Chapter 25: The Origin and Diversification of Eukaryotes Overview: Shape Changers Because eukaryotes have internal membranes, they can perform a wide variety of tasks that prokaryotes are unable to perform. An example is a Didinium eating a larger Paramecium The cytoskeleton allows the Didinium to change its shape enough to engulf the Paramecium Concept 25.1 Eukaryotes arose by endosymbiosis more than 1.8 billion years ago Endosymbiosis in Eukaryotic Evolution There is now considerable evidence that much protist diversity has its origins in endosymbiosis Endosymbiosis is the process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then organelle in the host cell Mitochondria evolved by endosymbiosis of an aerobic prokaryote