Human influences on ecosystems
IGCSE Biology Topic 20 7:43 English narration · English + 中文 subtitles burned in
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Transcript
A farmer spreads fertiliser on a field. Ordinary, useful work.
一位农民往田里撒化肥，这是普通而有用的工作。
Two kilometres away there is a river, full of fish.
两公里外有一条河，河里满是鱼。
Three weeks later those fish are floating dead.
三周后，那些鱼浮在水面上死了。 没有东西毒死它们。
Nothing poisoned them. So what killed them?
那么，是什么杀死了它们？
By the end of this lesson you will explain it, for six marks.
在这节课结束时，你将能解释它，拿下六分。
This is Topic Twenty: human influences on ecosystems.
这是第二十章：人类对生态系统的影响。
How we feed ourselves, what that costs the living world, and what we can do about it.
我们如何养活自己，这对生物世界造成了 什么代价，以及我们能做些什么。
More people means more food, and this is how farmers get it.
人更多就意味着需要更多粮食，而农民就是这样做到的。
Machinery lets them work large areas quickly.
机械让他们快速耕种 大面积土地。
Fertilisers raise the yield.
化肥提高产量。
Insecticides kill the insects that eat the crop.
杀虫剂杀死吃作物的昆虫。
Herbicides kill the weeds that compete with it.
除草剂杀死与作物竞争的 杂草。
And selective breeding improves crop plants and livestock.
选择育种改良农作物和牲畜。
Learn all five by name.
把这五种都按名称记住。
Two of them get pushed to the limit.
其中两种被推到了极限。
A monoculture is one crop grown over a huge area.
单一栽培是在一大片土地上只种一种作物。
The harvest is big and easy, but one pest or one disease can destroy all of it, and biodiversity falls.
收成大而且 容易采收，但一种害虫或一种病害就能把它全部毁掉，生物多样性也下降。
Intensive livestock farming keeps many animals in a small space.
集约化 畜牧把许多动物养在很小的空间里。
It needs less land, so fewer trees are cut down, and meat is cheaper — but disease spreads quickly in a crowded shed, and people worry about welfare.
它占地更少，所以砍的树更少，肉也更便宜—— 但在拥挤的畜舍里疾病传播很快，人们也担心福利。
Give both sides — that is the whole question.
两方面都要写——整道题问的 就是这个。
Growing all that food takes space, taken from wildlife.
种出这么多粮食需要空间，而这些空间取自野生生物。
This was forest.
这里曾经是森林。
Biodiversity is the number of different species living in an area, and here it has collapsed.
生物多样性指一个地区内不同物种的数量，而在这里它已经崩溃了。
Humans destroy habitats in three ways: clearing land for housing and farming, extracting natural resources such as mining, and polluting fresh water and the sea.
人类以三种 方式破坏栖息地：为住房和农业清理土地，开采自然资源例如采矿，以及污染 淡水和海洋。
Each one changes food webs.
每一种都会改变食物网。
Deforestation is the example the exam loves, and this diagram holds every mark.
森林砍伐是考试最爱考的例子，而这张图包含了全部得分点。
Cutting down forests — often to clear land for crops and agricultural machinery — lowers biodiversity and drives species extinct.
砍掉森林会降低 生物多样性，并使物种灭绝。
The soil washes away, with no roots to hold it.
土壤被冲走，因为没有根固定它。
There is more flooding, because bare land no longer soaks up rain.
洪水增多，因为 裸露的土地不再吸收雨水。
And there is more carbon dioxide in the air, because fewer trees take it in.
空气中的二氧化碳增多，因为能吸收它的树更少了。
Name them; never just write that it is bad.
要写出名称，千万不要只写它不好。
Now pollution, and the biggest question in this topic.
现在讲污染，也是本章最大的考点。
Untreated sewage and excess fertiliser both damage water ecosystems, in the same way.
未经处理的污水和过量的化肥都会破坏水生 生态系统，而且方式相同。
Watch what happens when the fertiliser reaches the water.
看看化肥进入水中之后发生了什么。
The algae bloom and block the light, the plants below them die, and the oxygen crashes.
藻类大量繁殖并 挡住光，下面的植物死去，氧气骤降。
That chain has a name: eutrophication.
这条链有一个名字：富营养化。
This is that chain, in the order the mark scheme wants.
这就是那条链，按评分标准要求的顺序。
Step one: the fertiliser washes in and adds nitrate ions.
第一步：化肥被冲进水里，增加了硝酸根 离子。
Step two: the producers — the algae — grow very fast.
第二步：生产者——藻类——快速大量生长。
Step three: the algae block the light, so the plants below them die.
第三步：藻类挡住光，下面的 植物死亡。
Step four: decomposition — decomposers feed on the dead material and multiply.
第四步：分解者以死去的物质为食并大量繁殖。
Step five: they respire aerobically and use up the dissolved oxygen.
第五步：它们进行 有氧呼吸，耗尽溶解氧。
Step six: the fish die.
第六步：鱼死了。
Now the real thing: a six-mark question from a real paper.
现在来看真题：一份真实试卷上的六分题。
A chicken farm is built beside a lake.
一个养鸡场建在湖边。
Two months later many of the fish are dead.
两个月后，湖里 许多鱼死了。
Explain how the farm caused this.
解释养鸡场是怎么造成这件事的。
Pause and try it yourself.
先暂停，自己试一试。
Ready?
好了吗？
Mark one: rain washes the manure into the lake.
第一分：雨水把粪便冲进湖里。
Mark two: it adds nitrate ions.
第二分：它增加了硝酸根离子。
Mark three: the algae grow very fast.
第三分：藻类快速 大量生长。
Mark four: the algae die and decomposers feed on them.
第四分：藻类死亡，分解者以它们为食。
Mark five: they carry out aerobic respiration and use up the oxygen.
第五分：它们进行有氧呼吸， 耗尽氧气。
Mark six: with less dissolved oxygen the fish die.
第六分：溶解氧减少，鱼就死了。
Here is the same chain for a different question: fertiliser washing into a river.
这是同一条链，写给另一道题：化肥被冲进河里。
Copy this wording.
把这个写法抄下来。
Every line is one marking point, and the last line is the one students miss.
每一行都是 一个得分点，而最后一行正是学生最容易漏掉的。
The fish die of no oxygen, not of poisoning, and it is the bacteria, not the algae, that take it.
鱼是缺氧而死，不是被毒死的， 而且耗掉氧气的是细菌，不是藻类。
Not all pollution washes away.
不是所有污染都会被冲走。
Non-biodegradable plastics do not rot, because microbes cannot break them down.
不可降解的塑料不会腐烂，因为微生物无法分解它们。
In the sea, animals swallow them or get tangled in them.
在海里，动物会吞下它们，或者被缠住。
On land they simply stay, for hundreds of years.
在陆地上，它们就那样留存几百年。
Almost every piece on this beach will outlast you.
这片海滩上几乎每一块塑料，都会比你活得更久。
Plastic also breaks into pieces too small to see.
塑料还会碎成小到看不见的颗粒。
Watch a pollutant an animal cannot break down and cannot get rid of.
看看一种动物既无法分解、也无法排出的污染物。
The tiny producers take it in.
微小的生产者把它吸收进去。
Each small fish eats many producers.
每条小鱼吃掉许多生产者。
Each big fish eats many small fish.
每条大鱼吃掉许多小鱼。
The bird at the top eats them all, and every speck ends up inside it.
最上面的鸟把它们全吃掉，每一粒最后都进到它体内。
Microplastics travel the same way.
微塑料也是这样传递的。
Now look up.
现在抬头看。
Sunlight passes through the atmosphere and warms the ground.
阳光穿过大气层，使地面变暖。
The ground sends that heat back out.
地面把热量辐射出去。
Greenhouse gases absorb some of it and send it down again, so the Earth stays warm.
温室气体 吸收其中一部分，又把它送回地面，所以地球保持温暖。
That is the natural greenhouse effect, and life depends on it.
这就是自然的温室效应， 生命依赖它。
The trouble starts when we add more of those gases.
麻烦从我们增加这些气体时开始。
Two gases matter most.
最重要的是两种气体。
Carbon dioxide comes from burning fossil fuels, and from deforestation — fewer trees take it in, while burning or rotting the felled trees gives more out.
二氧化碳来自燃烧化石燃料，也来自森林砍伐——树少了， 吸收的就少，而烧掉或腐烂的树又放出更多。
Methane comes from cattle, rice fields and rotting rubbish.
甲烷来自牛、稻田和腐烂的垃圾。
More of these gases means more heat trapped.
这些气体越多，被截留的热量就越多。
We call that the enhanced greenhouse effect, and it drives climate change.
我们把这叫做增强的温室效应， 它导致气候变化。
So what can we do?
那我们能做什么？
A sustainable resource is produced as fast as it is taken, so it never runs out.
可持续资源被取走的速度和它生成的速度一样快，所以永远不会 用完。
Forests need education, protected areas, quotas — limits on how much is cut — and replanting.
森林需要教育、保护区、配额，也就是限制砍伐量，以及重新种植。
Fish stocks need education, closed seasons, protected areas, net mesh sizes that let young fish escape, quotas and monitoring.
鱼类 资源需要教育、禁渔期、保护区、能让幼鱼逃走的网眼大小、配额和监测。
Now conservation, and saving endangered species. A species becomes endangered when its numbers fall far enough.
当一个物种的数量下降到足够低时，它就成为濒危物种。
The causes are the whole of this topic: climate change, habitat destruction, hunting, overharvesting, pollution and introduced species.
原因就是本章的全部内容： 气候变化、栖息地破坏、狩猎、过度捕捞、污染和外来物种。
We save them in four ways.
我们用四种方法拯救 它们。
We monitor and protect the species and its habitat.
我们监测并保护物种及其栖息地。
We educate people.
我们进行教育。
We run captive breeding in zoos, using artificial insemination or in vitro fertilisation — fertilisation outside the body.
我们在动物园进行圈养 繁殖，使用人工授精或体外受精。
And we store seeds safely in seed banks.
我们还把种子安全地保存在种子库里。
This is what success looks like: the giant panda, saved by protected habitat and captive breeding.
这就是成功的样子：大熊猫，靠保护栖息地和圈养繁殖被救了回来。
So why bother?
那为什么 要这么做？
To keep biodiversity conserved.
为了保持生物多样性。
To reduce extinction.
为了减少灭绝。
To protect fragile ecosystems.
为了保护脆弱的生态系统。
And to keep ecosystems working: recycling nutrients, and giving us food, drugs, fuel and genes.
也为了维持生态系统的运作：循环养分，提供食物、药物、燃料和基因。
One warning — a very small population loses genetic variation, so it cannot adapt when its world changes.
一个提醒——种群很小时会失去遗传变异，于是环境变化时它就无法适应。
Three marks students throw away.
三个学生白白丢掉的分。
First, in eutrophication write every link in order — the fish are not poisoned, they suffocate, and it is the decomposers that take the oxygen.
第一，写富营养化时要按顺序写出每一个环节——鱼不是 被毒死的，它们是窒息而死，而且是分解者耗掉了氧气。
Second, for monoculture and intensive farming give both an advantage and a disadvantage.
第二，单一栽培和集约化 养殖要同时给出一个优点和一个缺点。
Third, for a small population say the actual words: less genetic variation.
第三，对于小种群，要写出准确的词：遗传 变异减少。
Get those right, and this topic is yours.
把这几点做对，这个专题就是你的了。