Where Did Eukaryotic Cells Come From? – A Journey Into Endosymbiotic Theory


Life on Earth emerged at least three and a
half billion years ago as prokaryotes. These are the simple unicellular organisms. They have a membrane on the outside and a
wash of cellular machinery inside, all mixed together and touching, and sharing the same
environment. This worked, certainly. Life chugged along this way for nearly half
of the history of life on earth. But then, 1.8 billion years ago, something
remarkable happened. Something that led to a tremendous shift in
the scope and complexity of life. Something we should all be grateful for because,
without that leap, we would not exist. Cells started to…contain cells. Now this isn’t generally how it’s talked
about in science class. There you hear that Eukaryotes have quote
“membrane-bound organelles.” These are areas of the cell that are separated
from the rest of the cytoplasm by membranes, just as the cell itself is separated from
the rest of the universe by its membrane. It turns out, different activities require
different conditions, and these cells within cells allow for those different conditions. That, in short, is the secret of Eukaryotic
success. But how did it happen? Well, over decades of study we have determined
something shockingly peculiar. Something so odd that it makes us kind of
mad that we now discuss it as if it isn’t the miracle it is. 1.8 billion years ago, a cell consumed another
cell…but then it didn’t digest it…it let it reproduce inside of it, and they lived
together, and, over time, became the same organism. Or did they? This is what we call “Endosymbiotic Theory.” Mitochondrion appeared when the consumed cell
was adapted to live in an oxygen rich environment and chloroplasts appeared when the swallowed
cell was photosynthetic. This idea was deeply controversial when it
was first proposed, but as data have continued to come in, endosymbiotic theory has been
able to explain more and more about the realities we find. For example, that chloroplasts have their
own DNA which they use to create the proteins required for their function. And as we dive deeper into the microcosmos,
it just becomes obvious that this happens. This is Paramecium bursaria, a single-celled
protozoa, that has several hundred algal cells from the genus Chlorella living in its own cytoplasm, making it green. The algae live inside Paramecium bursaria
providing it with fuel in the form of sugar and other substances produced via photosynthesis. And Paramecium bursaria provides protection
for the algae from algae eaters and viruses. P. bursaria is regarded as a predatory protozoa,
it feeds on bacteria, small organisms, and, yes, algae and because of that it’s often
thought that the algae in it are temporary symbionts engulfed by Paramecium bursaria’s feeding
behavior. But in fact, many other protozoa acquire algae
in that manner for temporary use, but that is not the case for P. bursaria; its symbionts
are continuously inherited from generation to generation through cell division. The symbiotic Chlorella guide the Paramecium
to well lit areas, so they can photosynthesize more efficiently. The mutual relationship is extremely beneficial
for the Paramecium. Even when the Chlorella-containing Paramecium cells are put in nutrition-free saline solution they can survive for more than 3 months while cells that didn’t have Chlorella died within a week! This is another single-celled organism with
endosymbiotic algae, it’s a testate amoeba. A kind of amoeba that builds itself a shell. This species, like some kind of sculptural
artist, pulls bits and pieces of mineral from its environment to create these amazing looking
homes. You can see the amoeba extending from the
opening of the shell and you can see the green algae in its cytoplasm. Just like Paramecium bursaria, the algae
use sunlight to produce food sharing it with the amoeba while the amoeba provides protection. Some unicellular organisms don’t need oxygen
for growth, indeed the presence of free oxygen can affect them negatively or even kill them. These organisms are known as anaerobes. Such as this one, Metopus. It is an anaerobic ciliate we find in pond
sediment and it has an endosymbiotic relationship with methanogenic archaea. Now we haven’t talked much on this channel about archeans, but they are the third domain of life, along with bacteria and eukaryotes and, like bacteria, they are prokaryotic. We can’t wait to do our episode on them someday soon. Many of the single-celled eukaryotes living
in anaerobic environments contain symbiotic prokaryotes, some of these prokaryotes are
methanogens, meaning they can use free Hydrogen to generate energy and methane. The advantages of having these symbionts are not fully understood but while Metopus can live without the symbionts they grow faster when they have them. Endosymbiosis occurs in multicellular organisms
as well. This is a freshwater relative of jellyfish
and sea anemones, Hydra! It’s simply stuffed full of algal endosymbionts. We collected this Hydra from a nearby pond
and cultured it in our aquarium. The benefits provided by the symbiotic relationship here have been well documented, with scientists actually tracking how carbon moves from the
environment, into the algea, and then into the hydra, and studies have shown that up
to 69% of the caloric requirements of the hydra is satisfied by its algal symbionts. Nice. So, we see, some organisms temporarily pull
in symbionts, others pass them from generation to generation. Some can survive without them, and some cannot. When we look at the algal cells in P Bursaria,
we’re forced to ask if those cells are part of the organism, or if they’re
simply cells of one species living in the cells of another. If that’s the case, it’s worth asking
whether the mitochondria in you are you at all, or if they are just another extremely successful species of prokaryote that is particularly reliant on its host cell. As we look deeper and deeper down, the line
between organisms is harder and harder to find. Which is why, if you think hard enough you might begin to feel like our cells are more than just ourselves. Thank you for coming on this journey with
us as we explore the unseen world that surrounds…and inhabits us. Journey to the Microcosmos is produced by Complexly, which produces over a dozen shows on YouTube, including Scishow And we wanted to let you know that the SciShow team has just put out a really interesting new episode This year, of course, marks the 50th anniversary of the first time humans walked on the moon. And to celebrate, SciShow made their first documentary. The team traveled throughout the US. I even went to the UK to talk to experts. trying to figure out whether the moon landing was actually a good idea. and they got some really interesting answers, but I won’t spoil them. You can watch the episode at YouTube.com/SciShow or by clicking that link in the description. If you want to see more from our master of microscopes, James check out Jam and Germs on Instagram. And if you want to see more form us, That, my friends, is what that subscribe button is for.

100 Replies to “Where Did Eukaryotic Cells Come From? – A Journey Into Endosymbiotic Theory

  1. I am high as fuck right now and I just realized that our bodies are the universe our cells observe 🤯🤯🤯🤯🤯

  2. Don't believe all these theories about the origins of life. Life has always existed and has no origin. Origin of life can be regarded as infinite years ago. If Earth was created 12 billion years ago, life must have existed way before then.

  3. Cells
    Within cells
    Within cells
    Within cells
    Interlinked
    Within cells interlinked
    Within cells interlinked
    Within cells interlinked

  4. I always wondered if there were cells living in cells like how we have trillions of cells does each cell have trillions of cells and so on

  5. make sense …………………..to think that a super organism like the human body have evolved every single one of it's funtions by it's own is hard to even compute

  6. We can make some comparisons with human's businesses, as conglomerates, vertically or horizontally merged, simple companies, family companies, occasional associations… and keep coming to mind that human didn't not really invent those concepts. That kind of comparison might help to choose the right vocabulary for the living world at all levels.

  7. So I'm wondering, what is a single organism? From the very small to the very big, like the impressive fungi in Oregon, identity in the sense we usually mean it, is to be put into question.

  8. I'm curious, how sped up is the footage used for some of this? I'm just curious to the actual speed of some cells in specific shots…

  9. When you think about it… A human is really just a number of different organisms that live inside of one animal made entirely of skin.

  10. Keep wondering and asking, yet never finding. Observe and yet misunderstand what you find.
    Life as an accident is not reality, so stop the fiction and thank God for your curiosity and for his incomprehensible creation of life.

  11. The lines between unicellular organisms is blurred indeed, but for organelles, most biologists take the easy route: if I can take it out and it works just fine (thrives on it's own), it was an endosymbiont, maybe very early stage of plastid. If it can't do anything or dies, even provided the same environment as in the cell (minus the DNA stored in the nucleus) it was cellular machinery.
    Mitochondria and chloroplasts stored so much of their genome inside their cells nuclei that they ceased to be individual organisms. But we can put back some of their genes to transform them back into bacteria, which was already done.

    So, yes, our mitochondria are part of US, because they can't live without us, in the very real way that when you take them out, you're disrupting their genome. Doesn't happen with early endosymbionts like the Chlorella, because they have everything important still inside them.

  12. Your consciousness is just a way to feed your lazy cells

    WE ARE ALL SLAVES TO OUR CELLS! WE NEED TO UPLIFT THE SYSTEM

  13. I love the pronunciation/tone/flow of the Speaker …a model , images are just a piece of art ,
    thanks for sharing the Knowledge .

  14. Love the show. Keep it coming! The scientific accuracy and ability to make myself question my own existentialism is simply brilliant! Well done indeed!

  15. I'm not against the more slow and chill narration but that seems like a bit of overkill. Seems like Hank is pretending to be and old man.

  16. Life begun 3.5 billion years ago? How did you know that? And how did life begin? What happened? Imagination or reality?

  17. This channel is awesome! However I would like less sophisticated information throughout the whole video or put another way maybe add some more information as it relates to us in our daily lives. Such as where would we see these organisms around us. Are they in our backyard, our food, the water we drink, in our cars, inside of us??? Furthermore how did it get there and how do they keep surviving if we keep cleaning or destroying them in our living areas.

  18. i heard about this channel awhile ago on the pod but i'm binging it now because i saw john's most recent video where he mentions it in relation to the cold that he has, and i also have a cold right now so it seemed fitting to watch now

  19. Why is that so amazing, that one thing ate another and the thing in the stomach lived? You do that everyday… …what is really amazing, is my realisation on the origin of "life", that there is no origin. That all things are alive. Doubt that? Do you know how the moon formed? That is right, what Freeman Dyson would call "reproduction"…. oh ya….. And amino acids and enzymes too (I think we will soon find) come on icy commits. But fire and mineral precipitation are also "life" and from there, look out, because actually death was a misnomer/contrived idea too. Because who am I? The trillions of microbes? The cells in my cells? Oh ya…. And they are not going anywhere…. Because actually do you know what they are made of? Right-o star dust…. just like this planet earth….

  20. I love that you guys made this video! When people talk about endosymbiosis, they almost always talk about it as freak events happening in the distant past, which makes it seem sort of speculative. In actual fact, cells living symbiotically inside other cells is incredibly common.

  21. Creepy human shaped resemblance in the bottom left quarter of the screen at 3:12 almost looks like a dark haired person holding their hands together.

  22. I’d say that mitochondria are “us” because we simply cannot live without them. Without the mitochondria, there is no “us”.

  23. Eukaryotic cells are nucleated. What is the proof or even the possible mechanism that allowed the engulfed foreign prokaryotic cell to acquire the circular DNA of the host and create the immensely complicated nucleus with its new DNA that can now duplicate the combined host cell?

  24. As much as I hate Hank's machinegun narration in ScieShow I Lllove his chill talk here. Great job! Very impressive! The mix of the meaning, the music, the voice, and the footage is impeccable!

  25. Interesting how Darwin Religion modesl Evangelism. They both start with statement of faith and cleverly wrap visible reality with unvisible.
    Problem with Darwinism is that it used to compare Ape with human, now it has to compare "created" roll of paper with "random chance molecule" DNA factories and civilization.
    Less people buying that. Even carefully selected right brain dead "scientists" feel uneasy these days. I really feel sorry for professional lie tellers , what will their children say when they discover the truth?

  26. Way too much speculation presented as fact……billions of years ago BS…….what we do know as fact is that life is complex and purposeful……clearly designed which requires a designer…….

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