There is a theory that eukaryotic organisms originated from the evolution of single-celled prokaryotic organisms.
This theory is called endosymbiosis which can explain the proposed acids of organelles in eukaryotes such as mitochondria and chloroplasts.
Endosymbiotic Theory Definition
Endosymbiotic theory explains that some organelles of eukaryotes are derived from a symbiosis between separate single-celled organisms. According to this theory, mitochondria and plastids (e.g. Chloroplasts), and other possible organelles, represent free-living bacteria taken inside other cells as endosymbions. Molecular and biochemical evidence suggests mitochondria were developed from Proteobacteria and chloroplasts from cyanobacteria.
An endosymbiont is any organism that lives in the body or cells of another organism, i.e. forms endosymbiosis (Greek: endon “deep”, syn “together” and biosis “live”).
Endosymbiont theory is a theory that eukaryotic cells (animal, plant and human cells) were formerly derived from primitive prokaryotic cells (photosynthetic bacteria) that were ‘eaten’ by large prokaryotic cells (in this case archaea). Endosymbiont itself is derived from the word ‘endosymbiosis’ which refers to a symbiotic relationship between two or more cells in which one of them lives in the cell of its partner.
Photosynthetic bacteria that live in the body archaea establish mutually beneficial relationships with each other until it eventually develops and becomes the forerunner of the emergence of eukaryotic cells.
In short, this theory assumes that humans, animals and plants were the result of the evolution of primitive bacteria. What do you guys respond to after you know this? It’s kind of hard to believe for sure.
Endosymbiosis theory background
Endosymbiont theory is actually a concept that has been formulated for quite a long time, first in 1883 by a German scientist named Andreas Schimper. He hypothesized that chloroplasts are actually cyanobacteria that live in cells. The Schimper hypothesis were further investigated by Russian botanist Konstantin Mereschkowski who also suggested that chloroplasts were siybionts living in plant cells.
It’s just that this research stagnated and was forgotten for almost a century, until in 1967 the endosymbiont theory was known and accepted by a scientific audience thanks to the writings published by the American biologist Lynn Margulis.
This theory developed further by Lynn Margulis was also initially less attention-grabbing and often ridiculed by scientists. But gradually this theory was finally accepted and studied further by biologists to find out how the mechanism of evolution occurred so as to produce multicellular living things such as animals, plants and humans.
Margulis sought an alternative idea of the origin of eukaryotic cells, establishing that this was based on the prokaryotic union of progressive cells, in which one phagocytic cells to another, but instead of digesting them, made them part of it. This will give rise to the various organelles and structures of the current eukaryotes. In other words, it talks about endosymbiosis, one cell inserted into the inside of another cell, gaining mutual benefit through symbiotic relationships.
Endosymbiotic theory describes this gradual process in three consecutive large additions.
#1. First merge
In this step, cells that use sulfur and heat as a source of energy (thermoacidophilic arc) are joined by swimming bacteria (Espiroqueta). With this symbiosis, the ability to move some eukaryotic cells will begin thanks to the flagellum (how spe**rm) and the appearance of nuclear membranes, which provide greater DNA stability.
Archaea, although prokaryotes, are different domains of bacteria, and evolutionarily it has been explained that they are closer to eukaryotic cells.
#2. The second merger
Anaerobic cells, which oxygen is increasingly abundant in the toxic atmosphere, need help to adapt to new environments. The second composed merger is the unification of aerobic prokaryotic cells inside anaerobic cells, explaining the appearance of peroxysome and mitochondrial organelles. The first has the ability to neutralize the toxic effects of oxygen (especially free radicals), while the second gets oxygen energy (respiratory chain). With this step, eukaryotic cells of animals and fungi will have emerged.
#3. Third merger
The new aerobic cells, for some reason, perform endosymbiosis with prokaryotic cells that have the capacity of photosynthesis (obtain energy from light), thus giving rise to plant cell organelles, chloroplasts. With this latest addition, there is the origin of the plant kingdom.
In the last two additions, introduced bacteria will benefit protection and obtain nutrients, while hosts (eukaryotic cells) will each gain the ability to utilize oxygen and light, respectively.