1. The Protists Chapter 20

2. Protists General characteristics –Unicellular, colonial, simple multicellular organisms –Eukaryotic –Some exhibit both plant and animal characteristics Euglenoids Slime molds

3. Protists –Many are photosynthetic All have chlorophyll a Often called algae

4. Protists Evolutionary relationships of eukaryotes –Difficult problem Splits between many lineages of eukaryotes are ancient Have been events in which organisms (or parts of organisms) that are not closely related have joined to form new organisms Not many characters are shared by all members of group Shared characters often yield different results when analyzed cladistically

5. Protists –At base of eukaryotic tree Group of protists –Some lack mitochondria and live as parasites on other organisms –Rest of eukaryotes divided into two major clades One clade –Animals, fungi, slime molds, and small group of amoeboid organisms –None are photosynthetic –Most are motile (except fungi)

6. Protists Other clade –Variety of protist groups –Includes both photosynthetic and nonphotosynthetic protists

8. Photosynthetic Protists Commonly called algae Variety of life histories, body forms, ecological roles Often named for distinctive colors Unicellular, colonial, filamentous, sheetlike

9. Amoebozoa Clade of protists that includes amoebas and slime molds Traits combine aspects of fungi and animals –Animal characteristics Lack cell walls, engulf food, have motile cells at some phase of life cycle –Fungi and plant characteristics Form sporangia and nonmotile cells with cell walls

10. Amoebozoa –Two groups of slime molds Myxomycota Acrasiomycota MyxomycotaAcrasiomycota Plasmodial slime molds Cellular slime molds Contain thousands of nuclei with no membranes separating them Smaller, have fewer nuclei, and do have membranes between the nuclei

11. Alveolates Common character –System of alveoli Tiny membrane-enclosed sacs found beneath plasma membrane Clade composed of four ecologically and economically significant lineages –Ciliates Found in freshwater Have cilia and engulf food Often called protozoa Example: Paramecium

12. Alveolates –Foraminifera Characterized by hard shell Feeding strategies include active predation, scavenging, using sticky webs to trap food Shells –Common fossils –Important in dating geological strata and in oil exploration

13. Alveolates –Apicomplexa Parasitic or pathogenic protists Found to contain vestigial plastids Examples –Plasmodium (causes malaria) –Toxoplasma (causes toxoplasmosis)

14. Alveolates –Photosynthetic dinoflagellates Most are unicellular, motile, and marine Usually have two flagella (both emerge from same pore) –One is flat and ribbonlike, encircles cell in groove around middle, provides rotational movement –Other flagellum trails behind and provides forward movement Contain pigments –Chlorophylls a and c –Brown pigment (fucoxanthin)

15. Alveolates Chloroplasts surrounded by three or four membranes –May also contain a remnant nucleus Some are bioluminescent Overgrowth (bloom) can cause red tide

16. Euglenoids Typically single-celled Usually in freshwater but could be in salt or brackish water or soil A few are parasitic Lack cell wall –Flexible strips of proteins and microtubules under cell membrane Have two flagella

17. Euglenoids About one third of the 1,000 species have chloroplasts –Contain chlorophylls a and b, carotenoids –Three membranes around chloroplasts May have eyespot –Red or orange light-sensitive organelle –Pigment (astaxanthin) is a carotenoid has antioxidant properties Extracted and sold as health supplement

18. Euglenoids Never been observed to reproduce sexually Important in food chains of freshwater ecosystems Ecological indicators of water that is rich in organic matter

19. Heterokonts Clade also sometimes called Stramenopiles or Chromista All have two unequally sized flagella Heterokonts and alveolates share common ancestor

20. Heterokonts Includes –Oomycota (water molds and downy mildew) –Xanthophyta (golden algae) –Chrysophyta (golden algae) –Diatoms –Brown algae

21. Heterokonts Group Taxonomic name Number of species Key characteristics Brown algaePhaeophyta1,500 Two unequal lateral flagella; cell wall of algin + cellulose; chlorophylls a and c; filamentous to complex large kelps; mainly in shallow, cool, marine water DiatomsBacillariophyta8,000 Usually no flagella; cell wall of silica + pectin; chlorophylls a and c; carbohydrates stored as oil; mainly unicellular and free-floating; prominent as freshwater or saltwater phytoplankton Xanthophyta 400 Two flagella (various); cellulose cell wall; chlorophyll a (+ c in some), oil stored; mainly unicellular; mainly in freshwater Chrysophyta 300 Two unequal anterior flagella; cellulose cell wall (+ silica in some), chlorophylls a and c; mainly unicellular and in freshwater

22. Heterokonts Oomycota –Includes egg fungi, downy mildews, and water molds –Fungal characteristics Hyphae, produce spores, lack chlorophyll –Algal characteristics Cellulose cell walls, swimming spores, some cellular details, some metabolic pathways

23. Heterokonts Oomycota –Most are decomposers –Some are pathogens of important crops Downy mildew of grapes –Plasmopora viticola –Nearly destroyed French vineyards in nineteenth century Potato blight –Phytophthora infestans –Changed history of Ireland in 1840s

24. Heterokonts Diatoms –Important members of phytoplankton –Cell wall made out of silica Two parts (valves) to cell wall Fit together like halves of Petri dish –Shape of cell varies –Pigments Chlorophylls a and c Fucoxanthin

25. Heterokonts Diatoms –Store food reserves as oil –Some exhibit gliding motion –Stalked diatoms grow as epiphytes on seaweeds and kelps –Can also become attached to nonliving surfaces –Create algal turfs Coat shallow rocks in quiet freshwater or marine habitats Have as high a daily productivity per square meter as tropical rain forest

26. Heterokonts Diatoms –Dominate surfaces of salt mudflats –Extensive fossil record –Indicators for petroleum exploration –Silica shells form extensive deposits

27. Heterokonts Brown algae –Almost exclusively marine –More abundant in cool, shallow waters –More complex brown algae  kelps Chlorophylls a and c, fucoxanthin No grana in chloroplasts Store carbohydrates as mannitol or laminaran Cell walls composed of cellulose and alginates

28. Heterokonts Brown algae –Kelps Example –Macrocystis –Largest known kelp –Fast growth rate –Consists of »Holdfast – anchors »Stipes – stem-like structure »Blades – leaf-like »Gas-filled air bladder - buoyancy

29. Heterokonts Brown algae –Kelps Outer layer is protective and consists of cells that are also meristematic and contain chloroplasts  called meristoderm Region of cortex beneath meristoderm –Composed of parenchyma-like cells –Mucilage-secreting cells line canals through medulla Medulla –Innermost part of stipe –Loosely packed filaments of cells

30. Heterokonts Brown algae –Kelps Cells that function as sieve elements –Found in transition zone between cortex and medulla –Have sieve plates, form callose, adjoin one another to make continuous tubes –Mannitol moves through tubes No tissue that resembles xylem

31. The Plants Molecular data supports idea that red algae, green algae, and land plants belong in same clade Green algae –Not a natural monophyletic group –Gave rise to land plants

32. The Plants Red algae –Almost exclusively marine –Most abundant in warm water –Can grow to considerable depth –More complex forms called seaweeds Parenchyma-like tissue Holdfast for anchoring Stipes never very long Blades never have gas bladders

33. The Plants Red algae Pigments –Chlorophyll a and phycobilins Cell wall –Cellulose and sometimes agar or carrageenan Food storage molecule –Floridean starch

34. Comparison of Red and Brown Algae Brown algaeRed algae Evolutionary group HeterokontsPlants Common name KelpSeaweed Habitat Marine; cool, shallow water Marine; warm water; greater depths Pigments Chlorophylls a and c, fucoxanthin Chlorophyll a, phycobilins Food storage Mannitol or laminaranFloridean starch Cell wallCellulose and alginates Cellulose; sometimes also contains agar or carrageenan

35. The Plants Green algae –Mainly in freshwater habitats but could be in saltwater, on snow, in hot springs, on soil, on leaves and branches of terrestrial plants –Shared characteristics Chlorophylls a and b, carotenoid accessory pigments Food stored as starch Cellulose cell walls Formation of phragmoplast during mitosis Asymmetrically attached flagella

36. The Plants Green algae –Groups Chlorophyceae Ulvophyceae Charophytes

37. The Plants Green algae –Chlorophyceae Two flagella at anterior end Single, large, cup-shaped chloroplast Most have red-colored carotene eyespot Examples –Gonium –Volvox

38. The Plants Green algae –Ulvophyceae Sea lettuces Typically small, green seaweeds Consumed as food in many places Example –Caulerpa »Accidentally spread to areas with no natural limits to growth »Multiplied explosively »Produces toxins that are lethal to urchins and some fish »Has been discovered off coast of California

39. The Plants Green algae –Charophytes Group of ancient green algae Examples –Coleochaete »Once thought to be closest living relative to land plants –Chara »According to molecular characters → more closely related to land plants than Coleochaete

40. Ecological and Economic Importance of Algae Phytoplankton –Base of aquatic food chains –“grasses of the sea” –Unicellular –Produce about four times the amount of photosynthate that is produced by the Earth’s croplands each year –Bloom Algal overgrowth

41. Ecological and Economic Importance of Algae Help build tropical reefs –Coralline algae Certain red and green algae Create carbonate exoskeleton that becomes part of reef when alga die

42. Ecological and Economic Importance of Algae –Coralline algae Some algae grow symbiotically with coralline animals –Mutualistic relationship »Algae produces sugar and oxygen for animal »Cells of coral contribute CO 2, nitrogen, and minerals for alga –Usually dinoflagellate Symbiodinium microadriaticum –Has photosynthetic rate 10 times greater than phytoplankton »Protected and nourished by animal cytoplasm around it

43. Ecological and Economic Importance of Algae Medicine, food, and fertilizer –Laminaria Harvested off coast of China as source of iodine –Porphyra (nori) Cultivated Supplement to Japanese diet –limu used as food source by Polynesians in Hawaii

44. Ecological and Economic Importance of Algae Medicine, food, and fertilizer –Palmaria palmate red seaweed, dulce Used as food in British isles –Chondrus crispus Irish moss, red algae Used to make jelly desert called blancmange

45. Ecological and Economic Importance of Algae Medicine, food, and fertilizer –Good fertilizer or cattle feed supplements Compares favorably with manure as a fertilizer Enhances germination Increases uptake of nutrients Seems to give degree of resistance to frost, pathogens, and insects

46. Ecological and Economic Importance of Algae Uses of algal cell walls –Diatomite (diatomaceous earth) Rich deposit near Lompoc, California Uses of diatomite –Superior filter or clarifying material –Added to many materials to provide bulk, improve flow, increase stability »Dental impressions, grouting, paint, asphalt, pesticides –Abrasive

47. Ecological and Economic Importance of Algae Uses of algal cell walls –Agar Primarily obtained from red algae, Gelidium and Gracilaria Used as a culture medium Substance purified from agar (agarose) used for gel electrophoresis Used in baking industry –Added to icing to retard drying in open air or melting in cellophane packages Used as a bulk laxative

48. Ecological and Economic Importance of Algae Uses of algal cell walls –Carrageenan Reacts with proteins in milk to make stable, creamy, thick solution or gel –Used commercially in ice cream, whipped cream, fruit syrups, chocolate milk, custard, evaporated milk, bread, macaroni Added to dietetic, low-calorie foods Used in toothpaste, pharmaceutical jellies, and lotions Mainly comes from Irish moss, red algae

49. Ecological and Economic Importance of Algae Uses of algal cell walls –Algin Compound of brown algae Strongly absorbs water Used as an additive to beer, water-based paints, textile sizing, ceramic glaze, syrup, toothpaste, hand lotion

50. Ecological and Economic Importance of Algae –Algin Commercially harvested species –Macrocystis pyrifera – along California coast –Ascophyllum, Fucus, and Laminaria – off Maritime Canada, northeastern United States, England, China coast –Durvillea – from Australian waters

51. Algal Reproduction Asexual reproduction occurs more often than sexual reproduction Asexual methods of reproduction –Cell division (single-celled algae) –Fragmentation (filamentous algae) –Formation, liberation, germination of motile or nonmotile spores produced in sporangia

52. Algal Reproduction Three basic life cycles –Zygotic Only diploid phase of life cycle is single-celled zygote –Gametic Only haploid phase of life cycle is single-celled gamete –Sporic Multicellular gametophytes and sporophytes

53. Algal Reproduction Zygotic life cycle –Example: Ulothrix –Sexual reproduction Some of nuclei divide by mitotic divisions to produce many motile gametes inside wall of parent cell Parent cell is gametangium Ulothrix gamete approaches another suitable gamete Cells fuse forming diploid zygote cell with four flagella

54. Algal Reproduction Zygotic life cycle Zygote become spherical, loses flagella, enters resting stage When conditions are right, zygote becomes metabolically active Zygote divides by meiosis and produces + and – meiospores Meiospores are dispersed Each meiospore can germinate, divide by mitosis, produce a + or – haploid plant

55. Algal Reproduction Zygotic life cycle –Asexual reproduction Vegetative cell becomes sporangium 16 to 64 pear-shaped mitospores are released After period of activity, motile mitospores settle to bottom of pond, lose flagella, produce new plant by mitosis

57. Algal Reproduction Gametic life cycle –Example: diatoms –Sexual reproduction Diploid nucleus undergoes meiosis Produces four haploid nuclei (only 1 or 2 survive to become gametes) Gametangia near each other open, gametes emerge, fuse, form diploid zygote Zygote increases in size Secretes silica wall around itself, becomes vegetative diploid diatom

58. Algal Reproduction Gametic life cycle –Asexual reproduction Reproduce by cell division New cell wall forms within old one Progeny cell that inherits small wall segment of cell wall makes wall that is even smaller Pattern continues until critically small size is reached Cell division stops Cell then must reproduce sexually

60. Algal Reproduction Sporic life cycle with isomorphic generations –Identical looking gametophytes and sporophytes –Example: Ectocarpus Haploid phase has gametangia on side branches Mitosis within gametangium produces gametes Released isogamous gametes (look alike) represent + and – mating types

61. Algal Reproduction Sporic life cycle with isomorphic generations Plus and minus gametes fuse in open water → yields diploid zygote Zygote settles to bottom, germinates, divides by mitosis, produces diploid organism Diploid sporophyte looks identical to haploid gametophyte

62. Algal Reproduction Sporic life cycle with isomorphic generations Sporophyte produces two kinds of reproductive cells –Asexual sporangia develop on side branches »Release motile cells (diploid mitospore) capable of producing new individual (sporophyte) by itself –Spherical sporangium »Produces meiospores »Meiospores germinate, producing gametophytes

64. Algal Reproduction Sporic life cycle with heteromorphic generations –Gametophyte and sporophyte are not identical –Most highly developed in brown algae –Example: Laminaria Sporophyte generation with well-developed holdfast and long unbranched stipe with narrow blades

65. Algal Reproduction Sporic life cycle with heteromorphic generations Sporangia form in groups just below meristoderm on blade Single-celled sporangium undergoes meiosis Produces 8 to 64 meiospores Meiospores are released, swim, settle to bottom, produce gametophytes Some gametophytes produce female gametes, some produce male gametes

66. Algal Reproduction Sporic life cycle with heteromorphic generations Cells at tips of some male gametophyte filaments enlarge and function as antheridia –Nuclei undergo mitosis producing motile sperm Cells at tips of some female gametophyte filaments enlarge and function as oogonia –Nuclei undergo mitosis producing one to several large eggs –Eggs are extruded but remain attached

67. Algal Reproduction Sporic life cycle with heteromorphic generations Sperm cell fuses with egg Produces zygote which forms sporophyte Sporophyte separates from gametophyte, carried by currents to bottom, begins to develop into mature Laminaria sporophyte