Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 20
The Protists
(Sections 20.1 - 20.4)
Albia Dugger • Miami Dade College
20.1 Harmful Algal Blooms
• Aquatic protists include single-celled and multicellular
autotrophs and heterotrophs
• An algal bloom is a population explosion of an aquatic
protist, or of another aquatic microorganism
• Toxins released during some algal blooms can harm wildlife
and endanger human health
Key Terms
• protist
• Eukaryote that is not a fungus, animal, or plant
• algal bloom
• Population explosion of tiny aquatic producers
• toxin
• Chemical that is made by one organism and harms
another
Karenia brevis
• This dinoflagellate
produces brevetoxin,
which interferes with
nerve cells of people
and animals who inhale
or ingest it
20.2 A Collection of Lineages
• Protists are a collection of mostly single-celled eukaryotes
• Many have chloroplasts that evolved from cyanobacteria or
another protist
• The dominant stage of the life cycle may be haploid or diploid
• Protists are not a natural group, but a collection of lineages,
some only distantly related to one another
Protist Diversity
Protist Diversity
Fig. 20.2a, p. 312
Protist Diversity
Fig. 20.2b, p. 312
Protist Diversity
Fig. 20.2c, p. 312
Protist Diversity
Fig. 20.2d, p. 312
Protist Diversity
Fig. 20.2e, p. 312
Protist Groups
• Protists are not a single
lineage
• One proposed
eukaryotic family tree
with protist groups
indicated by tan boxes
Protist
Groups
diplomonads
parabasalids
Flagellated
trypanosomes Protozoans
euglenoids
radiolarians
foraminiferans
ancestral
cells
ciliates
dinoflagellates Alveolates
apicomplexans
water molds
diatoms
Stramenopiles
brown algae
red algae
chlorophyte algae
charophyte algae
land plants
Green
Algae
amoebas
Amoebozoans
slime molds
fungi
F
choanoflagellates
animals
Fig. 20.2f, p. 312
Key Concepts
• A Collection of Lineages
• Protists include many lineages of eukaryotic organisms,
some autotrophs and others heterotrophs
• Protists are not a clade; some groups are more closely
related to plants, or to fungi and animals, than to other
protists
20.3 Flagellated Protozoans
• Flagellated protozoans are single cells with no cell wall – a
protein covering (pellicle) helps maintain the cell’s shape
• flagellated protozoan
• Protist belonging to an entirely or mostly heterotrophic
lineage with no cell wall and one or more flagella
• pellicle
• Layer of proteins that gives shape to many unwalled,
single-celled protists
Diplomonads and Parabasalids
• Diplomonads and parabasalids have multiple flagella and are
adapted to oxygen-poor habitats
• Instead of mitochondria, they have organelles that produce
ATP by an anaerobic pathway
• Both groups include species that infect humans
A Diplomonad
• Diplomonads have two
more or less identical
nuclei
• Giardia lamblia causes
giardiasis, a waterborne
intestinal disease
A Parabasalid
• Trichomonas vaginalis
causes a sexually
transmitted disease
Trypanosomes
• trypanosome
• Parasitic flagellate with a
single mitochondrion and
a membrane-encased
flagellum
• Insects transmit
trypanosomes, such as
Trypanosoma brucei,
which causes African
sleeping sickness
Euglenoids
• euglenoid
• Flagellated protozoan with multiple mitochondria
• Some have chloroplasts that evolved by secondary
endosymbiosis from a green alga
• Typically live in fresh water
• Have a contractile vacuole
• contractile vacuole
• In freshwater protists, an organelle that collects and
expels excess water
Body Plan of Euglena
Body Plan of Euglena
long
flagellum
chloroplast
contractile vacuole
eyespot
ER nucleus
pellicle
Golgi body
mitochondrion
Fig. 20.4, p. 313
ANIMATION: Body plan of Euglena
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20.4 Mineral-Shelled Protozoans
• Foraminiferans and radiolarians are single-celled marine
protists with sieve-like shells
• They capture food with microtubule-reinforced cytoplasmic
extensions that protrude through the shell’s openings
• Both are marine heterotrophs and may be part of plankton
• plankton
• Community of tiny drifting or swimming organisms
Foraminiferans and Radiolarians
• foraminiferan
• Heterotrophic single-celled protist with a chalky calcium
carbonate shell and long cytoplasmic extensions
• Deposits of their remains are mined for chalk and
limestone
• radiolarian
• Heterotrophic single-celled protist with a glassy silica shell
and long cytoplasmic extensions that stick out through the
porous shell and capture prey
Foraminiferans and Radiolarians
Foraminiferans and Radiolarians
Fig. 20.5a, p. 314
Foraminiferans and Radiolarians
Fig. 20.5b, p. 314
Foraminiferans and Radiolarians
Fig. 20.5c, p. 314