Protists
Chapter 28
Changing Kingdom of Protists
 Discovered by Antoni Van Leeuwenhoek in pond water
 Once considered 1 kingdom, now known to be paraphyletic
 Some closer to other eukaryotic kingdoms than other protists
 Kingdom Protista dissolved now, used as a general term
 Each lineage is separate kingdom
Where Are We Going?
 Structural and biochemical adaptations
 Introduce groups of protists
Diversity in Protists
 Structurally different
 Most unicellular, some colonial, and some multicellular
 Considered simplest eukaryotes; at cellular level = complex
 Nutritionally different
 Photoautotrophs (chlorplasts), heterotrophic (absorb or ingest), or
mixotrophs (combine both)
 Arisen independently in lineages
 Reproduction and life cycles vary
 Some exclusively asexual, some exclusively sexual, others some
processes of meiosis, and some vary from any of the above
 Habitats
 Most aquatic/marine, some terrestrial, and some in other organisms
Endosymbiosis and Eukaryotic Evolution
 Unicellular organisms
engulfed other cells that
became organelles,
resulting in diversity of
protists
 Earliest got
mitochondria from alpha
proteobacteria
 Later a cyanobacterium
 Red and green algae
Multiple occurrences of
secondary endosymbiosis

 Became endosymbionts
themselves
Protist Supergroups
Hypotheses of
classifications have and
continue to change
 Current hypotheses is 5
supergroups
 All diagramed as
diverging simultaneously
because root of eukaryotes
unknown
 Don’t focus on specific
groups, but why important

Exploring Protist Diversity
Excavata
Chromalveolata
 Modified mitochondria and
 Important photosynthetic
flagella
 Parasites, predatory, and
photosynthetic species
 Giardia intestinalis – severe
diarrhea from feces water
organisms
 Diatoms, brown algae, and
pathogens
 Plasmodium - malaria and
Phytophthora - potato famine
Exploring Protist Diversity (cont.)
Rhizaria
Unikonta
 Amoebas that move by
 Amoebas that have lobe- or
thread-like pseudopodia
 Globigerina extend
pseudopodia through shell
tube pseudopodia, animals,
fungi and related protists
 Hypothesis that was 1st to
diverge
Exploring Protist Diversity (cont.)
Archaeplastida
 Red and green algae, land
plants
 All three structural types
 Key photosynthetic species
at food web base
 Volvox – colonial, separation
prevents reproduction
Excavates
 Each are monophyletic, but supergroup unconfirmed = controversial
 Diplomonads
 Mitochondria w/o fxnl ETC; energy from anaerobic paths
 2 nuclei, multiple flagella, and most are parasites
 Giardia intestinalis
 Parabasalids
 Reduced mitochondria; some energy anaerobically
 Trichomonas vaginalis – STD in males and females
 Euglenozoans
 Spiral or crystalline rod inside flagella of unknown origin
 Kinetoplastids are parasitic
 Trypanosoma: sleeping sickness; avoid detection by changing surface protein
 Euglenoids
 Mixotroph: in sunlight autotrophic, no sun heterotrophic
 Some engulf prey by phagocytosis
Chromalveolates
 Most controversial of all supergroups
 Alveolates
 Well supported hypothesis
 Membrane bound sacs under plasma membrane
 3 subgroups
 Stramenopiles
 Marine algae
 Photosynthetic organisms and heterotrophs
 Flagella are numerous, hair-like projections
 4 subgroups
Alveolates
 Dinoflagellates: cells reinforced by cellulose plates
 Flagella in groove for spin movement
 Marine and freshwater living near water’s surface
 Blooms cause ‘red tides’ in coastal water, killing inverts and fish
 Apicomplexans: parasites of animals
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Complex organelle end to penetrate host tissues
Sexual and asexual stages; need 2 different hosts
Plasmodium causes malaria (mosquitoes and humans)
Avoids detection like kinetoplastids
 Ciliates: use cilia to move and feed
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2 types of nuclei
Variation due to conjugation
Reproduce asexually by binary fission
Stentor and Paramecium
Stramenopiles
 Diatoms: unicellular algae with walls of silica arranged like a box
 Reproduce asexually by mitosis with daughters stored inside
 Accumulate in sediments, used as a filtering medium
 Golden algae: biflagellated, mixotrophic organisms
 Freshwater and marine plankton
 Colonial, can form protective cysts
 Brown algae: largest and most complex algae
 Most are marine on temperate coasts; edible (soups and algins)
 Body or thallus with: holdfast (root), stipe (stem), and blade (leaf)
 Oomycetes: water molds, white rusts, and downy mildews
 Cell walls of cellulose
 Similarity to fungi is example of convergent evolution
 Phytophthora infestans - potato blight, stalk and stem to black slime; crop
losses
Rhizarians
 Morphology differs, but DNA conforms monophyletic
group
 Forams: CaCO3 porous shell
 Nutrients from algae that live in the test
 Marine and fresh water living in sand or on rocks and algae
 Used to age sedimentary rocks
 Radiolarians: symmetrical internal skeletons of silica
Archaeplastida
 Red algae: accessory pigment varies by water depth
 Most abundant in warm coastal waters
 Porphyra used as crispy wraps for sushi
 Diverse life cycles and alternation of generations
 No flagellated stages in life and water currents for fertilization
 Green algae
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Descendants gave rise to land plants
Paraphyletic group
Freshwater, marine, and terrestrial
Sexual (biflagellated gametes) and asexual life cycles
Spirogyra,Volvox, and Ulva
Unikonts
 Recently proposed and very diverse, including protists, animals,
and fungi
 Amoebozoans
 Slime molds
 Plasmodial slime molds: brightly colored and produce fruiting bodies to
disperse spores
 Cellular slime molds: singular when food plentiful, but aggregates when
depleted
 Gymnamoebas
 In soil, freshwater, and marine environments
 Heterotrophs that seek and consume bacteria, protists, and detrius
 Entamoebas
 Parasites that infect all vertebrates and some invertebrates
 Entamoeba histolytica causes amebic dysentery; from water, food, or utensils
 Opisthokonts include animals, fungi, and protists
 Clades closely related within, but not between
Protist Supergroup Summary