Protists – The Simplest
Eukaryotes
Chapter 22 Part 1
Impacts, Issues
The Malaria Menace
 Plasmodium, a single-celled protist, causes
malaria – but also manipulates its mosquito and
human hosts to maximize its own survival
22.1 The Many Protist Lineages
 Protists are eukaryotic organisms that are not
fungi, plants, or animals
 Protists include many lineages of mostly singlecelled eukaryotes, some only distantly related to
one another
 No single trait is unique to protists
Classification and Phylogeny
Fig. 22-2a, p. 352
Fig. 22-2b, p. 352
Fig. 22-2c, p. 352
Fig. 22-2d, p. 352
Fig. 22-2e, p. 352
Fig. 22-2f, p. 352
diplomonads Flagellated
parabasalids Protozoans
trypanosomes
euglenoids
radiolarians
foraminiferans
prokaryotic
ancestor
ciliates
Alveolates
dinoflagellates
apicomplexans
water molds
diatoms Stramenopiles
brown algae
red algae
chlorophyte algae Green
charophyte algae Algae
land plants
amoebas Amoebozoans
slime molds
fungi
choanoflagellates
animals
Fig. 22-2f, p. 352
Protist Organization and Nutrition
 Most protists are single-celled, but some are
colonial or multicelled
 Protists can be autotrophs or heterotrophs, and
a few can switch between modes
 Some single-celled protists can develop into a
nonmotile, dormant cyst during hard times
Some Protist
Characteristics
Three General Protist Life Cycles
 Protists show great diversity in life cycles; most
reproduce both sexually and asexually
• Haploid-dominated life cycle (zygote is the only
diploid cell)
• Alternation of generations (haploid and diploid
multicelled forms)
• Diploid-dominated life cycle
Three General Protist Life Cycles
Fig. 22-3a, p. 353
zygote
fertilization
diploid (2n)
haploid (n)
meiosis
spores
gametes
mitosis
single cells or
multicelled body
Fig. 22-3a, p. 353
Fig. 22-3b, p. 353
mitosis
multicelled
body
zygote
fertilization
diploid (2n)
haploid (n)
meiosis
spores
gametes
multicelled
body
mitosis
Fig. 22-3b, p. 353
Fig. 22-3c, p. 353
mitosis
single cells or
multicelled body
zygote
diploid (2n)
fertilization
haploid (n)
meiosis
gametes
Fig. 22-3c, p. 353
zygote
fertilization
diploid (2n)
haploid (n)
meiosis
spores
gametes
single cells or
multicelled body
mitosis
zygote
fertilization
multicelled
body
diploid (2n)
haploid (n)
gametes
mitosis
mitosis
multicelled
body
meiosis
spores
mitosis
single cells or
multicelled body
zygote
diploid (2n)
fertilization
haploid (n)
gametes
meiosis
Stepped Art
Fig. 22-3, p. 353
22.1 Key Concepts
Sorting Out the Protists
 Protists include many lineages of single-celled
eukaryotic organisms and their closest
multicelled relatives
 Gene sequencing and other methods are
clarifying how protist lineages are related to one
another and to plants, fungi, and animals
22.2 Flagellated Protozoans
 Flagellated protozoans are single-celled
protists covered by a pellicle (proteins that help
cells retain shape)
 They swim in lakes, seas, and the body fluids of
animals
 They are typically heterotrophic and reproduce
asexually by binary fission
The Anaerobic Flagellates
 Diplomonads and parabasalids have multiple
flagella and live in oxygen-poor waters
• Hydrogenosomes produce ATP anaerobically
 Some infect humans and cause disease
• Giardia lamblia is an intestinal parasite
• Trichomonas vaginalis causes a sexually
transmitted disease
Giardia and Trichomonas
Fig. 22-4a, p. 354
Fig. 22-4b, p. 354
Fig. 22-4c, p. 354
Trypanosomes and Other Kinetoplastids
 Kinetoplastids are flagellated protozoans with a
single large mitochondrion
 Trypanosomes include human pathogens that
are transmitted by insects
• African sleeping sickness (T. brucei) is spread by
tsetse flies
• Chagas disease (T. cruzi) is spread by
bloodsucking bugs
Trypanosoma brucei
long flagellum attached
to undulating membrane
single, long
mitochondrion
Golgi body
ER
nucleus
vacuole
Fig. 22-5a, p. 354
red blood cell
of human host
flagellum attached to
undulating membrane
Fig. 22-5b, p. 354
The Euglenoids
 Euglenoids are flagellated protists related to
kinetoplastids that do not infect humans
• Most prey on bacteria
• Some have chloroplasts that evolved from green
algae and can detect light with an eyespot
• Most live in freshwater and have contractile
vacuoles that expel excess water
A Euglenoid: Euglena gracilis
Fig. 22-6a, p. 355
flagellum
5 µm
chloroplast
nucleus
mitochondrion
Fig. 22-6a, p. 355
Fig. 22-6b, p. 355
chloroplast
contractile vacuole
flagellum
eyespot
pellicle
ER
nucleus
Golgi body
mitochondrion
Fig. 22-6b, p. 355
Animation: Body plan of Euglena
22.3 Foraminiferans and Radiolarians
 Heterotrophic single cells with chalky or glassy
shells live in great numbers in the world’s
oceans; cytoplasm extends through many pores
Chalky-Shelled Foraminiferans
 Foraminiferans are single celled protists that
make calcium carbonate shells from CO2
• Helps stabilize atmospheric CO2 levels and
buffers pH of seawater
• Shells accumulate as chalk or limestone
 Most forams live on the seafloor; others drift as
part of the plankton
White Cliffs of Dover
 Chalky remains of foraminiferans and other
organisms with calcium-carbonate shells
Glassy-Shelled Radiolarians
 Radiolarians are heterotrophic protists with silica
shells beneath their plasma membrane
 Most are part of the marine plankton – vacuoles
filled with air keep radiolarians afloat
22.2-22.3 Key Concepts
Flagellated Protozoans and Shelled Cells
 Flagellated protozoans include single-celled
predators and some human parasites
 Foraminiferans and radiolarians are shelled,
single-celled heterotrophs; most live in seas