1. Kingdom Protista

2. Protists About 1.5 billion years old Are EUKARYOTIC organisms
With nuclei and membrane bound organelles
Are unicellular
Some live as individual cells while other live in groups (colonial)
Classification is difficult because they have characteristics in common with animals, plants and fungi; about 115,000 species

3. Evolution of Protists
Originally protists were thought to have evolved from prokaryotic cells that evolved nuclei

4. Endosymbiont Hypothesis
Lynn Marguilis (biologist) instead suggested that the first eukaryotic cell was formed by symbiosis among several prokaryotes (living together in close association)
Ie. Organelles in protists resemble monerans (eg. Mitochondria and chloroplasts resemble bacteria)

5. It is believed that prokaryotes started living within another prokaryote – both benefited from the relationship and eventually they could not live without one another. This gave rise to organelles in eukaryotes

6. Thus, organelles in eukaryotic cells probably evolved from symbiotic prokaryotes that lived inside a host cell (Endosymbiont Hypothesis)

7. Video