1. Protists
Chapter 25

2. Learning Objective 1
What features are common to the members of kingdom Protista?

3. Protists
Mostly unicellular eukaryotic organisms that live in aquatic environments

4. Sizes of Protists Unicellular organisms Colonies Coenocytes
microscopic
Colonies
loosely connected groups of cells
Coenocytes
multinucleate masses of cytoplasm
Multicellular organisms
composed of many cells

5. Chlamydomonas
A unicellular protist

6. Flagella Cell wall Nucleus Chloroplast Starch granule
Figure 25.1: Chlamydomonas, a unicellular protist.
Chlamydomonas is a motile organism with two flagella and a cup-shaped chloroplast.
Chloroplast
Starch granule
Fig. 25-1, p. 531

7. KEY CONCEPTS
Protists are a diverse group of eukaryotic organisms, most of which are microscopic

8. Learning Objective 2
Discuss in general terms the diversity inherent in the protist kingdom
means of locomotion
modes of nutrition
interactions with other organisms
habitats
modes of reproduction

9. Locomotion
Pseudopodia
Flagella
Cilia
Some are nonmotile

10. Nutrition
Protists obtain their nutrients autotrophically or heterotrophically

11. Interactions Protists are free-living or symbiotic
Symbiotic relationships range from mutualism to parasitism

12. Habitats Most protists live in
ocean
freshwater ponds
lakes
streams
Parasitic protists live in body fluids of hosts

13. Reproduction Many protists reproduce both sexually and asexually
Others reproduce only asexually

14. KEY CONCEPTS
Protists vary in body plan (unicellular, colonial, coenocytic, multicellular), method of motility (pseudopodia, cilia, flagella), nutrition type (autotrophic, heterotrophic), and mode of reproduction (asexual, sexual)

15. Learning Objective 3 What is the hypothesis of serial endosymbiosis?
Explain some evidence that supports it

16. Serial Endosymbiosis Hypothesis:
Mitochondria and chloroplasts arose from symbiotic relationships between larger cells and smaller prokaryotes that were incorporated and lived within them

17. Mitochondria Probably originated from aerobic bacteria
Ribosomal RNA data suggests
ancient purple bacteria were ancestors of mitochondria

18. Chloroplasts Single primary endosymbiotic event
in red algae, green algae, and plants
cyanobacterium incorporated into a cell
Multiple secondary endosymbioses
in euglenoids, dinoflagellates, diatoms, golden algae, brown algae
nonfunctional chloroplasts in apicomplexans

19. Chloroplast Evolution

20. Eukaryotic cell with mitochondria
Mitochondrion
Nucleus
Eukaryotic cell with mitochondria
Bacterial DNA
(a) Primary endosymbiosis
Cyanobacterium (ancestor of chloroplast)
Figure 25.2: Chloroplast evolution by primary and secondary endosymbiosis.
(a) In primary endosymbiosis, an ancient eukaryotic cell engulfed a cyanobacterium, which survived and evolved into a chloroplast. The ancient cell is depicted as a eukaryotic cell because mitochondria almost certainly evolved before chloroplasts.
Fig. 25-2a, p. 532

21. Eukaryotic cell with mitochondria
Chloroplast DNA
(b) Secondary endosymbiosis
Chloroplast with two membranes
Eukaryotic cell with mitochondria and chloroplasts
(red alga)
Figure 25.2: Chloroplast evolution by primary and secondary endosymbiosis.
(b) In a secondary endosymbiotic event, a heterotrophic eukaryotic cell (with mitochondria) engulfed a eukaryotic cell with chloroplasts (a red alga is depicted). The red alga survived and evolved into a chloroplast surrounded by three membranes (a dinoflagellate chloroplast is depicted). Other secondary endosymbiotic events resulted in more complex chloroplast membrane structures.
Chloroplast with three membranes
Eukaryotic cell with mitochondria and chloroplasts (dinoflagellate?)
Fig. 25-2b, p. 532

22. Eukaryotic cell with mitochondria Mitochondrion
Nucleus
Cyanobacterium (ancestor of chloroplast)
Bacterial DNA
Chloroplast DNA
Chloroplast with two membranes
Eukaryotic cell with mitochondria and chloroplasts (red alga)
(a) Primary endosymbiosis
Eukaryotic cell with mitochondria
Chloroplast with three membranes
Eukaryotic cell with mitochondria and chloroplasts (dinoflagellate?)
(b) Secondary endosymbiosis
Figure 25.2: Chloroplast evolution by primary and secondary endosymbiosis.
(b) In a secondary endosymbiotic event, a heterotrophic eukaryotic cell (with mitochondria) engulfed a eukaryotic cell with chloroplasts (a red alga is depicted). The red alga survived and evolved into a chloroplast surrounded by three membranes (a dinoflagellate chloroplast is depicted). Other secondary endosymbiotic events resulted in more complex chloroplast membrane structures.
Stepped Art
Fig. 25-2b, p. 532

23. Learning Objective 4
What kinds of data do biologists use to classify eukaryotes?

24. Relationships Among Protists
Protist kingdom
paraphyletic group
Determined by
ultrastructure (electron microscopy)
comparative molecular data

25. Eukaryote Phyla

26. Zooflagellates (diplomonads) Zooflagellates (euglenoids) Apicomplexans
Water molds
Brown algae
Land plants
Green algae
slime molds
Red algae
Plasmodial
slime molds
Animals
Fungi
Amoebas
Ciliates
Cellular A
Figure 25.3: Evolutionary relationships among eukaryotes.
Relationships among eukaryotes are diverse and debated; this cladogram presents just one interpretation. It is based on comparisons of four protein sequences among many eukaryotic phyla. Foraminiferans, actinopods, dinoflagellates, diatoms, and golden algae are not included. Groups within ovals represent separate eukaryotic kingdoms in the six-kingdom system used in this text. All other eukaryotes (without the ovals) are in kingdom Protista, a paraphyletic group. Node A indicates the common ancestor of red algae, green algae, and plants. (Based on S. L. Baldauf, A. J. Roger, I. Wenk-Siefert, and W. F. Doolittle, “A Kingdom-Level Phylogeny of Eukaryotes Based on Combined Protein Data,” Science, Vol. 290, Nov. 3, 2000.)
Ancestral eukaryote
Fig. 25-3, p. 533

27. Eukaryote Clades

28. Foraminiferans and actinopods Zooflagellates (diplomonads)
Excavates
Alveolates
Plants
Discicristates
Heterokonts
Cercozoa
Amoebozoa
Opisthokonts
Apicomplexans
Foraminiferans and actinopods
Zooflagellates (diplomonads)
Zooflagellates, (euglenoids)
Plasmodial slime molds
Cellular slime molds
Water molds
Brown algae
Green algae
Land plants
Red algae
Animals
Amoebas
Fungi
Ciliates ?
Figure 25.4: The eight monophyletic clades of eukaryotes.
The major groups of eukaryotes are superimposed over Figure Because classification of the protists is in a state of flux, biologists will modify this diagram as more data are collected and evaluated. (Based on S. L. Baldauf, “The Deep Roots of Eukaryotes,” Science, Vol. 300, June 13, 2003.)
Ancestral eukaryote
Fig. 25-4, p. 535

29. KEY CONCEPTS
Protists are descendants of early eukaryotes

30. Learning Objective 5
Why are zooflagellates no longer classified in a single phylum?
Distinguish among diplomonads, euglenoids, and choanoflagellates

31. Zooflagellates Mostly unicellular heterotrophs
Move by whiplike flagella
Polyphyletic
separated into several monophyletic groups

32. Diplomonads Diplomonads are excavates Diplomonads have
with a deep (excavated) oral groove
Diplomonads have
one or two nuclei
no mitochondria
no Golgi complex
up to eight flagella

33. Excavates

34. Nucleus
Figure 25.5: The excavates.
Flagella
50 µm
Fig. 25-5b, p. 536

35. Euglenoids Euglenoids are discicristates Euglenoids Trypanosoma
with disclike cristae in mitochondria
Euglenoids
are unicellular and flagellate
some are photosynthetic
Trypanosoma
causes African sleeping sickness

36. Discicristates

37. Flagellum for locomotion Paramylon body (stored food)
Eyespot
Contractile vacuole
Chloroplast
Nucleus
Paramylon body (stored food)
Figure 25.6: The discicristates.
Pellicle
25 µm
Fig. 25-6a, p. 537

38. Flagellum for locomotion
Nonemergent flagellum (indistinguishable in micrograph)
Eyespot
Contractile vacuole
Mitochondria (indistinguishable
in micrograph)
Chloroplast
Nucleolus
Nucleus
Chromatin
Figure 25.6: The discicristates.
Paramylon body (stored food)
Pellicle
Fig. 25-6b, p. 537

39. Trypanosome with undulating membrane
Red blood cells
Trypanosome with undulating membrane
Flagellum
Figure 25.6: The discicristates.
25 µm
Fig. 25-6c, p. 537

40. Choanoflagellates Choanoflagellates are opisthokonts Choanoflagellates
single posterior flagellum in flagellate cells
collar of microvilli surrounds base of flagellum
Choanoflagellates
are related to fungi and animals

41. Choanoflagellate

42. Lorica (protective cover)
Flagellum
Collar
of microvilli
Cell
Lorica (protective cover)
Figure 25.25: Choanoflagellate.
Choanoflagellates are free-living zooflagellates that obtain food by waving their flagella, causing water currents to carry bacteria and other small particles of food into the collar of microvilli. A colonial form is shown. Each cell is 5 to 10 μm long, not including the flagellum.
Stalk
Fig , p. 551

43. Learning Objective 6 Describe and compare these alveolates: ciliates
dinoflagellates
apicomplexans

44. Ciliates Alveolates move by hairlike cilia
micronuclei (for sexual reproduction)
macronuclei (for cell metabolism and growth)
undergo complex sexual reproduction (conjugation)

45. Ciliates

46. Cilia Food vacuoles Micronucleus Macronucleus Contractile vacuole
Figure 25.7: Ciliates.
[(d) by H. Machemer in K. G. Grell, Protozoology, © 1973 Springer-Verlag.]
50 µm
Fig. 25-7a, p. 538

47. Cilia Food vacuoles Food Micronucleus Macronucleus Oral groove
Figure 25.7: Ciliates.
[(d) by H. Machemer in K. G. Grell, Protozoology, © 1973 Springer-Verlag.]
Contractile vacuole
Anal pore
Food vacuole
Fig. 25-7b, p. 538

48. Cytopharynx Macronucleus 250 µm Fig. 25-7c, p. 538
Figure 25.7: Ciliates.
[(d) by H. Machemer in K. G. Grell, Protozoology, © 1973 Springer-Verlag.]
250 µm
Fig. 25-7c, p. 538

49. Cirri Fig. 25-7d, p. 538 Figure 25.7: Ciliates.
[(d) by H. Machemer in K. G. Grell, Protozoology, © 1973 Springer-Verlag.]
Fig. 25-7d, p. 538

50. Conjugation

51. First meiotic division in each cell 4 One haploid micronucleus 2
First meiotic division in each cell 4
One haploid
micronucleus
divides by
mitosis; others disintegrate
Haploid micronuclei fuse 6
Disintegrating macronuclei
Diploid nuclei (2n)
Macronuclei
Micronuclei (2n)
Disintegrating micronuclei
Figure 25.8: Conjugation in Paramecium caudatum. 1
Two sexually compatible individuals join at oral surfaces
Second meiotic division in each cell 3
Each conjugating cell exchanges micronucleus 5 7
Cells separate
Fig. 25-8, p. 539

52. Insert “Ciliate conjugation”
ciliate_conjugation.swf

53. Watch conjugation by clicking on the figure in ThomsonNOW.

54. Dinoflagellates
Mostly unicellular, biflagellate, photosynthetic alveolates
major producers in marine ecosystems
Alveoli
flattened vesicles under plasma membrane
contain cellulose plates with silicates
Some produce toxic blooms (red tides)

55. Dinoflagellates

56. Apicomplexans Parasites Apical complex of microtubules Plasmodium
produce sporozoites
are nonmotile
Apical complex of microtubules
attaches apicomplexan to host cell
Plasmodium
causes malaria

57. Plasmodium

58. Sporozoites (n) DIPLOID (2n) HAPLOID (n) Zygote (2n)
Infected female Anopheles
mosquito bites uninfected human and transmits Plasmodium
sporozoites to
human blood. 1
Anopheles mosquito
Liver cell
Liver
Sporozoites (n)
Meiosis
Merozoites released 2
Sporozoites enter liver cells and divide to produce merozoites. Merozoites released from liver cells infect red blood cells. 6
Zygote embeds
in mosquito’s stomach lining and produces sporozoites (spores), which are released and migrate to salivary glands.
DIPLOID (2n)
HAPLOID (n)
Red blood cells
Zygote (2n) 3
In blood cells, merozoites divide to form more merozoites, which infect more red blood cells. Some merozoites form gametocytes.
Anopheles mosquito
Figure 25.10: The life cycle of Plasmodium, the causative agent of malaria.
Gametes
Fertilization
Gametocytes 5
In mosquito’s digestive tract, gametocytes develop into gametes, and fertilization occurs. 4
Uninfected female Anopheles mosquito bites infected person and obtains Plasmodium
gametocytes.
Fig , p. 541

59. Insert “Apicomplexan life cycle”
malaria_v2.swf

60. Watch the life cycle of the malaria parasite by clicking on the figure in ThomsonNOW.

61. Learning Objective 7 Describe and compare these heterokonts:
water molds
diatoms
golden algae
brown algae

62. Water Molds Heterokonts Water molds Phytophthora
have two different kinds of flagella
Water molds
have coenocytic mycelium
reproduce asexually (biflagellate zoospores)
reproduce sexually (oospores)
Phytophthora
causes late blight of potato, sudden oak death

63. A Water Mold

64. Figure 25.11: The life cycle of Saprolegnia, a water mold.
Fig a, p. 542

65. Oospheres within oogonium 2
Meiosis results in haploid sperm nuclei within antheridia and haploid oospheres (eggs) within oogonia. 3
Sperm nuclei move into oospheres.
Antheridium (male reproductive structure)
Meiosis
Fertilization
HAPLOID (n) GENERATION
Haploid sperm nuclei 1
Saprolegnia
reproduces sexually by antheridia and oogonia.
Oospores
DIPLOID (2n) GENERATION 4
After fertilization, oospores develop from fertilized oospheres. Each oospore may develop into new mycelium.
SEXUAL REPRODUCTION
Oogonium (female reproductive structure)
Germination of oospore
Figure 25.11: The life cycle of Saprolegnia, a water mold.
Germination of the zoospore
Mycelium
Zoosporangium
Encysted secondary zoospore
ASEXUAL REPRODUCTION (by mitosis)
Zoospores
Secondary zoospore (bean-shaped) 5
Saprolegnia reproduces asexually by forming zoospores within zoosporangium.
Encysted primary zoospore
Primary zoospore (pear-shaped)
Fig b, p. 542

66. Diatoms Mostly unicellular heterokonts
with shells containing silica
major producers in aquatic ecosystems
Some are part of floating plankton
Some live on rocks and sediments
move by gliding

67. Diatoms

68. Golden Algae
Mostly unicellular, biflagellate freshwater and marine heterokonts
major component of tiny nanoplankton
Coccolithophorids
golden algae covered by tiny, overlapping scales of calcium carbonate

69. Golden Algae

70. Brown Algae Multicellular heterokonts Kelps (largest brown algae)
important in cooler ocean waters
Kelps (largest brown algae)
leaflike blades
stemlike stipes
anchoring holdfasts
gas-filled bladders for buoyancy

71. Brown Algae

72. Blade
Figure 25.14: Brown algae.
Stipe
Holdfast
Laminaria is widely distributed on rocky coastlines of temperate and polar seas. It grows to 2 m (6.5 ft.)
Fig a, p. 544

73. Learning Objective 8 Describe foraminiferans and actinopods
Why do many biologists classify them in the monophyletic group cercozoa?

74. Cercozoa Amoeboid cells Often have hard outer shells (tests)
through which cytoplasmic projections extend

75. Foraminiferans Secrete many-chambered tests
Pores through which cytoplasmic projections extend
to move and obtain food

76. Foraminiferans

77. Actinopods Mostly marine plankton Obtain food with axopods
slender cytoplasmic projections that extend through pores in shells
Radiolarians
actinopods with glassy shells

78. Actinopods

79. Learning Objective 9
Support the hypothesis that red algae and green algae should be included in a monophyletic group with land plants

80. Plants Monophyletic group including Based on red algae green algae
land plants
Based on
molecular data
presence of chloroplasts bounded by outer and inner membranes

81. Red Algae Mostly multicellular seaweeds
important in warm tropical ocean waters
Some red algae incorporate calcium carbonate in cell walls
important in reef building

82. Red Algae

83. Insert “Red alga life cycle”
porphyra.swf

84. Green Algae
Wide diversity in size, structural complexity, and reproduction
Botanists hypothesize that ancestral green algae gave rise to land plants

85. Green Algae

86. Chlamydomonas

87. ASEXUAL REPRODUCTION (by mitosis) –5
Both mating types reproduce asexually by mitosis; only (-) strain is shown. – –
Zoospores –
ASEXUAL REPRODUCTION (by mitosis) – – 4
Four haploid cells emerge, two (+)
and two
(-). 1
Gametes are produced by mitosis. + –
SEXUAL REPRODUCTION – – +
HAPLOID (n) GENERATION – – +
Figure 25.17: The life cycle of Chlamydomonas.
Chlamydomonas, a unicellular haploid green alga with two mating types, (+) and (−), is an example of isogamous sexual reproduction.
from a different strain
DIPLOID (2n) GENERATION 2
(+) and (-) gametes fuse, forming a diploid zygote. +
Meiosis
Fertilization 3
Meiosis occurs.
Zygote (2n)
Fig , p. 547

88. Insert “Green alga life cycle”
chlamydomonas_v2.swf

89. Ulva

90. DIPLOID (2n) GENERATION4
Mature haploid alga
Each zoospore develops into multicellular male or female individual.
Zoospores
Gamete 1
Male and female algae produce biflagellate gametes by mitosis.
HAPLOID (n) GENERATION
Zoospores
Anisogamous gametes
DIPLOID (2n) GENERATION
Figure 25.18: The life cycle of Ulva.
The green alga Ulva alternates between haploid and diploid multicellular generations, which are identical in overall appearance. Gametes are isogamous or anisogamous (shown), depending on the species. 3
Special
cells in diploid
alga undergo meiosis to form haploid zoospores.
Meiosis
Fertilization 2
Gametes fuse, forming zygote, which attaches to substrate and develops into multicellular individual.
Motile zygote
Mature diploid alga
Fig , p. 548

91. Spirogyra

92. Fig. 25-19a, p. 548 Figure 25.19: Conjugation in Spirogyra.
(a, b) Filaments of two different mating types of the green alga Spirogyra align, and conjugation tubes grow between cells of the two haploid filaments.
Fig a, p. 548

93. Fig. 25-19b, p. 548 Figure 25.19: Conjugation in Spirogyra.
(a, b) Filaments of two different mating types of the green alga Spirogyra align, and conjugation tubes grow between cells of the two haploid filaments.
Fig b, p. 548

94. Fig. 25-19c, p. 548 Figure 25.19: Conjugation in Spirogyra.
(c) The contents of one cell passes into the other through the conjugation tube.
Fig c, p. 548

95. Fig. 25-19d, p. 548 Figure 25.19: Conjugation in Spirogyra.
(d) The two cells fuse, forming a diploid zygote. Following a period of dormancy, the rounded zygote undergoes meiosis, restoring the haploid condition.
Fig d, p. 548

96. KEY CONCEPTS
Animals, fungi, and plants evolved from protist ancestors

97. Learning Objective 10 Describe and compare these amoebozoa: amoebas
plasmodial slime molds
cellular slime molds

98. Amoebas Use cytoplasmic extensions (pseudopodia) Entamoeba histolytica
to move and obtain food by phagocytosis
Entamoeba histolytica
parasitic amoeba
causes amoebic dysentery

99. Amoeba

100. Green alga Pseudopodia 100 µm Fig. 25-22, p. 549 Figure 25.22: Amoeba.
LM of a giant amoeba (Chaos carolinense). This unicellular protist, which moves and feeds by pseudopodia, is surrounding and ingesting a colonial green alga. Chaos amoebas are generally scavengers that feed on debris in freshwater habitats, but they ingest living organisms when the opportunity arises.
Pseudopodia
100 µm
Fig , p. 549

101. Plasmodial Slime Molds
Feeding stage is multinucleate plasmodium
Reproduction is by haploid spores produced within sporangia

102. Physarum

103. Figure 25.23: The plasmodial slime mold Physarum polycephalum.
Fig a, p. 550

104. Figure 25.23: The plasmodial slime mold Physarum polycephalum.
Fig b, p. 550

105. Cellular Slime Molds Feed as individual amoeboid cells
Reproduce by aggregating into a pseudoplasmodium (slug)
then form asexual spores

106. Dictyostelium

107. Insert “Cellular slime mold life cycle”
slime_mold.swf

108. KEY CONCEPTS
Biologists are making progress in understanding the evolutionary relationships among various protist taxa