Name: 細菌能長多大？生命與大小 3 (How Large Can a Bacteria get? Life & Size 3)
Uploaded: 2026-01-28T17:18:15.000Z
Duration: 10 min 41 s

程度副詞

This very second, your cells are combusting glucose molecules with oxygen to make energy available, which keeps you alive for another precious moment.

就在這一刻，你的細胞正燃燒葡萄糖分子和氧氣來產生能量，讓你又能再活一小段寶貴的時間。

To get the oxygen to your cells, you're breathing.

為了把氧氣送到你的細胞，你正在呼吸。

Breathing is an answer to a very hard problem.

呼吸就是一個很難的問題的解答。

How do you get the resources that your cells need to survive to the inside of your cells?

你該如何將細胞生存所需的資源送到細胞內部呢？

Every living thing has to solve this problem.

每個生物都必須解決這個問題。

And the solution is surprisingly different depending on one of the most important regulators of life size.

而這個解答，竟然會因為生命體最重要的調節器之一而有驚人的不同。

As we've discussed in other videos, at different scales, the physical laws of the universe have different consequences for its inhabitants.

就像我們在其他影片討論過的，在不同的尺度下，宇宙的物理定律對它的居民會有不同的後果。

Simple things like temperature, microgravity, or surface tension might not matter to you or be a deadly danger, depending on how big you are.

像溫度、微重力或表面張力這些簡單的事情，可能對你來說沒什麼大不了，或者可能是致命的危險，這都取決於你的體型大小。

Living things need a lot of different materials to keep themselves going, and

生物體需要很多不同的材料來維持運作，

they somehow need to transport them from the outside to the inside.

而且牠們得想辦法把這些材料從外面運輸到裡面。

This was a huge problem for the first things on the verge of being alive, because doing anything in our universe requires energy.

對於剛萌芽的生命來說，這是一個巨大的難題，因為在我們的宇宙中，做任何事都需要能量。

And the first living beings on Earth did not have the abundance of tools and techniques available that life has today, after billions of years of evolution.

而地球上最早的生命，不像現在經過數十億年進化後，擁有這麼豐富的工具和技術。

So at the very beginning, life needed to find a way to get good stuff inside and bad stuff outside of itself without using energy.

所以一開始，生命需要找到一種不用能量就能把好的東西送進來、壞的東西送出去的方法。

Luckily, the very first forms of life were very, very small.

幸運的是，最早期的生命形式非常非常小。

And because they were so small, they were able to use a free form of transport that was based on a physical law called diffusion.

因為牠們很小，所以能夠利用一種免費的運輸方式，這種方式是基於一個叫做擴散的物理定律。

Diffusion is the rule of the universe that molecules, especially in liquids or gases, are constantly moving around in all direct.

擴散是宇宙中的一個規則，分子，尤其是在液體或氣體中，會不斷地朝所有方向移動。

And because they move around and bump into each other and other molecules, they tend to spread.

因為牠們到處移動、互相碰撞，以及和其他分子碰撞，所以牠們會傾向於擴散開來。

For example, if you drop a sugar cube into water, then there is a lot of sugar in one place, and

舉個例子，如果你把一塊方糖丟進水裡，那麼一開始糖會集中在一個地方，

As sugar molecules dissolve in the water, they will start randomly bumping against the water molecules and other sugar molecules.

隨著糖分子在水中溶解，牠們會開始隨機地與水分子和其他糖分子碰撞。

Slowly, all the sugar molecules will spread out and form multiple phases of different concentrations.

慢慢地，所有的糖分子都會散開，形成不同濃度的多個階段。

These random movements continue endlessly until at some point, the sugar will be spread evenly in the water.

這些隨機的運動會一直持續下去，直到某個時刻，糖會均勻地分佈在水中。

The great thing about diffusion is that life can use it for free.

擴散最棒的地方在於，生命可以免費利用它。

It doesn't require energy, and life loves free things.

它不需要能量，而生命最喜歡免費的東西了。

So all life on Earth relies on diffusion.

所以地球上所有的生命都依賴擴散。

Let's look at the smallest living being on Earth, a bacterium.

我們來看看地球上最小的生物，一個細菌。

Specifically, its surfaces cell membranes allow for diffusion of certain molecules.

具體來說，牠的表面細胞膜允許某些分子擴散。

This specific bacterium consumes oxygen to live, while carbon dioxide is produced inside as a waste product.

這個特定的細菌消耗氧氣來生存，同時二氧化碳作為廢物在內部產生。

So inside the bacterium, there isn't a lot of oxygen, but a lot of carbon dioxide.

所以細菌內部氧氣不多，但二氧化碳很多。

Because of diffusion, these molecules will eventually spread evenly.

因為擴散作用，這些分子最後會均勻散開。

So the carbon Dioxide diffuses out, while oxygen is constantly replenished from the outside.

所以二氧化碳會擴散出去，而氧氣則不斷從外面補充進來。

But this kind of breathing only works for the very small world.

但這種呼吸方式只適用於非常小的世界。

Four bacteria, amoeba, or your cells, and a few very small animals.

像是細菌、變形蟲，或是你的細胞，還有一些非常小的動物。

Insects, for example, have a fine network of trachea tunnels with a pressure gradient where air very slowly can diffuse in and exchange gases with the insect cells.

舉例來說，昆蟲有一套精密的氣管隧道網絡，有壓力梯度，空氣可以非常緩慢地擴散進來，並與昆蟲細胞交換氣體。

But even insects seem to be able to contract their trachea, and

但即使是昆蟲，似乎也能收縮牠們的氣管，而且

at least some even have specialized breathing organs like spiracles and air sacs.

至少有些還有像氣門和氣囊這樣的專門呼吸器官。

At certain scales, diffusion is just too slow to keep cells alive.

在某些尺度下，擴散作用太慢，無法維持細胞存活。

The fundamental problem is that the exchange with the environment can only happen at the surface, and

根本問題是，與環境的交換只能在表面發生，而

diffusion of materials can only sustain a certain amount of insight.

材料的擴散只能維持一定的理解程度。

Tiny living things have only a little bit of inside or volume, and

小小的生物體內部或體積很小，

But what if we wanted to create a bacteria the size of a blue whale and had a very convenient enlargement machine?

但如果我們想創造一隻藍鯨大小的細菌，而且有一個很方便的放大機，會怎麼樣呢？

We would sadly be messed up by the square cube law.

我們會很遺憾地被平方立方定律打敗。

In a nutshell, it means that if you make something 10 times larger, its outside or surface would grow by 100, but

簡而言之，這意味著如果你把某樣東西放大10倍，它的外部或表面會增加100倍，但是

its insides or volume grows by 1000,000 times.

它的內部或體積會增加100萬倍。

If we compare the bacterium Pseudomonas aeruginosa with a blue whale, we see that the bacterium has 10 million times more surface in relation to its volume than the whale.

如果我們比較綠膿桿菌和藍鯨，會發現細菌相對於其體積的表面積是鯨魚的1000萬倍。

The bacterium has a lot of outsides, while the whale has a lot of insides.

細菌有很多外部，而鯨魚有很多內部。

If we make a bacterium the size of a whale, our giant bacteria now has too much insides, and

如果我們把細菌做成鯨魚的大小，我們巨大的細菌現在內部太多了，

most of its inside is now very far from its surface.

牠的內部大部分離表面都太遠了。

The oxygen our bacterium needs would never reach the inside.

我們細菌需要的氧氣根本無法到達內部。

Before it would run out of oxygen, our giant bacterium would just die.

在氧氣耗盡之前，我們巨大的細菌就會死掉。

Still, being bigger has many upsides, from making it harder to be eaten to making it easier to eat others.

不過，體型變大還是有很多好處，像是比較不容易被吃掉，也比較容易吃到別人。

But the size of cells is limited by the distance oxygen and nutrients can effectively diffuse to provide the inside with enough resources.

但細胞的大小會受到氧氣和養分擴散距離的限制，無法有效率地提供內部足夠的資源。

So life avoided this problem by forming multicellular structures, beings composed of many cells instead of one.

所以生命透過形成多細胞結構來避開這個問題，也就是由許多細胞組成的生物，而不是單一個細胞。

Because diffusion works better if you have many small units instead of one much bigger one.

這是因為如果你有很多小單位，而不是一個大單位，擴散的效果會比較好。

Over time, the cell buddies began to share work and specialize.

隨著時間過去，這些細胞夥伴開始分工合作、專精化。

Some cells concentrated on sensing the environment, others on digestion, others on movement.

有些細胞專注於感知環境，有些負責消化，有些負責移動。

The problem of diffusion and surface and energy limiting the size these first multicellular forms of life could attain.

擴散、表面積和能量限制了這些早期多細胞生命形式能達到的體型大小這個問題。

So in order to become even bigger, life solved the diffusion problem by having holes and caves and tunnels, and

所以為了變得更大，生命透過擁有孔洞、洞穴和通道來解決擴散問題，以及

So diffusion could happen easily in each one of the cells.

這樣擴散就可以在每個細胞中輕鬆進行。

Take yourself what you consider your outside.

Your skin has A surface area of about 2 square meters.

你的皮膚表面積大約是 2 平方公尺。

But your lungs have a surface area of about 70 square meters.

但你的肺部表面積大約有 70 平方公尺。

They aren't like balloons, they're more like sponges filled with many tightly packed tiny balloons surrounded by blood vessels.

它們不像氣球，更像充滿許多緊密排列的小氣球並被血管包圍的海綿。

When you breathe in, all these tiny balloons fill up with fresh air.

當你吸氣時，所有這些小氣球都會充滿新鮮空氣。

Blood filled up with CO2 is pumped around the balloons, and then the magic of diffusion happens.

充滿二氧化碳的血液會被泵送到這些小氣球周圍，然後擴散的奇蹟就發生了。

The oxygen diffuses into the blood where it's picked up by red blood cells, and

氧氣會擴散到血液中，被紅血球帶走，

the CO2 diffuses out of the blood and into your lungs where it can be breathed out again.

而二氧化碳則從血液擴散出來，進入你的肺部，然後可以再呼出去。

Your blood then carries oxygen rich blood into the furthest corners of your body and picks up the CO2.

你的血液接著會將富含氧氣的血液帶到身體最遠的角落，並帶走二氧化碳。

Waste diffusion in the body is effective at about 1 millimeter.

身體內的廢物擴散作用大約在 1 公釐的範圍內是有效的。

So every cell in your body is at most 1 millimetre away from a blood vessel.

所以你身體裡的每一個細胞，離血管最遠也不會超過 1 公釐。

So medium sized animals like you need a lot of blood vessels to reach every cell in the body.

所以像你這樣中型的動物，需要大量的血管才能到達身體的每個細胞。

Your body has around 100,000 kilometers of capillaries alone, the tiniest of your blood vessels, with a surface area of around 1,000 square meters.

你的身體光是微血管就有大約 10 萬公里長，這是你最小的血管，表面積約有 1,000 平方公尺。

This is true for all parts of you that want to exchange something with the outside world.

這對你身體裡所有想跟外界交換東西的部分都是一樣的。

Your body needs surfaces to take in nutrients from your food.

你的身體需要表面來吸收食物中的營養。

So your gut has the surface area of half a badminton court, roughly 40 square meters.

所以你的腸道表面積大約有半個羽球場那麼大，約 40 平方公尺。

The larger you are, the more hidden surfaces you need.

你體型越大，就需要越多隱藏的表面。

Its way to stay alive is to create sugar out of thin air and sunlight, so it needs as much surface area as possible.

樹要生存，就是靠從空氣和陽光製造葡萄糖，所以需要盡可能大的表面積。

An orange tree with 2000 leaves has a leaf surface area of 200 square meters.

一棵有 2000 片葉子的橘子樹，葉子表面積有 200 平方公尺。

But the surface inside the leaves where diffusion actually occurs is 6,000 square meters.

但葉子裡面實際發生擴散作用的表面，卻有 6000 平方公尺。

The same with roots, where water diffuses from the soil into countless tiny hairs that maximize the surface area.

根部也是一樣，水從土壤擴散到無數細小的根毛裡，這樣可以最大化表面積。

The roots of 1 square meter of grass add up to around 350 square meters of surface.

一平方公尺的草，它的根部加起來大約有 350 平方公尺的表面積。

If we look at the breathtaking diversity of life on this planet, it seems like everything is pretty different.

如果我們看看這個星球上令人驚嘆的生命多樣性，好像一切都很不一樣。

But some basic principles are the same for everybody and have not changed significantly for billions of years.

但有些基本原理對所有生物都一樣，而且數十億年來都沒有顯著改變。

If we look at the very, very small or the very, very big, waste goes out and fresh fuel comes in.

如果我們看非常非常小的東西，或是非常非常大的東西，廢物會排出，新鮮的燃料會進來。

Big animals just need a lot of complex plumbing to make it possible.

大型動物只需要複雜的管道系統來達成這件事。

Wow, that's a lot of complicated stuff about the immune system and all its cells.

哇，關於免疫系統和所有細胞，這真是太複雜了。

How could someone possibly understand all of this?

怎麼可能有人能理解這一切呢？

This overview is delightful and easy to grasp, but still scientifically accurate.

這個總覽令人愉快又容易理解，同時也科學準確。