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Chapter 28

Chapter 28. Protists. Overview: A World in a Drop of Water. Even a low-power microscope can reveal a great variety of organisms in a drop of pond water These amazing organisms belong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists

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Chapter 28

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  1. Chapter 28 Protists

  2. Overview: A World in a Drop of Water • Even a low-power microscope can reveal a great variety of organisms in a drop of pond water • These amazing organisms belong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists • Advances in eukaryotic systematics have caused the classification of protists to change significantly

  3. Concept 28.1: Protists are an extremely diverse assortment of eukaryotes • Protists are more diverse than all other eukaryotes and are no longer classified in a single kingdom • Most protists are unicellular, but there are some colonial and multicellular species

  4. 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

  5. Protists are also diverse in habitat, including freshwater and marine species Video: Stentor Video: Stentor Ciliate Movement

  6. Reproduction and life cycles are also highly varied among protists, with both sexual and asexual species

  7. LE 28-2 The freshwater ciliate Stentor, a unicellular protozoan (LM) 100 µm 100 µm Ceratium tripos, a unicellular marine dinoflagellate (LM) 4 cm Delesseria Sanguinea, a multicellular marine red alga 500 µm Spirogyra, a filamentous freshwater green alga (insert LM)

  8. Endosymbiosis in Eukaryotic Evolution • There is now considerable evidence that much of protist diversity has its origins in endosymbiosis

  9. 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

  10. LE 28-3 Plastid Dinoflagellates Secondary endosymbiosis Apicomplexans Red algae Cyanobacterium Primary endosymbiosis Stramenopiles Secondary endosymbiosis Heterotrophic eukaryote Plastid Euglenids Secondary endosymbiosis Green algae Chlorarachniophytes

  11. Concept 28.2: Diplomonads and parabasalids have modified mitochondria • A tentative phylogeny of eukaryotes divides eukaryotes into many clades

  12. LE 28-4 Animalia Fungi Plantae Chlorophyta Euglenozoa Parabasala Diplomonadida Radiolaria Rhodophyta Cercozoa Stramenopila Amoebozoa (Opisthokonta) Alveolata (Viridiplantae) Choanoflagellates Dinoflagellates Chlorarachniophytes Euglenids Ciliates Charophyceans Plants Diplomonads Oomycetes Foraminiferans Radiolarians Gymnamoebas Entamoebas Fungi Metazoans Red algae Diatoms Cellular slime molds Chlorophytes Parabasalids Brown algae Kinetoplastids Apicomplexans Golden algae Plasmodial slime molds Ancestral eukaryote

  13. Diplomonads and parabasalids are adapted to anaerobic environments • Both clades lack plastids • Their mitochondria do not have DNA, electron transport chains, and citric-acid cycle enzymes

  14. Diplomonads • Diplomonads have two nuclei and multiple flagella

  15. LE 28-5a 5 µm Giardia intestinalis, a diplomonad (colorized SEM)

  16. Parabasalids • Parabasalids include trichomonads, which move by means of flagella and an undulating part of the plasma membrane

  17. LE 28-5b Flagella Undulating membrane 5 µm Trichomonas vaginalis, a parabasalid (colorized SEM)

  18. Concept 28.3: Euglenozoans have flagella with a unique internal structure • Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites • Their main feature distinguishing them as a clade is a spiral or crystalline rod of unknown function inside their flagella

  19. LE 28-6 Flagella 0.2 µm Crystalline rod Ring of microtubules

  20. Kinetoplastids • Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast • They include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems

  21. The parasitic kinetoplastid Trypanosoma causes sleeping sickness in humans

  22. LE 28-7 9 µm

  23. Euglenids • Euglenids have one or two flagella that emerge from a pocket at one end of the cell • The glucose polymer paramylon is also characteristic of this clade Video: Euglena Video: Euglena Motion

  24. LE 28-8 Long flagellum Eyespot Light detector Short flagellum Nucleus Contractile vacuole Euglena (LM) 5 µm Plasma membrane Chloroplast Pellicle Paramylon granule

  25. Concept 28.4: Alveolates have sacs beneath the plasma membrane • Members of the clade Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane

  26. Dinoflagellates • Dinoflagellates are a diverse group of aquatic photoautotrophs and heterotrophs • They are abundant components of both marine and freshwater phytoplankton • Each has a characteristic shape that in many species is reinforced by internal plates of cellulose • Two flagella make them spin as they move through the water Video: Dinoflagellate

  27. LE 28-9 0.2 µm Flagellum Alveoli

  28. LE 28-10 Flagella 3 µm

  29. Rapid growth of some dinoflagellates is responsible for causing “red tides,” which can be toxic to humans

  30. Apicomplexans • Apicomplexans are parasites of animals and some cause serious human diseases • One end, the apex, contains a complex of organelles specialized for penetrating a host • They have a nonphotosynthetic plastid, the apicoplast • Most have sexual and asexual stages that require two or more different host species for completion

  31. LE 28-11 Inside mosquito Inside human Merozoite Sporozoites (n) Liver Liver cell Oocyst Apex MEIOSIS Merozoite (n) Red blood cell 0.5 µm Zygote (2n) Red blood cells FERTILIZATION Key Gametes Haploid (n) Gametocytes (n) Diploid (2n)

  32. Ciliates • Ciliates, a large varied group of protists, are named for their use of cilia to move and feed • They have large macronuclei and small micronuclei • The micronuclei function during conjugation, a sexual process that produces genetic variation • Conjugation is separate from reproduction, which generally occurs by binary fission

  33. LE 28-12 FEEDING, WASTE REMOVAL, AND WATER BALANCE Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis. Paramecium, like other freshwater protists, constantly takes in water by osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate excess water from radial canals and periodically expel it through the plasma membrane. Contractile vacuole Oral groove Cell mouth Thousands of cilia cover the surface of Paramecium. Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell. 50 µm Micronucleus The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore. Macronucleus CONJUGATION AND REPRODUCTION Meiosis of micronuclei produces four haploid micronuclei in each cell. Three micronuclei in each cell disintegrate. The remaining micro-nucleus in each cell divides by mitosis. Two cells of compatible mating strains align side by side and partially fuse. Compatible mates Macronucleus The cells swap one micronucleus. MEIOSIS Haploid micronucleus Diploid micronucleus Diploid micronucleus MICRONUCLEAR FUSION The cells separate. Two rounds of cytokinesis partition one maccronucleus and one macronucleus into each of four daughter cells. Micronuclei fuse, forming a diploid micronucleus. The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. Three rounds of mitosis without cytokinesis produce eight micronuclei. Key Conjugation Reproduction

  34. Video: Paramecium Cilia Video: Paramecium Vacuole Video: Vorticella Cilia Video: Vorticella Detail Video: Vorticella Habitat

  35. Concept 28.5: Stramenopiles have “hairy” and smooth flagella • The clade Stramenopila includes several groups of heterotrophs as well as certain groups of algae • Most have a “hairy” flagellum paired with a “smooth” flagellum

  36. LE 28-13 Hairy flagellum Smooth flagellum 5 µm

  37. Oomycetes (Water Molds and Their Relatives) • Oomycetes include water molds, white rusts, and downy mildews • They were once considered fungi based on morphological studies • Most oomycetes are decomposers or parasites • They have filaments (hyphae) that facilitate nutrient uptake • Their ecological impact can be great, as in Phytophthora infestans causing potato blight

  38. LE 28-14_3 Oogonium Germ tube Egg nucleus (n) Cyst Antheridial hypha with sperm nuclei (n) MEIOSIS ASEXUAL REPRODUCTION Zoospore (2n) FERTILIZATION Zygote germination Zygotes (2n) SEXUAL REPRODUCTION Zoosporangium (2n) Key Haploid (n) Diploid (2n)

  39. Video: Water Mold Oogonium Video: Water Mold Zoospores

  40. Diatoms • Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated silica • Fossilized diatom walls compose much of the sediments known as diatomaceous earth

  41. LE 28-15 3 µm

  42. Diatoms are a major component of phytoplankton and are highly diverse

  43. LE 28-16 Diatom diversity (LM) 50 µm

  44. Video: Diatoms Moving Video: Various Diatoms

  45. Golden Algae • Golden algae, or chrysophytes, are named for their color, which results from their yellow and brown carotenoids • The cells of golden algae are typically biflagellated, with both flagella near one end • Most are unicellular, but some are colonial

  46. LE 28-17 25 µm

  47. Brown Algae • Brown algae, or phaeophytes, are the largest and most complex algae • All are multicellular, and most are marine

  48. Brown algae include many species commonly called seaweeds • Seaweeds have the most complex multicellular anatomy of all algae

  49. LE 28-18 Blade Stipe Holdfast

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