Question

Supposedly, much of protist diversity is the rest of endosybiosis. Please explain that process in detail, including the evidence that the theory is plausible

Answer 1

The micro fossils discovered in the rocks more than 3.5 billion years old were the single celled prokaryotic organisms resembling the modern bacteria. These must have evolved in absence of oxygen. Over time, photosynthetic organisms might have evolved increasing the concentration of oxygen in the atmosphere. This has caused some organisms to extinct because they could not tolerate the high oxygen levels and some organisms to develop more effective metabolic pathways to metabolize the oxygen.

The prokaryotic cells evolved earlier were started to develop internal membranes some 2 billion years ago, due to which the evolution of eukaryotic cells had took place. The eukaryotic organelles like mitochondria and chloroplast resemble the prokaryotic cells. This has happened due to establishment of symbiotic relationship between prokaryotes that entered the eukaryotic cells. Thus, endosymbiotic theory states that the eukaryotic cells are produced from living communities formed by prokaryotic organisms.

The endosymbiotic hypothesis emphasizes that the mitochondria arose from the stable incorporation of aerobic bacterium in to other cells and the chloroplasts arose from incorporation of a cyanobacterium like organism performing the oxygenic photosynthesis. Thus, the physiology and metabolism of mitochondria and chloroplast along with their structure and sequence of genomes support the endosymbiotic hypothesis. The prokaryotic organisms, the mitochondria and the chloroplast contain 70S type of ribosomes and their 16S ribosomal RNA sequence is similar and characteristic to bacteria.