Protists
Chapter 25
Learning Objective 1
•
What features are common to the
members of kingdom Protista?
Protists
•
Mostly unicellular eukaryotic organisms
that live in aquatic environments
Sizes of Protists
•
Unicellular organisms
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•
Colonies
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loosely connected groups of cells
Coenocytes
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microscopic
multinucleate masses of cytoplasm
Multicellular organisms
•
composed of many cells
Chlamydomonas
•
A unicellular protist
Flagella
Cell wall
Nucleus
Chloroplast
Starch granule
Fig. 25-1, p. 531
KEY CONCEPTS
•
Protists are a diverse group of eukaryotic
organisms, most of which are microscopic
Learning Objective 2
•
Discuss in general terms the diversity
inherent in the protist kingdom
•
•
•
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means of locomotion
modes of nutrition
interactions with other organisms
habitats
modes of reproduction
Locomotion
•
•
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Pseudopodia
Flagella
Cilia
Some are nonmotile
Nutrition
•
Protists obtain their nutrients
autotrophically or heterotrophically
Interactions
•
Protists are free-living or symbiotic
•
Symbiotic relationships range from
mutualism to parasitism
Habitats
•
Most protists live in
•
•
•
•
•
ocean
freshwater ponds
lakes
streams
Parasitic protists live in body fluids of hosts
Reproduction
•
Many protists reproduce both sexually and
asexually
•
Others reproduce only asexually
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)
Learning Objective 3
•
What is the hypothesis of serial
endosymbiosis?
•
Explain some evidence that supports it
Serial Endosymbiosis
•
Hypothesis:
•
Mitochondria and chloroplasts arose from
symbiotic relationships between larger cells
and smaller prokaryotes that were
incorporated and lived within them
Mitochondria
•
Probably originated from aerobic bacteria
•
Ribosomal RNA data suggests
•
ancient purple bacteria were ancestors of
mitochondria
Chloroplasts
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Single primary endosymbiotic event
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in red algae, green algae, and plants
cyanobacterium incorporated into a cell
Multiple secondary endosymbioses
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in euglenoids, dinoflagellates, diatoms, golden
algae, brown algae
nonfunctional chloroplasts in apicomplexans
Chloroplast
Evolution
Mitochondrion
Nucleus
Eukaryotic cell with
mitochondria
Bacterial
DNA
(a) Primary
endosymbiosis
Cyanobacterium
(ancestor of
chloroplast)
Fig. 25-2a, p. 532
Eukaryotic cell with
mitochondria
Chloroplast DNA
(b) Secondary
endosymbiosis
Chloroplast with two
membranes
Eukaryotic cell with
mitochondria and
chloroplasts
(red alga)
Chloroplast with
three membranes
Eukaryotic cell with
mitochondria and
chloroplasts (dinoflagellate?)
Fig. 25-2b, p. 532
Mitochondrion
Nucleus
Eukaryotic cell with mitochondria
(a) Primary
endosymbiosis
Bacterial
DNA
Cyanobacterium
(ancestor of
chloroplast)
Eukaryotic cell with mitochondria
(b) Secondary
endosymbiosis
Chloroplast DNA
Chloroplast with two
membranes
Eukaryotic cell with mitochondria
and chloroplasts (red alga)
Chloroplast with
three membranes
Eukaryotic cell with mitochondria
and chloroplasts (dinoflagellate?)
Stepped Art
Fig. 25-2b, p. 532
Learning Objective 4
•
What kinds of data do biologists use to
classify eukaryotes?
Relationships Among Protists
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Protist kingdom
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paraphyletic group
Determined by
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ultrastructure (electron microscopy)
comparative molecular data
Eukaryote Phyla
A
Ancestral
eukaryote
Fig. 25-3, p. 533
Fungi
Animals
Cellular
slime molds
Plasmodial
slime molds
Amoebas
Land plants
Green algae
Red algae
Brown algae
Water molds
Ciliates
Apicomplexans
Zooflagellates
(euglenoids)
Zooflagellates
(diplomonads)
Eukaryote Clades
?
Ancestral
eukaryote
Fig. 25-4, p. 535
Plants
Heterokonts
Alveolates
Fungi
Animals
Amoebozoa
Opisthokonts
Cellular slime
molds
Plasmodial
slime molds
Amoebas
Foraminiferans
Cercozoa
and actinopods
Land plants
Green algae
Red algae
Brown algae
Water molds
Ciliates
Apicomplexans
Zooflagellates,
(euglenoids) Discicristates
Zooflagellates
(diplomonads) Excavates
KEY CONCEPTS
•
Protists are descendants of early
eukaryotes
Learning Objective 5
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Why are zooflagellates no longer classified
in a single phylum?
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Distinguish among diplomonads,
euglenoids, and choanoflagellates
Zooflagellates
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Mostly unicellular heterotrophs
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Move by whiplike flagella
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Polyphyletic
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separated into several monophyletic groups
Diplomonads
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Diplomonads are excavates
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with a deep (excavated) oral groove
Diplomonads have
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one or two nuclei
no mitochondria
no Golgi complex
up to eight flagella
Excavates
Nucleus
Flagella
50 µm
Fig. 25-5b, p. 536
Euglenoids
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Euglenoids are discicristates
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Euglenoids
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with disclike cristae in mitochondria
are unicellular and flagellate
some are photosynthetic
Trypanosoma
•
causes African sleeping sickness
Discicristates
Flagellum for
locomotion
Eyespot
Contractile
vacuole
Chloroplast
Nucleus
Paramylon body
(stored food)
Pellicle
25 µm
Fig. 25-6a, p. 537
Flagellum for
locomotion
Nonemergent flagellum
(indistinguishable in
micrograph)
Eyespot
Contractile
vacuole
Mitochondria
(indistinguishable
in micrograph)
Chloroplast
Nucleolus
Nucleus
Chromatin
Paramylon body
(stored food)
Pellicle
Fig. 25-6b, p. 537
Red
blood
cells
Trypanosome
with
undulating
membrane
Flagellum
25 µm
Fig. 25-6c, p. 537
Choanoflagellates
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Choanoflagellates are opisthokonts
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single posterior flagellum in flagellate cells
collar of microvilli surrounds base of flagellum
Choanoflagellates
•
are related to fungi and animals
Choanoflagellate
Flagellum
Collar
of microvilli
Cell
Lorica
(protective
cover)
Stalk
Fig. 25-25, p. 551
Learning Objective 6
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Describe and compare these alveolates:
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ciliates
dinoflagellates
apicomplexans
Ciliates
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Alveolates
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•
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move by hairlike cilia
micronuclei (for sexual reproduction)
macronuclei (for cell metabolism and growth)
undergo complex sexual reproduction
(conjugation)
Ciliates
Cilia
Food vacuoles
Micronucleus
Macronucleus
Contractile
vacuole
50 µm
Fig. 25-7a, p. 538
Cilia
Food vacuoles
Food
Micronucleus
Macronucleus
Oral groove
Contractile vacuole
Anal pore
Food vacuole
Fig. 25-7b, p. 538
Cytopharynx
Macronucleus
250 µm
Fig. 25-7c, p. 538
Cirri
Fig. 25-7d, p. 538
Conjugation
2 First meiotic
division in
each cell
Macronuclei
4 One haploid
micronucleus
divides by
mitosis; others
disintegrate
Diploid
nuclei (2n)
Disintegrating
macronuclei
Disintegrating
micronuclei
Micronuclei (2n)
1 Two sexually
compatible
individuals join
at oral surfaces
6 Haploid
micronuclei
fuse
3 Second
meiotic
division in
each cell
5 Each
conjugating
cell
exchanges
micronucleus
7 Cells
separate
Fig. 25-8, p. 539
Insert “Ciliate
conjugation”
ciliate_conjugation.swf
Watch conjugation by clicking
on the figure in ThomsonNOW.
Dinoflagellates
•
Mostly unicellular, biflagellate,
photosynthetic alveolates
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Alveoli
•
•
•
major producers in marine ecosystems
flattened vesicles under plasma membrane
contain cellulose plates with silicates
Some produce toxic blooms (red tides)
Dinoflagellates
Apicomplexans
•
Parasites
•
•
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Apical complex of microtubules
•
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produce sporozoites
are nonmotile
attaches apicomplexan to host cell
Plasmodium
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causes malaria
Plasmodium
Infected female Anopheles
mosquito bites uninfected
1
human and transmits
Plasmodium
sporozoites to
Anopheles
human blood.
mosquito
Liver cell Liver
Meiosis
Sporozoites
(n)
Merozoites
released
6 Zygote embeds
in mosquito’s
stomach lining
and produces
sporozoites
(spores), which
are released and
migrate to salivary
glands.
DIPLOID
(2n)
Zygote
(2n)
Fertilization
HAPLOID
(n)
Anopheles
mosquito
Gametes
5 In mosquito’s
digestive tract,
gametocytes develop
into gametes, and
fertilization occurs.
Red
blood
cells
2 Sporozoites enter liver
cells and divide to
produce merozoites.
Merozoites released
from liver cells infect
red blood cells.
3 In blood cells,
merozoites divide
to form more
merozoites, which
infect more red
blood cells. Some
Gametocytes merozoites form
gametocytes.
4 Uninfected female
Anopheles mosquito bites
infected person and
obtains Plasmodium
gametocytes.
Fig. 25-10, p. 541
Insert “Apicomplexan life
cycle”
malaria_v2.swf
Watch the life cycle of the
malaria parasite by clicking on
the figure in ThomsonNOW.
Learning Objective 7
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Describe and compare these heterokonts:
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•
•
•
water molds
diatoms
golden algae
brown algae
Water Molds
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Heterokonts
•
•
Water molds
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•
•
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have two different kinds of flagella
have coenocytic mycelium
reproduce asexually (biflagellate zoospores)
reproduce sexually (oospores)
Phytophthora
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causes late blight of potato, sudden oak death
A Water Mold
Fig. 25-11a, p. 542
2
Meiosis results in haploid sperm
nuclei within antheridia and haploid
oospheres (eggs) within oogonia.
Oospheres within oogonium
3 Sperm nuclei move into
oospheres.
Antheridium (male
Meiosis
reproductive structure)
1 Saprolegnia
reproduces
sexually by
antheridia
and
oogonia.
Oogonium
(female
reproductive
structure)
Fertilization
HAPLOID (n)
Haploid GENERATION
sperm
nuclei
DIPLOID (2n)
GENERATION
SEXUAL
REPRODUCTION
Oospores
4 After fertilization,
oospores develop
from fertilized
oospheres. Each
oospore may develop
into new mycelium.
Germination
of oospore
Germination of
Mycelium
Zoosporangium
the zoospore
Encysted
ASEXUAL
secondary
REPRODUCTION
Zoospores
zoospore
(by mitosis)
Secondary
5 Saprolegnia reproduces
zoospore
asexually by forming
(bean-shaped)
zoospores within
Encysted
zoosporangium.
primary
Primary zoospore
zoospore
Fig. 25-11b, p. 542
(pear-shaped)
Diatoms
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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
Diatoms
Golden Algae
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Mostly unicellular, biflagellate freshwater
and marine heterokonts
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major component of tiny nanoplankton
Coccolithophorids
•
golden algae covered by tiny, overlapping
scales of calcium carbonate
Golden Algae
Brown Algae
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Multicellular heterokonts
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important in cooler ocean waters
Kelps (largest brown algae)
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leaflike blades
stemlike stipes
anchoring holdfasts
gas-filled bladders for buoyancy
Brown Algae
Blade
Stipe
Holdfast
Laminaria is widely distributed on rocky coastlines of
temperate and polar seas. It grows to 2 m (6.5 ft.)
Fig. 25-14a, p. 544
Learning Objective 8
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Describe foraminiferans and actinopods
•
Why do many biologists classify them in
the monophyletic group cercozoa?
Cercozoa
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Amoeboid cells
•
Often have hard outer shells (tests)
•
through which cytoplasmic projections extend
Foraminiferans
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Secrete many-chambered tests
•
Pores through which cytoplasmic
projections extend
•
to move and obtain food
Foraminiferans
Actinopods
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Mostly marine plankton
•
Obtain food with axopods
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slender cytoplasmic projections that extend
through pores in shells
Radiolarians
•
actinopods with glassy shells
Actinopods
Learning Objective 9
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Support the hypothesis that red algae and
green algae should be included in a
monophyletic group with land plants
Plants
•
Monophyletic group including
•
•
•
•
red algae
green algae
land plants
Based on
•
•
molecular data
presence of chloroplasts bounded by outer
and inner membranes
Red Algae
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Mostly multicellular seaweeds
•
•
important in warm tropical ocean waters
Some red algae incorporate calcium
carbonate in cell walls
•
important in reef building
Red Algae
Insert “Red alga life
cycle”
porphyra.swf
Green Algae
•
Wide diversity in size, structural
complexity, and reproduction
•
Botanists hypothesize that ancestral green
algae gave rise to land plants
Green Algae
Chlamydomonas
–
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
–
–
(-).
SEXUAL
REPRODUCTION
+
HAPLOID (n)
GENERATION
DIPLOID (2n)
GENERATION
Meiosis
3
1 Gametes are
produced by
mitosis.
–
–
–
+
from a different
strain
2 (+) and (-)
+ gametes fuse,
Fertilization
forming a
diploid zygote.
Meiosis
occurs.
Zygote (2n)
Fig. 25-17, p. 547
Insert “Green alga life
cycle”
chlamydomonas_v2.swf
Ulva
4
Each zoospore develops
into multicellular male or
female individual.
Mature haploid alga
Zoospores
Zoospores
Gamete
1 Male and female
HAPLOID (n)
GENERATION
Anisogamous
gametes
3 Special
cells in
Meiosis
diploid
alga undergo
meiosis to
form haploid
zoospores.
algae produce
biflagellate
gametes by
mitosis.
DIPLOID (2n)
GENERATION
Fertilization
2 Gametes fuse, forming
Mature
diploid
alga
Motile
zygote
zygote, which attaches
to substrate and
develops into
multicellular individual.
Fig. 25-18, p. 548
Spirogyra
Fig. 25-19a, p. 548
Fig. 25-19b, p. 548
Fig. 25-19c, p. 548
Fig. 25-19d, p. 548
KEY CONCEPTS
•
Animals, fungi, and plants evolved from
protist ancestors
Learning Objective 10
•
Describe and compare these amoebozoa:
•
•
•
amoebas
plasmodial slime molds
cellular slime molds
Amoebas
•
Use cytoplasmic extensions (pseudopodia)
•
•
to move and obtain food by phagocytosis
Entamoeba histolytica
•
•
parasitic amoeba
causes amoebic dysentery
Amoeba
Green alga
Pseudopodia
100 µm
Fig. 25-22, p. 549
Plasmodial Slime Molds
•
Feeding stage is multinucleate plasmodium
•
Reproduction is by haploid spores produced
within sporangia
Physarum
Fig. 25-23a, p. 550
Fig. 25-23b, p. 550
Cellular Slime Molds
•
Feed as individual amoeboid cells
•
Reproduce by aggregating into a
pseudoplasmodium (slug)
•
then form asexual spores
Dictyostelium
Insert “Cellular slime
mold life cycle”
slime_mold.swf
KEY CONCEPTS
•
Biologists are making progress in
understanding the evolutionary
relationships among various protist taxa