Where Did Eukaryotic Cells Come From?
Summary
TLDRThe video script explores the pivotal moment 1.8 billion years ago when a cell consumed another cell and didn't digest it, leading to the emergence of eukaryotes through endosymbiosis. It delves into the symbiotic relationships between organisms like Paramecium bursaria and Chlorella algae, and the benefits of such alliances, including survival and energy production. The script challenges viewers to reconsider the boundaries of what constitutes an organism and ponders the nature of our own mitochondria.
Takeaways
- 🌿 Life on Earth began with prokaryotes, simple unicellular organisms, over 3.5 billion years ago.
- 🔬 A significant evolutionary leap occurred 1.8 billion years ago with the emergence of eukaryotes, which contain cells within cells.
- 🤔 The Endosymbiotic Theory suggests that eukaryotes evolved when one cell engulfed another but didn't digest it, leading to a symbiotic relationship.
- 🌱 Chloroplasts and mitochondria are examples of organelles that may have originated from endosymbiotic events with photosynthetic and oxygen-using bacteria, respectively.
- 🐠 Paramecium bursaria is a single-celled organism that hosts algal cells, illustrating a modern example of endosymbiosis where both parties benefit.
- 🌳 Algae within Paramecium bursaria provide energy through photosynthesis, while the organism offers protection, showcasing a mutualistic relationship.
- 🦠 Anaerobic organisms like Metopus, an anaerobic ciliate, have endosymbiotic relationships with methanogenic archaea, which can produce energy without oxygen.
- 🌈 Multicellular organisms like Hydra also exhibit endosymbiosis, with algal cells providing significant nutritional support.
- 🧬 The presence of algal cells within P. bursaria raises philosophical questions about the definition of an organism and the nature of life.
- 🔬 The study of endosymbiosis challenges traditional views of organism boundaries and suggests a more interconnected understanding of life.
Q & A
When did life on Earth first emerge according to the transcript?
-Life on Earth first emerged at least three and a half billion years ago as prokaryotes.
What significant event occurred 1.8 billion years ago in the history of life on Earth?
-A significant event that occurred 1.8 billion years ago was the beginning of endosymbiosis, where cells started to contain other cells.
What is the term for cells within cells in eukaryotes?
-The term for cells within cells in eukaryotes is 'membrane-bound organelles'.
What is the 'Endosymbiotic Theory' as mentioned in the script?
-The 'Endosymbiotic Theory' is the idea that certain organelles of eukaryotic cells, such as mitochondria and chloroplasts, originated from endosymbiotic events where one cell was taken up by another and both lived together.
How did mitochondria and chloroplasts come into existence according to the endosymbiotic theory?
-According to the endosymbiotic theory, mitochondria appeared when a cell adapted to live in an oxygen-rich environment was consumed but not digested, and chloroplasts appeared when a photosynthetic cell was swallowed and similarly not digested.
What is an example of a single-celled organism that has endosymbiotic algae?
-Paramecium bursaria is an example of a single-celled organism that has endosymbiotic algae, specifically Chlorella, living within its cytoplasm.
What benefits do the Chlorella algae provide to Paramecium bursaria?
-The Chlorella algae provide Paramecium bursaria with fuel in the form of sugar and other substances produced via photosynthesis.
How long can Paramecium bursaria with Chlorella survive in a nutrition-free saline solution?
-Paramecium bursaria with Chlorella can survive for more than 3 months in a nutrition-free saline solution.
What is the relationship between Metopus and methanogenic archaea?
-Metopus, an anaerobic ciliate, has an endosymbiotic relationship with methanogenic archaea, which can use free hydrogen to generate energy and methane.
What benefits do the algal endosymbionts provide to Hydra?
-The algal endosymbionts provide up to 69% of the caloric requirements of Hydra through photosynthesis.
What philosophical question does the script raise about the nature of organisms and their components?
-The script raises the philosophical question of whether the cells within an organism, such as the mitochondria in humans, are truly part of the organism or if they are separate entities that are simply reliant on the host cell.
Outlines
🌿 The Birth of Eukaryotes and Endosymbiosis
This paragraph delves into the pivotal moment in Earth's history when prokaryotes, simple unicellular organisms, underwent a transformative event 1.8 billion years ago. The narrative explains how these early cells began to contain other cells, leading to the emergence of eukaryotes. The 'Endosymbiotic Theory' is introduced, which posits that a cell consumed another cell but allowed it to reproduce within, eventually leading to a symbiotic relationship. This theory is exemplified by the development of mitochondria in oxygen-rich environments and chloroplasts in photosynthetic cells. The paragraph also discusses the controversial nature of this theory and how it has been supported by evidence such as the unique DNA of chloroplasts. It concludes with examples of endosymbiosis in single-celled organisms like Paramecium bursaria, which houses algal cells that provide it with nutrients and in return receive protection, highlighting the mutual benefits of such relationships.
🐠 Endosymbiosis in Diverse Organisms
The second paragraph explores the prevalence of endosymbiosis across various organisms, including anaerobic unicellular organisms like Metopus, which form symbiotic relationships with methanogenic archaea. It touches on the lesser-known domain of life, the archaea, which are prokaryotic like bacteria but distinct in their own right. The paragraph also discusses the benefits of endosymbiosis for organisms like Hydra, a freshwater relative of jellyfish and sea anemones, which rely heavily on algal endosymbionts for up to 69% of their caloric needs. The narrative ponders the blurry lines between different organisms and the concept of identity within a cell, challenging the viewer to consider whether components like mitochondria are truly part of an organism or independent entities. The paragraph ends with a call to subscribe for more content and a plug for SciShow's documentary on the moon landing's 50th anniversary.
Mindmap
Keywords
💡Prokaryotes
💡Eukaryotes
💡Endosymbiotic Theory
💡Mitochondria
💡Chloroplasts
💡Paramecium bursaria
💡Anaerobes
💡Hydra
💡Symbiosis
💡Methanogens
Highlights
Life on Earth began with prokaryotes, simple unicellular organisms, around 3.5 billion years ago.
A major evolutionary leap occurred 1.8 billion years ago with the emergence of cells containing cells, leading to more complex life forms.
Eukaryotes, cells with membrane-bound organelles, allow for different conditions necessary for various cellular activities.
The Endosymbiotic Theory suggests that mitochondria and chloroplasts originated from endosymbiotic events.
Chloroplasts have their own DNA, which is used to produce proteins essential for photosynthesis.
Paramecium bursaria, a single-celled protozoa, hosts algal cells that provide it with photosynthetic products in exchange for protection.
The symbiotic relationship between Paramecium bursaria and Chlorella algae is hereditary and mutually beneficial.
Testate amoebae, a type of amoeba, also have endosymbiotic algae that produce food and share it while receiving protection.
Anaerobic organisms like Metopus form endosymbiotic relationships with methanogenic archaea for energy production.
Multicellular organisms such as Hydra also engage in endosymbiosis with algae, with significant nutritional benefits.
Endosymbiosis can be temporary or hereditary, and some organisms are entirely dependent on their symbionts for survival.
The line between different organisms blurs as endosymbiosis challenges traditional views of individual organisms.
The mitochondria within our cells might be considered as separate prokaryotic species that are highly reliant on their host.
Our cells may contain more than just 'ourselves,' suggesting a complex ecosystem within our own bodies.
Journey to the Microcosmos is produced by Complexly, which also produces SciShow and other educational YouTube series.
SciShow has released a documentary for the 50th anniversary of the moon landing, exploring whether it was a good idea.
James, the master of microscopes, can be followed on Instagram for more fascinating microscopic insights.
Transcripts
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.
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