ฝึกพูดภาษาอังกฤษด้วยเทคนิค Shadowing จากวิดีโอ: How Large Can a Bacteria get? Life & Size 3

In and out.

⏸ หยุดชั่วคราว

ความเร็ว:

145 ประโยค

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In and out.

Staying alive is about doing things.

This very second, your cells are combusting glucose molecules with oxygen to make energy available,

which keeps you alive for another precious moment.

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

Breathing is an answer to a very hard problem.

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

Every living thing has to solve this problem

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

As we've discussed in other videos,

at different scales the physical laws of the universe have different consequences for its inhabitants.

Simple things like temperature, microgravity or surface tension might not matter to you or be a deadly danger,

depending on how big you are.

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

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

This was a huge problem for the first things on the verge of being alive,

because doing anything in our universe requires energy.

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.

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.

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

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.

Diffusion is the rule of the universe that molecules,

especially in liquids or gases,

are constantly moving around in all directions.

And because they move around and bump into each other and other molecules,

they tend to spread.

For example, if you drop a sugar cube into water,

then there is a lot of sugar in one place,

and in another place, there's none.

As sugar molecules dissolve in the water,

they will start randomly bumping against the water molecules and other sugar molecules.

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

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

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

It doesn't require energy.

And life loves free things.

So all life on earth relies on diffusion.

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

Specifically its surfaces.

Cell membranes allow for diffusion of certain molecules.

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

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

Because of diffusion these molecules will eventually spread evenly

so the carbon dioxide diffuses out while oxygen is constantly replenished from the outside.

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

for bacteria, amoeba or your cells,

and a few very small animals.

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.

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

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

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

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

and diffusion of materials can only sustain a certain amount of inside.

Tiny living things have only a little bit of inside or volume and a lot of outside or surface area.

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

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

In a nutshell, it means that if you make something 10 times larger,

its outside or surface would grow by 100,

but its insides or volume grows by 1000 times.

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.

The bacterium has a lot of outsides,

while the whale has a lot of insides.

If we make a bacterium the size of a whale,

our giant bacteria now has too much insides,

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

The oxygen our bacterium needs would never reach the inside before it would run out of oxygen.

Our giant bacterium would just die.

Still, being bigger has many upsides.

From making it harder to be eaten to making it easier to eat others.

But the size of cells is limited by the distance oxygen

and nutrients can effectively diffuse to provide the inside with enough resources.

So, life avoided this problem by forming multicellular structures.

Beings composed of many cells instead of one.

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

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

Some cells concentrated on sensing the environment,

others on digestion, others on movement.

But that still wasn't enough.

The problem of diffusion and surface and energy production remained,

limiting the size these first multicellular forms of life could attain.

So, in order to become even bigger,

life solved the diffusion problem by having holes and caves and tunnels and by folding in on itself,

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

Take yourself.

What you consider your outside,

your skin, has a surface area of about 2 square meters.

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

They aren't like balloons.

They're more like sponges filled with many tiny packed tiny balloons surrounded by blood vessels.

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

Blood filled up with CO2 is pumped around the balloons.

And then the magic of diffusion happens.

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

100

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

101

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

102

Diffusion in the body is effective at about 1 mm one millimeter

103

so every cell in your body is at most one millimeter away from a blood vessel.

104

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

105

Your body has around 100 000 kilometers of capillaries alone,

106

the tiniest of your blood vessels,

107

with a surface area of around 1 000 square meters.

108

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

109

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

110

so your gut has the surface area of half a badminton court,

111

roughly 40 square meters.

112

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

113

Take a tree.

114

Its way to stay alive is to create sugar out of thin air and sunlight.

115

So, it needs as much surface area as possible.

116

An orange tree with 2,000 leaves has a leaf surface area of 200 square meters.

117

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

118

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

119

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

120

If we look at the breathtaking diversity of life on this planet,

121

it seems like everything is pretty different.

122

And it is.

123

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

124

If we look at the very,

125

very small or the very,

126

very big, waste goes out and fresh fuel comes in.

127

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

128

This bird has magical powers.

129

Let's see a demonstration.

130

Bring in the latest scientific research.

131

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

132

How could someone possibly understand all of this?

133

Incredible!

134

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

135

Let's make it a bit more difficult.

136

Can she make all of evolution visible at a glance?

137

This is brilliant!

138

You can clearly see the relationships between species and how they evolved.

139

And look at those illustrations!

140

These posters are ready to be shared with the world.

141

These very special pieces of Kurzgesagt are now available on our shop along with many other sciencey products,

142

all researched with care and created with love by the Burbs with magical powers.

143

Every Kurzgesagt product you buy directly funds another moment we get to spend working on our videos.

144

Thank you so much for being a part of our story and for making this channel possible.

145

Thank you.

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