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THE PROTISTS

THE PROTISTS. Great Diversity. Unicellular to multicellular Colonial - Volvox Autotrophs to heterotrophs Mixotroph - Euglena Asexual to sexual reproduction Sessile to motile. Paramecium with food vacuoles stained red. Amoeba ingesting a Paramecium. Protist Diversity.

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THE PROTISTS

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  1. THE PROTISTS

  2. Great Diversity • Unicellular to multicellular • Colonial - Volvox • Autotrophs to heterotrophs • Mixotroph - Euglena • Asexual to sexual reproduction • Sessile to motile

  3. Paramecium with food vacuoles stained red Amoeba ingesting a Paramecium Protist Diversity • Animal-like Protists • heterotrophs, predators • Amoeba • Paramecium • Stentor

  4. Protist Diversity • Parasitic & pathogenic Protists • malaria • Giardia • trypanosomes

  5. Protist Diversity • Plant-like Protists • autotrophs, photosynthesis • Euglena • algae • diatoms

  6. Mobility • Cilia & Flagella • Not homologous to those of prokaryotes • Extensions of cytoskeleton • Pseudopods • “false-foot”

  7. Reproduction • Haploid stage is main stage of most protists • Modes of reproduction: • Asexual • Exchange gametes (2n), reproduce asexually • Conjugation

  8. Ecological Importance • Found anywhere there is water • Creep through damp sand and silt • Attach to submerged rocks • Drifting plankton • Phytoplankton are the bases of aquatic food chains • Algal blooms – red tide • Symbionts • Mutualism • Trichonympha • Parasitic • Plasmodium

  9. Euglena – Where does it belong?

  10. The dilemma… • Originally grouped as “mostly” unicellular eukaryotes • Problem: Paraphyletic grouping • Systematists have split protists into many kingdoms. • Now used as an informal term

  11. Endosymbiosis • Organelles were formerly prokaryotes • Led to mitochondria and plastids • Entered as undigested prey or parasite • Mutualism

  12. Paramecium & symbiont Chlorella Evidence of Endosymbiosis • Organelles show similarities with bacteria • Size • Enzymes and transport systems in the inner membrane • Binary fission • Single circular DNA & RNA • Mitochondria lacks histones like prokaryotes • Ribosomes resemble those of bacteria

  13. The Chimera • Made up of prokaryote parts • Closest living prokaryotic relative? • rRNA analysis • Mitochondria – proteobacteria • Plastids – cyanobacteria • Not genetically self-sufficient • Genes for some of its proteins are in cell’s nucleus • Proteins in the organelle are chimera of polypeptides encoded in organelle & nucleus DNA • Hypothesis: endosymbionts transferred DNA to host genome (transformation)

  14. Secondary Endosymbiosis

  15. Secondary Endosymbiosis • Plastids are scattered throughout phylogenetic tree of eukaryotes • Differ in the number of membranes • Plastids were acquired independently several times during the early evolution of eukaryotes • Two waves: • Primary endosymbiont – cyanobacteria • Secondary endosymbiont – algae containing plastids • Evidence: • Cryptomonad algae – plastids contain remnants of nucleus, and ribosomes

  16. “Web”of Life • Eukaryotes evolved by a fusion of species from separate phylogenetic lineages. • Primitive cells of the ancestral community swapped DNA • Replace tree with a web-like phylogeny?

  17. Back to the “Kingdom Problem”(?)

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