Endosymbiotic Theory
Summary
TLDRThe video script explores the endosymbiotic theory, a scientific explanation for the evolution of eukaryotic cells from prokaryotic ones through symbiotic relationships. It describes how larger prokaryotes engulfed smaller ones, leading to the formation of mitochondria and chloroplasts. The script emphasizes the theory's support from evidence such as separate DNA in organelles and their bacterial-like division, highlighting endosymbiosis as an ongoing process in nature, exemplified by termites' digestive symbiosis.
Takeaways
- 🔬 Scientific theories are explanations supported by evidence, testable, and repeatedly tested.
- 🌿 The endosymbiotic theory explains how eukaryotic cells evolved from prokaryotic ones.
- 🧬 Prokaryotes lack a nucleus and membrane-bound organelles, whereas eukaryotes have these features.
- 🌱 Some prokaryotes could photosynthesize, while others used oxygen to produce energy.
- 🍄 The theory suggests that larger prokaryotes engulfed smaller ones, which then lived symbiotically inside them.
- 🌳 The engulfed bacteria that used oxygen are believed to have evolved into mitochondria.
- 🌞 Bacteria that could photosynthesize are thought to have evolved into chloroplasts.
- 🧬 Mitochondria and chloroplasts have their own DNA, similar to bacterial DNA.
- 📏 The size and division methods of mitochondria and chloroplasts are similar to bacteria.
- 🔍 Secondary endosymbiosis is a concept to explore for understanding other eukaryotic structures and organelles.
- 🐜 Endosymbiosis is not just a historical event; it occurs today, such as in termites that have bacteria to help digest wood.
Q & A
What is the main difference between a scientific theory and a common use of the word 'theory'?
-A scientific theory is an explanation of a scientific event supported by scientific evidence, testable, and tested repeatedly, unlike a common use of 'theory' which might imply an educated guess without the need for empirical evidence.
What does the endosymbiotic theory explain?
-The endosymbiotic theory explains how eukaryotic cells could have evolved from prokaryotic cells through a process where larger prokaryotes engulfed smaller ones, which then lived in symbiosis, eventually leading to the development of membrane-bound organelles like mitochondria and chloroplasts.
What are the key characteristics of prokaryotic cells?
-Prokaryotic cells are characterized by the absence of a nucleus and membrane-bound organelles, unlike eukaryotic cells which have a nucleus and other membrane-bound organelles.
How do mitochondria and chloroplasts relate to the endosymbiotic theory?
-Mitochondria and chloroplasts are thought to have evolved from prokaryotes that were engulfed by larger cells. They are believed to be the remnants of these symbiotic relationships, as they have their own DNA and divide in a manner similar to bacteria.
What evidence supports the endosymbiotic theory?
-Evidence supporting the endosymbiotic theory includes the presence of separate DNA in mitochondria and chloroplasts, the similarity in size to bacteria, and the division patterns that resemble bacterial division.
Why might ancient eukaryotes have had an advantage due to endosymbiosis?
-Ancient eukaryotes likely had an advantage due to endosymbiosis because the engulfed prokaryotes provided additional functions such as energy production through photosynthesis and ATP generation, which could enhance their survival and adaptability.
What is the difference between heterotroph and autotroph eukaryotic cells in the context of the endosymbiotic theory?
-Heterotroph eukaryotic cells are believed to have evolved from engulfing bacteria that used oxygen to produce ATP, leading to the development of mitochondria. Autotroph eukaryotic cells, on the other hand, are thought to have engulfed photosynthetic bacteria, leading to the evolution of chloroplasts, allowing them to produce their own food.
How does the endosymbiotic theory relate to current biological processes?
-The endosymbiotic theory is not only a historical explanation but also relates to ongoing biological processes, as endosymbiosis is still observed in modern organisms, such as termites that have prokaryotes in their gut to help digest wood.
What is secondary endosymbiosis and how does it expand on the endosymbiotic theory?
-Secondary endosymbiosis is a process where a eukaryotic cell engulfs another eukaryotic cell that already contains organelles like mitochondria or chloroplasts, leading to more complex cellular structures and additional layers of endosymbiotic relationships.
How do mitochondria and chloroplasts' DNA arrangements support the endosymbiotic theory?
-The DNA in mitochondria and chloroplasts is arranged in a circular form, similar to bacterial DNA, which supports the theory that these organelles evolved from prokaryotic bacteria that were engulfed and formed symbiotic relationships within larger cells.
Outlines
🔬 The Endosymbiotic Theory
The paragraph introduces the concept of scientific theories, emphasizing that they are evidence-based explanations of scientific events that are testable and have been tested repeatedly. It then delves into the endosymbiotic theory, a favorite theory that explains the evolution of eukaryotic cells from prokaryotic ones. The theory suggests that larger prokaryotes engulfed smaller ones, which then lived symbiotically within them, eventually leading to the development of eukaryotic cells. The paragraph provides a brief overview of prokaryotic and eukaryotic cells, highlighting their differences and similarities. It also sets the stage for the detailed explanation of the endosymbiotic theory in the following paragraphs.
Mindmap
Keywords
💡Scientific Theory
💡Endosymbiotic Theory
💡Prokaryotes
💡Eukaryotes
💡Mitochondria
💡Chloroplasts
💡Symbiosis
💡DNA
💡Secondary Endosymbiosis
💡Termites
Highlights
Scientific theories are explanations supported by evidence and are testable.
Endosymbiotic theory explains the evolution of eukaryotic cells from prokaryotic ones.
Prokaryotes lack a nucleus and membrane-bound organelles.
Eukaryotes have a nucleus and other membrane-bound organelles.
Prokaryotes and eukaryotes share common cellular features like cell membrane and ribosomes.
Prokaryotes existed over 2 billion years ago with variety including photosynthetic abilities.
Endosymbiotic theory suggests some large prokaryotes engulfed and did not digest smaller bacteria.
Engulfed bacteria lived as symbionts, leading to the first heterotroph eukaryote cells.
Some eukaryotes engulfed photosynthetic bacteria, leading to the first autotroph eukaryote cells.
Bacteria that used oxygen evolved into mitochondria, and those using sunlight into chloroplasts.
Nearly all eukaryote cells have mitochondria, while some also have chloroplasts for photosynthesis.
Mitochondria and chloroplasts have their own DNA, similar to bacterial DNA.
The size and division method of mitochondria and chloroplasts are similar to bacteria.
Endosymbiosis is not just historical; it occurs today, such as in termites' digestive systems.
Termites have prokaryotes in their gut that help digest wood.
Endosymbiotic theory provides insights into the evolution of modern eukaryotes from prokaryotes.
Secondary endosymbiosis is a concept to explore for understanding other eukaryotic structures.
Stay curious and explore more about endosymbiosis and its implications.
Transcripts
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There are a lot of amazing theories in science.
General theory of Relativity …Atomic theory…The cell theory.
And one thing we want to point out about a scientific theory is that it’s a lot different
from how you might use the word ‘theory’ in your daily life.
A scientific theory is not an educated guess.
A scientific theory is an explanation of a scientific event supported by scientific evidence---it
must be testable and tested over and over and over again.
And while theories can be changed or even disproven,
you do want to realize there are a lot of
facts behind them.
One of our favorite theories of all time---is the endosymbiotic theory.
We love it, because we just find the events in this theory to be amazing.
The theory gives an explanation for how eukaryote cells could have evolved from prokaryotic
cells that lived in symbiosis.
Prokaryote symbiosis means these organisms lived together.
So just a recap from our intro to cells video: when you think of prokaryote, think of ‘pro’
rhyming with NO.
No nucleus.
No membrane-bound organelles.
Eukaryotes on the other hand---remember “eu” rhymes with “do” and they DO have a nucleus
and other membrane-bound organelles.
Both prokaryotes and eukaryotes ARE cells though---and therefore they do have a few
things in common that cells have including a cell membrane, cytoplasm, ribosomes, and
genetic material.
But just look at these two cell types and you will see that one is WAY more simple.
So what explanation does the endosymbiotic theory provide for how eukaryote cells
could have evolved from prokaryote cells?
A long, long time ago…seriously, a long time---over 2 billion years ago
there were prokaryotes.
Much like there are today.
They had been around for a long time.
Just as there are in many organisms, there was variety in prokaryotes.
Some of these prokaryotes had photosynthetic abilities, which means, they could make their
food using sunlight energy.
These were photosynthetic bacteria.
Some of these prokaryotes were bacteria that had the ability to use oxygen to produce ATP
energy.
And some prokaryotes were larger and could consume others.
Engulfing them.
So obviously, they had to be larger.
The endosymbiotic theory is that some of these large cells engulfed some of these
small bacteria---but instead of those small bacteria getting digested, some of them remained
intact and they actually began to live as symbionts.
That means, they lived together!
This is believed to be the ancestor heterotroph eukaryote cell.
Eventually SOME of these cells engulfed the small bacteria that could do photosynthesis
in addition and there was more living as symbionts.
This is believed to be the ancestor autotroph eukaryote.
Now it’s time to do a little reveal.
We consider the bacteria that used oxygen to produce their own energy to have evolved
into what is now mitochondria.
And the bacteria that use sunlight energy to produce their own food?
Well we consider those to have evolved into what
are now chloroplasts.
It is likely that these ancient eukaryotes had an advantage in their endosymbiosis.
It is also likely that the mitochondria developed first before chloroplasts, because if you
remember from our intro to cells video, nearly all
eukaryote cells have mitochondria.
It’s just that eukaryote cells that can do photosynthesis can have both mitochondria
and chloroplasts.
Now if you remember our beginning about theories, you may be wondering, where are the facts
for this?
We’ll give you a few of the facts.
First, mitochondria and chloroplasts have their OWN DNA!
Yes!
Separate DNA from what is found in the nucleus.
Not to mention that their DNA is arranged in a similar way to prokaryote DNA---specifically,
bacterial DNA.
The size of mitochondria and chloroplasts tends to be similar to the size of bacteria
and when mitochondria and chloroplasts divide---which they can divide all on their own, independently---they
divide in a way that is similar to how bacteria divide.
So the endosymbiotic theory provides an explanation for how modern eukaryotes evolved from prokaryotes.
There’s obviously more questions you may want to explore---for example, what about
some of the other structures and organelles in eukaryotes?
Well keep exploring---secondary endosymbiosis is
a great place to start.
One last thing we want to make sure to emphasize.
Endosymbiosis isn’t just reserved for a theory that explains a past event in ancient
history.
No because endosymybiosis is actually happening today
with many other kinds of organisms.
One of our favorite examples?
The termite!
Yes, termites can have prokaryotes that live in
their gut and help them digest wood.
And without them?
Well let’s just say that digesting wood won’t happen
so well…
Well that’s it for the Amoeba Sisters, and we remind you to stay curious!
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