Protists – The Simplest
Eukaryotes
Chapter 22 Part 2
22.4 The Ciliates
 Ciliates are heterotrophic single cells that move
about with the help of cilia
 Ciliates reproduce asexually by binary fission or
sexually by conjugation
Ciliate Lifestyles
 Most ciliates are free-living predators that hunt
bacteria, other protists, and one another in
freshwater habitats and the oceans
• Example: Paramecium
 Some ciliates are parasites of animals
• Balantidium coli is a parasite of humans
Ciliates: Predator and Prey
 Didinium and Paramecium
prey
prey disappearing
into predator’s
oral opening
predator
Fig. 22-9, p. 357
Ciliate Structure: Paramecium
contractile vacuole
pellicle
Fig. 22-10a, p. 357
Fig. 22-10 (b-c), p. 357
food vacuole
(being emptied)
gullet
cilia
trichocysts
cilium
pellicle
filled
emptied
micronucleus contractile
contractile
vacuole
vacuole
macronucleus
alveolus
intact
trichocyst
Fig. 22-10 (b-c), p. 357
Animation: Paramecium body plan
Alveolates
 Three groups of protists characterized by tiny
sacs beneath their plasma membrane
• Ciliates
• Dinoflagellates
• Apicomplexans
22.5 Dinoflagellates
 Dinoflagellates (“whirling flagellates”) are
mostly marine single-celled alveolate protists
 Some are predators or parasites; others are
photosynthetic members of the plankton or
symbionts in corals
Algal Blooms and Toxins
 Algal blooms
• Great increases in free-living photosynthetic
dinoflagellates or other protists in habitats
enriched with nutrients such as agricultural runoff
• Blooms of certain species cause “red tides” that
can sicken humans and kill aquatic organisms
 Some dinoflagellates toxins kill directly
• Neurotoxic shellfish poisoning (Karenia brevis)
Karenia brevis and Algal Blooms
Bioluminescent Dinoflagellates
22.6 The Cell-Dwelling Apicomplexans
 Apicomplexans are parasitic alveolates that
spend part of their life inside host cells
• Plasmodium causes malaria
• Toxoplasma gondii causes toxoplasmosis
 Apicomplexans infect a variety of animals from
worms to insects to humans
• Life cycle may involve more than one species
Life Cycle of Plasmodium
G Plasmodium zygotes
develop inside the gut of
sporozoite
female mosquitoes. They
become sporozoites,
which migrate to the
insect’s salivary
glands.
A Mosquito bites human,
bloodstream carries the
sporozoites to liver.
D Some of the
merozoites enter
liver, cause more
malaria episodes.
E Others develop into male,
female gametocytes that are
released into bloodstream.
male gametocyte in red blood cell
sporozoites
B Sporozoites asexually
reproduce in liver cells.
merozoite
C Offspring (merozoites)
enter blood, invade red
blood cells, reproduce
asexually. They can do so
often, over a prolonged
period. Disease symptoms
(fever, chills, shaking) get
more and more severe.
F Female mosquito bites, sucks blood
from infected human. Gametocytes in
blood enter her gut, mature into
gametes, which fuse to form zygotes.
Fig. 22-13, p. 359
sporozoite
G Plasmodium zygotes
develop inside the gut of
female mosquitoes. They
become sporozoites,
A Mosquito bites human,
which migrate to the
bloodstream carries the
insect’s salivary
sporozoites to liver.
glands.
D Some of the
merozoites enter
liver, cause more
malaria episodes.
sporozoites
B Sporozoites
asexually reproduce
in liver cells.
merozoite
F Female mosquito
bites, sucks blood
from infected human.
Gametocytes in blood
enter her gut, mature
into gametes, which
fuse to form zygotes.
E Others develop
into male, female
gametocytes that are
released
intobloodstream.
male gametocyte in
red blood cell
C Offspring
(merozoites) enter
blood, invade red
blood cells,
reproduce
asexually. They can
do so often, over a
prolonged period.
Disease symptoms
(fever, chills,
shaking) get more
and more severe.
Stepped Art
Fig. 22-13, p. 359
Animation: Apicomplexan life cycle
22.4-22.6 Key Concepts
The Alveolates
 Ciliated protozoans, dinoflagellates, and
apicomplexans are single-celled
photoautotrophs, predators, and parasites
 Their shared trait is a unique layer of sacs under
the plasma membrane
22.7 The Stramenopiles
 Stramenopiles
• Colorless filamentous molds, photosynthetic
single cells, and large seaweeds belong to the
stramenopile lineage
The Diatoms
 Diatoms are single-celled or colonial protists
that have a two-part silica shell
• Shells accumulate on the seafloor (diatomaceous
earth)
 Most are photosynthetic, with a brown accessory
pigment (fucoxanthin)
• Major components of phytoplankton
Diatoms
The Multicelled Brown Algae
 Brown algae are multicelled protists that live in
temperate or cool seas; ranging from
microscopic filaments to giant kelp
 Some brown algae are used commercially
• Thickeners (algins), food, fertilizer, herbal
supplements (bladderwrack)
Bladderwrack
Kelps
 Giant kelp (Macrocystis) is the largest protist
• Life cycle: alternation of generation with
multicellular haploid and diploid bodies and a
dominant sporophyte generation
• Ecologically important kelp forests (Pacific)
 Sargassum forms large floating mats
• Important Atlantic habitat (Sargasso Sea)
Giant Kelp
Fig. 22-16a, p. 360
Fig. 22-16b, p. 360
bladder
stipe
blade
holdfast
Fig. 22-16b, p. 360
The Heterotrophic Water Molds
 Water molds (oomycotes) form a mesh of
filaments made up of diploid cells with cellulose
cell walls
 Water molds decompose organic matter in
aquatic habitats, are aquatic parasites
(Saprolegnia), or infect plants
Parasitic Water Molds
 Filaments of Saprolegnia infect fish in aquaria
22.8 The Plant Destroyers
 Water molds include economically and
ecologically important plant pathogens that infect a
wide variety of crop plants, as well as forest trees
• Phytopthora infestans ruined Irish potato crops
• Phytopthora ramorum recently infected North
American forests
Phytopthora: The Plant Destroyers
22.7-22.8 Key Concepts
The Stramenopiles
 Diatoms and brown algae are stramenopiles,
most of which are photoautotrophs
 The colorless water molds, which include major
plant pathogens, are also stramenopiles
22.9 Green Algae
 Green algae are photosynthetic single-celled
and multicelled protists
 Like land plants, they have cellulose in their cell
walls, store sugars as starch, and have
chloroplasts descended from cyanobacteria
The Chlorophytes
 Most green algae are chlorophytes
•
•
•
•
•
•
Chlorella: Single celled, grown as health food
Chlamydomonas: Single celled, freshwater alga
Volvox: Colonial, freshwater alga
Cladophora: Forms long filaments
Ulva: “Sea lettuce”
Codium fragilis: Branching marine alga
Chlorophyte Algae
Chlamydomonas Life Cycle
A thick-walled
resistant zygote
develops.
Zygote
(cross-section)
nuclear
fusion
surface
view of
zygote
Diploid Stage
Haploid Stage
meiosis and
germination
haploid cell
(– strain)
haploid cell
(+ strain)
cytoplasmic
fusion
Gametes –
of different
mating types
meet.
Meiosis produces haploid, flagellated
cells that reproduce asexually.
SEXUAL
REPRODUCTION:
ASEXUAL
ASEXUAL
REPRODUCTION:
Mainly when REPRODUCTION:
nitrogen levels are
low and light is of a
More spores
certain quality and
are produced.
+ intensity, the cells
develop into
gametes. +
More spores
are produced.
–
Fig. 22-20, p. 362
A thick-walled resistant zygote
develops.
Zygote
(cross-section)
nuclear
fusion
Diploid Stage
Haploid Stage
meiosis and
germination
haploid cell
(– strain)
haploid cell
(+ strain)
cytoplasmic
fusion
Gametes –
of different
mating types
meet.
Meiosis produces haploid, flagellated
cells that reproduce asexually.
SEXUAL
REPRODUCTION:
ASEXUAL
ASEXUAL
REPRODUCTION:
Mainly when REPRODUCTION:
nitrogen levels are
low and light is of a
More spores
certain quality and
are produced.
+ intensity, the cells
develop into
gametes. +
More spores
are produced.
–
Stepped Art
Fig. 22-20, p. 362
Animation: Green alga life cycle
Charophyte Algae
 Charophyte algae include several lineages that
form a clade with land plants
• Desmids: A single-celled, freshwater group
• Spirogyra: Forms long filaments
• Stoneworts (Chara): Closely related to land plants
Charophyte Algae
22.10 Red Algae Do It Deeper
 Red algae are mostly multicelled marine algae
that live in clear, warm waters
 Red accessory pigments (phycobilins) allow red
algae to live at greater depths than other algae
Red Alga Antithamnion plumula
Red Algae Life Cycle
 Red and green algae share a common ancestor
with chloroplasts derived from cyanobacteria
 Life cycles vary and are often complex, with both
asexual and sexual phases; there is no
flagellated stage
Red Algae Life Cycle: Porphyra
sporophyte (2n)
zygote
fertilization
Diploid Stage
Haploid Stage
meiosis
germinating
spore (n)
male
gametes
female
gametes
gametophyte (n)
Fig. 22-23, p. 364
sporophyte (2n)
zygote
fertilization
Diploid Stage
Haploid Stage
meiosis
germinating
spore (n)
male
gametes
female
gametes
gametophyte (n)
Stepped Art
Fig. 22-23, p. 364
Animation: Red alga life cycle
22.9-22.10 Key Concepts
The Closest Relatives of Land Plants
 Red algae and green algae are photosynthetic
single cells and multicelled seaweeds
 One lineage of multicelled green algae includes
the closest living relatives of land plants
22.11 Amoeboid Cells at the Crossroads
 How can organisms be so much alike and still
show tremendous diversity?
 Amoebozoans provide clues to how signaling
pathways of multicelled organisms evolved
• Cell-to-cell communication may have originated in
single-celled amoeboid ancestors
Amoebozoans
 Amoebozoans send out pseudopods, move
about, and capture food
• Most have no cell walls, shell, or pellicles
 Amoebas live as single cells
• Example: Amoeba proteus, a freshwater predator
 Slime molds are “social amoebas”
• Plasmodial and cellular slime molds
Plasmodial Slime Molds
 Plasmodial slime molds spend most of their
lives as a plasmodium
• A streaming multinucleated mass that feeds on
microbes and organic matter
• Undergoes mitosis many times without cell division
• Develops into spore-bearing fruiting bodies
Amoeba and Plasmodial Slime Mold
Cellular Slime Molds
 Cellular slime molds spend most of their lives
as individual amoeboid cells that feed on
bacteria and reproduce by mitosis
 When food runs out, thousands of cells form a
“slug” that migrates, forms a fruiting body, and
produces spores and new diploid amoeboid cells
• Example: Dictyostelium discoideum
Cell-to-Cell Communication: Cyclic AMP
 In the cellular slime mold Dictyostelium, the
nucleotide cyclic AMP is the signal that induces
solitary amoeboid cells to stream together
• Triggers gene expression which causes cells to
differentiate into components of a stalk or spores
 Cyclic AMP also functions in signaling pathways
of multicelled organisms
Cellular Slime Mold Life Cycle:
Dictyostelium discoideum
A Spores give rise
to amoeboid cells.
E A fruiting
body forms
with resting
spores atop
a stalk.
Mature
fruiting
body
B Cells feed
and multiply
by mitosis.
C When food is
scarce, cells
aggregate.
Migrating
slug
stage
D The cells form a slug.
It may start to develop
as a fruiting body right
away, or migrate about.
In the slug, cells
become prestalk (red)
and prespore (tan) cells.
Fig. 22-26, p. 365
Animation: Cellular slime mold life cycle
22.11 Key Concepts
Relatives of Fungi and Animals
 A great variety of amoeboid species formerly
classified as members of separate lineages are
now united as the amoebozoans
 They are the closest living protistan relatives of
fungi and animals
Comparing Prokaryotes and Eukaryotes
Animation: Amoeboid motion
Animation: Body plan of Euglena
Animation: Ciliate conjugation
Video: Malaria
Video: Sudden oak death
Video: Sudden oak death
Video: Kelp Forest Channel Islands, CA