Prokaryotic symbionts yielded eukaryote

There were new processes and structures in the world when protists first developed.  These included the membrane-enclosed nucleus; mitochondria; endomembrane system; chloroplasts;cytoskeleton;9-2 flagellates; linear DNA with multiple chromosomes wrapped around proteins; and diploid stages, meiosis, mitosis, sex.

The prokaryotes meanwhile struggled more so than in the beginning;  their small genome would limit the number of genes coding for metabolic activity.  The more genes the greater a chance at surviving.

Possible trends probably related to the development of endosymbiosis

1. multi-cellular prokaryotes (division of labor in cyanobacteria).
2. bacterial communities (interspecies metabolic product transfers aid each colony).
3. the sucking-in of the plasma membrane, also called in-folding of the membrane to form the endomembrane system.

So it is hypothesized that the prokaryotes were ingested by larger prokaryotes and these ingested prokaryotes formed the important organelles:  mitochondrion and chloroplast.
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a photosynthetic (possible cyano-bacteria) or aerobic heterotrophic (possibly undigested organism or parasite) prokaryote exists first outside and independent of another larger prokaryote. the smaller prokaryote enters the larger for any number of reasons: example, a world with more oxygen would make having another aerobe releasing free oxygen an advantage over other organisms because it would be a self-supporting powerhouse. the photosynthetic prokaryote develops into a chloroplast; its pure function to store energy.  The aerobic heterotroph develops into a mitochondrion; its soul purpose to release the stored energy.

What supports this theory?

1. size:
   mitochondria and chloroplasts are about the size of bacteria.
2. DNA:
   mitochondria and chloroplasts have circular DNA and do not undergo mitosis but binary fission like bacteria.
3. Proteins:
   mitochondria and chloroplasts have similar transport and membrane proteins to bacteria.
   mitochondria and chloroplasts have their own tRNA and ribosomes to translate their mRNA into protein.
4. Ribosomes specifically:
   in mitochondria and chloroplasts, these are closer in size, biochemistry, and antibiotic sensitivity to bacteria than eukaryotes.
   M- and CrRNA base sequences more closely look like those of eubacteria rRNA than the ribosomal RNA in the cytoplast.
5. Protist Diversity:
   the large amount of sexual divergence between members of Protista implies experimentation at such a stage of life.

Next:  "Archaezoa."