Protists

1
Chapter 28
Protists
2
Overview Living Small

• Even a low-power microscope can reveal a great
  variety of organisms in a drop of pond water
• Protist is the informal name of the group of
  mostly unicellular eukaryotes
• Advances in eukaryotic systematics have caused
  the classification of protists to change
  significantly
• Protists constitute a polyphyletic group, and
  Protista is no longer valid as a kingdom

3
Figure 28.1
1 ?m
4
Concept 28.1 Most eukaryotes are single-celled
organisms

• Protists are eukaryotes
• Eukaryotic cells have organelles and are more
  complex than prokaryotic cells
• Most protists are unicellular, but there are some
  colonial and multicellular species

5
Structural and Functional Diversity in Protists

• Protists exhibit more structural and functional
  diversity than any other group of eukaryotes
• Single-celled protists can be very complex, as
  all biological functions are carried out by
  organelles in each individual cell

6

• 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

7

• Some protists reproduce asexually, while others
  reproduce sexually, or by the sexual processes of
  meiosis and fertilization

8
Endosymbiosis in Eukaryotic Evolution

• There is now considerable evidence that much
  protist diversity has its origins in
  endosymbiosis
• Endosymbiosis is the process in which a
  unicellular organism engulfs another cell, which
  becomes an endosymbiont and then organelle in the
  host cell
• Mitochondria evolved by endosymbiosis of an
  aerobic prokaryote
• Plastids evolved by endosymbiosis of a
  photosynthetic cyanobacterium

9
Figure 28.2
Plastid
Dinoflagellates
Secondaryendosymbiosis
Membranesare representedas dark lines inthe
cell.
Apicomplexans
Red alga
Cyanobacterium
1
2
3
Primaryendosymbiosis
Stramenopiles
Plastid
Heterotrophiceukaryote
Secondaryendosymbiosis
One of thesemembranes waslost in red andgreen
algaldescendants.
Euglenids
Secondaryendosymbiosis
Green alga
Chlorarachniophytes
10

• The plastid-bearing lineage of protists evolved
  into red and green algae
• The DNA of plastid genes in red algae and green
  algae closely resemble the DNA of cyanobacteria
• On several occasions during eukaryotic evolution,
  red and green algae underwent secondary
  endosymbiosis, in which they were ingested by a
  heterotrophic eukaryote

11
Five Supergroups of Eukaryotes

• It is no longer thought that amitochondriates
  (lacking mitochondria) are the oldest lineage of
  eukaryotes
• Many have been shown to have mitochondria and
  have been reclassified
• Our understanding of the relationships among
  protist groups continues to change rapidly
• One hypothesis divides all eukaryotes (including
  protists) into five supergroups

12
Figure 28.3a
Diplomonads Parabasalids Euglenozoans
Excavata
Dinoflagellates Apicomplexans Ciliates Diatoms
Golden algae Brown algae Oomycetes
Alveolates
Chromalveolata
Stramenopiles
Cercozoans Forams Radiolarians
Rhizaria
Red algae Chlorophytes Charophytes Land plants
Greenalgae
Archaeplastida
Slime molds Gymnamoebas Entamoebas Nucleariids
Fungi Choanoflagellates Animals
Amoebozoans
Unikonta
Opisthokonts
13
Figure 28.3aa
Diplomonads Parabasalids Euglenozoans
Excavata
Dinoflagellates Apicomplexans Ciliates Diatoms
Golden algae Brown algae Oomycetes
Alveolates
Chromalveolata
Stramenopiles
14
Figure 28.3ab
Cercozoans Forams Radiolarians
Rhizaria
Red algae Chlorophytes Charophytes Land plants
Greenalgae
Archaeplastida
15
Figure 28.3ac
Slime molds Gymnamoebas Entamoebas Nucleariids
Fungi Choanoflagellates Animals
Amoebozoans
Unikonta
Opisthokonts
16
Concept 28.2 Excavates include protists with
modified mitochondria and protists with unique
flagella

• The clade Excavata is characterized by its
  cytoskeleton
• Some members have a feeding groove
• This controversial group includes the
  diplomonads, parabasalids, and euglenozoans

17
Figure 28.UN01
Diplomonads
Parabasalids
Excavata
Kinetoplastids
Euglenozoans
Euglenids
Chromalveolata Rhizaria Archaeplastida Unikonta
18
Diplomonads and Parabasalids

• These two groups lack plastids, have modified
  mitochondria, and most live in anaerobic
  environments
• Diplomonads
• Have modified mitochondria called mitosomes
• Derive energy from anaerobic biochemical pathways
• Have two equal-sized nuclei and multiple flagella
• Are often parasites, for example, Giardia
  intestinalis (also known as Giardia lamblia)

19
Figure 28.3b
5 ?m
Giardia intestinalis, a diplomonadparasite
20

• Parabasalids
• Have reduced mitochondria called hydrogenosomes
  that generate some energy anaerobically
• Include Trichomonas vaginalis, the pathogen that
  causes yeast infections in human females

21
Figure 28.4
Flagella
5 ?m
Undulatingmembrane
22
Euglenozoans

• Euglenozoa is a diverse clade that includes
  predatory heterotrophs, photosynthetic
  autotrophs, and parasites
• The main feature distinguishing them as a clade
  is a spiral or crystalline rod of unknown
  function inside their flagella
• This clade includes the kinetoplastids and
  euglenids

23
Figure 28.5
Flagella
0.2 ?m
8 ?m
Crystalline rod (cross section)
Ring of microtubules (cross section)
24
Kinetoplastids

• Kinetoplastids have a single mitochondrion with
  an organized mass of DNA called a kinetoplast
• They include free-living consumers of prokaryotes
  in freshwater, marine, and moist terrestrial
  ecosystems
• This group includes Trypanosoma, which causes
  sleeping sickness in humans
• Another pathogenic trypanosome causes Chagas
  disease

25
Figure 28.6
9 ?m
26

• Trypanosomes evade immune responses by switching
  surface proteins
• A cell produces millions of copies of a single
  protein
• The new generation produces millions of copies of
  a different protein
• These frequent changes prevent the host from
  developing immunity

27
Euglenids

• Euglenids have one or two flagella that emerge
  from a pocket at one end of the cell
• Some species can be both autotrophic and
  heterotrophic

Video Euglena
Video Euglena Motion
28
Figure 28.7
Long flagellum
Eyespot
Short flagellum
Lightdetector
Contractile vacuole
Nucleus
Chloroplast
Plasma membrane
Pellicle
Euglena (LM)
5 ?m
29
Concept 28.3 Chromalveolates may have originated
by secondary endosymbiosis

• Some data suggest that the clade Chromalveolata
  is monophyletic and originated by a secondary
  endosymbiosis event
• The proposed endosymbiont is a red alga
• This clade is controversial and includes the
  alveolates and the stramenopiles

30
Figure 28.UN02
Excavata
Dinoflagellates
Apicomplexans Ciliates
Alveolates
Chromalveolata
Diatoms
Golden algae Brown algae Oomycetes
Stramenopiles
Rhizaria Archaeplastida Unikonta
31
Alveolates

• Members of the clade Alveolata have
  membrane-bounded sacs (alveoli) just under the
  plasma membrane
• The function of the alveoli is unknown
• The alveolates include
• Dinoflagellates
• Apicomplexans
• Ciliates

32
Figure 28.8
Flagellum
Alveoli
Alveolate
0.2 ?m
33
Dinoflagellates

• Dinoflagellates have two flagella and each cell
  is reinforced by cellulose plates
• They are abundant components of both marine and
  freshwater phytoplankton
• They are a diverse group of aquatic phototrophs,
  mixotrophs, and heterotrophs
• Toxic red tides are caused by dinoflagellate
  blooms

Video Dinoflagellate
34
Figure 28.9
Flagella
3 ?m
35
Apicomplexans

• Apicomplexans are parasites of animals, and some
  cause serious human diseases
• They spread through their host as infectious
  cells called sporozoites
• One end, the apex, contains a complex of
  organelles specialized for penetrating host cells
  and tissues
• Most have sexual and asexual stages that require
  two or more different host species for completion

36

• The apicomplexan Plasmodium is the parasite that
  causes malaria
• Plasmodium requires both mosquitoes and humans to
  complete its life cycle
• Approximately 900,000 people die each year from
  malaria
• Efforts are ongoing to develop vaccines that
  target this pathogen

37
Figure 28.10-3
Inside mosquito
Inside human
Merozoite
Sporozoites (n)
Liver
Livercell
Oocyst
Apex
MEIOSIS
Red bloodcell
0.5 ?m
Merozoite (n)
Zygote (2n)
Red bloodcells
FERTILIZATION
Gametes
Key
Gametocytes (n)
Haploid (n) Diploid (2n)
38
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
• Genetic variation results from conjugation, in
  which two individuals exchange haploid
  micronuclei
• Conjugation is a sexual process, and is separate
  from reproduction, which generally occurs by
  binary fission

39
Figure 28.11
Contractilevacuole
Oral groove
Cell mouth
Cilia
50 ?m
Micronucleus
Food vacuoles
Macronucleus
(a) Feeding, waste removal, and water balance
Key
Conjugation Asexualreproduction
MEIOSIS
Haploidmicronucleus
Diploidmicronucleus
Compatiblemates
Diploidmicronucleus
The originalmacronucleusdisintegrates.
MICRONUCLEAR FUSION
(b) Conjugation and reproduction
40
Video Paramecium Cilia
Video Paramecium Vacuole
Video Vorticella Cilia
Video Vorticella Detail
Video Vorticella Habitat
41
Stramenopiles

• The clade Stramenopila includes important
  phototrophs as well as several clades of
  heterotrophs
• Most have a hairy flagellum paired with a
  smooth flagellum
• Stramenopiles include diatoms, golden algae,
  brown algae, and oomycetes

42
Figure 28.12
Hairyflagellum
Smoothflagellum
5 ?m
43
Diatoms

• Diatoms are unicellular algae with a unique
  two-part, glass-like wall of hydrated silica
• Diatoms usually reproduce asexually, and
  occasionally sexually

44
Figure 28.3c
50 ?m
Diatom diversity
45
Figure 28.13
40 ?m
46

• Diatoms are a major component of phytoplankton
  and are highly diverse
• Fossilized diatom walls compose much of the
  sediments known as diatomaceous earth
• After a diatom population has bloomed, many dead
  individuals fall to the ocean floor undecomposed

47

• This removes carbon dioxide from the atmosphere
  and pumps it to the ocean floor

Video Diatoms Moving
Video Various Diatoms
48
Golden Algae

• Golden algae 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
• All golden algae are photosynthetic, and some are
  mixotrophs
• Most are unicellular, but some are colonial

49
Figure 28.14
Flagellum
Outer container
Living cell
25 ?m
50
Brown Algae

• Brown algae are the largest and most complex
  algae
• All are multicellular, and most are marine
• Brown algae include many species commonly called
  seaweeds
• Brown algae have the most complex multicellular
  anatomy of all algae

51

• Giant seaweeds called kelps live in deep parts of
  the ocean
• The algal body is plantlike but lacks true roots,
  stems, and leaves and is called a thallus
• The rootlike holdfast anchors the stemlike stipe,
  which in turn supports the leaflike blades

52
Figure 28.15
Blade
Stipe
Holdfast
53
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
• Heteromorphic generations are structurally
  different, while isomorphic generations look
  similar

54

• The diploid sporophyte produces haploid
  flagellated spores called zoospores
• The zoospores develop into haploid male and
  female gametophytes, which produce gametes
• Fertilization of gamates results in a diploid
  zygote, which grows into a new sporophyte

55
Figure 28.16-2
Key
Haploid (n) Diploid (2n)
Sporangia
MEIOSIS
10 cm
Sporophyte(2n)
Zoospore
Female
Developingsporophyte
Gametophytes (n)
Zygote(2n)
Male
Egg
FERTILIZATION
Mature femalegametophyte(n)
Sperm
56
Figure 28.16a
10 cm
57
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
  potato blight caused by Phytophthora infestans

58
Figure 28.17-3
Oogonium
Germ tube
Egg nucleus (n)
Cyst
Antheridialhypha withsperm nuclei (n)
MEIOSIS
Hyphae
ASEXUAL REPRODUCTION
Zoospore(2n)
FERTILIZATION
Zygotegermination
Zygotes (oospores) (2n)
SEXUAL REPRODUCTION
Zoosporangium(2n)
Key
Haploid (n) Diploid (2n)
59
Video Water Mold Oogonium
60
Concept 28.4 Rhizarians are a diverse group of
protists defined by DNA similarities

• DNA evidence supports Rhizaria as a monophyletic
  clade
• Amoebas move and feed by pseudopodia some but
  not all belong to the clade Rhizaria
• Rhizarians include radiolarians, forams, and
  cercozoans

61
Figure 28.UN03
Excavata Chromalveolata
Radiolarians Foraminiferans Cercozoans
Rhizaria
Archaeplastida Unikonta
62
Radiolarians

• Marine protists called radiolarians have tests
  fused into one delicate piece, usually made of
  silica
• Radiolarians use their pseudopodia to engulf
  microorganisms through phagocytosis
• The pseudopodia of radiolarians radiate from the
  central body

63
Figure 28.18
Pseudopodia
200 ?m
64
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
• Many forams have endosymbiotic algae

65
Figure 28.3d
100 ?m
Globigerina, a foram in the supergroup Rhizaria
66
Cercozoans

• Cercozoans include most amoeboid and flagellated
  protists with threadlike pseudopodia
• They are common in marine, freshwater, and soil
  ecosystems
• Most are heteroptrophs, including parasites and
  predators

67

• Paulinella chromatophora is an autotroph with a
  unique photosynthetic structure
• This structure evolved from a different
  cyanobacterium than the plastids of other
  photosynthetic eukaryotes

68
Figure 28.19
Chromatophore
5 ?m
69
Concept 28.5 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
• Land plants are descended from the green algae
• Archaeplastida is the supergroup that includes
  red algae, green algae, and land plants

70
Figure 28.UN04
Excavata Chromalveolata Rhizaria
Red algae
Chlorophytes Charophytes
Green algae
Archaeplastida
Land plants
Unikonta
71
Red Algae

• Red algae are reddish in color due to an
  accessory pigment called phycoerythrin, which
  masks the green of chlorophyll
• The color varies from greenish-red in shallow
  water to dark red or almost black in deep water
• Red algae are usually multicellular the largest
  are seaweeds
• Red algae are the most abundant large algae in
  coastal waters of the tropics

72
Figure 28.20
Bonnemaisoniahamifera
20 cm
8 mm
Dulse (Palmaria palmata)
Nori
73
Green Algae

• Green algae are named for their grass-green
  chloroplasts
• Plants are descended from the green algae
• Green algae are a paraphyletic group
• The two main groups are chlorophytes and
  charophyceans
• Charophytes are most closely related to land
  plants

74

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

75

• Larger size and greater complexity evolved in
  chlorophytes by
• The formation of colonies from individual cells
• The formation of true multicellular bodies by
  cell division and differentiation (e.g., Ulva)
• The repeated division of nuclei with no
  cytoplasmic division (e.g., Caulerpa)

76
Figure 28.3e
20 ?m
50 ?m
Volvox, a colonial freshwater green alga
77
Figure 28.21
(a) Ulva, or sea lettuce
2 cm
(b) Caulerpa, an intertidal
chlorophyte
78
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
79

• Most chlorophytes have complex life cycles with
  both sexual and asexual reproductive stages

Video Chlamydomonas
80
Figure 28.22
?
1 ?m
Flagella
Cell wall
?
Gamete (n)
?
?
Nucleus
Zoospore
FERTILIZATION
Mature cell (n)
ASEXUAL REPRODUCTION
Crosssection ofcup-shapedchloroplast
SEXUAL REPRODUCTION
Zygote (2n)
(TEM)
?
?
MEIOSIS
?
?
Key
Haploid (n) Diploid (2n)
81
Figure 28.22a-1
Zoospore
Mature cell (n)
ASEXUAL REPRODUCTION
Key
Haploid (n) Diploid (2n)
82
Figure 28.22a-2
?
?
Gamete (n)
?
?
Zoospore
FERTILIZATION
Mature cell (n)
ASEXUAL REPRODUCTION
SEXUAL REPRODUCTION
Zygote (2n)
?
?
MEIOSIS
?
?
Key
Haploid (n) Diploid (2n)
83
Concept 28.6 Unikonts include protists that are
closely related to fungi and animals

• The supergroup Unikonta includes animals, fungi,
  and some protists
• This group includes two clades the amoebozoans
  and the opisthokonts (animals, fungi, and related
  protists)
• The root of the eukaryotic tree remains
  controversial
• It is unclear whether unikonts separated from
  other eukaryotes relatively early or late

84
Figure 28.UN05
Excavata Chromalveolata Rhizaria Archaeplastida
Amoebozoans
Nucleariids Fungi
Unikonta
Choanoflagellates Animals
85
Figure 28.23
RESULTS
Choanoflagellates Animals Fungl Amoebozoans
Unikonta
Commonancestorof alleukaryotes
Diplomonads
Excavata
Euglenozoans Alveolates Stramenopiles Rhizarian
s
Chromalveolata
Rhizaria
DHFR-TSgenefusion
Red algae Green algae
Archaeplastida
Plants
86
Amoebozoans

• Amoebozoans are amoeba that have lobe- or
  tube-shaped, rather than threadlike, pseudopodia
• They include slime molds, gymnamoebas, and
  entamoebas

87
Figure 28.3f
100 ?m
A unikont amoeba
88
Slime Molds

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

89
Plasmodial Slime Molds

• Many species of plasmodial slime molds are
  brightly pigmented, usually yellow or orange

Video Plasmodial Slime Mold
Video Plasmodial Slime Mold Streaming
90
Figure 28.24
4 cm
FERTILIZATION
Feedingplasmodium
Zygote (2n)
Matureplasmodium(preparing to fruit)
Youngsporangium
Amoeboid cells (n)
Flagellatedcells (n)
Maturesporangium
Germinatingspore
Spores (n)
MEIOSIS
1 mm
Stalk
Key
Haploid (n) Diploid (2n)
91
Figure 28.24a-1
Feedingplasmodium
Matureplasmodium(preparing to fruit)
Youngsporangium
Maturesporangium
Stalk
Key
Haploid (n) Diploid (2n)
92
Figure 28.24a-2
Feedingplasmodium
Matureplasmodium(preparing to fruit)
Youngsporangium
Amoeboid cells (n)
Flagellatedcells (n)
Maturesporangium
Germinatingspore
Spores (n)
MEIOSIS
Stalk
Key
Haploid (n) Diploid (2n)
93
Figure 28.24a-3
FERTILIZATION
Feedingplasmodium
Zygote (2n)
Matureplasmodium(preparing to fruit)
Youngsporangium
Amoeboid cells (n)
Flagellatedcells (n)
Maturesporangium
Germinatingspore
Spores (n)
MEIOSIS
Stalk
Key
Haploid (n) Diploid (2n)
94
Figure 28.24b
4 cm
95
Figure 28.24c
1 mm
96

• At one point in the life cycle, plasmodial slime
  molds form a mass called a plasmodium (not to be
  confused with malarial Plasmodium)
• The plasmodium is not multicellular
• It is undivided by plasma membranes and contains
  many diploid nuclei
• It extends pseudopodia through decomposing
  material, engulfing food by phagocytosis

97
Cellular Slime Molds

• Cellular slime molds form multicellular
  aggregates in which cells are separated by their
  membranes
• Cells feed individually, but can aggregate to
  form a fruiting body
• Dictyostelium discoideum is an experimental model
  for studying the evolution of multicellularity

98
Figure 28.25-1
Spores(n)
Emergingamoeba(n)
Solitaryamoebas (n)
600 ?m
ASEXUAL REPRODUCTION
Fruitingbodies(n)
Aggregatedamoebas
Migratingaggregate
200 ?m
Key
Haploid (n) Diploid (2n)
99
Figure 28.25-2
Spores(n)
FERTILIZATION
Emergingamoeba(n)
Zygote(2n)
SEXUAL REPRODUCTION
Solitaryamoebas (n)
600 ?m
MEIOSIS
Amoebas (n)
ASEXUAL REPRODUCTION
Fruitingbodies(n)
Aggregatedamoebas
Migratingaggregate
200 ?m
Key
Haploid (n) Diploid (2n)
100
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
Video Amoeba Pseudopodia
101
Entamoebas

• Entamoebas are parasites of vertebrates and some
  invertebrates
• Entamoeba histolytica causes amebic dysentery,
  the third-leading cause of human death due to
  eukaryotic parasites

102
Opisthokonts

• Opisthokonts include animals, fungi, and several
  groups of protists

103
Concept 28.7 Protists play key roles in
ecological communities

• Protists are found in diverse aquatic
  environments
• Protists often play the role of symbiont or
  producer

104
Symbiotic Protists

• Some protist symbionts benefit their hosts
• Dinoflagellates nourish coral polyps that build
  reefs
• Wood-digesting protists digest cellulose in the
  gut of termites

105
Figure 28.26
10 ?m
106

• Some protists are parasitic
• Plasmodium causes malaria
• Pfiesteria shumwayae is a dinoflagellate that
  causes fish kills
• Phytophthora ramorum causes sudden oak death

107
Photosynthetic Protists

• Many protists are important producers that obtain
  energy from the sun
• In aquatic environments, photosynthetic protists
  and prokaryotes are the main producers
• In aquatic environments, photosynthetic protists
  are limited by nutrients
• These populations can explode when limiting
  nutrients are added

108
Figure 28.27
Otherconsumers
Herbivorousplankton
Carnivorousplankton
Protistanproducers
Prokaryoticproducers
109

• Biomass of photosynthetic protists has declined
  as sea surface temperature has increased
• If sea surface temperature continues to warm due
  to global warming, this could have large effects
  on
• Marine ecosystems
• Fishery yields
• The global carbon cycle

110
Figure 28.28
In regions between theblack lines, a layer of
warm waterrests on top of colder waters.
Growth
Growth
Higher Lower
SST SST
In the yellow regions, high SSTs increase
thetemperature differences between warm and
coldwaters, which reduces upwelling.
111
Figure 28.UN06
112
Figure 28.UN06a
113
Figure 28.UN06b