Chapter 28(2)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 28
Protists

• Overview: A World in a Drop of Water
• Even a low-power microscope
– Can reveal an astonishing menagerie of
organisms in a drop of pond water
Figure 28.1
50 m

• These amazing organisms
– Belong to the diverse kingdoms of mostly
single-celled eukaryotes informally known as
protists
• Advances in eukaryotic systematics
– Have caused the classification of protists to
change significantly

• Concept 28.1: Protists are an extremely
diverse assortment of eukaryotes
• Protists are more diverse than all other
eukaryotes
– And are no longer classified in a single
kingdom
• Most protists are unicellular
– And some are colonial or multicellular

• 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

• Protist habitats are also diverse in habitat
• And including freshwater and marine
species
Figure 28.2a–d
100 m
100 m
4 cm
500 m
The freshwater ciliate Stentor,
a unicellular protozoan (LM)
Ceratium tripos, a unicellular marine dinoflagellate (LM)
Delesseria sanguinea, a multicellular marine red alga
Spirogyra, a filamentous freshwater green alga (inset LM)
(a)
(b)
(c)
(d)

• Reproduction and life cycles
– Are also highly varied among protists, with
both sexual and asexual species

• A sample of protist diversity
Table 28.1

Endosymbiosis in Eukaryotic Evolution
• There is now considerable evidence
– That much of protist diversity has its origins in
endosymbiosis

• The plastid-bearing lineage of protists
– Evolved into red algae and green algae
• On several occasions during eukaryotic
evolution
– Red algae and green algae underwent
secondary endosymbiosis, in which they
themselves were ingested

Cyanobacterium
Heterotrophic
eukaryote
Primary
endosymbiosis
Red algae
Green algae
Secondary
endosymbiosis
Secondary
endosymbiosis
Plastid
Dinoflagellates
Apicomplexans
Ciliates
Stramenopiles
Euglenids
Chlorarachniophytes
Plastid
Alveolates
Figure 28.3
• Diversity of plastids produced by secondary
endosymbiosis

• Concept 28.2: Diplomonads and parabasalids
have modified mitochondria
• A tentative phylogeny of eukaryotes
– Divides eukaryotes into many clades
Figure 28.4
Diplomonads
Parabasalids
Kinetoplastids
Euglenids
Dinoflagellates
Apicomplexans
Ciliates
Oomycetes
Diatoms
Goldenalgae
Brownalgae
Chlorarachniophytes
Foraminiferans
Radiolarians
Gymnamoebas
Entamoebas
Plasmodialslimemolds
Cellularslimemolds
Fungi
Choanoflagellates
Metazoans
Redalgae
Chlorophytes
Charophyceans
Plants
Ancestral eukaryote
Chlorophyta
Plantae
Rhodophyta
Animalia
Fungi
(Opisthokonta) (Viridiplantae)
Diplomonadida
Parabasala
Euglenozoa
Alveolata Stramenopila
Cercozoa
Radiolaria
Amoebozoa

• Diplomonads and parabasalids
– Are adapted to anaerobic environments
– Lack plastids
– Have mitochondria that lack DNA, an electron
transport chain, or citric-acid cycle enzymes

Diplomonads
• Diplomonads
– Have two nuclei and multiple flagella
Figure 28.5a
5 µm
(a) Giardia intestinalis, a diplomonad (colorized SEM)

Parabasalids
• Parabasalids include trichomonads
– Which move by means of flagella and an
undulating part of the plasma membrane
Figure 28.5b (b) Trichomonas vaginalis, a parabasalid (colorized SEM)
Flagella
Undulating membrane 5 µm

• Concept 28.3: Euglenozoans have flagella with
a unique internal structure
• Euglenozoa is a diverse clade that includes
– Predatory heterotrophs, photosynthetic
autotrophs, and pathogenic parasites

• The main feature that distinguishes protists in
this clade
– Is the presence of a spiral or crystalline rod of
unknown function inside their flagella
Flagella
0.2 µm
Crystalline rod
Ring of microtubulesFigure 28.6

Kinetoplastids
• Kinetoplastids
– Have a single, large mitochondrion that
contains an organized mass of DNA called a
kinetoplast
– Include free-living consumers of bacteria in
freshwater, marine, and moist terrestrial
ecosystems

• The parasitic kinetoplastid Trypanosoma
– Causes sleeping sickness in humans
Figure 28.7
9 m

Euglenids
• Euglenids
– Have one or two flagella that emerge from a
pocket at one end of the cell
– Store the glucose polymer paramylon
Figure 28.8
Long flagellum
Short flagellum
Nucleus
Plasma membrane
Paramylon granule
Chloroplast
Contractile vacuole
Light detector: swelling near the
base of the long flagellum; detects
light that is not blocked by the
eyespot; as a result, Euglena moves
toward light of appropriate
intensity, an important adaptation
that enhances photosynthesis
Eyespot: pigmented
organelle that functions
as a light shield, allowing
light from only a certain
direction to strike the
light detector
Pellicle: protein bands beneath
the plasma membrane that
provide strength and flexibility
(Euglena lacks a cell wall)
Euglena (LM)
5 µm

• Concept 28.4: Alveolates have sacs beneath
the plasma membrane
• Members of the clade Alveolata
– Have membrane-bounded sacs (alveoli) just
under the plasma membrane
Figure 28.9
Flagellum
Alveoli0.2 µm

Dinoflagellates
• Dinoflagellates
– Are a diverse group of aquatic photoautotrophs
and heterotrophs
– Are abundant components of both marine and
freshwater phytoplankton

• Each has a characteristic shape
– That in many species is reinforced by internal
plates of cellulose
• Two flagella
– Make them spin as they move through the
water
Figure 28.10
3µm
Flagella

• Rapid growth of some dinoflagellates
– Is responsible for causing “red tides,” which
can be toxic to humans

Apicomplexans
• Apicomplexans
– Are parasites of animals and some cause
serious human diseases
– Are so named because one end, the apex,
contains a complex of organelles specialized
for penetrating host cells and tissues
– Have a nonphotosynthetic plastid, the
apicoplast

Figure 28.11
Inside mosquito Inside human
Sporozoites
(n)
Oocyst
MEIOSIS
Liver
Liver cell
Merozoite
(n)
Red blood
cells
Gametocytes
(n)
FERTILIZATION
Gametes
Zygote
(2n)
Key
Haploid (n)
Diploid (2n)
Merozoite
Red blood
cell
Apex
0.5 µm
• Most apicomplexans have intricate life cycles
– With both sexual and asexual stages that often require
two or more different host species for completionAn infected Anopheles
mosquito bites a person,
injecting Plasmodium
sporozoites in its saliva.
1 The sporozoites enter the person’s
liver cells. After several days, the sporozoites
undergo multiple divisions and become
merozoites, which use their apical complex
to penetrate red blood cells (see TEM below).
2
The merozoites divide asexually inside the
red blood cells. At intervals of 48 or 72 hours
(depending on the species), large numbers of
merozoites break out of the blood cells, causing
periodic chills and fever. Some of the merozoites
infect new red blood cells.
3
Some merozoites
form gametocytes.
4
Another Anopheles mosquito
bites the infected person and picks
up Plasmodium gametocytes along
with blood.
5Gametes form from gametocytes.
Fertilization occurs in the mosquito’s
digestive tract, and a zygote forms.
The zygote is the only diploid stage
in the life cycle.
6
An oocyst develops
from the zygote in the wall
of the mosquito’s gut. The
oocyst releases thousands
of sporozoites, which
migrate to the mosquito’s
salivary gland.
7

Ciliates
• Ciliates, a large varied group of protists
– Are named for their use of cilia to move and
feed
– Have large macronuclei and small micronuclei

• The micronuclei
– Function during conjugation, a sexual process
that produces genetic variation
• Conjugation is separate from reproduction
– Which generally occurs by binary fission

Figure 28.12
50 µm
Thousands of cilia cover
the surface of Paramecium.
The undigested contents of food
vacuoles are released when the
vacuoles fuse with a specialized
region of the plasma membrane
that functions as an anal pore.
Paramecium, like other freshwater
protists, constantly takes in water
by osmosis from the hypotonic environment.
Bladderlike contractile vacuoles accumulate
excess water from radial canals and periodically
expel it through the plasma membrane.
Food vacuoles combine with
lysosomes. As the food is digested,
the vacuoles follow a looping path
through the cell.
Paramecium feeds mainly on bacteria.
Rows of cilia along a funnel-shaped oral
groove move food into the cell mouth,
where the food is engulfed into food
vacuoles by phagocytosis.
Oral groove
Cell mouth
Micronucleus
Macronucleus
FEEDING, WASTE REMOVAL, AND WATER BALANCE
• Exploring structure and function in a ciliate
Contractile Vacuole

CONJUGATION AND REPRODUCTION
8 7
2
MICRONUCLEAR
FUSION
Diploid
micronucleus
Diploid
micronucleus
Haploid
micronucleus
MEIOSIS
Compatible
mates
Key
Conjugation
Reproduction
Macronucleus
Two cells of compatible
mating strains align side
by side and partially fuse.
1 Meiosis of micronuclei
produces four haploid
micronuclei in each cell.
2
3 Three micronuclei in each cell
disintegrate. The remaining micro-
nucleus in each cell divides by mitosis.
The cells swap
one micronucleus.
4
The cells
separate.
5
Micronuclei fuse,
forming a diploid
micronucleus.
6Three rounds of
mitosis without
cytokinesis
produce eight
micronuclei.
7The original macro-
nucleus disintegrates.
Four micronuclei
become macronuclei,
while the other four
remain micronuclei.
8Two rounds of cytokinesis
partition one macronucleus
and one micronucleus
into each of four daughter cells.
9

• Concept 28.5: Stramenopiles have “hairy” and
smooth flagella
• The clade Stramenopila
– Includes several groups of heterotrophs as
well as certain groups of algae

• Most stramenopiles
– Have a “hairy” flagellum paired with a “smooth”
flagellum
Smooth
flagellum
Hairy
flagellum
5 µmFigure 28.13

Oomycetes (Water Molds and Their Relatives)
• Oomycetes
– Include water molds, white rusts, and downy
mildews
– Were once considered fungi based on
morphological studies

• Most oomycetes
– Are decomposers or parasites
– Have filaments (hyphae) that facilitate nutrient
uptake

• The life cycle of a water mold
Figure 28.14
Cyst
Zoospore
(2n)
ASEXUAL
REPRODUCTION
Zoosporangium
(2n)
Germ tube
Zygote
germination
FERTILIZATIONSEXUAL
REPRODUCTION
Zygotes
(oospores)
(2n)
MEIOSIS
Oogonium
Egg nucleus
(n) Antheridial
hypha with
sperm nuclei
(n)
Key
Haploid (n)
Diploid (2n)
Encysted zoospores
land on a substrate and
germinate, growing into
a tufted body of hyphae.
1 Several days later,
the hyphae begin to
form sexual structures.
2 Meiosis produces
eggs within oogonia
(singular, oogonium).
3 On separate branches of the
same or different individuals, meiosis
produces several haploid sperm nuclei
contained within antheridial hyphae.
4
Antheridial hyphae grow like
hooks around the oogonium and
deposit their nuclei through
fertilization tubes that lead to the
eggs. Following fertilization, the
zygotes (oospores) may develop
resistant walls but are also
protected within the wall of the
oogonium.
5
A dormant period
follows, during which the
oogonium wall usually
disintegrates.
6
The zygotes germinate
and form hyphae, and the
cycle is completed.
7
The ends
of hyphae
form tubular
zoosporangia.
8
Each zoospor-
angium produces
about 30
biflagellated
zoospores
asexually.
9

• The ecological impact of oomycetes can be
significant
– Phytophthora infestans causes late blight of
potatoes

Diatoms
• Diatoms are unicellular algae
– With a unique two-part, glass-like wall of
hydrated silica
Figure 28.15
3µm

• Diatoms are a major component of
phytoplankton
– And are highly diverse
Figure 28.16
50 µm

• Accumulations of fossilized diatom walls
– Compose much of the sediments known as
diatomaceous earth

Golden Algae
• Golden algae, or chrysophytes
– Are named for their color, which results from
their yellow and brown carotenoids
• The cells of golden algae
– Are typically biflagellated, with both flagella
attached near one end of the cell

• Most golden algae are unicellular
– But some are colonial
Figure 28.17
25 µm

Brown Algae
• Brown algae, or phaeophytes
– Are the largest and most complex algae
– Are all multicellular, and most are marine

• Brown algae
– Include many of the species commonly called
seaweeds
• Seaweeds
– Have the most complex multicellular anatomy
of all algae
Figure 28.18
Blade
Stipe
Holdfast

• Kelps, or giant seaweeds
– Live in deep parts of the ocean
Figure 28.19

Human Uses of Seaweeds
• Many seaweeds
– Are important commodities for humans
– Are harvested for food
Figure 28.20a–c
(a) The seaweed is
grown on nets in
shallow coastal
waters.
(b) A worker spreads
the harvested sea-
weed on bamboo
screens to dry.
(c) Paper-thin, glossy sheets
of nori make a mineral-rich wrap
for rice, seafood, and vegetables
in sushi.

Alternation of Generations
• A variety of life cycles
– Have evolved among the multicellular algae
• The most complex life cycles include an
alternation of generations
– The alternation of multicellular haploid and
diploid forms

• The life cycle of the brown alga Laminaria
Figure 28.21
Sporophyte
(2n)
Zoospores
Female
Gametophytes
(n)
MEIOSIS
FERTILIZATION
Developing
sporophyte
Zygote
(2n)
Mature female
gametophyte
(n)
Egg
Sperm
Male
Sporangia
Key
Haploid (n)
Diploid (2n)
The sporophytes of this seaweed
are usually found in water just below
the line of the lowest tides, attached
to rocks by branching holdfasts.
1
In early spring, at the end of
the main growing season, cells on
the surface of the blade develop
into sporangia.
2
Sporangia produce
zoospores by meiosis.
3
The zoospores are all
structurally alike, but
about half of them develop
into male gametophytes
and half into female
gametophytes. The
gametophytes look
nothing like the sporo-
phytes, being short,
branched filaments that
grow on the surface of
subtidal rocks.
4
Male gametophytes release
sperm, and female gametophytes
produce eggs, which remain
attached to the female gameto-
phyte. Eggs secrete a chemical
signal that attracts sperm of the
same species, thereby increasing
the probability of fertilization in
the ocean.
5
Sperm fertilize
the eggs.
6
The zygotes
grow into new
sporophytes,
starting life
attached to
the remains of
the female
gametophyte.
7

• Concept 28.6: Cercozoans and radiolarians
have threadlike pseudopodia
• A newly recognized clade, Cercozoa
– Contains a diversity of species that are among
the organisms referred to as amoebas
• Amoebas were formerly defined as protists
– That move and feed by means of pseudopodia
• Cercozoans are distinguished from most other
amoebas
– By their threadlike pseudopodia

Foraminiferans (Forams)
• Foraminiferans, or forams
– Are named for their porous, generally
multichambered shells, called tests
Figure 28.22
20 µm

• Pseudopodia extend through the pores in the
test
• Foram tests in marine sediments
– Form an extensive fossil record

Radiolarians
• Radiolarians are marine protists
– Whose tests are fused into one delicate piece,
which is generally made of silica
– That phagocytose microorganisms with their
pseudopodia

• The pseudopodia of radiolarians, known as
axopodia
– Radiate from the central body
Figure 28.23
200 µm
Axopodia

• Concept 28.7: Amoebozoans have lobe-
shaped pseudopodia
• Amoebozoans
– Are amoeba that have lobe-shaped, rather
than threadlike, pseudopodia
– Include gymnamoebas, entamoebas, and
slime molds

Gymnamoebas
• Gymnamoebas
– Are common unicellular amoebozoans in soil
as well as freshwater and marine
environments

• Most gymnamoebas are heterotrophic
– And actively seek and consume bacteria and
other protists
Figure 28.24
Pseudopodia
40 µm

Entamoebas
• Entamoebas
– Are parasites of vertebrates and some
invertebrates
• Entamoeba histolytica
– Causes amebic dysentery in humans

Slime Molds
• Slime molds, or mycetozoans
– Were once thought to be fungi
• Molecular systematics
– Places slime molds in the clade Amoebozoa

Plasmodial Slime Molds
• Many species of plasmodial slime molds
– Are brightly pigmented, usually yellow or
orange
Figure 28.25
4 cm

• At one point in the life cycle
– They form a mass called a plasmodium
Figure 28.26
Feeding
plasmodium
Mature
plasmodium
(preparing to fruit)
Young
sporangium
Mature
sporangium
Spores
(n)
Germinating
spore
Amoeboid cells
(n)
Zygote
(2n)
1 mm
Key
Haploid (n)
Diploid (2n)
MEIOSIS
SYNGAMY
Stalk
Flagellated cells
(n)
The feeding stage
is a multinucleate
plasmodium that lives
on organic refuse.
1 The plasmodium
takes a weblike form.
2
The plasmodium erects
stalked fruiting bodies (sporangia)
when conditions become harsh.
3
Within the bulbous
tips of the sporangia,
meiosis produces haploid
spores.
4
These cells are
either amoeboid or
flagellated; the two
forms readily convert
from one to the other.
6
The cells unite
in pairs (flagellated
with flagellated
and amoeboid with
amoeboid), forming
diploid zygotes.
7
The resistant spores disperse
through the air to new locations
and germinate, becoming active
haploid cells when conditions
are favorable.
5

• The plasmodium
– Is undivided by membranes and contains
many diploid nuclei
– Extends pseudopodia through decomposing
material, engulfing food by phagocytosis

Cellular Slime Molds
• Cellular slime molds form multicellular
aggregates
– In which the cells remain separated by their
membranes

• The life cycle of Dictyostelium, a cellular slime
mold
Spores
(n)
Emerging
amoeba
Solitary amoebas
(feeding stage)
ASEXUAL
REPRODUCTIONFruiting
bodies
Aggregated
amoebas
Migrating
aggregate
SYNGAMY
MEIOSIS
SEXUAL
REPRODUCTION
Zygote
(2n)
Amoebas
600 µm
200 µm
Key
Haploid (n)
Diploid (2n)Figure 28.27
In the feeding
stage of the life
cycle, solitary haploid
amoebas engulf bacteria.
1 During sexual repro-
duction, two haploid
amoebas fuse and
form a zygote.
2
The zygote
becomes a giant
cell (not shown)
by consuming
haploid amoebas.
After developing a
resistant wall, the
giant cell undergoes
meiosis followed by
several mitotic
divisions.
3
The resistant
wall ruptures,
releasing new
haploid amoebas.
4
When food is depleted,
hundreds of amoebas
congregate in response to a
chemical attractant and form
a sluglike aggregate (photo
below left). Aggregate
formation is the beginning
of asexual reproduction.
5
The aggregate migrates for a
while and then stops. Some of the
cells dry up after forming a stalk that
supports an asexual fruiting body.
6
Other
cells crawl
up the stalk
and develop
into spores.
7
Spores
are released.
8
In a favorable
environment, amoebas
emerge from the spore
coats and begin feeding.
9

• Dictyostelium discoideum
– Has become an experimental model for
studying the evolution of multicellularity

• Concept 28.8: Red algae and green algae are
the closest relatives of land plants
• Over a billion years ago, a heterotrophic protist
acquired a cyanobacterial endosymbiont
– And the photosynthetic descendants of this
ancient protist evolved into red algae and
green algae

Red Algae
• Red algae are reddish in color
– Due to an accessory pigment call
phycoerythrin, which masks the green of
chlorophyll

• Red algae
– Are usually multicellular; the largest are
seaweeds
– Are the most abundant large algae in coastal
waters of the tropics
Figure 28.28a–c
(a) Bonnemaisonia hamifera. This red alga
has a filamentous form.
Dulse (Palmaria palmata). This edible
species has a “leafy” form.
(b)
A coralline alga. The cell walls of
coralline algae are hardened by calcium
carbonate. Some coralline algae are
members of the biological communities
around coral reefs.
(c)

Green Algae
• Green algae
– Are named for their grass-green chloroplasts
– Are divided into two main groups: chlorophytes
and charophyceans
– Are closely related to land plants

• Most chlorophytes
– Live in fresh water, although many are marine
• Other chlorophytes
– Live in damp soil, as symbionts in lichens, or in
snow
Figure 28.29

• Chlorophytes include
– Unicellular, colonial, and multicellular forms
Volvox, a colonial freshwater chlorophyte. The colony is a hollow
ball whose wall is composed of hundreds or thousands of
biflagellated cells (see inset LM) embedded in a gelatinous
matrix. The cells are usually connected by strands of cytoplasm;
if isolated, these cells cannot reproduce. The large colonies seen
here will eventually release the small “daughter” colonies within
them (LM).
(a)
Caulerpa, an inter-
tidal chlorophyte.
The branched fila-
ments lack cross-walls
and thus are multi-
nucleate. In effect,
the thallus is one
huge “supercell.”
(b)
Ulva, or sea lettuce. This edible seaweed has a multicellular
thallus differentiated into leaflike blades and a rootlike holdfast
that anchors the alga against turbulent waves and tides.
(c)
20 µm
50 µm
Figure 28.30a–c

Figure 28.31
Flagella
Cell wall
Nucleus
Regions
of single
chloroplast
Zoospores
ASEXUAL
REPRODUCTION
Mature cell
(n)
SYNGAMY
SEXUAL
REPRODUCTION Zygote
(2n)
MEIOSIS
1 µm
Key
Haploid (n)
Diploid (2n)

+
+ 
+
+
• Most chlorophytes have complex life cycles
– With both sexual and asexual reproductive
stages In Chlamydomonas,
mature cells are haploid and
contain a single cup-shaped
chloroplast (see TEM at left).
1
In response to a
shortage of nutrients, drying
of the pond, or some other
stress, cells develop into gametes.
2
Gametes of opposite
mating types (designated
+ and –) pair off and
cling together. Fusion of
the gametes (syngamy)
forms a diploid zygote.
3
The zygote secretes
a durable coat that
protects the cell against
harsh conditions.
4
After a dormant period, meiosis
produces four haploid individuals (two
of each mating type) that emerge from
the coat and develop into mature cells.
5
When a mature cell repro-
duces asexually, it resorbs its
flagella and then undergoes two
rounds of mitosis, forming four
cells (more in some species).
6
These daughter cells develop flagella
and cell walls and then emerge as
swimming zoospores from the wall of
the parent cell that had enclosed them.
The zoospores grow into mature haploid
cells, completing the asexual life cycle.
7

Chapter 28(2)

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