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人类的精子vs.抹香鲸 – 译学馆
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人类的精子vs.抹香鲸

Human sperm vs. the sperm whale - Aatish Bhatia

1977年 物理学家爱德华•珀塞尔计算得出
In 1977, the physicist Edward Purcell
如果你推一下细菌 然后松手
calculated that if you pusha bacteria and then let go,
它会在约百万分之一秒内停止移动
it will stop in abouta millionth of a second.
这段时间内
In that time, it will have traveled less
细菌走过的距离不超过一个原子直径
than the width of a single atom.
对精子和其它微生物来说 这一结论同样适用
The same holds true for a spermand many other microbes.
而这一切都源于它们超小的尺寸
It all has to do with being really small.
微生物居住在一个我们完全陌生的世界
Microscopic creatures inhabita world alien to us,
这个世界里 在水中移动一英寸都是件极困难的事
where making it through an inch of water is an incredible endeavor.
但为何(体型)大小对游泳者影响甚远呢?
But why does size matterso much for a swimmer?
是什么使精子的世界
What makes the world of a spermso fundamentally different
与抹香鲸的世界如此天差地别呢?
from that of a sperm whale?
为了找到答案 我们需要深入了解一下流体物理学
To find out, we need to dive into the physics of fluids.
这儿有个可参照的方法
Here’s a way to think about it.
设想你正在泳池中游泳
Imagine you are swimming in a pool.
池中除了你 就是一堆水分子
It’s you and a whole bunchof water molecules.
水分子与你的数量比是一万亿兆亿比一
Water molecules outnumber youa thousand trillion trillion to one. So,
用你巨人般的身躯推开它们很容易
pushing past themwith your gigantic body is easy,
但如果你非常小
but if you were really small,
假设你有差不多一个水分子那么大
say you were about the sizeof a water molecule,
突然之间
all of a sudden, it’s like you’re swimming
你似乎身处人堆之中游泳
in a pool of people.
你不再能简单地拨动微小的水分子
Rather than simply swishing byall the teeny, tiny molecules,
现在每一个水分子对你来说
now every single water molecule is
都是挡在你前路上的
like another person you have to push past
必须推开的人
to get anywhere.
1883年 物理学家奥斯本•雷诺兹
In 1883, the physicist Osborne Reynolds
发现可以用一个简单的数字
figured out that there isone simple number
来预测流体运动规律
that can predict how a fluid will behave.
它被称为“雷诺兹数”
It’s called the Reynolds number,
雷诺兹数由几个简单参数组成
and it depends on simple properties
比如游泳者的大小
like the size of the swimmer,
它的速度 流体密度
its speed, the density of the fluid,
以及流体的粘性或者粘度
and the stickiness,or the viscosity, of the fluid.
也就是说 不同大小的生物
What this means is that creaturesof very different sizes
所处的世界也大为不同
inhabit vastly different worlds.
举个例子 由于其巨大的体型
For example, because of its huge size,
抹香鲸就处在一个高雷诺兹数的世界
a sperm whale inhabits the large Reynolds number world.
扇动下尾巴
If it flaps its tail once,
就可以游动相当一段距离
it can coast ahead for an incredible distance. Meanwhile,
与此同时 精子就处在一个低雷诺兹数的世界
sperm livein a low Reynolds number world.
如果一个精子不再扇动尾巴
If a sperm were to stop flapping its tail,
它连一个原子的距离都无法移动
it wouldn’t even coast past a single atom.
为了体会精子的感受
To imagine what it wouldfeel like to be a sperm,
你需要将自己带到精子的雷诺兹数环境
you need to bring yourself downto its Reynolds number.
想象你身处一个充满糖浆的浴缸里
Picture yourself in a tub of molasseswith your arms moving
你胳膊的移动速度像时钟分针那么缓慢
about as slow as the minutehand of a clock,
之后 你就能理解
and you’d have a pretty good idea
精子所面对的环境了
of what a sperm is up against. So,
那么 微生物都是怎么移动自己的呢?
how do microbesmanage to get anywhere? Well,
其实它们中的许多完全不游动
many don’t bother swimming at all.
只是静静地等着食物飘过来
They just let the food drift to them.
有点像一头懒牛
This is somewhat like a lazy cow that waits
静静地等着嘴边草再长出来
for the grass under its mouth to grow back.
但也有许多微生物确实会游动
But many microbes do swim,
这就要说到微生物神奇的适应能力了
and this is where those incredible adaptations come in.
它们使用的其中一个技巧是 改变自己鞭毛的形状
One trick they can use is to deform the shape of their paddle.
通过巧妙地弯曲鞭毛
By cleverly flexing their paddle
来使发力滑动比归位滑动
to create more drag on the power stroke
获得更大的拉力
than on the recovery stroke,
使单细胞生物如草履虫
single-celled organisms like paramecia
得以在水分子大军中缓慢移动
manage to inch their waythrough the crowd of water molecules.
但是还有更天才的解决办法
But there’s an even moreingenious solution
那就是细菌和精子的办法
arrived at by bacteria and sperm.
它们不必前后摆动它们的鞭毛
Instead of waggingtheir paddles back and forth,
它们像螺旋拔塞器一样转起来
they wind them like a cork screw.
正如酒瓶上的螺旋拔塞器一样
Just as a cork screw
把绕转运动变为前行运动
on a wine bottle converts winding motion into forward motion,
这些小生物们摆动它们螺旋般的尾巴
these tiny creaturesspin their helical tails
来推动自己在像木塞一样 阻力巨大的水里前行
to push themselves forward in a world where water feels as thick as cork.
其它方式就更奇怪了
Other strategies are even stranger.
一些细菌
Some bacteria take Batman’s approach.
它们使用抓钩来拉动自己
They use grappling hooksto pull themselves along.
它们甚至可以借用抛出抓钩的惯性
They can even use this grappling hook
将自己带出
like a sling shot and fling themselves forward.
另一些用到了化学工程
Others use chemical engineering.
幽门螺杆菌只在我们胃里面的
H. pylori lives onlyin the slimy, acidic mucus
黏黏的酸性粘液中生存
inside our stomachs.
它释放一种化学成分 抑制周围的粘液
It releases a chemicalthat thins out the surrounding mucus,
这样它就可以在粘液中滑行
allowing it to glide through slime.
可能并不意外的 这些家伙也负责胃溃疡
Maybe it’s no surprise that these guys are also responsible for stomach ulcers. So,
所以 当你真的
when you look really closely
仔细观察我们的身体和周围的世界
at our bodies and the world around us,
你会发觉
you can see all sorts
所有的微生物都在黏黏的环境中找到聪明的移动方式
of tiny creatures finding clever ways to get around in a sticky situation.
没有这些适应性 细菌永远不会找到宿主
Without these adaptations,bacteria would never find their hosts,
精子也永不会与卵子相遇
and sperms would nevermake it to their eggs,
这表示你也永不会患上胃溃疡
which means you would neverget stomach ulcers,
因为你压根就出生不了
but you would also never be bornin the first place.

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视频概述

解析微生物在粘稠环境下是如何游动的

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