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Unformatted text preview: Chapter 22 The Protists The Protists 2 Outline Protist Biology Protist Evolution Protist Diversity Green Algae Red Algae Brown Algae Diatoms Dinoflagellates Protist Diversity, cont. Euglenoids Zooflagellates Pseudopods Ciliates Sporozoans Slime Molds Water Molds The Protists 3 General Biology of the Protists Classified into the Domain Eukarya & the Kingdom Protista Morphology: Most unicellular Many with amazingly high level of strucrural and functional complexity Life cycles: Asexual reproduction common Sexual reproduction may occur when conditions deteriorate Some life cycles simple, many extremely complex Origin of the Eukaryotic Cell 4 The Protists 5 Ecology of Protists
Protists are of enormous eco-logical importance Photoautotrophic forms: Produce oxygen Function as producers in both freshwater and saltwater ecosystems Major component of plankton Organisms that are suspended in the water Serve as food for heterotrophic protists and animals Many protists are symbionts Ranges from strict parasitism to mutualism Coral reefs greatly aided by symbiotic photoautotrophic protists in tissues of corals The Protists 6 Evolution of Protists Complexity and diversity of protists makes them difficult to classify Many classification schemes proposed None has broad support Cannot be classified as plants, animals, or fungi Could be split into as many as a dozen kingdoms The scheme chosen for this discussion is Protist Diversity 7 Phylum Chlorophyta Approximately 7,500 species Inhabit a variety of environments including oceans, freshwater, snowbanks, tree bark, and turtles backs Many are symbionts with fungi, plants, or animals Morphology varied Majority unicellular, but many are filamentous or colonial Some are multicellular and resemble leaves of lettuce The Protists Diversity of Protists: Green Algae The Chlorophyta 8 Plants thought to be derived from Chlorophyta because both groups: Have a cell wall that contains cellulose Possess chlorophylls a and b, and A minute (<25 m), actively moving flagellate Inhabits still, freshwater pools Fossil ancestors date back over a billion years Anatomy: Definite cell wall Single, large, cup-shaped chloroplast Chloroplast with a pyrenoid where starch is synthesized Many with a bright red eyespot, or stigma on chloroplast Two long, whip-like flagella Project from the anterior end Green Algae: Chlamydomonas The Protists 9 Electron Micrograph of Chlamydomonas 10 Green Algae: Chlamydomonas
Most often reproduces asexually The Protists 11 As many as 16 daughter cells within parent cell Escape by digesting the parent cell Occasionally reproduces sexually Gametes fuse to form a zygote Becomes a heavy-walled, resistant zygospore Goes into a period of dormancy Upon germination produces four zoospores by meiosis "Spore" - a reproductive cell that develops into a new organism without fusing with another cell "Zoospore" - flagellated spores, typical of aquatic species Reproduction in Chlamydomonas 12 Green Algae: Spirogyra The Protists 13 Filamentous green algae Found in green masses on the surfaces of ponds and streams Has ribbon-like, spiraled chloroplasts Sexual reproduction by conjugation: A temporary union during which the cells exchange genetic material Two filaments line up parallel to each other Cell contents of one filament move into the cells of the other filament Forms diploid zygospores In spring, undergo meiosis to produce new haploid filaments Spirogyr a 14 Green Algae: Multicellular Forms Ulva Multicellular green alga Commonly called sea lettuce Thallus (body) is two cells thick Can be as much as a meter long The Protists 15 Sexual cycle involves alternation of generations Similar to higher plants, except Both generations look exactly alike, and The gametes all look the same Multicellular Green Algae 16 Green Algae: Colonial Forms The Protists 17 Volvox A colony is a loose association of independent cells A Volvox colony: A hollow sphere Thousands of cells arranged in a single layer surrounding a watery interior Each cell of colony resembles a Chlamydomonas cell Flagella beat in a coordinated fashion Some cells are specialized for reproduction Each can divide asexually to form a new daughter colony within the parental colony Leaves parental colony by releasing an enzyme that dissolves away a portion of the parental colony Volvo x 18 The Protists Diversity of Protists: Red Algae The Rhodophyta 19 Multicellular About 5,000 species Live mostly in warmer seawater, some as deep as 200 m Economic Importance Agar - capsules; dental impressions; cosmetics; culture medium; electrophoresis; food prep. Carrageen - an emulsifying agent used in chocolate, low-fat foods, & cosmetics The reddish-black wrappings around sushi rolls consist of processed Porphyra blades Red Algae 20 The Protists Diversity of Protists: Brown Algae The Phaeophyta 21 About 1,500 species Most live in colder ocean waters along rocky coasts No unicellular or colonial brown forms Morphology: Some small forms with simple filaments Others large multicellular forms that may exceed 200 m in length Pigments: Chlorophylls a and c Fucoxanthin (a type of carotinoid pigment) gives them their color Excess food stored as a carbohydrate called laminarin Brown Algae 22 The Protists 23 The Phaeophyta Multicellular forms of green, red, and brown algae are called seaweeds Laminaria (a kelp), and Fucus, (rockweed), are common intertidal seaweeds Nereocystis and Macrocystis often form forest-like thickets in deeper waters Sargassum forms floating masses where other organisms find shelter Harvested for food and fertilizer Macrocystis is source of algin, a thickener for foods The Protists 24 The Phaeophyta Laminaria shows tissue differentiation Transport organic nutrients in a tissue resembling phloem Life cycle Most brown algae have alternation of generations In some species of Fucus Meiosis produces gametes instead of spores The adult is always diploid, as in animals 25 The Protists Diversity of Protists: Yellow-green Algae The Chrysophyta Diatoms (formerly Bacillariophyta) are the most numerous unicellular algae in the oceans Significant portion of phytoplankton Cell wall Two valves, with the larger valve acting as a lid (like a mint tin) Contains silica Diatomaceous earth used as Filtering agents Sound-proofing materials Polishing abrasives The Protists Diversity of Protists: Dinoflagellates The Pyrrophyta About 4,000 species of unicellular aquatic and marine 26 organisms Morphology: Cell is usually bounded by protective cellulose plates impregnated with silicates Typically with two flagella One in a longitudinal groove with its distal end free The other lies in a transverse groove that encircles the organism Symbiotic dinoflagellates in corals called zooxanthellae Dinoflagellates provide their host with organic nutrients Corals provide wastes that fertilize the algae Some lack chloroplasts and are parasitic Gymnodinium brevis may cause "red tide" Produce a powerful neurotoxin that has caused massive fish kills Consume shellfish during outbreak can cause respiratory Diatoms and Dinoflagellates 27 Fish Kill and Dinoflagellate Bloom 28 29 The Protists Diversity of Protists: The Euglenoids Phylum Euglenophyta Small freshwater unicellular organisms Difficult to classify Have two flagella and an eyespot (shades a photoreceptor) One flagellum much longer than the other Projects out of an anterior, vase-shaped invagination Called a tinsel flagellum because of hair-like projections Cell bounded by flexible pellicle Chloroplasts: Surrounded by three rather than two membranes With a pyrenoid which produces an unusual type of carbohydrate called paramylon Euglena 30 Diversity of Protists: Zooflagellates Phylum Zoomastigophora The Protists 31 Colorless heterotrophs Most symbiotic and many parasitic Well known for causing various diseases in humans Trypanosoma African sleeping sickness - Tsetse fly Chagas disease Kissing bug Most common flagellate in human digestive tract Causes severe diarrhea Cysts are transmitted in contaminated water Beavers are important reservoir hosts Giardia lamblia Trichomonas vaginalis Sexually transmitted protist, Infects urogenital organs; a common cause of vaginitis Zooflagellates 32 Giardia lamblia 33 Diversity of Protists: Protists with Pseudopods The Protists 34 Pseudopods form when cytoplasm streams forward in a particular direction Amoeboids (phylum Rhizopoda) are protists that move and ingest their food with pseudopods Phagocytize food Entamoeba histolytica - a parasite of the human colon; Causes amoebic dysentery Can be fatal Foraminiferans (phylum Foraminifera) and radiolarians (phlyum Actinopoda) Both have a skeleton (test) of either calcite or silica Protists with Pseudopods 35 The Protists Diversity of Protists: The Ciliates Phylum Ciliophora 36 Ciliates (phylum Ciliophora) are among the most complex of the protozoans Hundreds of cilia beat in coordinated rhythm Most are holozoic, swallowing food whole Divide by transverse binary fission during asexual reproduction Two nuclei of differing types Micronucleus Heredity Macronucleus Metabolism Ciliates 37 38 The Protists Diversity of Protists: The Sporozoans Phylum Apicomplexa Nonmotile obligate parasites Most serious parasitic disease of human is malaria Plasmodium spp Kills 3,000,000 people each year Transmitted by mosquito Toxoplasma Humans get from cats Causes birth defects and mental retardation when pregnant mom exposed Life Cycle of Plasmodium vivax 39 The Protists Diversity of Protists: Slime Molds Plasmodial Slime Molds - Phylum Myxomycota 40 Body in the form of a plasmodium Diploid, multinucleated, cytoplasmic mass Enveloped by a slimy sheath Eventually produces sporangium which in turn produces spores Cellular Slime Mold - Phylum Acrasiomycota Body in the form of individual amoeboid cells Later aggregate into pseudoplasmodium Plasmodial Slime Molds 41 42 The Protists Diversity of Protists: Water Molds - Phylum Oomycota Most live in the water Phylum name refers to the enlarged tips (called oogonia) where eggs are produced Body filamentous, appearing like true Fungi Cell walls largely of cellulose rather than chitin The organism is diploid (not haploid as in the fungi) Phytophthora infestans caused the 1840's potato famine in Ireland Saprolegnia is often seen as a white, cottonlike coating on dead aquarium fish Water Mold 43 The Protists 44 Review Protist Biology Protist Evolution Protist Diversity Green Algae Red Algae Brown Algae Diatoms Dinoflagellates Protist Diversity, cont. Euglenoids Zooflagellates Pseudopods Ciliates Sporozoans Slime Molds Water Molds Ending Slide Chapter 22 The Protists ...
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