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最大的单细胞生物是什么? – 译学馆
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最大的单细胞生物是什么?

What is the biggest single-celled organism? - Murry Gans

大象是一种有着惊人比例的生物
The elephant is a creature of epic proportions,
它巨大的身体 比显微镜下的细胞大千万亿倍同时
and yet it owes its enormity to more than 1,000 trillion microscopic cells,
在针尖一般大小的地方
and on the epically small end of things,
可能存在着约数百万的单细胞生物
there are likely millions of unicellular species,
但是几乎没有是能用肉眼看到的
yet there are very few we can see with the naked eye.
为什么呢?
Why is that?
为什么不存在单细胞的大象
Why don’t we get unicellular elephants,
或是蓝鲸
or blue whales,
亦或是棕熊呢?
or brown bears?
为了探寻答案 我们得深入观察一个细胞的内部
To find out, we have to peer into a cell’s guts.
这里是运作大部分细胞功能的地方
This is where most of the cell’s functions occur,
细胞膜把它们封闭在内
enclosed by a cellular membrane
也作为细胞质进出的通道
that acts as the doorway into and out of the cell.
所有细胞消耗的来源
Any resources the cell needs to consume,
或者是其需要排出的代谢废物
or waste products it needs to expel,
需要首先通过细胞膜
first have to pass through this membrane.
但这个系统中存在一种生物学的特性
But there’s a biological quirk in this set up.
细胞的表面积与体积以不同的速率增长
A cell’s surface and volume increase at different rates.
细胞有着多种形状
Cells come in many shapes,
但是将它们想象成立方体在数学上会更容易计算
but imagining them as cubes will make the math easy to calculate.
一个立方体有六个面
A cube has six faces.
它们就是细胞膜 组成细胞的表面区域
These represent the cell membrane, and make up its surface area.
立方体的边长为1微米
A cube measuring one micrometer on each side,
也就是1米的百万分之一
that’s one millionth of a meter,
所以表面积就是6平方微米
would have a total surface area of six square micrometers.
体积是1立方微米
And its volume would be one cubic micrometer.
因此每1个单位的体积
This would give us six units of surface area
对应6个单位的表面积
for every single unit of volume,
也就是比例为6:
a six to one ratio.
1但是如果将这个立方体放大十倍
But things change dramatically if we make the cube ten times bigger,
就大不同了边长变为10微米
measuring ten micrometers on each side.
这个细胞的表面积会变为600平方微米
This cell would have a surface area of 600 square micrometers
体积变为1000立方微米
and a volume of one thousand cubic micrometers,
比例仅为0.6:
a ratio of only .6 to one.
1每单位体积仅与不到一个单位的表面积相合作
That’s less than one unit of surface area to service each unit of volume.
随着立方体增大 它的体积增加得比表面积快得多
As the cube grows, its volume increases much faster than its surface area.
内部物质远多于细胞膜
The interior would overtake the membrane,
仅留下很小的表面让细胞质快速进出
leaving too little surface area for things to quickly move in and out of the cell.
巨大的细胞将被代谢废物所堵塞 最终死亡瓦解
A huge cell would back up with waste and eventually die and disintegrate.
拥有许多小的细胞还有一个好处
There’s another plus to having multitudes of smaller cells, too.
即便一个细胞被刺穿、感染或杀死也不会太糟如今
It’s hardly a tragedy if one gets punctured, infected, or destroyed.
也有一些例外的大型细胞
Now, there are some exceptionally large cells
适应并瞒过了系统
that have adapted to cheat the system,
比如人体最长的细胞
like the body’s longest cell,
从脊椎的底部延伸至脚底的神经细胞
a neuron that stretches from the base of the spine to the foot.
为了弥补长度的影响
To compensate for its length, it’s really thin,
它非常细直径仅为几微米
just a few micrometers in diameter.
另一个例子在你的小肠里
Another example can be found in your small intestine,
那里有折叠成小拇指形状的结构
where structures called villi fold up into little fingers.
叫做绒毛每根绒毛由细胞膜高度折叠的细胞组成
Each villus is made of cells with highly folded membranes
上面有细小的凸起 称为微绒毛 来增加表面积
that have tiny bumps called microvilli to increase their surface area.
那单细胞生物呢?
But what about single-celled organisms?
杉叶蕨藻 一种绿色的约30厘米长的水藻
Caulerpa taxifolia, a green algae that can reach 30 centimeters long,
被认为是世界上最大的单细胞生物
is believed to be the largest single-celled organism in the world
多亏其独特的生物学结构
thanks to its unique biological hacks.
像植物一样的结构增加了它的表面强度
Its surface area is enhanced with a frond-like structure.
它进行光合作用 组成食物分子而且
It uses photosynthesis to assemble its own food molecules
它在一个细胞内
and it’s coenocytic.
有多个细胞核
That means it’s a single cell with multiple nuclei,
使得它像多细胞生物一样 只是细胞之间不分离
making it like a multicellular organism but without the divisions between cells.
即使是最大的单细胞生物也有极限
Yet even the biggest unicellular organisms have limits,
没有能长到像大象、蓝鲸和熊那样大小的
and none grows nearly as large as the elephant, whale, or bear.
但是在每一个巨大生物内部 是上万亿的小细胞
But within every big creature are trillions of minuscule cells
完美保持着它们的微型身材
perfectly suited in all their tininess
推动地球上巨灵的进化生长
to keeping the Earth’s giants lumbering along.

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