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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

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Chapter 28

Changing kingdom of protists
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
Where Are We Going?

  • Structural and biochemical adaptations

  • Introduce groups of protists

Diversity in 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
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
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
Exploring Protist Diversity



Modified mitochondria and flagella

Parasites, predatory, and photosynthetic species

Giardia intestinalis – severe diarrhea from feces water

Important photosynthetic organisms

Diatoms, brown algae, and pathogens

Plasmodium - malaria and Phytophthora - potato famine

Exploring protist diversity cont
Exploring Protist Diversity (cont.)



Amoebas that move by thread-like pseudopodia

Globigerina extend pseudopodia through shell

Amoebas that have lobe- or tube pseudopodia, animals, fungi and related protists

Hypothesis that was 1st to diverge

Exploring protist diversity cont1
Exploring Protist Diversity (cont.)


  • Red and green algae, land plants

  • All three structural types

  • Key photosynthetic species at food web base

  • Volvox – colonial, separation prevents reproduction


  • 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

      • Giardiaintestinalis

  • Parabasalids

    • Reduced mitochondria; some energy anaerobically

    • Trichomonasvaginalis – 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


  • 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


  • 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

    • 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

    • 2 types of nuclei

    • Variation due to conjugation

    • Reproduce asexually by binary fission

    • Stentor and Paramecium


  • 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

    • Phytophthorainfestans - potato blight, stalk and stem to black slime; crop losses


  • 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


  • 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

    • Descendants gave rise to land plants

    • Paraphyletic group

    • Freshwater, marine, and terrestrial

    • Sexual (biflagellated gametes) and asexual life cycles

    • Spirogyra,Volvox, and Ulva


  • 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

      • Entamoebahistolytica causes amebic dysentery; from water, food, or utensils

  • Opisthokonts include animals, fungi, and protists

  • Clades closely related within, but not between