l Chapter 28 l The Origins of Eukaryotic Diversity

General characteristics l Classification criteria –eukaryotes –not animal, plant or fungi

Protist Diversity l The full spectrum of modes of life –from unicellular to multicellular –autotrophic to heterotrophic –asexual to sexual reproduction –pathogenic to beneficial –sessile to mobile

Mobility l How Protists move –flagellum –cilia –pseudopod

Protists l Ingestive (animal-like); ameoba, paramecium, stentor l Absorptive (fungus-like) l Photosynthetic (plant-like); alga, kelp

The Endosymbionic Theory l Mitochondria and chloroplasts were formerly from small prokaryotes living within larger cells (Margulis)

Endosymbiosis Ancestral eukaryotic cell Eukaryotic cell with mitochondrion internal membrane system aerobic bacterium mitochondrion Endosymbiosis l Evolution of eukaryotes –origin of mitochondria –engulfed aerobic bacteria, but did not digest them –mutually beneficial relationship natural selection!

mitochondrion chloroplast Eukaryotic cell with chloroplast & mitochondrion Endosymbiosis photosynthetic bacterium Endosymbiosis l Evolution of eukaryotes –origin of chloroplasts –engulfed photosynthetic bacteria, but did not digest them –mutually beneficial relationship natural selection! Eukaryotic cell with mitochondrion

l Evidence –structural mitochondria & chloroplasts resemble bacterial structure –genetic mitochondria & chloroplasts have their own circular DNA, like bacteria –functional mitochondria & chloroplasts move freely within the cell mitochondria & chloroplasts reproduce independently from the cell Theory of Endosymbiosis Lynn Margulis

Protist Systematics & Phylogeny, I l 1- Groups lacking mitochondria; early eukaryotic link; Giardia (human intestinal parasite; severe diarrhea); Trichomonas (human vaginal infection) l 2- Euglenoids; autotrophic & heterotrophic flagellates; Trypanosoma (African sleeping sickness; tsetse fly)

Protist Systematics & Phylogeny, II l Alveolata: membrane-bound cavities (alveoli) under cell surfaces; dinoflagellates (phytoplankton); Plasmodium (malaria); ciliates (Paramecium)

Protist Systematics & Phylogeny, III l Stamenophila: water molds/mildews and heterokont (2 types of flagella) algae; numerous hair-like projections on the flagella; most molds are decomposers and mildews are parasites; algae include diatoms, golden, and brown forms

Protist Systematics & Phylogeny, IV l Rhodophyta: red algae; no flagellated stages; phycobilin (red) pigment l Chlorophyta: green algae; chloroplasts; gave rise to land plants; volvox, ulva

Protist Systematics & Phylogeny, V l Affinity uncertain: l Rhizopods: unicellular with pseudopodia; amoebas l Actinopods: ‘ray foot’ (slender pseudopodia; heliozoans, radiolarians

Protist Systematics & Phylogeny, VI l Mycetozoa: slime molds (not true fungi); use pseudopodia for locomotion and feeding; plasmodial and cellular slime molds

Protist Diversity l Beneficial & necessary Protists –phytoplankton small algae + diatoms much of the world’s photosynthesis produces ~90% of atmospheric oxygen –zooplankton heterotrophic protists + animals key ecological role at base of marine food web