1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ch. 28 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

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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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Protists: Chapter 28

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Protists are also diverse in habitat, including freshwater and marine species Reproduction and life cycles are also highly varied among protists, with both sexual and asexual species

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

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endosymbiosis in Eukaryotic Evolution There is now considerable evidence that much of protist diversity has its origins in endosymbiosis

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

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

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 28.2: Diplomonads and parabasalids have modified mitochondria A tentative phylogeny of eukaryotes divides eukaryotes into many clades

11. Alveolata Diplomonadida Parabasala Euglenozoa Ancestral eukaryote Stramenopila Amoebozoa(Opisthokonta) (Viridiplantae) Cercozoa Radiolaria Fungi Animalia Rhodophyta Chlorophyta Plantae Plants Chlorophytes Charophyceans Red algaeMetazoansFungi Choanoflagellates Cellular slime molds Plasmodial slime molds GymnamoebasEntamoebasRadiolarians Chlorarachniophytes Foraminiferans Brown algae Golden algae Oomycetes Diatoms Ciliates Apicomplexans Euglenids Dinoflagellates Kinetoplastids Diplomonads Parabasalids

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diplomonads Diplomonads have two nuclei and multiple flagella

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

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parabasalids Parabasalids include trichomonads, which move by means of flagella and an undulating part of the plasma membrane

16. Flagella Trichomonas vaginalis, a parabasalid (colorized SEM) Undulating membrane 5 µm

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

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

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The parasitic kinetoplastid Trypanosoma causes sleeping sickness in humans

21. LE 28-7 9 µm

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

23. 5 µm Euglena (LM) Plasma membrane Nucleus Short flagellum Eyespot Light detector Contractile vacuole Chloroplast Paramylon granule Pellicle Long flagellum

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

26. 0.2 µm Alveoli Flagellum

27. 3 µm Flagella

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rapid growth of some dinoflagellates is responsible for causing “red tides,” which can be toxic to humans

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

30. Sporozoites (n) Inside mosquito Oocyst Zygote (2n) MEIOSIS Merozoite (n) Liver cell Liver FERTILIZATION Gametes Gametocytes (n) Red blood cells Inside human Merozoite Apex Red blood cell 0.5 µm Haploid (n) Key Diploid (2n) Malaria

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

32. LE 28-12 FEEDING, WASTE REMOVAL, AND WATER BALANCE CONJUGATION AND REPRODUCTION MEIOSIS MICRONUCLEAR FUSION Haploid micronucleus Diploid micronucleus Diploid micronucleus Contractile vacuole Oral groove Cell mouth Micronucleus Macronucleus 50 µm Thousands of cilia cover the surface of Paramecium. 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. 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. Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell. 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. Compatible mates Two cells of compatible mating strains align side by side and partially fuse. Macronucleus 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. The cells swap one micronucleus. The cells separate. Key Micronuclei fuse, forming a diploid micronucleus. Conjugation Reproduction Two rounds of cytokinesis partition one maccronucleus and one macronucleus into each of four daughter cells. The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. Three rounds of mitosis without cytokinesis produce eight micronuclei.

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

34. Smooth flagellum Hairy flagellum 5 µm

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

36. LE 2814_3 Egg nucleus (n) MEIOSIS FERTILIZATION Haploid (n) Key Diploid (2n) Oogonium Antheridial hypha with sperm nuclei (n) SEXUAL REPRODUCTION Zygote germination Zygotes (2n) Zoosporangium (2n) Zoospore (2n) Cyst Germ tube ASEXUAL REPRODUCTION

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

38. 3 µm

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diatoms are a major component of phytoplankton and are highly diverse

40. 50 µm Diatom diversity (LM)

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

42. 25 µm

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Brown Algae Brown algae, or phaeophytes, are the largest and most complex algae All are multicellular, and most are marine

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Brown algae include many species commonly called seaweeds Seaweeds have the most complex multicellular anatomy of all algae

45. Blade Stipe Holdfast

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Giant seaweeds called kelps live in deep parts of the ocean

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48. Human Uses of Seaweeds Many seaweeds are important commodities Many are harvested for food

49. The seaweed is grown on nets in shallow coastal waters. A worker spreads the seaweed on bamboo screens to dry. Paper-thin, glossy sheets of nori make a nutritious wrap for rice, seafood, and vegetables in sushi.

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alternation of Generations A variety of life cycles have evolved among the multicellular algae The most complex life cycles include an alternation of generations, the alternation of multicellular haploid and diploid forms

51. Developing sporophyte Zygote (2n) FERTILIZATION Mature female gametophyte (n) Egg Sperm MEIOSIS Haploid (n) Key Diploid (2n) Sporangia Sporophyte (2n) Zoospores Female Gametophytes (n) Male

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 28.6: Cercozoans and radiolarians have threadlike pseudopodia A newly recognized clade, Cercozoa, contains species among the organisms called amoebas Amoebas were formerly defined as protists that move and feed by means of pseudopodia Cercozoans are distinguished from most other amoebas by their threadlike pseudopodia

53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Foraminiferans (Forams) Foraminiferans, or forams, are named for porous, generally multichambered shells, called tests Pseudopodia extend through the pores in the test Foram tests in marine sediments form an extensive fossil record

54. 20 µm

55. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Radiolarians Marine protists called radiolarians have tests fused into one delicate piece, usually made of silica Radiolarians phagocytose microorganisms with their pseudopodia The pseudopodia of radiolarians, known as axopodia, radiate from the central body

56. 200 µm Axopodia

57. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 28.7: Amoebozoans have lobe-shaped pseudopodia Amoebozoans are amoeba that have lobe- shaped, rather than threadlike, pseudopodia They include gymnamoebas, entamoebas, and slime molds

58. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gymnamoebas 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

59. Pseudopodia 40 µm

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Entamoebas Entamoebas are parasites of vertebrates and some invertebrates Entamoeba histolytica causes amebic dysentery in humans

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Slime Molds Slime molds, or mycetozoans, were once thought to be fungi Molecular systematics places slime molds in the clade Amoebozoa

62. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plasmodial Slime Molds Many species of plasmodial slime molds are brightly pigmented, usually yellow or orange

63. 4 cm

64. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At one point in the life cycle, plasmodial slime molds form a mass called a plasmodium The plasmodium is undivided by membranes and contains many diploid nuclei It extends pseudopodia through decomposing material, engulfing food by phagocytosis

65. 1 mm MEIOSIS Haploid (n) Key Diploid (2n) Zygote (2n) SYNGAMY Feeding plasmodium Mature plasmodium (preparing to fruit) Young sporangium Mature sporangium Spores (n) Stalk Amoeboid cells (n) Germinating spore Flagellated cells (n)

66. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Slime Molds Cellular slime molds form multicellular aggregates in which cells are separated by their membranes Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity

67. 600 µm MEIOSIS Haploid (n) Key Diploid (2n) Zygote (2n) SYNGAMY Migrating aggregate Emerging amoeba SEXUAL REPRODUCTION Amoebas Spores (n) Solitary amoebas (feeding stage) ASEXUAL REPRODUCTION Fruiting bodies Aggregated amoebas 200 µm

68. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 28.8: 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

69. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Red Algae Red algae are reddish in color due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll Red algae are usually multicellular; the largest are seaweeds Red algae are the most abundant large algae in coastal waters of the tropics

70. Bonnemaisonia hamifera, a filamentous red alga. Dulse (Palmaria palmata). This edible species has a “leafy” form. A coralline alga. The cells walls of corralline algae are hardened by calcium carbonate. Some coralline algae are members of the biological communities called coral reefs.

71. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Green Algae Green algae are named for their grass-green chloroplasts Two main groups: chlorophytes and charophyceans They are closely related to land plants

72. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most chlorophytes live in fresh water, although many are marine Other chlorophytes live in damp soil, as symbionts in lichens, or in snow

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74. Chlorophytes include unicellular, colonial, and multicellular forms

75. Calperpa, an inter-tidal chlorophyte. The branched filaments lack cross-walls and thus are multinucleate. In effect, the thallus is one huge “supercell.” 50 µm Volox, a colonial freshwater chlorophyte. The colony is a hollow ball whose wall is composed of hundreds or thousands of biflagellated cells (see inset LM) embedded in a gelatinous matrix. The cells are usually connected by strands of cytoplasm; if isolated, these cells cannot reproduce. The large colonies seen here will eventually release the small “daughter” colonies within them (LM). Ulva, or sea lettuce. This edible seaweed has a multicellular thallus differentiated into leaflike blades and a rootlike holdfast that anchors the alga against turbulent waves and tides. 20 µm

76. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages

77. MEIOSIS Haploid (n) Key Diploid (2n) SYNGAMY SEXUAL REPRODUCTION Zoospores ASEXUAL REPRODUCTION Mature cell (n) Zygote (2n) Regions of single chloroplast Nucleus Flagella Cell wall 1 µm

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