LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 28
Protists
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
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Protista is no longer valid as a kingdom
© 2011 Pearson Education, Inc.
Figure 28.1
1 m
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
• Most protists are unicellular, but there are some
colonial and multicellular species
© 2011 Pearson Education, Inc.
• 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
– Some protists reproduce asexually, while others
reproduce sexually, or by the sexual processes of
meiosis and fertilization
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 28.2
Plastid
Dinoflagellates
Secondary
endosymbiosis
Membranes
are represented
as dark lines in
the cell.
Apicomplexans
Red alga
Cyanobacterium
1 2
3
Primary
endosymbiosis
Heterotrophic
eukaryote
Stramenopiles
Secondary
endosymbiosis
One of these
membranes was
lost in red and
green algal
descendants.
Plastid
Euglenids
Secondary
endosymbiosis
Green alga
Chlorarachniophytes
• 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 28.3a
Parabasalids
Euglenozoans
Excavata
Diplomonads
Apicomplexans
Ciliates
Diatoms
Stramenopiles
Golden algae
Chromalveolata
Alveolates
Dinoflagellates
Brown algae
Oomycetes
Forams
Radiolarians
Green
algae
Chlorophytes
Charophytes
Land plants
Archaeplastida
Red algae
Rhizaria
Cercozoans
Gymnamoebas
Entamoebas
Opisthokonts
Nucleariids
Fungi
Choanoflagellates
Animals
Unikonta
Amoebozoans
Slime molds
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
© 2011 Pearson Education, Inc.
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)
© 2011 Pearson Education, Inc.
• Parabasalids
– Have reduced mitochondria called
hydrogenosomes that generate some energy
anaerobically
– Include Trichomonas vaginalis, the pathogen that
causes yeast infections in human females
© 2011 Pearson Education, Inc.
Figure 28.4
5 m
Flagella
Undulating
membrane
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
© 2011 Pearson Education, Inc.
Figure 28.5
Flagella
0.2 m
8 m
Crystalline rod
(cross section)
Ring of microtubules
(cross section)
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
© 2011 Pearson Education, Inc.
Figure 28.6
9 m
• 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 28.7
Long flagellum
Eyespot
Short flagellum
Contractile vacuole
Light
detector
Nucleus
Chloroplast
Plasma membrane
Euglena (LM)
Pellicle
5 m
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
© 2011 Pearson Education, Inc.
Figure 28.UN02
Excavata
Diatoms
Golden algae
Brown algae
Oomycetes
Stramenopiles
Chromalveolata
Dinoflagellates
Apicomplexans Alveolates
Ciliates
Rhizaria
Archaeplastida
Unikonta
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 28.9
3 m
Flagella
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
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
Figure 28.10-1
Inside human
Merozoite
Liver
Liver
cell
Apex
Red blood
cell
Merozoite
(n)
0.5 m
Red blood
cells
Gametocytes
(n)
Key
Haploid (n)
Diploid (2n)
Figure 28.10-2
Inside mosquito
Inside human
Merozoite
Liver
Liver
cell
Apex
Red blood
cell
Merozoite
(n)
Zygote
(2n)
0.5 m
Red blood
cells
FERTILIZATION
Gametes
Gametocytes
(n)
Key
Haploid (n)
Diploid (2n)
Figure 28.10-3
Inside mosquito
Inside human
Merozoite
Sporozoites
(n)
Liver
Liver
cell
Apex
Oocyst
MEIOSIS
Red blood
cell
Merozoite
(n)
Zygote
(2n)
0.5 m
Red blood
cells
FERTILIZATION
Gametes
Gametocytes
(n)
Key
Haploid (n)
Diploid (2n)
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
© 2011 Pearson Education, Inc.
Figure 28.11a
Oral groove
Contractile
vacuole
50 m
Cell mouth
Cilia
Micronucleus
Macronucleus
Food vacuoles
(a) Feeding, waste removal, and water balance
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
© 2011 Pearson Education, Inc.
Diatoms
• Diatoms are unicellular algae with a unique twopart, glass-like wall of hydrated silica
• Diatoms usually reproduce asexually, and
occasionally sexually
© 2011 Pearson Education, Inc.
40 m
Figure 28.13
• 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
© 2011 Pearson Education, Inc.
• This removes carbon dioxide from the
atmosphere and “pumps” it to the ocean floor
Video: Diatoms Moving
Video: Various Diatoms
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 28.14
Flagellum
Outer container
Living cell
25 m
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
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
Figure 28.15
Blade
Stipe
Holdfast
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 28.UN03
Excavata
Chromalveolata
Rhizaria
Radiolarians
Foraminiferans
Cercozoans
Archaeplastida
Unikonta
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
© 2011 Pearson Education, Inc.
Figure 28.18
Pseudopodia
200 m
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
• Paulinella chromatophora is an autotroph with a
unique photosynthetic structure
• This structure evolved from a different
cyanobacterium than the plastids of other
photosynthetic eukaryotes
© 2011 Pearson Education, Inc.
Figure 28.19
Chromatophore
5 m
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
© 2011 Pearson Education, Inc.
Figure 28.UN04
Excavata
Chromalveolata
Rhizaria
Chlorophytes
Charophytes
Green algae
Land plants
Archaeplastida
Red algae
Unikonta
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
© 2011 Pearson Education, Inc.
Figure 28.20
Bonnemaisonia
hamifera
20 cm
8 mm
Dulse (Palmaria palmata)
Nori
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
© 2011 Pearson Education, Inc.
• Most chlorophytes live in fresh water,
although many are marine
• Other chlorophytes live in damp soil, as
symbionts in lichens, or in snow
© 2011 Pearson Education, Inc.
•
Larger size and greater complexity evolved in
chlorophytes by
1. The formation of colonies from individual cells
2. The formation of true multicellular bodies by
cell division and differentiation (e.g., Ulva)
3. The repeated division of nuclei with no
cytoplasmic division (e.g., Caulerpa)
© 2011 Pearson Education, Inc.
Figure 28.21
2 cm
(b) Caulerpa, an
intertidal
chlorophyte
(a) Ulva, or sea lettuce
• Most chlorophytes have complex life cycles with
both sexual and asexual reproductive stages
Video: Chlamydomonas
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 28.UN05
Excavata
Chromalveolata
Rhizaria
Archaeplastida
Amoebozoans
Unikonta
Nucleariids
Fungi
Choanoflagellates
Animals
Figure 28.23
RESULTS
Choanoflagellates
Animals
Unikonta
Fungl
Common
ancestor
of all
eukaryotes
Amoebozoans
Diplomonads
Excavata
Euglenozoans
Alveolates
Chromalveolata
Stramenopiles
DHFR-TS
gene
fusion
Rhizarians
Rhizaria
Red algae
Green algae
Plants
Archaeplastida
Amoebozoans
• Amoebozoans are amoeba that have lobe- or
tube-shaped, rather than threadlike, pseudopodia
• They include slime molds, gymnamoebas, and
entamoebas
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Opisthokonts
• Opisthokonts include animals, fungi, and several
groups of protists
© 2011 Pearson Education, Inc.
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
.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
10 m
Figure 28.26
• Some protists are parasitic
– Plasmodium causes malaria
– Pfiesteria shumwayae is a dinoflagellate that
causes fish kills
– Phytophthora ramorum causes sudden oak death
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 28.27
Other
consumers
Herbivorous
plankton
Carnivorous
plankton
Prokaryotic
producers
Protistan
producers
• 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
© 2011 Pearson Education, Inc.
Figure 28.28
Growth Growth
Higher SST
Lower SST
In regions between the
black lines, a layer of warm water
rests on top of colder waters.
In the yellow regions, high SSTs increase the
temperature differences between warm and cold
waters, which reduces upwelling.
Figure 28.UN06