MadSci Network: Evolution

Re: Are there two different evolutions; one for plants and one for animals?

Date: Sat Nov 20 16:49:56 1999
Posted By: Andrew D. Brabban, Faculty, Biology, The Evergreen State College
Area of science: Evolution
ID: 942673101.Ev

This question has been clarified over the last few years by 2 things; the 
identification of the Archaea and the acceptance of the endosymbiont 
theory. About 20 years ago through the study of a type of RNA present in 
all cells, the 5 kingdom system 4 of which were eukaryotic was shown not to 
be a valid model (Animals, plants, protists and fungi, the 5th being 
prokaryotes). Nowadays no scientist uses the 5 kingdom system and instead 
we use the 3 kingdom (domain) system (Eukaryotes, Bacteria and Archaea). 
These techniques were then applied to consider the mitochondria and 
chloroplast, the major difference between plant and animal cells and the 
endosymbiont theory was born. According to this theory, a larger prokaryote 
(bacteria or Archaea) (or perhaps early eukaryote (animals, plants fungi 
and algae)) engulfed or surrounded a smaller prokaryote some 1.5 billion 
years ago.  Instead of digesting the smaller organism the large one and the 
smaller one entered into a co-operative relationship (symbiosis), where 
both organisms benefited and neither was harmed. The larger organism gained 
excess ATP (energy) provided by the "protomitochondrion" and excess sugar 
provided by the "protochloroplast", while providing a stable environment 
and the raw materials the endosymbionts required. Over millions of years 
the two organisms became so the same that they are now one. They are so 
dependant today that eukaryotic cells cannot survive without mitochondria 
(likewise photosynthetic eukaryotes (plants) cannot survive without 
chloroplasts), and the endosymbionts can not survive outside their hosts. 
Nearly all eukaryotes have mitochondria. What other evidence survives to 
support the theory. Well the mitochondrion and chloroplast have their own 
DNA (this is very similar to that in bacteria and cyanobacteria), own 
ribosomes, thay react to toxins like bacteria, and finally divide just like 

If you would to know more and see some explanatory diagrams go to my course 

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