The Kingdom Protista

What is a Protist? Eukaryotic Most are unicellular May include more than 200,000 species Protists are everything the other kingdoms are not – they are not animals, plants, fungi, or prokaryotes

Evolution of Protists – Endosymbiont Theory Protists were first eukaryotic organisms on Earth Endosymbiont Theory – theory that eukaryotic cells formed from a symbiosis among several different prokaryotic organisms Mitochondria, chloroplasts, cilia, and flagella, all began as endosymbionts Both host and endosymbiont benefited from the relationship Eventually, the endosymbionts lost ability to live on their own and became organelles.

Evolution of Protists – Endosymbiont Theory (continued) Evidence? Cyanophora paradoxa, protist whose “chloroplasts” are actually blue-green bacteria that can be removed and can live on their own. Present-day eukaryotic cells may be descended from more than one organism.

Classification of Protists Biologists do not agree on how best to classify protists Obtain nutrition many protists that are heterotrophic considered “animal-like” other protists that are autotrophic are considered “plant-like” external digestion (decomposers or parasites) are considered “fungus-like” These are artificial categories!! Likely to be reclassified as more research is done on protists

How Protists are Classified are classified by Animallike Funguslike Plantlike which include which which which Parasites Take in food from the environment Produce food by photosynthesis Obtain food by external digestion Decomposers