In what ways are protists important? The Protists A diverse assemblage of eukaryotes that ARENʼT fungi, plants, or animals Base of many food chains - especially in aquatic settings Clarify water by filtering out small particles Some are parasites that cause diseases in other organisms Some have economic uses for humans Some are involved in important symbiotic relationships Why can termites eat wood? Because of symbiotic hypermastigotes (a group of parabasilids) living in the termite gut working together with Archaean methanogens Fig 28.26 (SEM) And they are a spectacular group of organisms Where Did Eukaryotic Cells come from? First found in fossil record about 2.1 billion years ago (Prokaryote fossils to 3.5 BYA) Two major features to explain: - membrane-bounded organelles (mitochondria and plastids) - internal membrane systems Origin of Organelles Idea is that the ancestors of eukaryotic cells were symbiotic consortiums of prokaryotic cells Has come to be called the endosymbiont theory
Lynn Margulis The Ideas of the Endosymbiont Theory (Fig 25.9) Mitochondria are the descendents of aerobic heterotrophic bacteria Chloroplasts are the descendants of photosynthetic bacteria - very likely cyanobacteria Person who led the development of the endosymbiont theory Evidence that Supports the Endosymbiont Theory Origin of Eukaryotes Fig.25.9 Endosymbiotic relationships exist in the modern world, e.g., some species of dinoflagellates are endosymbiotic in corals Plastids and mitochondria about the same size as typical prokaryotic cells Evidence (cont.) Similar membrane proteins (inner membrane) Reproduce by a process similar to binary fission Contain circular DNA molecules Ribosomal RNA sequences in organelles more similar to prokaryotes What organisms have eukaryotic cells? Animals (mitochondria) Plants (mitochondria and plastids) Fungi (mitochondria) Protists (mitochondria, some have plastids)
The Protists Flagella and Cilia (Fig 6.23) Incredible diversity of organisms - your text recognizes 21 clades at probably the Phylum or Kingdom level Typically found in aquatic or damp environments, or in body fluids, tissues, or cells of host organisms Most have flagella or cilia at some stage in their life cycle Structurally distinct from the flagella of prokaryotes Eukaryotic flagella and cilia have a similar structure involving microtubules Human sperm Ciliate Cilia and Flagella in Action Cilia and Flagella Protist Size Most are single-celled, but their cell structure can be very complex Ciliates (e.g., Paramecium, Vorticella) are among the most complex of all cells Some are multicellular and individuals can be as large as 60 meters in length - the kelps (brown algae) Kelp (Brown Algae) Protist Nutrition Nutritionally diverse - photoautotrophs - chemoheterotrophs Also are mixotrophs e.g., Euglena Definitely donʼt need a microscope to see this protist!
Nutrition Three major means of obtaining nutrition amongst protists: - Ingestive ( animal-like ), sometimes called protozoa - Absorptive ( fungus-like ) - Photosynthetic ( plant-like ), sometimes called algae Distinct nutritional mechanisms may be found within one Clade Protistan Phylogeny Kingdom Protista was a diverse group of organisms that were, in many cases, not closely related Phylogeny is currently in a state of flux DNA sequence data have been, and will continue to be, very helpful Splitting of Kingdom Protista into 21 clades (Phyla? Kingdoms?) has been proposed These clades have been placed into 5 supergroups in your text Fig 28.3 Protistan Diversity A quick look at 9 of the 21 protist clades described in Campbell et al. Why not look at ALL 21 clades? Supergroup Excavata Getting a Ph.D. - Thatʼs where you learn more and more about less and less until you know everything about nothing Intro Bio Course - Thatʼs where you learn less and less about more and more until you know nothing about everything I want you to know something about something... Evidence: - Excavated feeding groove - DNA sequence similarities Evidence supporting this supergroup is rather weak and investigation is ongoing
The Parabasalids Have modified mitochondria called hydrogenosomes Most familiar member Trichomonas vaginalis - cause of a common sexually transmitted disease Trichomonas Fact Sheet at the CDC Each cell possesses 4 flagella Trichomonas vaginalis (Fig. 28.4) The Euglenozoans Two major groups: the kinetoplastids the euglenids The Kinetoplastids One large mitochondrian per cell Organized mass of DNA inside the mitochondrian - called the kinetoplast Genus Trypanosoma cause of African sleeping sickness Disease is vectored by the Tsetse fly (Glossina spp.) Invariably fatal if left untreated Tsetse Fly Fig. 28.6 Red blood cell Trypanosome
Supergroup Chromalveolata Evidence: - DNA sequence similarities - Chloroplast structure similarities Highly controversial supergroup The Alveolates Characterized by the presence of small membrane-bounded cavities under their cell membrane Three major groups: Dinoflagellates Apiocomplexans Ciliates The Dinoflagellates Dinoflagellates Both marine and freshwater Most species unicellular Important component of plankton About 50% of known species are photosynthetic Most species have elaborate cell walls Ceratium (light microscope) Peridinium (SEM) Red Tide Red Tide Boat Dead Fish Dinoflagellate population explosions Water stained brownish-red (xanthophylls) Toxins produced by the dinoflagellates can kill fish, invertebrates, seabirds Some types of toxins can accumulate in shellfish - causing poisoning in humans
Karenia brevis Karenia brevis (SEM) One species of dinoflagellate that causes red tides Produces a toxin that kills fish and invertebrates Human exposure to the toxin may cause a variety of symptoms, including death - Called neurotoxic shellfish poisoning Location of Karenia blooms (data from December 2004) Unit 1 Exam Available Monday 15 September through Tuesday 23 September READ: COLL Testing Facility Policies and Procedures in the Course Introduction Learning Module Go to Center for On-Line Learning, room 60 Carver Hall to take the exam The Cilates Ciliates Many beautiful freshwater species Use cilia to move and feed Have very complex cells, e.g., each cell has one micronucleus and one macronucleus Micronuclei participate in sexual reproduction; macronuclei in controlling cell functions Stentor spp. Paramecium spp.
The Stramenopiles Paramecium feeding Some species are photoautotrophic, some are heterotrophic Characterized by the presence hairlike projections on one of their (typically) two flagella Stramenopile Flagella (Fig 28.12) Four major groups: Diatoms Brown algae (includes kelp ) Golden algae Oomycetes (water molds) The Diatoms glass-like cell walls - made of hydrated silica important photosynthetic organisms in plankton fresh water and marine large number of species (estimated to be ~ 100,000) Diatom Diversity (Fig 28.3) Diatoms Diatom Art
Diatomaceous Earth Huge amounts of ancient diatom cell walls Various uses: filtering medium metal polishes reflective paint pesticide nanotechnology SEM of Diatom Supergroup Archaeplastida Evidence: - DNA sequence similarity - Chloroplast structure similarities This supergroup is well supported by the available evidence The Red Algae Red Algae (Fig 28.19) No flagella present at any stage of the life cycle Most abundant in tropical oceans Most are multicellular ~ 6,000 described species Some species are heterotrophic Red Algae Accessory pigments allow photosynthesis at great depths - as deep as 260 meters Effective at absorbing blue light Human Uses Cell wall extracts: carageenan - commonly eaten by people agar - microbiological culturing media
Fig. 28.19 How do you feel about sushi? The Green Algae Most species (~7,000) found in fresh water Cell walls with a relatively high percent of cellulose Can be unicellular, colonial/filamentous, or multicellular Can be motile (flagella) or non-motile Single-celled Green Alga - Eremosphaera viridis Chlamydomonas Chloroplasts Nucleus Unicellular and motile green alga Important model genetic system - much research is done with this organism Colonial Green Alga - Volvox (Fig. 28.3) Volvox
Filamentous Green Alga - Ulothrix spp. Multicellular Green Alga - Ulva spp. (Fig. 28.21) Green Algal Life Cycles Can be quite complex with both sexual and asexual reproduction Most gametes have two flagella Gametes may be isogamous or anisogamous Some multicellular species exhibit alternation of generations (as do all plants) - may be heteromorphic or isomorphic An example of a green algal life cycle Oedogonium is a genus of filamentous green algae Oedogonium Life Cycle Oedogonium life cycle Anisogamous Meiosis leads to production of zoospores (not gametes) Gametes are produced by mitosis Asexual macrozoospores are also produced by mitosis
Supergroup Unikonta Evidence: - DNA sequence similarities This supergroup is well supported by the available evidence The Amoebozoans Four major groups: Plasmodial slime molds Cellular slime molds Gymnamoebas (free-living) Entamoebas (parasitic) Plasmodial Slime Molds Feeding stage is an called a plasmodium (Fig. 28.24) The plasmodium is a coenocytic mass Multinucleate cytoplasm undivided by walls or membranes Live in moist habitats, e.g., rotting logs The plasmodium engulfs food by phagocytosis as do ameobas Cool Slime Mold Slime mold in action Planet Earth - Jungles 23:20
Response to the Environment Start ~ 48 hours Growth away from detergent End Slime Mold Reproduction If available water or food insufficient, produces resistant spores through meiosis Each sporangium produces many spores (Fig. 28.24) Gymnamoebas Unicellular Found in soil, freshwater, and marine habitats Heterotrophs that often consume prokaryotes and other protists as their food Move by producing pseudopodia Amoeba spp. (Fig. 28.3) Attack of the Killer Amoeba Studying organisms too small to see without a microscope is 1. Boring beyond human tolerance 2. Very boring 3. More interesting than I expected - but still boring 4. Remarkably interesting 5. More interesting than any previous experience in my life
The most interesting (or least boring) group weʼve studied so far is 1. Archaea 2. Bacteria 3. Excavata 4. Chromalveolata 5. Archaeplastida 6. Unikonta