THE KINGDOMLESS PROTISTS

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THE KINGDOMLESS PROTISTS
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• Characteristics

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• The first eukaryotes arose somewhere around two
  billion years ago perhaps about the same time the
  atmosphere oceans became Oxygen rich.
• Protists are extremely diverse. They are found in
  most aquatic environments as well as in moist
  soils, and leaf litter.
• Many protists are unicellular but others are
  multicellular (think kelp) and may be up to 60 m.
  long.
• They are aerobic and have mitochondria (sites of
  ATP production)

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Protists are diverse
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They also have diverse metabolic mechanisms

• Photoautotrophs (the plant-like protists, and
  algae)
• Heterotrophs (animal-like protists, protozoans)
• Mixotrophs combine photosynthesis and
  heterotrophic nutrition (fungus-like protists)

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Plant like protists
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Animal like protists
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Fungi like protists
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• Most have flagella or cilia. These locomotor
  appendages are different than those of bacteria
  in that they are extensions of the cytoplasm and
  have a 92 arrangement of the microtubules.

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Trichomonas with flagella
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Cilia
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• Mitosis occurs in most protists
• Reproduction varies asexual, sexual, syngamy
  (where two gametes unite, shuffle genes, and then
  reproduce asexually). Diverse sexual life
  histories can be found among the different
  species.

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Reproduction (asexual and sexual with syngamy)
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Sexual Reproduction in Plasmodium
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• Many form cysts which can withstand harsh
  conditions

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Cysts
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• The protists play diverse ecological roles and
  are found in almost all aquatic environments,
  many species are important components of plankton
  (zoo- and phytoplankton)

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How did these first eukaryotes evolve?

• Autogenous model - eukaryotes arose from
  prokaryotes that showed a specialization of
  membranes (derived from the infoldings of the
  plasma membrane).

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• Endosymbiotic model - small prokaryotes lived
  symbiotically within larger prokaryotes.
  Evidence in support of this includes the
  existence of endosymbiots, similarities between
  bacteria and mitochondria and chloroplasts
  (similar cell sizes between mitochondria,
  chloroplasts, and average bacterium, all
  reproduce by binary fission, similar ribosomal
  components, one of the algal-like protists,
  Cyanophora, looks like a chloroplast, and
  circular DNA

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• The origin of eukaryotes may actually have
  involved a combination of the two.

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Tentative phylogeny of the eukaryotes
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• Group Excavata

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Diplomonoadida and ParabasalaGiardia and other
diplomonads are unique (they have modified
mitochondria called mitosomes , and two haploid
nuclei), Trichomonas vaginalis is the most well
known parabasalid. Both of these are parasites
with Giardia causing hikers diarrhea and
Trichomonas causing a vaginitis.
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Euglenozoans are divided into Eugelnids and
Kinetoplastids and include autotrophic,
hetertrophic (including parasites), and
mixotrophic protists that utilize flagella for
movement

• Euglenids . These protists produce
  polysaccharide, paramylon, for glucose storage
  that is characteristic of this taxon. Some of
  these organisms are mixotrophs (see above). Most
  of the euglenoids are found in freshwater.

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• Kinetoplastids possess one large mitochondrion
  that contains a mass of DNA called a kinetoplast.
  They are heterotrophic. Some are free-living,
  some symbiotic with other organisms (e.g., living
  in the guts of termites) and some are parasitic
  e.g., Trypanosoma (African Sleeping Sickness and
  Chagas disease).

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Euglena and Trypanosoma
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• Supergroup Chromalveolates

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• Alveolates Unicellular protists with subsurface
  sacs or cavities (alveoli). The function of the
  alveoli is unknown but they may have a role in
  stabilizing the cell membrane and regulating the
  cells water and ion content. These protists are
  ecologically diverse. They are divided into
  three subgroups

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• The apicomplexans are about 3,900 species which
  are heterotrophic, all parasitic (of animals),
  nonmotile, and have very complex life cycles with
  sexual and asexual stages and multiple hosts.
  Examples Plasmodium species (malaria and
  Toxoplasma (flu-like symptoms, birth defects)

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• The ciliates. These protists have cilia for
  movement and food acquisition. They are also
  heterotrophic. They have tough but flexible
  pellicles. They are found in freshwater
  environments and are unique in that they posses
  several nuclei (a macronucleus and several
  micronuclei). An example is Paramecium.

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• The dinoflagellates. Many are part of the
  phytoplankton but some are heterotrophic. Most
  are marine but some live in freshwater. Most are
  unicellular. Blooms of these organisms cause
  problems (e.g., ride tides) and one particularly
  nasty species, Pfisteria piscicida is a carnivore
  that causes fish kills, lesions on humans who
  come into contact with it and even neurological
  problems. Other species are responsible for
  toxic alga blooms called red tides.

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• Stramenopiles at some stage all of these protists
  have flagella with distinctive hair-like
  projections. They are important as primary
  producers

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• Diatoms. They are yellow to brown in color.
  They have unique glass-like walls of silica and
  are also components of phytoplankton. They
  reproduce asexually. An example of dead diatoms
  is diatomaceous earth. Dead diatoms also contain
  Carbon that is pumped to the benthos

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• Brown algae. They are the largest and most
  complex protists (e.g., true multicellularity).
  Sea weeds are members of the brown, red and green
  algae. Most are marine. An example is kelp

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• Golden algae. There are freshwater and marine
  species. They are also components of the
  plankton. Some are photosynthetic but many are
  mixotroph

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• Oomycetes. These are the water molds, white
  rusts, and downy mildews. They were previously
  considered to be fungi and some are very
  destructive plant pathogens.

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• Group Rhizaria.
• These are amoebas that move and feed by
  pseudopodia. Note that there are other amoebas
  in another group

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• Forams. 90 are fossils. They are
  heterotrophic, marine and have porous shells
  (with pseudopodia extending through pores of the
  shell) with CaCO3 (calcium carbonate). The
  shells are called tests

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• Radiolarians have delecate skeletons often made
  of silica and are components of plankton that
  form slender pseudopodia (called axopodia).
  Including heliozoans (sun animals freshwater)
  and radiozoans (primarily marine species)

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• Supergroup Archaeplastida

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• Green algae contain chlorophyll a and b, and
  carotenoids.
• There are more than 7,000 species most of which
  are mostly aquatic, fresh water but there are
  also marine green algae and symbiotic species.
• They range in morphological complexity from
  single-cells to colonial forms to true
  multicellularity.
• They often have complicated life cycles (most
  have both asexual and sexual stages) and some
  have alternations of generations like plants like
  other taxa of algae

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• Red algae. There are about 60,000 species. Most
  are multicellular

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• Supergroup Unikonta
• includes animals, fungi, and some protists.

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• Ameobozoans
• More amoebas

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• Gymnamoebas are the simplest unicellular
  protests. They lack flagella and move and feed
  via lobe-like pseudopodia. There are many
  free-living species that are found in freshwater,
  marine environments, and moist soil.

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Entamoebas are parasitic amoebas
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• Mycetozoa. Like many of the protists, this group
  is so diverse that it should be a kingdom. Slime
  molds (fungus animals) are neither fungi or
  animals. They use pseudopodia for feeding and
  movement. They have complex life cycles

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• Plasmodial slime molds are usually pigmented, are
  heterotrophic with a feeding stage, an ameboid
  mass or plasmodium composed of a relatively large
  super cell with multiple nuclei (mitosis occurs
  but not cytokinesis) and when harsh conditions
  arise, sporangia form which produce spores.
  These spores will germinate when conditions are
  appropriate for the feeding stage (plasmodium)
  and the resulting cells will eventually form a
  new plasmodium

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• Cellular slime molds. When contrasted with
  plasmodial slime molds, the cellular slime molds
  have (1) only one diploid stage (the zygote), (2)
  have a feeding stage consists of individual cells
  functioning as individual units that forms a
  multicellular aggregate when is food is scarce,
  (like a plasmodium except that there are multiple
  cells instead of one super cell with multiple
  nuclei), and (3) have fruiting bodies that
  function in asexual reproduction. They also have
  no flagellated stages in their life cycles

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Two important evolutionary trends from the
protists

• Unicelluar gt Filamentous gt Colonial without
  division of labor gt Colonial with division of
  labor gt True Multicellularity (which evolved
  independently several times)
• Asexual gt Sexual Reproduction. Note the
  complicated life cycles of some of the protists.
  Also note the evolution of anisogamy
  (particularly oogamy) from isogamy