Endosymbiosis Theory: Fact or Fiction?


 endosymbiosis (1)

To be honest, this theory of endosymbiosis is not a new term I’ve come across. I’ve actually heard about this for a long time, especially in my first semester of UWI studying Biology. But I never really got it, it never clicked in my head, I was a lot like this actually


And now this semester it has come back to haunt me *insert horror music here*


So I decided it was time for me to get this concept fully understood in my head. Now, I’m a very simple person, I like to learn in simple ways. No complicated terms to mess me up, just saying things in layman’s terms. Thank God for this video I found that does just that! Take a look if you like cute, funny drawings and want to grasp the concept of the endosymbiotic theory in no time.


Cute vid right?

What does endosymbiosis mean? If you watched the vid I couldn’t explain it any better than he did. But who was little Jon and little Jim? Well, little Jon was a primitive aerobic bacteria that became engulfed by the host cell (big fat tony) and since their relationship proved to be beneficial to both of them, little Jon became mitochondria. Can you guess what little Jim, the photosynthetic bacteria, became? Chloroplast! That’s right.


Now, am I just supposed to accept this theory as fact? Where’s the evidence? How can I be sure this is true?

Let’s look at three main factors:

  1. DNA

bacteria (1)

Mitochondria and chloroplasts have striking similarities to the primitive bacteria cells. They have their own DNA, which is separate from the DNA found in the nucleus of the cell. And both organelles use their DNA to produce many proteins and enzymes required for their function. Also, the DNA in mitochondria and chloroplasts are circular, not linear as in eukaryotic cells.

       2. Membranes


A double membrane surrounds both mitochondria and chloroplasts, further evidence that each was ingested or engulfed by a primitive host.

3. Reproduction


The two organelles also reproduce like bacteria, replicating their own DNA and directing their own division. Scientists found that the asexual reproduction that occurs in our cells is pretty much similar to the binary fission that happens in the bacteria.

So after all of this, do I understand this theory? Yes, FINALLY!


The evidence is all there and cannot be denied.  I hope my post helps you understand this theory a little bit better!

What about you? Do you think the endosymbiotic theory is fact or fiction?










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