没什么比你想要一个东西, There's nothing quite so terrible as needing something
而且它就在你面前 可你得不到它更惨的了. that's sitting right in front ofyou, but not being able to get it.
比如 你正坐着救生艇在大海上漂流. Like, say you're on a lifeboat in the ocean and you're
你超渴 这里有3亿立方英里的水在你面前, super thirsty, and there's 300 million cubic miles of water
但你却不能喝它. sitting right in front of you, but you can't drink any of it.
( Google 查不到此人 而且原视频下也有人问这家伙是谁.. ) Or having to sit next to Meghan Kale every day in English class
或是每天上英语课时都坐在 Meghan Kale 旁边. but knowing she's really, dramatically out of your league.
你知道她 超正点的... A lot of organisms on Earth find themselves
有很多生物发现自己 in this situation pretty much constantly.
总是会碰到这种情况 Except that the thing that's everywhere that they can't have
这东西到处都是 但它们就是没法得到 isn't water... or physical closeness, its nutrients,
我说的不是水... 也不是靠近辣妹 是营养成分 specifically nitrogen and phosphorous.
特别是氮和磷 Of course, there are tons of elementst hat cycle around the Earth,
当然 地球上在不断循环的元素可谓多了去了 hanging out in one place or form for a while
它们待在这里一阵子 然后跑到下一个地方去 before moving on to the next.
它们待在这里一阵子 然后跑到下一个地方去 And as you know, living things need a bunch of stuff.
如你所知 生物的生存需要很多东西 Animals, for instance, need oxygen, carbon and hydrogen.
拿动物举例 动物需要氧 碳和氢 These elements basically cover the water cycle
这些元素基本上都包含在 and the carbon cycle thatI talked about last time,
我们上次谈的 水循环和碳循环里了 but we're also about 3% nitrogen and 1% phosphorous.
但我们也需要大约 3％ 的氮 以及 1％ 的磷 Those numbers might not sound super significant,
这些数字听起来可能不大 but even though we've just got teensy bits of this stuff
但我们很需要它 in our bodies, we need nitrogen to make amino acids, which make
我们需要氮来制造氨基酸 proteins, which make our whole bodies up, and DNA and RNA too.
氨基酸组成了蛋白质 蛋白质组成了我们整个身体 DNA and RNA also require phosphorous,
而 DNA 和 RNA 需要磷 not to mention that phosphorous is the P in ATP,
更不用提 ATP 里的 P 是磷 and the phospho-in phospholipid bilayer.
磷脂双分子层里也有磷 So, we might not need a ton of this stuff, but it is important...
也许我们不需要一大堆磷 但它很重要 and it's hanging out everywhere.
它们到处都是 The air we breathe is mostly nitrogen, and the water and rocks
我们呼吸的空气里大部分都是氮 all around us are jam-packed full of phosphorous.
水和石头里富含磷 But like I said, they're rarely in a form that's biologically available.
但就像我说的 它们很少形成 生物可以直接拿去用的形式 And as per usual, the organisms that solve
一般 生物利用植物来解决这个问题 this problem are the plants.
一般 生物利用植物来解决这个问题 Anything else that needs these nutrients are just going to have
任何需要这些营养物质的生物 to eat some plants, or eat something that ate some plants.
都得吃一些植物 或是吃一些吃植物的动物 But how do plants solve this problem?
但植物是怎么解决这个问题的? And why is it a problem in the first place?
为什么它是个很重要的问题? Well, give me a few minutes... I'll explain.
好吧 给我几分钟 我会解释的 So let's talk about the nitrogen cycle first,
我们先来谈谈 氮循环 since nitrogen really is actually all around us, like,
因为氮就在我们的身边 I can feel it right now! There it is, in the air.
就像我能感觉到它一样! 它们就在空气里 So why is it so hard to get this stuff that's constantly
那为什么我们不能从空气里直接获取氮 surrounding us in the air into our actual bodies to be useful for us?
然后给我们的身体用? Because even though nitrogen gas makes up around 78 %
即使空气的 78% 是氮气 of the atmosphere, you'll notice here that nitrogen gas is made up
你会注意到 氮气是由氮分子组成的 of two nitrogen atoms stuck together with a triple bond.
氮分子由2个原子组成 它们以三键连接 And it's one thing to break a part a single covalent bond, but three!?
破一个键都很难了 还来3个? So, as you can imagine,
所以你可以想象 those two nitrogen atoms are a total pain to pry a part,
掰开这2个氮原子有多难 but that molecule has to be split in order for
但植物为了生存必须摄取氮 a plant to get at the pieces.
但植物为了生存必须摄取氮 In fact, plants can assimilate a bunch of different forms of nitrogen:
事实上 植物可以吸收很多不同形式的氮 nitrates, nitrites to a lesser extent,
比如 硝酸盐 亚硝酸盐 and even ammonium, which is
甚至是铵 what you get when you mix ammonia with water.
当你把氨和水混合 就得到了铵 But all that darn nitrogen gas in the atmosphere
但空气中那些氮 is beyond their powers of assimilation.
植物就搞不定了 So plants need help taking advantage of this ocean of nitrogen
所以植物需要利用海洋里的氮 that we're all swimming in, which is why they need to have
他们需要海洋的 that nitrogen "fixed"so that they can use it.
"固氮作用" 把氮气转化为含氮化合物 Even though plants aren't wily enough to wrangle those two nitrogen
虽然植物无法把2个氮原子分开 atoms apart, certain nitrogen fixing bacteria are.
但固氮细菌可以做到 These bacteria hang out in soil or water or even form symbiotic
这些细菌在土里 水里 甚至是 relationships with the root nodules of some plants,
和某些植物的根住在一起 互利共生 most of which are legumes.
其中大部分是豆科植物 That's a pretty big family of plants: soybeans,
豆科植物是个非常大的家族: 包括大豆 clover, peanuts, and kudzu. All legumes.
苜蓿 花生 葛根 等等等等 So these bacteria just sit around
那些细菌只是坐在那里 把空气里的氮转成氨 converting atmospheric nitrogen into ammonia,
那些细菌只是坐在那里 把空气里的氮转成氨 which then becomes ammonium when it's mixed with water
当氨和水混合时 就成了铵 which can be used by plants.
就可以被植物吸收了 They do this with a special enzyme called nitrogenase, which is
细菌是通过固氮酶做到这一点的 the only biological enzyme that can break that crazy triple bond.
这是唯一一种可以掰开三键的生物酶 Ammonia can also be made by decomposers: fungi, protists or
氨也可以被分解者做出来 比如真菌 原生生物 other kinds of bacteria that munch
或是其他种类的细菌 on your proteins and DNA after you die.
它们在你死后会拆了你的蛋白质和DNA But they're not picky, they like poop and urine, too.
但他们不挑剔 它们连翔和尿也分解 Then once this has happened, other bacteria known as
一旦这发生了 其他细菌被称为 nitrifying bacteria can take this ammonia and convert it into nitrates,
硝化细菌 它们可以把氨转化成硝酸盐 3 oxygens atoms attached to a nitrogen atom,
也就是3个氧原子连着1个氮原子 and nitrites, 2 oxygens attached to a nitrogen
或是转成亚硝酸盐 2个氧原子连着1个氮原子 and those are even easier than ammonium for plants to assimilate.
对植物来说 这俩东西比铵容易吸收得多 So, the take-home here is, if it wasn't for these bacteria,
所以如果没有这些细菌的话 there'd be a whole lot less biologically available nitrogen
就没有那么多氮以生物可利用的形式存在了 hanging around, and as a result, there'd be a lot fewer
而结果是 这个星球上的生物会变少 livings things on the planet.
而结果是 这个星球上的生物会变少 So, as usual: thanks, bacteria. We owe you one.
所以像往常一样: 谢谢你 细菌 我们欠你一个人情 But I should mention that it's not just bacteria who can
但我应该指出 不只是细菌可以 wrangle those two nitrogen atoms apart.
拆开这2个氮原子 Lightning, of all things, has enough energy to break
闪电 有足够的能量打破 the bonds between nitrogens, which is obviously awesome
氮原子之间的化学键 这显然是件好事 and therefore worth mentioning.
因此值得一提 And in the 20 th century, smarty pants humans also figured out
并且在20世纪 有个聪明的家伙 various ways to synthetically fix a ton of nitrogen all at once,
发明了各种方法来固氮 (把氮气变成含氮化合物) which is why we have synthetic fertilizers now
这就是为什么 我们现在有人工合成化肥 and so much food growing all over the place.
而且我们还能到处种食物 Once the atmospheric nitrogen is converted into a form that
一旦空气里的氮转成植物可利用的形式后 plants can use to make DNA, RNA and amino acids,
植物可以用它来制造 DNA RNA 和氨基酸 organic nitrogen takes off up the food chain.
把有机氮带入食物链 Animals eat the plants and use all that sweet,
动物吃掉植物 然后获得那些氮 sweet bioavailable nitrogen to make our own amino acids.
来制作氨基酸 And then we pee or poop it out, or die, and the decomposers
之后氮会被尿出来或拉出来 或我们死掉 然后那些分解者 go to town on it, breaking it down into ammonia,
就会跑过去 把氮分解成氨 and it just keeps going... until one day that organic nitrogen
它会不断的循环... 直到有一天那些有机氮 finds itself in denitrifying bacteria, whose job it is
发现自己碰到了 反硝化细菌 to metabolize the nitrogen oxides and turn them back into
这些家伙会代谢氮氧化物 把它们变回氮气 nitrogen gas using a special enzyme called nitrate reductase.
它们是用 硝酸还原酶 做到这一点的 These guys do their business and then release
这些家伙做自己的事 然后释放 the N2 back into the atmosphere.
N2 回到空气中 And that, my friends, is the nitrogen cycle.
我的朋友 这就是氮循环 If you remember nothing else, remember that:
如果你把前面的东西都忘了 记住下面这个就好: a) you owe bacteria a solid because they were smart enough to make
A) 你欠了细菌一个大人情 因为他们很聪明 an enzyme that could bust open the triple bonds of nitrogen gas,
知道怎么用酶拆开氮原子的三键 b) you owe plants a solid for wrestling nitrogen into their bodies
B) 你也欠植物的 因为它们把氮放到自己的身体里 so that you can just eat a carrot and not have to think about it, and
让你可以直接吃根胡萝卜解决问题 而不用担心去哪儿找氮 c) nitrogen is awesome and everywhere,
C) 氮很棒 而且无处不在 and yet also elusive and deserving of your respect.
也值得你尊重 So, moving on to the phosphorus cycle.
现在 我们来讲 磷循环 The interesting thing about phosphorous is that it's the only
磷有趣的事情是 它是我们讨论过的元素中 element we're going to talk about that doesn't involve the atmosphere.
唯一不存在于空气中的元素 Phosphorous wants nothing to do with your air!
磷和你的空气啥关系都没有 However, the lithosphere, fancy word for the Earth's crust,
然而 岩石圈 这是个指地壳的花哨词 is amply supplied with phosphorous.
到处都是磷 Rocks contain inorganic phosphates, especially sedimentary
岩石中含有无机磷酸盐 特别是那些沉积的石头 rocks that originated in old ocean floors and lake beds
它们来自远古的河床以及湖床 where living things died and sank to the bottom where their
那些生物死亡后 掉到水底 phosphorous-rich bodies piled up
富含磷的尸体堆积起来 and made phosphorous-rich rocks over time.
随时间的推移 变成了富含磷的石头 Unfortunately, there aren't a lot of rock-eating organisms
不幸的是 地球上会吃石头的生物不多 on Earth, just a couple of bacteria,
只有几种细菌会这么干而已 which are called lithotrophs, by the way.
顺带说一句 这种细菌叫无机营养菌 However, when these rocks are re-exposed and water erodes them,
然而 当这些岩石重见天日 并且被水侵蚀后 some of the phosphates are dissolved into the water.
有一些磷会被水溶解 These dissolved phosphates are immediately available to,
这些溶解的磷立马就可以被植物吸收和使用 and assimilated by, plants, which are then eaten by animals.
然后被动物吃掉 From here, the same thing goes for the decomposers
这里 分解者干的事也一样 as with the nitrogen cycle: when a leaf drops,
就像氮循环里一样: 当树掉叶子时 or something poops or dies, the decomposers break it down
或动物拉便便 或动物死了 分解者会去分解它 and release the phosphate back into the soil or water.
把磷释放回土里或水里 And phosphates get about as much downtime in the soil as a
磷在土壤中待的时间 20 dollar bill on the sidewalk.
就像20美元的钞票在人行道上待的时间一样 Decomposed phosphate is immediately re-assimilated
分解的磷马上就被植物吸收了 back into plants, and this little cycle just keeps going and going:
这个小循环会不断的继续 plants to the animal to the decomposers,
植物 -> 动物 -> 分解者 to the soil and back into a plant.
->土壤 -> 植物 That is, until that atom of phosphorus makes its way
也就是说 直到磷原子到达大海或河流之前 into some kind of body of water.
这循环会一直这么折腾 Because aquatic and marine ecosystems need phosphorus like crazy.
由于水生和海洋生态系统非常需要磷 Once a phosphorous atom makes it's way into a deep lake or ocean,
磷原子一旦到了湖泊或大海 it cycles around among the organisms there:
它会在那里一直循环 algae, plankton, fish.
藻类 浮游生物 鱼. And this cycling can go on for a long time.
这个循环可以持续很长时间 I mean, not as long as a phosphorus atom trapped in a rock,
我的意思是 虽然没磷原子困在石头里那么长时间 that can be millions of years.
但它也可以有个几百万年 But by some estimates, a single phosphorus atom can be caught
有些人估计 单个磷原子 in a biological cycle for 100,000 years.
可以在生物循环中 循环10万年 Eventually, it's in something that dies and falls into a hole
最终 那个磷原子随着某个死掉的生物掉进了一个洞里 so deep that decomposers can't survive there.
那个洞深到分解者无法生存 Then sedimentation builds up and turns into rock,
然后沉淀变成石头 which are eventually uplifted into mountains, and exposed,
最终抬升成山 暴露出来 and the phosphates are weathered back out.
磷又重见天日了 It's a cycle!
这是个循环! So, yeah. That's the deal with nitrogen and phosphorus:
所以 是的 living things need them, but even though they're all over the place,
生物需要他们 但尽管他们到处都是 they're at a premium in biological systems because they're hard
但它们在生物系统中也不是什么省油的灯 因为它们很难获得 to get at, either because they have to be converted into a form
一方面是因为它得转成生物可利用的形式 that organisms can use or they're locked away underground.
或是有时它藏在地底下 But you know who the smartest monkeys are? Us!
但你知道最聪明的猴子是谁吗? 我们! And yeah, you can bet your face that we've figured out
是的 我们已经想通了 how to unleash all kinds of nitrogen and phosphorus
如何释放各种氮和磷 onto this big, green planet.
到这个大大的绿色星球上 Mostly in an effort to help feed our children and each other.
不都是为了喂养我们的后代以及我们自己吗 We usually mean well, but we can be a bit overbearing sometimes.
我们以为我们在做有益的事情，但很多时候会过犹不及 It's just the human way to see something in Nature that seems
人类就是这样嘛 喜欢把自然界中看起来不好的 to be lacking or imperfect and try to make it the best thing ever.
东西改进一下 把它变得更好 So with the phosphorus and nitrogen cycles,
所以针对磷和氮循环 we have introduced fertilizers: lots and lots of fertilizers,
我们弄出了化肥: 很多很多化肥 the main ingredients of which are, you guessed it:
主要成份是.... 你猜对了: nitrogen and phosphorus.
氮和磷 The story of how we learned to synthesize nitrogen into ammonia
关于我们是怎么学会把氮转化成氨 for fertilizers and chemical weapons is a very, very interesting
然后用于化肥和化学武器的故事 非常非常有趣 one involving an evil lunatic, and I suggest as soon
这故事涉及到一个邪恶的疯子 as this is over, you watch this video on Fritz Haber,
你可以去看看我们在 scishow 频道做的关于 弗里茨·哈伯 的视频 the guy who made all of this happen during World War I.
这家伙在第一次世界大战期间完成了这一切 You've heard of too much of a good thing, right?
你听过太多好事了 对吧? Well, through the miracle of synthetic fertilizers,
好吧 通过合成肥料 we're able to grow much, much more food than we ever have before,
我们能比以前种出多得多的食物 and as a result, ecosystems all over the world are being bombarded
而结果是 世界各地的各种生态系统 by these incredible amounts of nitrogen and phosphorous.
正在被大量氮和磷影响 This takes us to into the next chapter in our exploration of ecology:
这带领我们到达下一章的生态学探索: the human impacts on the biosphere.
人类对生物圈的影响 Sometimes out of our desire to make nature better,
有时 我们只是希望大自然变得更好 sometimes out of stupid human selfishness,
有时 我们只是纯粹出于自私 and most often, both,
但不论目的是哪种 we've ended up really messing up the environment in more ways
我们大部分情况都在直接或间接的搅乱自然环境 than we can count.
我们大部分情况都在直接或间接的搅乱自然环境 And that's what we're going to be talking about next week.
这正是我们下周要谈论的话题 Be sure to wear your gas mask and hazmat gloves.
记得要戴防毒面具和危险品手套 And thank you for watching this episode of Crash Course Ecology.
感谢 收看本集生态学速成班 This episode was written by Jesslyn Shields,
本集剧本作者是 贾瑟琳·谢尔 Blake DePastino and myself.
布雷克·滴帕斯蒂诺 和 我自己 Our technical director is Nick Jenkins, he's also filming this,
我们的技术总监是 尼克·詹金斯 他还负责拍摄 and he will also be editing it. Sorry Nick.
和编辑节目 抱歉了尼克 Graphics are courtesy of Peter Winkler
图形是 彼得·温克勒 and sound is from Michael Aranda
声音是 迈克尔·阿兰达 There's a table of contents over there if you want
旁边有张表