all, such as bones and roots.
还有一些部分根本没有被吃掉，比如骨头和根。
After a few links there is too little energy left to feed anything more, which is why food chains usually have fewer than five trophic levels.
几个环节之后，剩下的能量就不足以再养活什么了。
That is also why eating crop plants beats eating animals fed on those crops.
这也是为什么直接吃农作物比吃用农作物喂养的动物更划算。
A full exam question.
一道完整的考题。
Producers in a field trap forty thousand kilojoules; the primary consumers receive four thousand.
田里的生产者固定了四万千焦；初级消费者得到四千千焦。
First, find the percentage passed on.
第一步，求传递的百分比。
Divide by the level below, then times one hundred.
用下面一层去除，再乘以一百。
Four thousand divided by forty thousand, times one hundred, gives ten percent.
四千除以四万，乘以一百，得到百分之十。
Second, apply that ten percent again.
第二步，把这个百分之十再用一次。
Ten percent of four thousand kilojoules is four hundred kilojoules — only one percent of what the plants trapped.
四千的百分之十是四百千焦——只是植物所固定能量的百分之一。
Use the ten percent at every step, never once for the whole chain.
每一步都要用一次这个百分之十，绝不能整条链只用一次。
Energy flows one way, but nutrients are recycled.
能量单向流动，养分却被循环利用。
Carbon dioxide in the air is the shared pool.
空气中的二氧化碳是大家共用的库。
Photosynthesis takes it out and locks the carbon into plants.
光合作用把它取走，把碳锁进植物里。
Feeding passes that carbon to animals.
取食把碳传给动物。
Respiration sends it straight back.
呼吸作用把它直接送回去。
When living things die, decomposition returns their carbon.
生物死亡后，分解作用把碳还回来。
Over millions of years dead material becomes fossil fuels, and combustion — burning them — returns that carbon to the air.
经过数百万年，死去的物质变成化石燃料， 燃烧时把碳释放出来。
Nitrogen next, supplement only.
接下来是氮，属于补充部分。
Living things need nitrogen for proteins, but nitrogen gas in the air is useless until it is changed.
生物需要氮来制造蛋白质， 但空气中的氮气必须先被转化才有用。
Microorganisms do most of the work.
大部分工作由微生物完成。
Nitrogen fixation does that first step: lightning, and some bacteria.
固氮作用做的就是这第一步：闪电，还有一些细菌。
Plants absorb nitrate ions to build amino acids and proteins; animals get theirs by feeding and digestion.
植物吸收硝酸根离子来合成氨基酸和蛋白质；动物则通过取食和消化获得氮。
Decomposition breaks dead protein into ammonium ions, and deamination in the liver releases nitrogen compounds from excess amino acids.
分解作用把死去的蛋白质分解成铵离子， 而肝脏中的脱氨作用把多余氨基酸中的含氮物质释放出来。
Nitrification turns those back into nitrate ions.
硝化作用把它们变回硝酸根离子。
Denitrification returns nitrogen gas to the air.
反硝化作用把氮气送回空气中。
Three words that fit inside each other.
三个词，一个套着一个。
A population is a group of organisms of one species, living in the same area, at the same time.
种群是同一个物种的一群生物， 生活在同一区域、同一时间。
All three parts are needed: one species, one area, one time.
三个部分都要写到：一个物种、一个区域、一个时间。
A community is all the populations of the different species there.
群落是那里所有不同物种的种群的总和。
And an ecosystem is that community plus its environment, all interacting.
生态系统就是这个群落加上它的环境，所有部分相互作用。
In a new place with limited resources, a population follows this S-shaped curve.
在一个资源有限的新环境里，种群会沿着这条 S 形曲线增长。
Four phases.
有四个时期。
The lag phase: slow growth, the numbers are still small.
延迟期：增长缓慢，数量还很少。
The exponential phase: very fast growth, plenty of food and space.
对数期：增长非常快，食物和空间都很充足。
The stationary phase: the curve flattens at the carrying capacity, births now equal deaths.
稳定期：曲线在环境容纳量处变平，出生数此时等于死亡数。
And the death phase: numbers fall, as food runs out, wastes build up, or disease spreads.
衰亡期：数量下降，因为食物耗尽、废物积累，或者疾病蔓延。
Four things control the growth rate.
有四样东西控制增长速率。
Food supply, which runs short first.
食物供应，它通常最先不够。
Competition, for food and space.
竞争，争夺食物和空间。
Predation, being eaten.
捕食，也就是被吃掉。
And disease, which spreads fast in a crowd.
还有疾病，在拥挤时传播得很快。
Now explain the curve.
现在来解释曲线。
While it rises, births beat deaths, because resources are plentiful.
曲线上升时，出生多于死亡，因为资源充足。
At the top, births and deaths are equal, because a limiting factor holds it back.
到了顶部，出生和死亡相等，因为有一个限制因素在拖住它。
In the exam, describe the shape, then give the reason.
考试时，先描述形状，再给出原因。
Both halves earn marks.
两部分都能得分。
Two ways humans damage a food web.
人类破坏食物网有两种方式。
Overharvesting means taking too many of one species.
过度捕捞：把一个物种取走太多。
Overfishing is the classic case, and the numbers crash.
过度捕鱼是典型例子，数量会骤降。
And introducing a foreign species: a new arrival with no predators here, so it spreads and crowds out the natives.
还有引入外来物种：新来者在这里没有天敌，于是大量繁殖，把本地物种排挤出去。
In a web question, trace the arrows outward through the web, and say which populations rise and which fall.
做食物网题时，顺着箭头往外追，说出哪些种群会增加、哪些会减少。
That is the answer they want.
这就是他们要的答案。
Three marks students throw away.
三个学生常丢的分。
First, arrow direction.
第一，箭头方向。
The arrow points from the eaten to the eater; it shows which way the energy flows.
箭头从被吃的生物指向吃它的生物； 它表示能量流动的方向。
Second, the ten percent rule.
第二，百分之十的规则。
Apply the ten percent at every step, not once for the whole chain.
每一步都要用一次百分之十，而不是整条链只用一次。
Third, the population definition: it needs all three parts, one species, one area, one time.
第三，种群的定义：三个部分都要写全——一个物种、一个区域、一个时间。
Get those right, and this topic is yours.
把这些做对，这个专题就是你的了。