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

4. 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

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

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

8. LE 28-2 The freshwater ciliate Stentor, a unicellular protozoan (LM)
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)

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

10. 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

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

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

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

14. 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

15. Diplomonads
Diplomonads have two nuclei and multiple flagella

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

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

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

19. 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

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

21. 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

22. The parasitic kinetoplastid Trypanosoma causes sleeping sickness in humans

23. LE 28-7
9 µm

24. 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

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

26. 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

27. Video: Dinoflagellate
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

28. LE 28-9
0.2 µm
Flagellum
Alveoli

29. LE 28-10
Flagella
3 µm

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

31. 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

32. Inside mosquito Inside human MEIOSIS FERTILIZATION Key
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
Gametocytes
(n)
Haploid (n)
Diploid (2n)

33. 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

34. FEEDING, WASTE REMOVAL, AND WATER BALANCE CONJUGATION AND REPRODUCTION
LE 28-12
FEEDING, WASTE REMOVAL, AND WATER BALANCE
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
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.
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
Macronucleus
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.
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.
The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei.
Three rounds of mitosis without cytokinesis produce eight micronuclei.
Micronuclei fuse, forming a diploid micronucleus.
Key
Conjugation
Reproduction

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

36. 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

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

38. 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

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

40. Video: Water Mold Oogonium Video: Water Mold Zoospores

41. 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

42. LE 28-15
3 µm

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

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

45. Video: Various Diatoms
Video: Diatoms Moving
Video: Various Diatoms

46. 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

47. LE 28-17
25 µm

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

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

50. LE 28-18
Blade
Stipe
Holdfast

51. Giant seaweeds called kelps live in deep parts of the ocean

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

54. The seaweed is grown on nets in shallow coastal waters.
LE 28-20
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.

55. 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

56. LE 28-21 Key Haploid (n) Diploid (2n) Sporangia MEIOSIS Sporophyte
Zoospores
Female
Developing
sporophyte
Gametophytes
(n)
Zygote
(2n)
Egg
FERTILIZATION
Male
Mature female
gametophyte
(n)
Sperm

57. 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

58. 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

59. LE 28-22
20 µm

60. 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

61. LE 28-23
Axopodia
200 µm

62. 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

63. Video: Amoeba Pseudopodia
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
Video: Amoeba Pseudopodia
Video: Amoeba

64. LE 28-24
Pseudopodia
40 µm

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

66. Slime Molds Slime molds, or mycetozoans, were once thought to be fungi
Molecular systematics places slime molds in the clade Amoebozoa

67. Plasmodial Slime Molds
Many species of plasmodial slime molds are brightly pigmented, usually yellow or orange
Video: Plasmodial Slime Mold Streaming
Video: Plasmodial Slime Mold

68. LE 28-25
4 cm

69. 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

70. LE 28-26 Feeding Mature plasmodium plasmodium (preparing to fruit)
Zygote
(2n)
Young
sporangium
SYNGAMY
1 mm
Mature
sporangium
Amoeboid cells
(n)
Key
Spores
(n)
Germinating
spore
MEIOSIS
Haploid (n)
Flagellated cells
(n)
Diploid (2n)
Stalk

71. 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

72. LE 28-27 Emerging amoeba Spores (n) Zygote (2n) SEXUAL REPRODUCTION
SYNGAMY
Emerging
amoeba
Spores
(n)
Zygote
(2n)
SEXUAL
REPRODUCTION
Solitary amoebas
(feeding stage)
600 µm
MEIOSIS
Amoebas
ASEXUAL
REPRODUCTION
Fruiting
bodies
Aggregated
amoebas
Key
Haploid (n)
Diploid (2n)
Migrating
aggregate
200 µm

73. 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

74. 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

75. LE 28-28 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.
Bonnemaisonia hamifera, a
filamentous red alga.

76. Green Algae Green algae are named for their grass-green chloroplasts
Two main groups: chlorophytes and charophyceans
They are closely related to land plants

77. Most chlorophytes live in fresh water, although many are marine
Other chlorophytes live in damp soil, as symbionts in lichens, or in snow

79. Chlorophytes include unicellular, colonial, and multicellular forms
Video: Volvox Colony
Video: Volvox Daughter
Video: Volvox Female Spheroid
Video: Volvox Flagella
Video: Volvox Inversion 1
Video: Volvox Inversion 2
Video: Volvox Sperm and Female

80. LE 28-30
20 µm
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).
Calperpa, an
inter-tidal chlorophyte. The branched filaments lack cross-walls and thus are multinucleate. In effect, the thallus is one huge “supercell.”
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.

81. Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages
Video: Chlamydomonas

82. LE 28-31 Flagella 1 µm Cell wall Nucleus Zoospores SYNGAMY Mature cell
ASEXUAL
REPRODUCTION
SEXUAL
REPRODUCTION
Regions
of single
chloroplast
Zygote
(2n)
MEIOSIS
Key
Haploid (n)
Diploid (2n)