01/11 9th Protist Evolution

What's the difference between a bacterium and a simple protist?Were simpleprotiststhe first eukaryotic organisms to evolve? Probably. A protist is a eukaryote, so each cell has anucleus. Otherwise, simple protists, like the Paramecium and amoeba, can be fairly similar tobacteria.Evolution ofProtistsScientists think that protists are the oldest eukaryotes. If so, they must have evolved from prokaryoticcells. How did this happen? Theendosymbiotic theoryprovides the most widely-accepted explanation. That’s because it is well supported by evidence.The First EukaryoticCellsAccording to the endosymbiotic theory, the first eukaryotic cells evolved from asymbiotic relationshipbetween two or more prokaryotic cells. Smaller prokaryotic cells were engulfed by (or invaded) larger prokaryotic cells. The small cells (now calledendosymbionts) benefited from the relationship by getting a safe home and nutrients. The large cells (now calledhosts) benefited by getting some of the organic molecules orenergyreleased by the endosymbionts. Eventually, the endosymbionts evolved intoorganellesof the host cells. After that, neither could live without the other.As shown inFigurebelow, some of the endosymbionts were aerobicbacteria. They were specialized to break down chemicals and releaseenergy. They evolved into themitochondriaof eukaryotic cells. Some of the small cells were cyanobacteria. They were specialized forphotosynthesis. They evolved into the chloroplasts of eukaryotic cells. SummaryScientists think that protists are the oldest eukaryotes.Protists most likely evolved from prokaryotic cells, as explained by the endosymbiotic theory. This theory is well-supported by evidence.Review:Answer the following questions in the space provided below:How did the first eukaryotic cells evolve, according to endosymbiotic theory?Identify two pieces of evidence for endosymbiotic theory. Explain how this evidence supports the theory.How are additional mitochondria produced?