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Chapter 28 / Protists
I. Introduction
A. Eukaryotes
1. 1st eukaryotic organisms
2. most are unicellular
3. considered “simple”
B. Protist diversity (ecological grouping)
1. comprised of:
a. protozoans--heterotrophs
free-living or symbiotic
b. slime molds
} saprotrophs
c. water molds
d. algae—autotrophs
2. formerly, lumped in single,
kingdom [but, paraphyletic]
--now up to 20 different kingdoms!
C. Protist life-styles
1. all require moist/wet environments
2. many are aquatic—plankton
3. many are motile
cilia, flagella, amoeboid motion, drift in currents
4. reproduce asexually (most also sexually)
Part I: Protozoans
II. Protozoans
--heterotrophic, similar to animals
A. Clade Amoebozoa—amoebae with lobe-shaped pseudopodia
1. unicellular (Rhizopods: Gymnamoebas and Entamoebas)
or aggregates of cells (the slime molds)
2. locomotion—by pseudopodia
also means to engulf food—phagocytosis
3. internal structure
contractile vacuole, food vacuole, lysosomes, nucleus
4. some free-living, some parasitic
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B. Clades Cercozoa and Radiolaria—
amoebae w/ thread-like pseudopodia
1. Actinopoda
a. have skeletons of silica: single fused piece in radiolarians, unfused plates (maybe
chitinous) in heliozoans
b. some marine (radiolarians), some live in fresh water (heliozoans)
c. have very thin pseudopodia, called axopodia
2. Foraminifera—the forams (clade Cercozoa)
a. multichambered, porous shells (tests)
b. marine organisms
c. locomotion: pseudopodia extend through pores; also used for feeding and building
shell
d. >90% of described forams are fossils
e. Many forams form symbioses with algae
C. Clade Alveolata: ciliates, apicomplexans, dinoflagellates
--have alveoli, small membrane-bound cavities, under the cell surface
--may help stabilize the cell surface and regulate water and ion content
1. Ciliophora—the ciliates
a. unicellular, most in freshwater
b. cilia
c. structures:
i. 2 nuclei: micronucleus and macronucleus
ii. oral groove
iii. food vacuole
iv. contractile vacuole
v. trichocysts to capture prey
d. genetic recombination via conjugation
2. Apicomplexa—the apicomplexans
a. all parasitic
b. locomotion—flexing
c. no contractile vacuoles
d. produces spores in 1st host, used to infect 2nd host
Plasmodium, causes malaria
sexual reproduction occurs in Anopheles mosquito host
a. mosquito ingests infected blood
b. reproduction in mosquito→salivary glands
c. transmits to human through bite
d. liver
e. red blood cells
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3. Dinoflagellates
unicellular or colonial
2 flagella
cellulose shells
many autotrophic
some cause red tides
D. Clade Euglenozoa
1. Euglenids
unicellular
1 flagella
some heterotrophs, some autotrophs
Euglena: chloroplasts, eye spot
2. Kinetoplastids
• have a single large mitochondrion and a unique organelle,
the kinetoplast—houses extranuclear DNA
• are symbionts
Trypanosoma
--causes African Sleeping Sickness
E. Clade Parabasla
--lack mitochondria
E.g. Trichonympha, Trichomonas vaginalis:
F. Clade Diplomonadida
multiple flagella,
two separate nuclei,
simple cytoskeleton,
no mitochondria or plastids
Giardia lamblia
Part II: Algae
Algal characteristics:
1. can have chlorophyll a and b, c, or d
2. possess accessory pigments
e.g., carotenoids, phycobillins
3. size range: microscopic to macroscopic
Dissimilarities to plants
1. lack cuticle, true roots, stems, and leaves
2. lack true gametangia--reproductive organ surrounded by extra layer of nonreproductive cells
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III. Algal Taxonomy and Diversity
A. Clade Alveolata—Dinoflagellates
1. unicellular or colonial
2. 2 flagella
3. cellulose shells
4. many autotrophic: may be endosymbionts with coral and mollusks
5. some cause red tides--release paralytic toxins
B. Clade Stramenopila—Bacillariophytes / Diatoms
1. unicellular or colonial
2. 2 part silica shell
3. most autotrophic
4. yield diatomaceous earth
5. plankton--important in Arctic/Antarctic food chain
C. Clade Euglenozoa—Clade Euglenophyta
1. unicellular; freshwater
2. 1 exposed flagellum, other in reservoir
3. some heterotrophs, some autotrophs
4. Euglena: chloroplasts, eye spot (stigma), paramylon granules
5. has flexible pellicle
6. increase with eutrophication
D. Clade Chlorophyta--the green algae
1. very diverse: include unicellular, colonial, multicellular forms
2. some characteristics similar to plants
e.g., photosynthetic pigments: chlorophyll a and b and carotenoids
cellulose in cell walls
similar mitotic division (some)
3. flagellated cells at some point in life
4. aquatic or terrestrial
5. sexual reproduction:
isogamous, anisogamous, oogamous
E. Clade Strameopila—Clade Phaeophyta--the brown algae
1. marine; mainly cooler waters
2. chlorophyll a and c and carotenoids
3. large multicellular (kelp) have specialized body parts: blade, stipe, holdfast, float
F. Clade Stramenopila, Clade Chrysophyta--golden algae
1. colonial (some unicellular), 2 flagella per cell
2. important component of freshwater plankton
3. chlorophyll a and c and carotenoids and xanthophyll
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G. Clade Rhodophyta--the red algae
1. most marine (warmer waters)
2. multicellular, no motile cells
3. contain phycoerythrin and phycocyanin; chlorophyll a and d
4. used to make agar, carrageenan
Part III: The Fungal-like Protists
IV. Slime and Water Molds
--similar to fungi in lifestyle (saprophytic) and appearance
--dissimilar to fungi by possession of:
flagellated cells
centrioles
cellulose in cell wall
A. Clade Amoebozoa-Clade Myxogastrida
plasmodium: can creep like amoeba
Reproduction: sporangia→haploid spores→
swarm cell or myxamoeba→zygote→
plasmodium
B. Clade Amoebozoa-Clade Dictylostelida
feeding stage: single, haploid amoeboid cell
can aggregate→pseudoplasmodium (slug) →
spores
C. Clade Stramenopila—Clade Oomycota--water molds
produce flagellated cells at 1 point in life cycle
like fungi, form mycelium; cell walls may contain chitin
Reproduction: asexual (favorable conditions)
sexual--oospores (less favorable conditions)
Some are important pathogens.