The Theory of Symbiosis

 

The theory of symbiosis is a theory of evolution that seeks to show how the prokaryotic organisms developed from eukaryotic cells. It proposes that this development took place following the symbiosis of the organelles that distinguished the eukaryote cells (Martin, Garg & Zimorski, 2015). This theory further states that mitochondria, plastids, and other organelles that seem to have undergone endosymbiosis while they were essentially prokaryotes that essentially were free-living. A result of this situation is that mitochondria seem to be related to Rickettsialles proteobacteria, and plastids such as chloroplasts seem to be related to nitrogen-fixing filamentous cyanobacteria. One of the biggest supporting evidences concerning the theory of symbiosis is that new mitochondria tend to form only through binary fission, and this is especially considering that cells cannot create new plastids. Moreover, the theory suggests that porins, which are essentially transport proteins, can be found in the outer membranes of bacterial cell membranes, mitochondria, and chloroplasts; showing a common origin of these organisms. Finally, evidence shows that some mitochondria and plastids have certain DNA molecules that are extremely similar to the DNA contained in bacteria; further advancing the theory of symbiosis (Morelli & Rosano, 2016).

Weaknesses

One of the most significant weaknesses of this theory is the claim stating that circular mitochondria DNA is similar to the binary fusion found in bacteria. An important difference is that the most pertinent components tend to be more eukaryotic in form than prokaryotic, which is in addition to the fact that replication is different between mitochondrial DNA and bacterial DNA. Moreover, despite their being enclosed in a double membrane, the structures of bacteria and mitochondria are essentially different and this is to such an extent that when antibiotics are administered, they end up in a situation where they are better able to distinguish between the mitochondrial and bacterial membranes (Harish & Kurland, 2017). This is an important factor because it shows that membranes are structurally different, meaning that the theory of symbiosis is disproved. One of the biggest arguments made by proponents of the symbiotic theory is that mitochondria and bacteria share similar characteristics, especially when it comes to size and shape. However, findings show that mitochondria have more of a bacillus shape and are not spherical as initially assumed.

Strengths

The biggest strength of the theory of symbiosis is that it advances the theory of evolution. This is especially considering that it advances the theory, proposed by Charles Darwin, of natural selection. The symbiotic relationship between cells and organisms seems to have played a role in the evolution of diverse organisms because many of them ended up coming together to advance certain characteristics. The theory of symbiosis also shows that organisms, which developed as a result of the symbiotic relationship, ended up in a situation where they not only grew apart, but in some instances came together in order to ensure their own survival (Booth, 2014). Only the strongest were able to make sure that they passed on their DNA to future generations, while at the same time advancing a situation where they either out-competed other species, or were able to avoid extinction.