Chapter 28

Protists

Changing Kingdom of Protists

Discovered by Antoni Van Leeuwenhoek in pond waterOnce considered 1 kingdom, now known to be

paraphyleticSome closer to other eukaryotic kingdoms than other

protistsKingdom Protista dissolved now, used as a general term

Each lineage is separate kingdom

Where Are We Going?Structural and biochemical adaptationsIntroduce groups of protists

Diversity in ProtistsStructurally different

Most unicellular, some colonial, and some multicellularConsidered simplest eukaryotes; at cellular level =

complexNutritionally different

Photoautotrophs (chlorplasts), heterotrophic (absorb or ingest), or mixotrophs (combine both)Arisen independently in lineages

Reproduction and life cycles varySome exclusively asexual, some exclusively sexual,

others some processes of meiosis, and some vary from any of the above

HabitatsMost 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 DiversityExcavata ChromalveolataModified

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.)Rhizaria Unikonta

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 (cont.)

ArchaeplastidaRed and green algae,

land plantsAll three structural

typesKey photosynthetic

species at food web base

Volvox – colonial, separation prevents reproduction

ExcavatesEach are monophyletic, but supergroup unconfirmed

= controversialDiplomonads

Mitochondria w/o fxnl ETC; energy from anaerobic paths2 nuclei, multiple flagella, and most are parasites

Giardia intestinalisParabasalids

Reduced mitochondria; some energy anaerobicallyTrichomonas vaginalis – STD in males and females

EuglenozoansSpiral or crystalline rod inside flagella of unknown originKinetoplastids are parasitic

Trypanosoma: sleeping sickness; avoid detection by changing surface protein

EuglenoidsMixotroph: in sunlight autotrophic, no sun heterotrophicSome engulf prey by phagocytosis

ChromalveolatesMost controversial of all supergroupsAlveolates

Well supported hypothesisMembrane bound sacs under plasma

membrane3 subgroups

StramenopilesMarine algaePhotosynthetic organisms and heterotrophsFlagella are numerous, hair-like projections4 subgroups

AlveolatesDinoflagellates: cells reinforced by cellulose plates

Flagella in groove for spin movementMarine and freshwater living near water’s surfaceBlooms cause ‘red tides’ in coastal water, killing

inverts and fishApicomplexans: parasites of animals

Complex organelle end to penetrate host tissuesSexual and asexual stages; need 2 different hostsPlasmodium causes malaria (mosquitoes and humans)Avoids detection like kinetoplastids

Ciliates: use cilia to move and feed2 types of nucleiVariation due to conjugationReproduce asexually by binary fissionStentor and Paramecium

StramenopilesDiatoms: unicellular algae with walls of silica arranged

like a boxReproduce asexually by mitosis with daughters stored insideAccumulate in sediments, used as a filtering medium

Golden algae: biflagellated, mixotrophic organismsFreshwater and marine planktonColonial, can form protective cysts

Brown algae: largest and most complex algaeMost 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 celluloseSimilarity to fungi is example of convergent evolutionPhytophthora infestans - potato blight, stalk and stem to

black slime; crop losses

Rhizarians

Morphology differs, but DNA conforms monophyletic group

Forams: CaCO3 porous shellNutrients from algae that live in the test Marine and fresh water living in sand or on rocks and

algaeUsed to age sedimentary rocks

Radiolarians: symmetrical internal skeletons of silica

ArchaeplastidaRed algae: accessory pigment varies by water

depthMost abundant in warm coastal watersPorphyra used as crispy wraps for sushiDiverse life cycles and alternation of generations

No flagellated stages in life and water currents for fertilization

Green algaeDescendants gave rise to land plantsParaphyletic group Freshwater, marine, and terrestrialSexual (biflagellated gametes) and asexual life

cyclesSpirogyra,Volvox, and Ulva

UnikontsRecently proposed and very diverse, including

protists, animals, and fungiAmoebozoans

Slime moldsPlasmodial slime molds: brightly colored and produce fruiting

bodies to disperse sporesCellular slime molds: singular when food plentiful, but

aggregates when depletedGymnamoebas

In soil, freshwater, and marine environmentsHeterotrophs that seek and consume bacteria, protists, and

detriusEntamoebas

Parasites that infect all vertebrates and some invertebratesEntamoeba histolytica causes amebic dysentery; from

water, food, or utensils

Opisthokonts include animals, fungi, and protistsClades closely related within, but not between

Protist Supergroup Summary