... evolved. (see p33, Fig1.27,Ridge,2001) The intracellular bacterium (the symbiont) was assimilated into the larger host cell; the bacterial partner transferred many bacterial genes to the host's nucleus, which resulted in the loss of independence, and new metabolic properties for the host. In most of these interactions, the larger host protoctist takes into its cells a smaller symbiont, instead of being eaten or killed is used whilst alive as a source of new materials or properties. The most common interaction is between heterotrophic protoctists (forams and ciliates) and algae. The acquisition of chloroplasts, by endosymbiosis was the next innovation for sexual groups of protoctists. This acquisition allowed a switch to autotrophy and once they could photosynthesise they had a abundant energy source (light). It also provided oxygen for aerobic metabolism and new biosynthetic abilities. Chloroplasts were not required from cyanobacterium (primary endosymbiosis which only happened once), but from another eukaryote by a process ...

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