1. Protists The Unicellular Eukaryotes

2. Some Basics:  200 000 species  difficult to classify  no “ typical ” protist  most aquatic, some terrestrial  only characteristic that all protists share is that they are not animals, plants or fungi  most single-celled  Binary fission and conjugation

3. Metabolism - can be parasitic/pathogenic - parasites * sleeping sickness * malaria Examples: - Amoeba - Sporozoans - ciliates like Paramecium - most are decomposers - prefer cool, damp habitats Examples: - Molds (water, slime) - single- celled (vs. multicellular fungi kingdom) - contains chlorophyll - photosynthesize Examples: - Euglena – unicellular, flagellates, heterotrophic at night - Algae – single-celled, colonies, multicellular (Note: responsible for 50-75% of all photosynthesis on Earth) PROTISTS HeterotrophicAutotrophic Plant-likeFungus-likeAnimal-like

4. Origin of Eukaryotes  First eukaryotic organism thought to have evolved about 1.5 billion years ago. Prokaryotes are as old as 4 billion years  Protozoans (protists) possibly evolved from the 1st eukaryotes by Endosymbiosis  Endosymbiosis – often one prokaryote lives inside another becoming dependent upon each other

5. Endosymbiosis wha???  Endo = "within“  Endocytosis = (cyto = cell) a process of 'cell eating' - cells are engulfed, but then usually digested as food....  Endosymbiosis = cells are engulfed, but not digested...cells live together in a mutually benefiting relationship, or symbiosis

6. Origin of Eukaryotes  Eukaryotic cells more complex than prokaryotic cells:  Membrane-bound nucleus and organelles  Many chromosomes that occur in pairs.  Protists, fungi, plants & animals are composed of eukaryotic cells.

7. Infolding of membrane system forming nucleus and ER Origin of Eukaryotes Endomembrane infolding

8. Origin of Eukaryotes: Cholorplasts and Mitochondria  Mitochondria and chloroplasts (endosymbionts) were prokaryotes that invaded larger cells (host cell)  Mitochondria provided energy for the host cell and chloroplasts converted solar energy into molecular energy  Endosymbiont, ancestral mitochondria:  Aerobic, heterotrophic & prokaryotic  Endosymbiont ancestral chloroplasts:  Anaerobic, autotrophic and prokaryotic

9. Origin of Eukaryotes  Ancestral chloroplasts were photosynthetic, prokaryotes that became endosymbionts (cyanobacteria)  Relationship began as parasitic or undigested prey  Assumed here that endomembrane infolding evolved first, i.e., cell already evolved nucleus, ER, …

10.  See separate slide show

11. Scientific Evidence for Theory of Endosymbiosis  Membranes of chloroplasts and mitochondria are similar to those of living prokaryotes  The ribosomes found in these organelles are more similar to prokaryotic ribosomes than to ribosomes found in eukaryotes  These organelles reproduces by binary fission within the cell  Each organelle contains a circular chromosome and gene sequences match those of living prokaryotes

12. Work  Please read p60-66  Please complete p67 #2,3,4