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  • At this very second, you are on a narrow ledge between life and death.

  • You probably don't feel it, but there's an incredible amount of activity

  • going on inside you,

  • and this activity can never stop.

  • Picture yourself as a Slinky falling down an escalator moving upwards.

  • The falling part represents the self-replicating processes of your cells.

  • The escalator represents the laws of physics driving you forwards.

  • To be alive is to be in motion but never arriving anywhere.

  • If you reach the top of the escalator, there's no more falling possible, and you are dead forever.

  • Somewhat unsettlingly, the universe wants you to reach the top.

  • How do you avoid that? And why are you alive?

  • [Amazing-sounding Kurz Intro Music]

  • All life is based on the cell.

  • A cell is a piece of the dead universe that separated itself from the rest so it could do its own thing for a while.

  • When this separation breaks down, it dies and joins the rest of the dead universe again.

  • Unfortunately, the universe would like for life to be done with doing its own thing.

  • For some reason, it's not a fan of exciting things, but tries to be as boring as possible.

  • We call this principle "entropy," and it's a fundamental rule of our universe.

  • It's pretty complicated and counterintuitive, so we'll explain it in detail in another video.

  • For now, all you need to know is living things are inherently exciting.

  • A cell is filled up with millions of proteins and millions more simpler molecules like water.

  • Thousands of complex, self-replicating processes are happening up to hundreds of thousands of times every second.

  • To stay alive and exciting, it has to constantly work to keep itself from achieving entropy and becoming boring and dead.

  • The cell has to maintain a separation from the rest of the universe.

  • It's doing this, for example, by keeping the concentration of certain molecules different on the inside and the outside

  • by actively pumping out excess molecules.

  • To do stuff like this, a cell needs energy.

  • Energy is the ability of things in the universe to do work; to move or manipulate a thing; to create change.

  • This ability cannot be created or destroyed.

  • The set amount of energy in the universe will never change.

  • We don't know why, it just is that way.

  • So, billions of years ago, one of the most crucial challenges for the first living beings was to get usable energy.

  • We don't know a lot about the first cells, except that they got their energy from simple chemical reactions.

  • And they found the ultimate energy transfer system: the energetic building block of life.

  • The molecule Adenosine Triphosphate, or ATP.

  • Its structure makes it uniquely good at accepting and releasing energy.

  • When a cell needs energy, for example, to pump out molecules or to repair a broken micro machine,

  • it can break down ATP, and use the chemical energy to do work and create change.

  • This is why living beings are able to do stuff.

  • We don't know when or how exactly the first ATP molecule was made on earth.

  • But every living thing we know uses ATP, or something very similar, to keep its internal machinery running.

  • It's crucial for almost every process.

  • Plants, fungi, bacteria, and animals need to survive.

  • Without ATP, no life on Earth.

  • Possibly anywhere.

  • While breaking down chemicals for energy is nice and all,

  • early life did miss out on the greatest available source of energy:

  • The Sun.

  • The Sun merges atoms and radiates photons away that carry energy into the solar system.

  • But this energy is raw and indigestible.

  • It needs to be refined.

  • After hundreds of millions of years of evolution, finally, a cell figured out how to eat the Sun.

  • It absorbed radiation and converted much of it into neat little chemical packages that it could use to stay alive.

  • We call this process: Photosynthesis.

  • You take photons that are wobbly with electromagnetic energy,

  • and use a part of this energy to merge and combine different molecules together.

  • The electromagnetic energy is converted into chemical energy stored in the ATP molecule.

  • This process became even better, as some cells learned to create better chemical packages:

  • Glucose, or sugar.

  • Easy to break down, high in energy, and pretty tasty.

  • This is so convenient, that some cells decided that instead of doing all that pesky photosynthesis work themselves,

  • they would just swallow other cells that did, and take their glucose and ATP.

  • This is widely considered one of the biggest anime betrayals in evolutionary history.

  • And so things went on.

  • Photosynthesizing cells could mostly harness energy at their surfaces,

  • which limited their maximum energy production,

  • which limited their evolutionary avenues somewhat.

  • So, time passed.

  • Some cells made sugar, others ate them.

  • Evolution did its thing, but overall things stayed pretty much the same for hundreds of millions of years.

  • Until, one day, a cell ate another, and did not kill it.

  • Instead, they became one cell.

  • Nothing had changed that day, but Earth would be different forever.

  • This cell became the ancestor of all animals on this planet.

  • Blue whales, amoeba.

  • Dinosaurs, jellyfish.

  • Pink fairy armadillos, and Sunda colugos.

  • And of course, you.

  • All can trace back their existence to this moment.

  • The merging of two living beings is so important,

  • because when those two cells became one, they became way more powerful.

  • The formerly independent cell in the inside, could stop trying to survive.

  • It could concentrate on one thing: make ATP.

  • It became the powerhouse of the cell: the first mitochondria.

  • The host cell's job became to ensure survival in the dangerous world,

  • and provide the mitochondria with food.

  • Mitochondria basically reverse photosynthesis, in a similarly complex process.

  • They take sugar molecules that we got from eating other living things,

  • combust them with oxygen and precursor molecules, to make new, energy-rich ATP molecules.

  • This process works like a tiny furnace and spits out waste products like CO2,

  • water, and a little bit of kinetic energy that you experience as body heat.

  • This first division of labor, meant the new cell had way more energy available than any cell before,

  • which meant more possibilities for evolution to enable more complex cells.

  • At some point, these cells began to form small groups or communities,

  • which lead to multicellular life, and finally, to you.

  • Today, you are a pile of trillions of cells, each filled with dozens,

  • if not hundreds of little machines that provides you with usable energy to stay alive.

  • If this process is interrupted, even for a few minutes, you die.

  • (Teaser of Kurzgesagt: Science War, coming in 2021.)

  • But if life is so fragile, wouldn't it be a good idea to store ATP, like we store sugar in our fat cells,

  • so we don't die if we stop breathing for a while?

  • If life has solved so many problems to make you live today, what's up with the dying quickly thing?

  • Even simple bacteria like E. Coli make about 50 times their body weight in ATP for every cell division.

  • Your trillions of cells need a lot of ATP to keep you around.

  • Every day, your body produces and converts about 90 million, billion, billion molecules of ATP: about your own body weight.

  • You need a whole person's worth of ATP just to make it through a single day.

  • Even storing enough ATP to last you a few minutes is basically impossible.

  • An ATP molecule is really good for shifting energy around quickly,

  • but it's terrible for storage, since it has only one percent of a glucose molecule's energy at three times its mass.

  • So ATP is constantly produced and used up fairly quickly.

  • This was the short and simplified story of the molecule that allows you to be different from the dead universe,

  • and to be the slinky on the escalator.

  • It is a weird story.

  • There is this molecule you need to survive at all times.

  • You need it to keep moving, because even a short break brings your slinky to a stop.

  • And you need to make it yourself.

  • It's like driving a car at full speed while producing fuel in the trunk

  • with junk that you pick up from the side of the road.

  • As far as we know, this all began billions of years ago,

  • when tiny parts of the dead universe came together and became

  • something else for a moment.

  • It could keep itself going.

  • It could grow.

  • That moment set the slinky in motion, and it's been going ever since.

  • From the very first cells, to you watching this now.

  • At some point, you will merge with the rest of the dead universe again.

  • Maybe you'll tell it stories about your adventures.

  • Maybe not.

  • But before you find out,

  • you get to do what life does best.

  • Making a dead universe, much more interesting.

  • (With a Supreme Slinky poster in your room.)

  • If you are currently bored for whatever reason, and you want to make your life more interesting,

  • we've got something for you.

  • We partnered with Skillshare: an online learning community

  • that offers thousands of classes for all skill levels on tons of creative skills like

  • illustration, animation, cooking, creative writing, or film and video.

  • Learning something while creating stuff for yourself is pretty fun and fulfilling.

  • If you want to learn animation, we made a few Skillshare classes

  • where we explained how we animated scenes from our videos, with video lessons and hands-on projects.

  • You can get unlimited access to all classes for less than $10 a month, with an annual premium membership,

  • and, the first 1,000 Kurzgesagt viewers to click the link in the description will get a two month free trial.

  • And if you're just getting started, for beginners who want to dip a toe into illustrations similar to ours,

  • we recommend "Vector Illustration: Using Creative Constraints to Find Your Style" by Rick Berkelmans.

  • Just try something to improve your skills, and at the same time,

  • fight the boredom of being stuck inside.

  • If you want to get creative with new skills and support Kurzgesagt, give it a try!

  • *Quack*

  • Duck: Why am I floating with no purpose in this universe?

At this very second, you are on a narrow ledge between life and death.

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為什麼你還活著--生命、能量和ATP。 (Why Are You Alive – Life, Energy & ATP)

  • 18 1
    Summer 發佈於 2021 年 01 月 14 日
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