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Chapter 28

Chapter 28. Protists. Overview: Living Small. Protist is the informal name of the kingdom of mostly unicellular eukaryotes Advances in eukaryotic systematics have caused the classification of protists to change significantly; therefore Protista is no longer valid as a kingdom.

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Chapter 28

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  1. Chapter 28 Protists

  2. Overview: Living Small • Protist is the informal name of the kingdom of mostly unicellular eukaryotes • Advances in eukaryotic systematics have caused the classification of protists to change significantly; therefore Protista is no longer valid as a kingdom

  3. Concept 28.1: Most eukaryotes are single-celled organisms • Protists are eukaryotes and thus have organelles and are more complex than prokaryotes • Most protists are unicellular, but there are some colonial and multicellular species

  4. Structural and Functional Diversity in Protists • Protists exhibit more structural and functional diversity than any other group of eukaryotes • Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell

  5. Protists can reproduce asexually or sexually, or by the sexual processes of meiosis and fertilization (syngamy) • 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

  6. Endosymbiosis in Eukaryotic Evolution • There is now considerable evidence that much protist diversity has its origins in endosymbiosis • Mitochondria evolved by endosymbiosis of an aerobic prokaryote • Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium • The plastid-bearing lineage of protists evolved into red algae and green algae • On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote

  7. Fig. 28-02-2 Plastids evolved from gram - cyanobacterium Plastid Dinoflagellates Secondary endosymbiosis Apicomplexans Red alga Cyanobacterium Primary endosymbiosis Stramenopiles Plastid Heterotrophic eukaryote Secondary endosymbiosis Over the course of evolution, this membrane was lost. Euglenids Secondary endosymbiosis Green alga Chlorarachniophytes

  8. Five Supergroups of Eukaryotes • It is no longer thought that amitochondriates are the oldest lineage of eukaryotes • One hypothesis divides all eukaryotes (including protists) into five supergroups

  9. Fig. 28-03a Diplomonads Excavata Parabasalids Euglenozoans Dinoflagellates Apicomplexans Alveolates Ciliates Chromalveolata Diatoms Golden algae Brown algae Stramenopiles Oomycetes Chlorarachniophytes Rhizaria Forams Radiolarians Red algae Chlorophytes Archaeplastida Green algae Charophyceans Land plants Slime molds Gymnamoebas Amoebozoans Entamoebas Nucleariids Unikonta Fungi Opisthokonts Choanoflagellates Animals

  10. Fig. 28-03b EXCAVATA "the excavates" no plastids, multiple flagella made of flagellin, 2 nucloeli, parasitic and free living Giardia modified mitichondria anaerobic Diplomonads releases H, Trichomonas, STD Parabasalids grooved body Excavata crystaline rod inside flagella, kinetoplastids and Euglenids Euglenozoans Diplomonad Parabasalid Trichomonas vaginalis STD Giardia intestinalis Kinetoplastid Euglenid Trypanosoma Euglena Chaga's disease and Sleeping Sickness

  11. Fig. 28-03c Chromalveolates alveoli under the plasma membrane Dinoflagellates Apicomplexans Alveolates Ciliates DNA sequence how old they are Chromalveolata Diatoms Golden algae Brown algae Stramenopiles Oomycetes 2 flagella, one covered with fine stiff hairs and the other one smooth

  12. Alveolates apex mitochondria nucleus • Dinoflagelates cells reinforced by cellulose plates • 2 flagella in grooves • marine and freshwater plankton • auto, mixo and heterotrophic • toxic "red tide" • dino= whirl • Apicomplexa parasites • apex=tip • modified plastid • complex lifecycle, 2 or more hosts • malaria "bad air" • P. falciparium, P. vivax, P. malariae, P. ovale • Ciliates cilia used for locomotion and feeding • macro and micronucleus • sexual reproduction by conjugation • Paramecium

  13. Feeding, water balance and waste removal Conjugation and Reproduction of Paramecium Contractile vacuole cillia Oral groove mouth micronucleus macronucleus food vacuoles align side by side and partially fuse four haploid nucleoli are produced in each one 1.compatible mates three of which desintegrate MEIOSIS DNA exchange HAPLOID DIPLOID 2 rounds of cytokinesis producing four daughter cells DIPLOID MICRONUCLEAR FUSION Key two micronuclei 3 rounds of mitosis 4 micronuclei become macronuclei fuse into one micronucleus haploid (n) diploid (2n)

  14. Stramenopiles (stramen= straw, pilos= hair) flagellum outer container living cell blade • Diatomsglass like wall made of hydrated silica, 2 parts overlaping • walls with lacework of holes and grooves • asexual reproduction more common • 100,000 species, very diverse • stores energy in form of oil and glucose polymer laminarin • fossilized= diatomaseous earth • biological carbon pump= carbon cycle • Golden Algaecolor due to carotenoids • biflagellated at one end of the cell • freshwater and marine plankton • all photosynthetic and some mixotropic (phagocytosis) • uni and multicellular • protective cysts that may survive decades • Brown Algae multicellular • mostly marine "sea weed" • carotenoids in plastids • similarities with plants evolved independantly (analogous) • gel-forming polysaccharides cushions the thali from waves • polysaccharides also prevent drying when exposed to air • algin (found in cell walls) used as thickening agent in foods • hetero- or isomorphic alternation of generations stipe

  15. Fig. 28-16-2 Alternation of Generations 1. found in water just below the line of lowest tide Sporangia located on surface of blade holdfast 10 cm MEIOSIS Sporophyte (2n) originate in sporangia Zoospore Female zygotes develop into sporophytes while attached to the remains of the female gametophyte Developing sporophyte Gametophytes (n) half develop into males and the other half to females Zygote (2n) Mature female gemetophyte (n) Male Egg FERTILIZATION eggs secrete a chemical signal attracting sperm Sperm Key Haploid (n) Diploid (2n)

  16. Oomycetes • "egg fungus" • water molds, white rusts and downy mildews • convergent evolution • *similarities with fungus: multicellular hyphae • *differences: cell walls made of chitin • no plastids • decomposers and/or parasites • water molds live in freshwater, rusts and mildews are plant parasites • *potato late blight • genetic engineering is passing resistant genes to domesticated crops

  17. Fig. 28-17-3 Oogonium hyphae develop sexual structures 1.zoospores germinate on a substrate Germ tube Egg nucleus (n) Cyst MEIOSIS Antheridial ♂ hypha with sperm nuclei (n) Hyphae ASEXUAL REPRODUCTION Zoospore (2n) FERTILIZATION Zygote germination Zygotes (oospores) (2n) SEXUAL REPRODUCTION Zoosporangium (2n) Key Haploid (n) Diploid (2n) zygote forms hypha antheridia grows around the oogonium depositing the sperm using fertilization tubes dormant period in which the oogonium wall desintegrates Life Cycle of Oomycetes

  18. Fig. 28-03d Rhizarians vary in morphology but very similar in molecular systematics referred as "amoebas" 2ry endosymbiosis with green algae plastid surrounded by 4 membranes vestigial nucleus called nucleomorph Chlorarachniophytes threadlike pseudopods calcium carbonate shells Rhizaria Forams silica shells Radiolarians

  19. Foraminifera pseudopodia shell made of CaCO3 • foramen= hole • ferre= to bear • found in ocean and freshwater • porous shell known as tests • form the sedimentary rocks • symbiotic algae

  20. Radiolaria pseudopods • symmetrical internal skeleton made of silica • pseudopodia reinforced by microtubules • marine

  21. Fig. 28-03e Archaeoplastida red and green algae, and land plants unicellular and multicellular species Red algae Chlorophytes Green algae Archaeplastida Charophyceans Land plants

  22. Concept 28.5: Red algae and green algae are the closest relatives of land plants • Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont • The photosynthetic descendants of this ancient protist evolved into red algae and green algae • Land plants are descended from the green algae • Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants

  23. Red algaeare reddish in color due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll • The color varies from greenish-red in shallow water to dark red or almost black in deep water • Red algae are usually multicellular; the largest are seaweeds • Red algae are the most abundant large algae in coastal waters of the tropics

  24. Fig. 28-19 Bonnemaisonia hamifera Red Algae Rhodophytes rodo=red phycoerythrin masks chlorophyll in shallower waters= less phycoerythin may lack pigments, act as parasites tropical oceans, freshwater and terrestrial multicellular alternation of generation cycle no flagellated states in life cycle water currents bring gametes together 8 mm Dulse (Palmaria palmata) Nori. The red alga Porphyra is the source of a traditional Japanese food. The seaweed is grown on nets in shallow coastal waters. The harvested seaweed is spread on bamboo screens to dry. Paper-thin, glossy sheets of nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi.

  25. Green algaeare named for their grass-green chloroplasts • Plants are descended from the green algae • The two main groups are chlorophytes and charophyceans • Most chlorophytes live in fresh water, although many are marine • Other chlorophytes live in damp soil, as symbionts in lichens, or in snow • Chlorophytes include unicellular, colonial, and multicellular forms • Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages

  26. Fig. 28-21 Ulva, or sea lettuce Chlamydomonas 2 cm Caulerpa, an intertidal chlorophyte

  27. Fig. 28-22-2 Life Cycle of Chlamydomonas when environment declines gametes are developed 1.mature cell, contains single cup shaped chloroplast Chlamydomonas gametes fused forming diploid zygote – Flagella 1 µm Cell wall + Gamete (n) – + Nucleus Zoospore FERTILIZATION Mature cell (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Zygote (2n) Cross section of cup-shaped chloroplast undergoes 2 rounds of mitosis emerging as zoospores (n) MEIOSIS Key Haploid (n) Diploid (2n) coat is secreted to protect zygote from harsh conditions after dormancy meiosis produces 4 haploid cells (n), 2 of each mating type (+/-)

  28. Fig. 28-03f Unikonta Slime molds Amoebozoans Gymnamoebas Entamoebas Nucleariids Unikonta Fungi Opisthokonts Choanoflagellates Animals

  29. Concept 28.6: Unikonts include protists that are closely related to fungi and animals • The supergroup Unikonta "one flagella" includes animals, fungi, and some protists • This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists) • The root of the eukaryotic tree remains controversial • It is unclear whether unikonts separated from other eukaryotes relatively early or late

  30. Fig. 28-23 Hypothesis about the Eukaryotic Tree Choanoflagellates Animals Unikonta Fungi Common ancestor of all eukaryotes Amoebozoans Diplomonads Excavata Euglenozoans Alveolates Chromalveolata Stramenopiles DHFR-TS gene fusion Rhizaria Rhizarians Red algae Green algae Archaeplastida Plants

  31. Amoebozoans are amoeba that have lobe- or tube-shaped, rather than threadlike, pseudopodia • They include gymnamoebas, entamoebas, and slime molds Amoeba proteus pseudopods engolfing a small green algae

  32. Slime Molds • Slime molds, or mycetozoans, were once thought to be fungi • Molecular systematics places slime molds in the clade Amoebozoa • Many species of plasmodial slime moldsare brightly pigmented, usually yellow or orange • Plasmodium is an example

  33. Fig. 28-24-3 repeated mitotic division w/o cytoplasmic division forms feeding plasmodium 4 cm 1. feeding stage multinucleated lives on organic matter ameboid or flagellated stages can convert from one to the other Feeding plasmodium FERTILIZATION Zygote (2n) mature plasmodium takes a weblike form Mature plasmodium (preparing to fruit) sporangia or fruiting bodies Young sporangium Flagellated cells (n) Amoeboid cells (n) Mature sporangium Germinating spore Spores (n) germination occurs in favorable conditions MEIOSIS 1 mm Stalk Life Cycle of Plasmodial Slime Mold Key Haploid (n) Diploid (2n)

  34. Cellular Slime Molds • Form multicellular aggregates in which cells are separated by their membranes • Cells feed individually, but can aggregate to form a fruiting body

  35. Fig. 28-5-2 in favorable conditions amoebas emerge Spores (n) 2 fuse to form a zygote FERTILIZATION Emerging amoeba (n) other cells crawl up the stalk and develop into spores Zygote (2n) SEXUAL REPRODUCTION 1.Solitary amoebas (n) 600 µm MEIOSIS Fruiting bodies (n) ASEXUAL REPRODUCTION Amoebas (n) Aggregated amoebas becomes a giant cell that eats other amoebas and develop thick wall Migrating aggregate the cell multiplies by meiosis and several mitosis events, rupturing and releasing the new haploid amoebas a stalk is formed supporting an asexual fruiting body. Some of the cells dry up by this time Cellular Slime Mold Life Cycle when food is scared amoebas congregate in responce to a chemical attraction forming a slug-like aggregate Key Haploid (n) Diploid (2n) 200 µm

  36. Gymnamoebas (Gymno=naked) • Gymnamoebas are common unicellular amoebozoans in soil as well as freshwater and marine environments • Most gymnamoebas are heterotrophic and actively seek and consume bacteria and other protists

  37. Entamoebas are parasites of vertebrates and some invertebrates • Entamoeba histolytica causes amebic dysentery in humans

  38. Opisthokonts opistho=posterior • the flagella is located in the posterior of the cell • Include animals, fungi, and several groups of protists • these are more related to fungi than to the rest of protists, therefore will be seen in future chapters

  39. Concept 28.7: Protists play key roles in ecological relationships • Protists are found in diverse aquatic environments • Protists often play the role of symbiont • Some protist symbionts may benefit their hosts • Dinoflagellates nourish coral polyps that build reefs • Hypermastigotesdigest cellulose in the gut of termites

  40. Some protists are parasitic • Plasmodium sp. causes malaria • Pfiesteria shumwayae is a dinoflagellate that causes fish kills

  41. Photosynthetic Protists • ecological producers and consumers • Many protists are important producersthat obtain energy from the sun • In aquatic environments, photosynthetic protists and prokaryotes are the main producers • The availability of nutrients can affect the concentration of protists other consumers herbivorous plankton carnivorous plankton bacteria soluble organic matter protistan producers The End

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