First

First, according to our text book, the endosymbiotic theory was first thought of by Lynn Margulis. Endosymbiotic theory is the theory that ancestors of mitochondria and chloroplasts were bacteria that was living within other cells in a double sided beneficial partnership. The intracellular bacteria in this double sided beneficial partnership is called an endosymbiont. Over a period of time, each partner became absolutely necessary to each other to function. The endosymbiont eventually lost key features like the ability to replicate independently and the loss of its own cell wall. (Anderson, D. G., et al. 2016)
Now I’ll give you some evidence endosymbiosis. According to WordPress.com, the endosymbiotic theory is a thought that mitochondria and chloroplasts were once bacteria entering a eukaryotic cell by endocytosis to form a relationship with each other. I will describe a few common characteristics and abilities between the bacteria and these organelles, mitochondria and chloroplast, that will show strong evidence that this endosymbiotic theory is correct. (WordPress)
Something else that shows a close the relationship between bacteria, the mitochondria and chloroplast is the similarities they share with how each one functions. Purple aerobic bacteria and the mitochondria share extremely close similar characteristics. Oxygen is used in the making of ATP for purple aerobic bacteria as well as in the mitochondria. They both utilize the Krebs Cycle and oxidative phosphorylation by using oxygen to create more and more ATP. The chloroplasts also show characteristics that very much resemble photosynthetic bacteria. Both chloroplasts and photosynthetic bacteria have similar chlorophyll that use light energy to turn into chemical energy. (WordPress)
These organelles and bacteria also are similar in a size perspective. Chloroplasts, mitochondria, and prokaryotes size can be anywhere from one micron to even ten microns. If the chloroplasts, mitochondria, and prokaryotes sizes were all over the place like one being one micron and a different one being fifty microns, the endosymbiotic theory would look as if it were false because it’s something that would make them less related to each other. (WordPress)
Another good piece of evidence that helped in supporting endosymbiosis was the debate if the mitochondria and chloroplasts have their own DNA or not and if these organelles in fact did have their own DNA, to see if this DNA resembled the DNA in bacteria. This was found to be true for ribosomes, chlorophyll, protein synthesis, DNA, and RNA. (WordPress) Chloroplasts, and mitochondria both carry genetic information that is necessary for their function. This also includes genes for certain ribosomal proteins and ribosomal RNAs that make their 70S ribosomes. These ribosomes differ from the typical 80S ribosomes that characterize eukaryotic cells which are in fact equivalent to the bacterial 70S ribosomes. (Anderson, D. G., et al., 2016). Both of these organelles’ DNA divides independently within the eukaryotic cell. This ground of independence by dividing on their own separately from the other organelles in the eukaryotic cells shows that they are indeed not very related to some of the organelles of a eukaryotic cell and because they are not related, it seems even more right that the mitochondria and chloroplasts could have once been prokaryotic cells from bacteria that entered a eukaryotic cell by endocytosis to form this symbiotic relationship that they share. (WordPress)
Some more logic evidence that seems to really help us to think that the endosymbiotic theory is in fact correct is that both of these organelles, mitochondria and chloroplasts, have a double phospholipid bilayers. It is thought that this happened when the mitochondria and chloroplast was coming as bacteria and entering a eukaryotic cell by endocytosis. You’re probably thinking that photosynthetic bacteria, resembling chloroplast, and purple aerobic bacteria, close to resembling the mitochondria, only have one phospholipid bilayer. This is correct but when either photosynthetic bacteria or purple aerobic bacteria use endocytosis to enter another cell, it forms a bond with a vesicle and forms the second layer to their double phospholipid bilayer. (WordPress)
As you can see, there is significant amount of evidence that I provided to show that endosymbiosis does indeed exists.