Protists

The Protists
A diverse assemblage of eukaryotes
that ARENʼT
fungi, plants, or animals
Why can termites eat wood?
Because of
symbiotic
hypermastigotes
(a group of
parabasilids) living
in the termite gut
working together
with Archaean
methanogens
Fig 28.26 (SEM)
Where Did Eukaryotic Cells come from?
First found in fossil record about 2.1
billion years ago
(Prokaryote fossils to 3.5 BYA)
Two major features to explain:
- membrane-bounded organelles
(mitochondria and plastids)
- internal membrane systems
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In what ways are protists important?
Base of many “food chains” - especially
in aquatic settings
Clarify water by filtering out small
particles
Some are parasites that cause
diseases in other organisms
Some have economic uses for humans
Some are involved in important
symbiotic relationships…
And… they are a spectacular group
of organisms
Origin of Organelles
Idea is that the ancestors of
eukaryotic cells were symbiotic
consortiums of prokaryotic cells
Has come to be called the
“endosymbiont theory”

Lynn Margulis
Person who led the development of the endosymbiont theory
Origin of
Eukaryotes
Fig.25.9
Evidence (cont.)
Similar membrane proteins (inner
membrane)
Reproduce by a process similar to
binary fission
Contain circular DNA molecules
Ribosomal RNA sequences in
organelles more similar to
prokaryotes
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The Ideas of the Endosymbiont
Theory (Fig 25.9)
Mitochondria are the descendents of
aerobic heterotrophic bacteria
Chloroplasts are the descendants of
photosynthetic bacteria - very likely
cyanobacteria
Evidence that Supports the
Endosymbiont Theory
Endosymbiotic relationships exist in
the modern world, e.g., some
species of dinoflagellates are
endosymbiotic in corals
Plastids and mitochondria about the
same size as typical prokaryotic
cells
What organisms have eukaryotic cells?
Animals (mitochondria)
Plants (mitochondria and plastids)
Fungi (mitochondria)
Protists (mitochondria, some have
plastids)

The Protists
Incredible diversity of organisms -
your text recognizes 21 clades at
probably the Phylum or Kingdom
level
Typically found in aquatic or damp
environments, or in body fluids,
tissues, or cells of host organisms
Most have flagella or cilia at some
stage in their life cycle
Cilia and Flagella in Action
Cilia and Flagella
Kelp (Brown Algae)
Definitely donʼt need a microscope to see this protist!
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Structurally
distinct from
the flagella of
prokaryotes
Eukaryotic
flagella and
cilia have a
similar
structure
involving
microtubules
Flagella and Cilia (Fig 6.23)
Protist Size
Human sperm
Ciliate
Most are single-celled, but their cell
structure can be very complex
Ciliates (e.g., Paramecium,
Vorticella) are among the most
complex of all cells
Some are multicellular and
individuals can be as large as 60
meters in length - the “kelps”
(brown algae)
Protist Nutrition
Nutritionally diverse
- photoautotrophs
- chemoheterotrophs
Also are
“mixotrophs”
e.g., Euglena

Nutrition
Three major means of obtaining
nutrition amongst protists:
- Ingestive (“animal-like”), sometimes
called “protozoa”
- Absorptive (“fungus-like”)
- Photosynthetic (“plant-like”),
sometimes called “algae”
Distinct nutritional mechanisms may be
found within one Clade
Fig 28.3
Why not look at ALL 21 clades?
Getting a Ph.D. - Thatʼs where you learn
more and more about less and less until
you know everything about nothing
Intro Bio Course - Thatʼs where you learn
less and less about more and more until
you know nothing about everything
I want you to know something about
something...
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Protistan Phylogeny
“Kingdom Protista” was a diverse group of
organisms that were, in many cases, not
closely related
Phylogeny is currently in a “state of flux”
DNA sequence data have been, and will
continue to be, very helpful
Splitting of “Kingdom Protista” into 21
clades (Phyla? Kingdoms?) has been
proposed
These clades have been placed into 5
“supergroups” in your text
Protistan Diversity
A quick look at 9 of the 21 protist
clades described in Campbell et al.
Supergroup Excavata
Evidence:
- Excavated feeding groove
- DNA sequence similarities
Evidence supporting this “supergroup” is
rather weak and investigation is ongoing

The Parabasalids
Have modified mitochondria called
“hydrogenosomes”
Most familiar member Trichomonas
vaginalis - cause of a common
sexually transmitted disease
Trichomonas Fact Sheet at the CDC
Each cell possesses 4 flagella
The Euglenozoans
Two major groups:
the kinetoplastids
the euglenids
Tsetse Fly
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Trichomonas vaginalis
(Fig. 28.4)
The Kinetoplastids
One large mitochondrian per cell
Organized mass of DNA inside the
mitochondrian - called the “kinetoplast”
Genus Trypanosoma
cause of “African sleeping sickness”
Disease is vectored by the “Tsetse fly”
(Glossina spp.)
Invariably fatal if left untreated
Fig.
28.6
Red blood cell Trypanosome

Supergroup Chromalveolata
Evidence:
- DNA sequence similarities
- Chloroplast structure similarities
Highly controversial “supergroup”
The Dinoflagellates
Both marine and freshwater
Most species unicellular
Important component of “plankton”
About 50% of known species are
photosynthetic
Most species have elaborate cell
walls
Boat
“Red Tide”
Dead Fish
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The Alveolates
Characterized by the presence of
small membrane-bounded cavities
under their cell membrane
Three major groups:
Dinoflagellates
Apiocomplexans
Ciliates
Ceratium (light
microscope)
Dinoflagellates
Red Tide
Peridinium
(SEM)
Dinoflagellate population explosions
Water stained brownish-red
(xanthophylls)
Toxins produced by the
dinoflagellates can kill fish,
invertebrates, seabirds
Some types of toxins can
accumulate in shellfish - causing
poisoning in humans

Karenia brevis
One species of dinoflagellate that
causes red tides
Produces a toxin that kills fish and
invertebrates
Human exposure to the toxin may
cause a variety of symptoms,
including death - Called “neurotoxic
shellfish poisoning”
Location of Karenia blooms
(data from December 2004)
The Cilates
Many beautiful freshwater species
Use cilia to move and feed
Have very complex cells, e.g., each
cell has one micronucleus and one
macronucleus
Micronuclei participate in sexual
reproduction; macronuclei in
controlling cell functions
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Karenia brevis (SEM)
Unit 1 Exam
Available Monday 15 September
through Tuesday 23 September
READ: “COLL Testing Facility Policies
and Procedures” in the Course
Introduction Learning Module
Go to Center for On-Line Learning,
room 60 Carver Hall to take the exam
Ciliates
Stentor spp. Paramecium spp.

Paramecium feeding
Stramenopile Flagella (Fig 28.12)
The Diatoms
glass-like cell walls - made of
hydrated silica
important photosynthetic organisms
in “plankton”
fresh water and marine
large number of species (estimated
to be ~ 100,000)
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The Stramenopiles
Some species are photoautotrophic,
some are heterotrophic
Characterized by the presence hairlike
projections on one of their
(typically) two flagella
Four major groups:
Diatoms
Brown algae (includes “kelp”)
Golden algae
Oomycetes (water molds)
Diatom Diversity
(Fig 28.3)
Diatoms
Diatom Art

Diatomaceous Earth
Huge amounts of ancient diatom cell walls
Various uses:
filtering medium
metal polishes
reflective paint
pesticide
nanotechnology
The Red Algae
SEM of Diatom
No flagella present at any stage of the
life cycle
Most abundant in tropical oceans
Most are multicellular
~ 6,000 described species
Some species are heterotrophic
Red Algae
Accessory
pigments allow
photosynthesis
at great depths -
as deep as 260
meters
Effective at
absorbing blue
light
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Supergroup Archaeplastida
Evidence:
- DNA sequence similarity
- Chloroplast structure similarities
This “supergroup” is well supported
by the available evidence
Red Algae (Fig 28.19)
Human Uses
Cell wall extracts:
carageenan - commonly
eaten by people…
agar - microbiological
culturing media

Fig. 28.19
How do you feel about sushi?
Chloroplasts
Nucleus
Single-celled Green Alga -
Eremosphaera viridis
Colonial Green Alga - Volvox (Fig. 28.3)
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The Green Algae
Most species (~7,000) found in fresh
water
Cell walls with a relatively high
percent of cellulose
Can be unicellular,
colonial/filamentous, or multicellular
Can be motile (flagella) or non-motile
Chlamydomonas
Unicellular and motile green alga
Important model genetic system - much
research is done with this organism
Volvox

Filamentous Green Alga -
Ulothrix spp.
Green Algal Life Cycles
Can be quite complex with both sexual
and asexual reproduction
Most gametes have two flagella
Gametes may be isogamous or
anisogamous
Some multicellular species exhibit
alternation of generations (as do all
plants)
- may be heteromorphic or
isomorphic
Oedogonium Life Cycle
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Multicellular
Green Alga -
Ulva spp.
(Fig. 28.21)
An example of a green algal
life cycle
Oedogonium is a genus of
filamentous green algae
Anisogamous
Oedogonium life cycle
Meiosis leads to production of
“zoospores” (not gametes)
Gametes are produced by mitosis
Asexual “macrozoospores” are also
produced by mitosis

Supergroup Unikonta
Evidence:
- DNA sequence similarities
This “supergroup” is well supported by
the available evidence
Plasmodial Slime Molds
Feeding stage is an called a
“plasmodium” (Fig. 28.24)
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The Amoebozoans
Four major groups:
Plasmodial slime molds
Cellular slime molds
Gymnamoebas (free-living)
Entamoebas (parasitic)
The plasmodium is a
“coenocytic mass”
Multinucleate
cytoplasm undivided
by walls or
membranes
Live in moist habitats,
e.g., rotting logs
The plasmodium
engulfs food by
“phagocytosis” as do
ameobas
Cool Slime Mold Slime mold in “action”
Planet Earth - Jungles 23:20

Response to the Environment
~ 48 hours
Start End
Growth away from detergent
Gymnamoebas
Unicellular
Found in soil, freshwater, and marine
habitats
Heterotrophs that often consume
prokaryotes and other protists as
their food
Move by producing pseudopodia
Attack of the Killer Amoeba
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Slime Mold Reproduction
If available water or food insufficient,
produces resistant spores through
meiosis
Each
sporangium
produces
many spores
(Fig. 28.24)
Amoeba spp. (Fig. 28.3)
Studying organisms too small to see
without a microscope is…
1. Boring beyond
human tolerance
2. Very boring
3. More interesting
than I expected - but
still boring
4. Remarkably
interesting
5. More interesting
than any previous
experience in my life

The most interesting (or least boring)
group weʼve studied so far is
1. Archaea
2. Bacteria
3. Excavata
4. Chromalveolata
5. Archaeplastida
6. Unikonta
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