Kingdom Protista

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Kingdom Protista

• AP Biology Ch. 28

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Introduction to the Protists

• Earliest Eukaryotes
• Arose about 1 billion years before the first true
  plants, animals or fungi
• Earliest protist fossils are around 2.1 billion
  years old
• The first billion years of eukaryote evolution
  appears to have produced several very divergent
  lineages
• For Example some are animal-like, some
  plant-like and some fungus-like

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Protists are EXTREMELY DIVERSE

• The ONLY thing that ALL protists share in common
  is that they are ALL EUKARYOTES
• Protists are considered to be the simplest
  eukaryotic organisms, HOWEVER
• At the cellular level, many protists are
  extremely complex
• Otherwise, diversity is the rule
• Cellularity most are unicellular, but some are
  colonial and some are multicellular
• Animal-like, plant-like, fungus-like
  characteristics
• 60,000 different species!

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Great Diversity
brown algae diatoms
dinoflagellates ciliates
euglenoids
red algae
green algae
miscellaneous?
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3 Groupings of Protists

• Keep in mind that these groupings have NO
  taxonomic significance
• This means that these groupings do not imply true
  evolutionary relationships, but are just a
  convenient way to talk about members of this
  incredibly diverse and poorly organized kingdom

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3 Groupings of Protists

• Animal-like Protists
• The Protozoans
• Called animal-like because they ingest food (like
  animals)
• Includes members like amoeba, paramecium, etc.

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3 Groupings of Protists

• Fungus-like Protists
• These are organisms that obtain nutrition from
  absortption of nutrients from the
  environmentlike fungi do.
• Includes members like slime molds

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3 Groupings of Protists

• Plant-like Protists
• Also called photosynthetic protists or ALGAE
• Includes organisms like Volvox and Kelp.
• All algae share the photosynthetic pigment
  chlorphyll a in common.
• Differ in their accessory pigments

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Movement in Protists

• Most protists (though NOT all) are motile
• Most protists have either cilia or flagella at
  some point in their life cycle
• Remember that eukaryotic and prokaryotic flagella
  are NOT homologous
• Euk. extensions of cytoplasm bundles of
  microtubules (92) covered by cell membrane
• Prok. crank mechanism attached to cell surface

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Reproduction in Protists

• Reproduction is highly varied among protists
• Mitosis does occur in most protists
• Protists may be asexual or sexual reproducers
• Protists may produce cysts
• Resistant cells that can survive harsh conditions
• Something like a bacterial endospore

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Where Protists are Found

• Anywhere there is water.
• Maybe just moisture

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Some Important Protist Groups

• Plankton
• Communities of organisms that drift passively or
  swim weakly at the waters surface
• Basis of marine and freshwater food chains is
  phytoplankton
• Phytoplankton account for ½ of all photosynthesis
• Free living protists
• Symbiotic protists
• Implies mutualistic or beneficial relationships
• Parasitic protists
• Host is harmed

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Origin of Eukaryotic Cells from Prokaryotes

• Many structures are unique to eukaryotic cells
• Membrane enclosed nucleus
• Mitochondria
• Chloroplasts
• ER
• Cytoskeleton
• 92 flagella
• Multiple linear chromosomes
• Two processes are thought to have led to the
  origin of these structures in eukaryotes.

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Origin of Eukaryotic Cells from Prokaryotes 2
processes

• Endomembrane System (ER) may have evolved from
  infoldings of the prokaryotic cell membrane
• Endosymbiosis
• Mitochondria and chloroplasts were once small
  prokaryotes
• Became involved in a symbiotic relationship with
  larger cells

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Origin of Eukaryotic Cells from Prokaryotes
Endosymbiosis

• Ancestors of mitochondria Aerobic heterotrophic
  prokaryotes
• Ancestors of chloroplasts photosynthetic
  prokaryotes (probably cyanobacteria)
• May have entered larger cell as undigested prey
  or as internal parasites
• Provided host with nourishment
• Such endosymbiotic relationships are observed
  today

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Origin of Eukaryotic Cells from Prokaryotes
Additional Evidence Supporting the Endosymbiotic
Hypothesis

• Chloroplasts and mitochondria are both the
  appropriate size to be descendents of bacteria
• Inner membranes of chloroplasts and mitochondria
  have enzymes and transport systems similar to
  modern prokaryotes
• Mitochondria and chloroplasts replicate by a
  process similar to binary fission
• Both contain a circular DNA molecule that is not
  associated with histone proteins
• Ribosomes in both are more like prokaryotes than
  eukaryotes

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Origin of Eukaryotic Cells
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Kingdom Protista is BAD Taxonomy/Systematics

• Kingdom Protista has been a dumping ground for
  organisms that did not fit nicely into any of the
  other eukaryotic kingdom
• Kingdom Protista is Paraphyletic made up of
  organism groups that do NOT share a common
  ancestor
• Kingdom Protista is now considered obsolete
• Scientists are working on sorting out the members
  of Protista into 5 new candidate kingdoms that
  are all monophyletic
• Remember monophyletic all members come from
  one common ancestor

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Problems with Protist Classification

• Too Diverse!
• doesnt reflect any evolutionary relationship
  amongst all kingdom members
• paraphyletic

Somethingsnot right here!
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New Protist Classification (from 6th ed.)
1 Kingdom Split into 8 Kingdoms?
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Candidate Kingdom Archaezoa

• Uniting characteristic of these members
• All lack mitochondria
• Called archaezoa to emphasize their ancient
  ancestry
• The lineages of these protists go back to before
  the endosymbiotic creation of mitochondria

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Candidate Kingdom Euglenozoa

• Common characteristic of all Euglenozoans is
  flagella
• Most members are autotrophic, but may also be
  heterotrophic (by absorption or ingestion)
• Euglenoids and Kinetoplastids
• Famous parasite in this group
• Trypanosoma
• Causes African Sleeping Sickness
• Two hosts required TseTse Fly and Human

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Euglena

• Click HERE to see Euglena Movies

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Trypanosome

• Click HERE for more on Trypanosomes

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Candidate Kingdom Alveolata

• Common characteristic
• all possess small membrane bound cavities
  (alveoli) under their cell surfaces
• Contains 3 large groups
• Dinoflagellates
• Photosynthetic flagellates
• Apicomplexans
• parasites
• Ciliates
• All members move by means of cilia

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Dinoflagellates

• Found in phytoplankton at oceans surface
• Responsible for Red Tides
• Toxins produced by dinoflagellates cause massive
  fish kills and may harm humans also
• Pfiesteria
• Characteristics
• Cellulose cell plates armor
• 2 flagella perpendicular to each other
• Results in spinning motion

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Dinoflagellates
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Apicomplexans

• ALL parasites
• Used to be called sporozoans
• Famous member
• Plasmodium
• Causes malaria
• 2 hosts required
• Mosquito
• Human
• Liver and blood cells

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Ciliates

• All have cilia
• Most live as solitary cells in fresh water
• 2 nuclei
• Micronucleus
• Required for sexual process
• Not involved in maintenance, growth or other
  routine functions
• Macronucleus
• Controls everyday functioning of the cell

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Reproduction in ciliates

• Mostly binary fission
• Macronucleus splits (NO mitosis)
• Sometimes conjugation
• Micronucleus is exchanged between individuals
• No REPRODUCTION no babies - just exchange of
  genes
• Meiosis and syngamy (fusion of genetic material)
  do occur in the micronucleus

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Conjugation
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Protists that Use Pseudopods Classification not
certain according to your text

• Amoebas etc. are in this group that does not have
  a candidate kingdom yet.
• Pay attention to feeding and locomotor mechanisms

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Pseudopods

• Extensions of cytoplasm
• Used for movement and feeding
• Organisms that use pseudopods are generally
  heterotrophs. They eat
• Bacteria
• Other protists
• Detritus (decaying matter)
• May also be PARASITES

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Groups of Protists with Psueudopods

• Rhizopods
• The amoeba
• Actinopods
• ray foot possess rays or extensions
• Foraminiferans
• Calcium carbonate shells

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The Rhizopods

• Amoeba
• ALL unicellular
• Can move directionally (taxis)
• Reproduce asexually only
• Both freshwater and marine habitats
• Some can be parasitic amoebic dysentery spread
  by contaminated food, water, etc.
• Click HERE to see an amoeba movie

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The Actinopods

• ray foot - Named for the slender pseupodia that
  radiate from them (axipodia)
• Internal skeleton
• Plankton
• Microorganisms stick to the axipodia and are
  phagocytized.

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The Actinopods

• Includes the heliozoans
• Freshwater
• Silica (glassy) or chitin skeletons
• Includes the radiolarians
• Mostly marine
• Silica skeletons
• At death, skeletons of actinopods sink to the
  seafloor where the accumulate into ooze that is
  hundreds of meters thick in places.

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Foraminiferans

• All marine
• Named for porous shells
• Made of calcium carbonate
• Strands of cytoplasm extend through pores in
  shell

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Candidate Kingdom Myceteozoa (actually a newly
added 6th candidate kingdom)

• The Slime Molds
• Plasmodial Slime Molds
• Cellular Slime Molds
• Basic Characteristics
• Resemble fungi
• Appearances ONLY due to CONVERGENT evolution
  NOT homologies
• Closest relatives of the slime molds are probably
  the amoebas

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Plasmodial Slime Molds

• Brightly pigmented
• Orange and yellow
• Heterotrophic
• Two body forms
• One for obtaining food
• The other for reproductioin

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Plasmodial Slime Molds

• Plasmodium the amoeboid mass that acts as the
  feeding stage of the slime mold
• Can get several cm large
• Actually unicellular!
• Cytoplasmic streaming helps distribute nutrients
  and oxygen throughout the slime mold.
• Engulfs food via phagocytosis

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Plasmodial Slime Molds

• If food source is gone or conditions become poor
  for the plasmodium
• It ceases growth
• Differentiates into a stage that functions in
  sexual reproduction

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Cellular Slime Molds

• Feeding stage composed of solitary cells that
  function individually
• When food is depleted, the cells for an aggregate
  the functions as a unit.
• The cells always maintain their individual
  identity which is different from the plasmodial
  slime mold
• Haploid cells dominate (only zygote is diploid)
• Fruiting bodies function in asexual reproduction

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Cellular Slime Molds life cycle
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Cellular Slime Mold - Stages
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Candidate Kingdom Stramenopila

• Includes photosynthetic autotrophs and some
  heterotrophs
• Common characteristic is fine hair-like
  projections on flagella
• Evidence suggests that the photosynthetic members
  of this kingdom did NOT get their c-plasts from
  the cyanobacteria like all other photoautotrophs
• Instead theirs are descended from red algae

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Photosynthetic Members of Kingdom Stramenopila

• Diatoms
• Yellow/brown
• Walls are made of silica and an organic matrix
• Shoebox and lid
• Shells make sediments called diatomaceous earth
• Filtering medium abrasive (toothpaste!)

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Diatom Photos
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Photosynthetic Members of Kingdom Stramenopila

• Golden Algae
• 2 flagella attached at one end of the cell
• Can absorb or ingest food particles
• mixotrophic
• Some colonial species

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Photosynthetic Members of Kingdom Stramenopila

• Brown Algae
• Multicellular
• Marine
• Kelp
• Called Seaweeds
• This title is also used to refer to green and red
  algae

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Photosynthetic Members of Kingdom Stramenopila

• More on seaweeds / kelp
• Inhabit intertidal zones very challenging
• 60 meters long
• Cell walls gelatinous to help cushion against
  waves
• Food source and
• Thickeners for pudding, salad dressing, ice cream
• Also lubricants
• Complex structures are ANALOGOUS to plants
• Thallus plant-like seaweed body
• Holdfast root like structure anchors plant
• Stipe stem-like structure
• Blades leaf-like structure
• Air-filled floats hold blades up toward light

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Kelp
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Kelp Life Cycle
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Hetertrophic Members of Kingdom Stramenopila

• Oomycota
• Water molds most are decomposers (often seen on
  dead aquarium fish)
• White rusts plant parasite
• Downy mildew plant parasite
• All heterotrophic
• Filaments/hyphae are analogous to fungi, cell
  walls are made of cellulose (NOT chitin)
• Diploid is dominant form haploid is dominant in
  fungi
• Have flagellated cells fungi dont
• Large egg fertilized by a small sperm

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Water Mold Life Cycle
Water mold on Dead fish
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Candidate Kingdom Rodophyta Red Algae

• No flagella but did not evolve before flagella
  existed
• DNA analysis suggests that red algae are not that
  ancient. Flagella were lost during evolution
• Accessory pigment (phycobillins) make the red
• Red absorbs short waves of light most efficiently
  
• These are the only waves that make it to deep
  water
• Red algae will appear very dark at great depths
  but be almost green in shallower water
• The deeper the algae the redder its color

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Red Algae
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Red Algae
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Candidate Kingdom Chlorophyta?

• Green Algae
• Classification is still in question
• Separate from plants or with plants?
• Certainly the plants and the green algae share a
  common ancestor
• Chloroplasts are very similar

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Green Algae

• 7000 species
• Most are freshwater
• Some even enter into a mutualistic relationship
  with fungi to form a lichen
• May be unicellular, colonial or multicellular
• Complex life histories (repro cycles)
• Most reproduce by way of biflagellated gametes
• Some even use amoeboid gametes

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Examples of Green Algae

• Chlamydomonas
• Primitive species
• All life stages haploid except zygote

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Chlamydomonas Life Cycle
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Reproductive Modes Observed in Green Algae

• Isogamy
• Fusion of gametes of similar size
• Anisogamy
• Fusion of gametes of different size
• Oogamy is one type
• Egg is large and non motile sperm flagellated

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Multicellularity Arose Many Times

• More variations are possible for complex
  structures than simpler ones
• Evolution of eukaryotes broke one barrier to
  diversification Multicellularity broke another
• The link between unicellular and multicellular
  organisms is colonial organisms
• Division of Labor
• Different cells take on different jobs and become
  very proficient at those jobs
• Example loss of flagella in some cells combined
  with more efficient performance of other cell
  functions

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