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AP Biology LECTURE NOTES: Chapter 28 Protists FIGURE 28.1 – Too diverse for one kingdom: though systematists have split the five-kingdom system’s Protista into many kingdoms, “protist” is still a convenient informal term for the great diversity of eukaryotes that are NOT plants, fungi, or animals. Most protists are unicellular • And some are colonial or multicellular • Protist habitats are also diverse including freshwater and marine species Protists, the most nutritionally diverse of all eukaryotes, include • Photoautotrophs, which contain chloroplasts • Heterotrophs, which absorb organic molecules or ingest larger food particles • Mixotrophs, which combine photosynthesis and heterotrophic nutrition Reproduction and life cycles are also highly varied among protists, with both sexual and asexual species • Mitosis occurs in all protists • Some protists are exclusively asexual • Other can also reproduce sexually or at least employ the sexual process of meiosis and syngamy – Syngamy is the process of cellular union during fertilization FIGURE 28.4 – The origin and early diversification of eukaryotes. Among the most fundamental questions in biology is how the complex eukaryotic cell evolved from much simpler prokaryotic cells. How did compartmental organization of the eukaryotic cell evolve from the simpler prokaryotic condition? • In one process, the endomembrane system – the nuclear envelope, ER, Golgi, and related structures – may have evolved from specialized infoldings of the prokaryotic plasma membrane. • Another process, called endosymbiosis, probably led to mitochondria, plastids, and some other features of eukaryotic cells. Mitochondria & plastids evolved from endosymbiotic bacteria: • Plastids are a general term for the class of eukaryotic organelles that includes chloroplasts • Chloroplasts and mitochondria are descendants of cyanobacteria and aerobic, heterotrophic prokaryotes, respectively, that took up residence within evolving eukaryotic cells. There is now considerable evidence that much of protist diversity has its origins in endosymbiosis. The plastidbearing lineage of protists evolved into red algae and green algae. On several occasions during eukaryotic evolution, Red algae and green algae underwent secondary endosymbiosis, in which they themselves were ingested. The evidence for the endosymbiotic origin of chloroplasts and mitochondria include: • Both chloroplasts and mitochondria are the appropriate size to be descendents of bacteria • The inner membranes of both have several enzymes and transport systems resembling those of modern prokaryotes • Both replicate by a process similar to binary fission • Both contain their own separate genome of a single, circular DNA molecule • The ribosomes of chloroplasts and mitochondria are more similar to prokaryotic ribosomes than eukaryotic ribosomes AP Biology LECTURE NOTES: Chapter 28 Protists TABLE 28.1 – The origin and early diversification of eukaryotes. Among the most fundamental questions in biology is how the complex eukaryotic cell evolved from much simpler prokaryotic cells. Structural and biochemical adaptations help seaweeds survive and reproduce at the ocean’s margins. • Seaweeds include the thallus-forming marine species among the brown, red, and green algae. Some algae have life cycles with alternating multicellular haploid and diploid generations. • Haploid gametophytes and diploid sporophytes take turns producing one another. Multicellularity originated independently many times. • In addition to seaweeds and other multi-cellular protists, multicellularity evolved in the ancestors of plants, fungi, and animals. Most protists are classified by their method of obtaining nutrients: • Animal-like protists are heterotrophs • Plant-like protists photosynthesize • Fungus-like protists are parasites or decomposers FIGURE 28.11, 28.13, 28.14, 28.15 - Diversity of Animal-Like Protists Phylum Name Common Name Traits/Characteristics 1. Rhizopoda Amoeba 2. Actinopoda Foraminiferans Actinopods 3. Zoomastingina Zooflagellates 4. Ciliophora Ciliates • • • • • • • • • • • • • • • • 5. Apicomplexa Sporozoa • • Sarcodines (amoeboid-like movement) use pseudopods (false feet) for movement have highly perforated shell of calcium carbonate move with cytoplasmic extensions “ray foot” that go through the perforated shell fossil shells form in marine sediments many are planktonic flagellated protozoans undulating membranes mostly unicellular free-living, parasitic, or endosymbionts Ex: • Giardia (from feces infected water) • Trichomonas vaginalis (vaginal infections) • Trichonymphs digest cellulose in termites • Trypanosoma (parasitic) causes African Sleeping Sickness use cilia to move and feed most live in fresh water – solitary 2 or more nuclie • macronucleus with 50 or more copies of genome • micornuclei that are requried for conjugation extremely complex – contractile vacuoles used for water balance, mouth, anal pore Ex: • stentors and paramecium parasitic, form sporozoites (infectious cells that have specialized structures at the apex to help penetrate into host) Ex: • Plasmodium (causes malaria) AP Biology LECTURE NOTES: Chapter 28 Protists FIGURE 28.21, 28.23 & 28.24 - Diversity of Algae & Plant-like Protists Phylum Name Common Name Traits/Characteristics 1. Euglenophyta Euglenoids 2. Dinoflagellata Dinoflagellates 3. Bacillariophyta Diatoms 4. Chrysophyta Golden Algae 5. Chlorophyta Green Algae 6. Phaeophyta Brown Algae 7. Rhodophyta Red Algae • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • unicellular with 1-3 flagella common in freshwater has pellicle (protein strips that wrap over membrane) eyespot for phototaxis photoautotrophs, but some can become heterotrophs w/out light cause algal blooms – harmful to freshwater systems major component of photosynthetic phytoplankon 2 flagella – spinning movement blooms cause red tides (toxic from xanthophylls pigment) can produce toxins that kill fish some are bioluminescent glass shells of silica freshwater/marine plankton – extremely abundant major constituents of marine sediment asexual reproduction is most common major primary producers of fresh water & marine ecosystems yellow/brown carotene and xanthophylls pigment 2 flagella unicellular or colonial freshwater and marine plankton most closely related to land plants both chlorophyll a, b, and carotenoids (like land plants) have cellulose in cell walls (like land plants) use starch to store polysaccharides (like land plants) single celled and colonial most produce flagellated cells at some part of life cycle can be very diverse (volvox colonies, ulva sea lettuce) some form mutualistic relationships with fungi (lichens) complex sexual and asexual life cycles • isogamous – 2 flagellated gametes of equal size • anisogamous – gametes differ in size • oogamous – non mobile large egg w/ small flagellated male multicellular flagellated sperm fucoxanthin (brown pigment) most have alternation of generations life cycle • thallus = body • holdfast = rootlike system • stripe = stemlike system • blades = leaf like organs Ex: giant kelp multicellular phycobilin (red accesory pigment) – makes red algae efficient at greater ocean depths because pigment is specialized for absorbing blue wavelengths of light for photosynthesis no flagellated stage; dependent on ocean currents for fertilization AP Biology LECTURE NOTES: Chapter 28 Protists FIGURE 28.16, 28.29 & 28.30 - Diversity of Fungal-like Protists Phylum Name Common Name Traits/Characteristics 1. Acrasiomycota Cellular Slime Molds • • • • 2. Myxomycota Plasmodial Slime Molds • • • 3. Oomycota Water Molds Downey Mildews White Rust • • • • • fungal-like and amoeba-like characteristics unicellular amoeboid feeding stage multi-cellular slug-like aggregation stage – forms fruiting bodies that produce “spores” that germinate into amoebas cAMP released by amoebas that experience food deprivation which signals the aggregation stage brightly pigmented yellow or orange plasmodium is an amoeboid feeding mass that is NOT multicellular; it is unicellular, but multinucleated (caused by multiple mitotic divisions w/out cytokinesis) plasmodium dries up and forms fruiting bodies • meiotic division within the fruiting bodies create haploid spores that are amoeboid or flagellated. fertilization allows for plasmodium formation parasitic or saprobes (obtain energy from dead matter) closest to actual fungi have mycelium (main body) made up of hyphae (threadlike filaments that secrete enzymes for digestion) they are coenocytic (have many nuclei within a single cell) but lack the “cross walls” or septa which partition the filaments into cellular components, as found in true fungi. Ecology of Animal-Like Protists • • Not so Good: Can be parasitic/cause disease – Malaria, African Sleeping Sickness, Cryptosporidium Good: Symbiosis – Termites have beneficial animal like protists called Trichonympha in their stomachs – Break down cellulose in wood so termites can use it as food Ecology of Plant-Like Protists • • • Most unicellular species beneficial Act as producers in the marine food chain – Form Phytoplankton for consumer organisms to eat – Approx. ½ of the photosynthesis on earth - produce large amount of oxygen Symbiosis: Coral Reefs, Clams – Provide food via photosynthesis, receive a home Ecology of Fungi-Like Protists • • • The ecological impact of oomycetes can be significant – Phytophthora infestans causes late blight of potatoes – Irish Potato Famine – Overgrowth of water mold caused by wet and cool conditions Slime molds and water molds are the MOST important recyclers of organic material Why is the earth not littered with dead organisms? – Tissues broken down by Fungi Like Protists and other decomposers Beneficial Aspects of Algae • • • • • • • • • • Food for humans, food for invertebrates and fishes Animal feed Soil fertilizers and conditioners in agriculture Treatment of waste water Diatomaceous earth (= diatoms) Chalk deposits Phycocolloids (agar, carrageenan from red algae; alginates from brown algae) Drugs Model system for research Phycobiliproteins for fluorescence microscopy Detrimental Aspects of Algae • • • • • • Blooms of freshwater algae Red tides and marine blooms Toxins accumulated in food chains Damage to cave paintings, frescoes, and other works of art Fouling of ships and other submerged surfaces Fouling of the shells of commercially important bivalves