PROTISTA

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PROTISTA
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O2 ACCUMULATION

• Oxygenic photosynthesis arose in prokaryotes 2.5
  billion years ago
• The earths atmosphere was radically changed
• O2 was toxic to cells
• Energy-rich organic molecules no longer
  accumulated
• Biotically produced organic molecules became the
  primary source of energy and carbon

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RAPID EVOLUTION

• Rapid evolutionary change typically follows major
  environmental changes
• Punctuated equilibrium
• A tolerance to O2 arose in many populations
• The ability to use O2 metabolically quickly
  followed in many of these groups
• New ways arose to acquire use organic molecules
• Various species interactions arose
• Symbiosis, predation
• Early eukaryotic cells arose

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EARLY EUKARYOTES

• The earliest eukaryotes were protists
• gt2.1 billion years ago
• Significantly different from their prokaryotic
  ancestors
• e.g., Membrane-bound nucleus containing DNA
  associated with histone proteins
• e.g., Mitochondria and sometimes chloroplasts
• e.g., Other internal membrane-bound organelles
• e.g., Mitotic (and eventually meiotic) cell
  division

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PROTISTS

• Very diverse group
• gt60,000 known species
• Most are unicellular
• Some are colonial
• Some are multicellular
• Not simple at the cellular level
• Remember, a unicellular organism must carry out
  all basic functions of life within a single cell
• Cells within a multicellular organism can become
  specialized, and need not carry out all such
  functions

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NUTRITION

• Protists are the most nutritionally diverse
  eukaryotic group
• Most are aerobic, and possess mitochondria
• Some lack mitochondria and live in anaerobic
  environments
• Some lack mitochondria, but possess mutualistic,
  respiring bacteria

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NUTRITION

• Protists are the most nutritionally diverse
  eukaryotic group
• Some are photoautotrophs
• Some are chemoheterotrophs
• Some are both photoautotrophs and
  chemoheterotrophs

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KINGDOM PROTISTA

• The traditional Kingdom Protista does not
  represent a monophyletic group
• Multiple monophyletic lineages are grouped
• These groups should represent separate kingdoms
• Exactly how to divide Kingdom Protista into
  multiple kingdoms is not entirely clear

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MAJOR PROTISTAN GROUPS
branch leading to plants
branch leading to fungi
branch leading to animals
charophytes
green algae
amoeboid protozoans
Stramenopiles
Alveolates
red algae
brown algae
ciliates
chrysophytes
sporozoans
oomycotes
?
dinoflagellates
crown of eukaryotes (rapid divergences)
slime molds
euglenoids
kinetoplastids
parabasalids (e.g., Trichomonas)
diplomonads (e.g., Giardia)
Endosymbiotic origins from prokaryotic ancestors
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MAJOR PROTISTAN GROUPS
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MONOPHYLETIC GROUPS

• We will discuss several monophyletic groups
• Ancient flagellates
• Flagellated protozoans
• Amoeboid protozoans
• Alveolates
• Stramenophiles
• Plant lineage
• Slime molds

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ANCIENT FLAGELLATES

• Parabasilids and Diplomonads
• Free-living predatory and parasitic cells
• Some possess both flagella and pseudopods
• Evolutionary link with amoebae?

Trichomonas vaginalis
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ANCIENT FLAGELLATES

• Parabasilids
• e.g., Trichomonas vaginalis, a trichomonad
• Sexually transmitted
• A causative agent of vaginitis
• Swelling, itching, burning
• Can damage urinary and reproductive tracts

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ANCIENT FLAGELLATES

• Diplomonads
• e.g., Giardia lamblia
• Internal parasite of various animals
• e.g., humans, cattle, beavers, etc.
• gt20 of human population infected at any given
  time
• Fecal-oral infection route
• Encysted cells shed in feces
• Infection via feces-contaminated water
• Often causes only mild intestinal upsets
• Can cause severe gastroenteritis
• Girardiasis

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FLAGELLATED PROTOZOANS

• Euglenoids Kinetoplastids
• Possess one or more flagella
• All are heterotrophic

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FLAGELLATED PROTOZOANS

• Euglenoids
• gt1,000 species
• Free-living, flagellated cells
• Most are photoautotrophs
• Chloroplasts with chlorophylls a b
• (Just like plants)
• Arose in parallel to chloroplasts in green algae
• Some are chemoheterotrophs
• Possess a pellicle
• Flexible, protein-rich cell covering

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FLAGELLATED PROTOZOANS

• Kinetoplastids
• e.g., Trypanosoma brucei
• Causative agent of African sleeping sickness
• Neurological disease
• Transmission vector is tsetse fly

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AMOEBOID PROTOZOANS

• Sarcodina
• Ancestors lost their permanent motile structures
• Move by pseudopod formation/cytoplasmic streaming
• Various groups
• Rhizopods
• Naked amoebas foraminiferans
• Actinopods
• Radiolarans heliozoans

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AMOEBOID PROTOZOANS

• Rhozopods Naked Amoebas
• Found in damp soil, saltwater, fresh water
• Cytoskeletal elements change continually
• Most are free-living phagocytes
• Engulf other protozoans bacteria
• Some are opportunistic parasites

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AMOEBOID PROTOZOANS

• Rhizopods Foraminiferans
• Most live on the seafloor
• Perforated external shell
• Contains calcium carbonate
• Mucus-covered pseudopods extend through
  perforations
• Most named species (99) are extinct
• Fossilized remains mined for chalk, cement

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AMOEBOID PROTOZOANS

• Actinopods Radiolarans
• Numerous in fossil record
• Silica-hardened parts
• Components of plankton
• Drifting aquatic communities
• Some species form colonies

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AMOEBOID PROTOZOANS

• Actinopods Heliozoans
• Pseudopods radiate like suns rays
• Sun animals
• Vacuoles impart buoyancy

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ALVEOLATES

• Possess tiny membrane-bound sacs (alveoli)
  beneath outer membrane
• May stabilize cell surface
• Three groups
• Ciliates
• Sporozoans
• Dinoflagellates

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CILIATES

• e.g., Paramecium
• Many possess numerous cilia
• Motile structures
• Beat in synchronized fashion
• Prey on bacteria, algae, each other
• 65 are free-living and motile
• Others attach to some substrate
• Some form colonies
• 30 are symbionts

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CILIATES

• Reproduce sexually and asexually
• Similar to most protozoans in this regard
• Asexual process is binary fission
• Not to be confused with prokaryotic fission
• Sexual process is conjugation
• Not to be confused with bacterial conjugation

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CONJUGATION
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CONJUGATION
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SPOROZOANS

• Parasitic alveolates completing a portion of
  their life cycle within specific host cells
• Form motile infective cells (sporozoites)
• Many cause serious diseases
• e.g., Cryptosporidium ? cryptosporidiosis
• e.g., Pneumocystis carinii ? pneumonia
• Common secondary infection in AIDS patients
• e.g., Toxoplasma ? toxoplasmosis
• Cat ? human
• e.g., Plasmodium ? malaria

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MALARIA

• Caused by 4 different species of Plasmodium
• Has infected gt 100 million people
• 1 million die yearly in Africa alone
• Shaking, chills, fever, sweats
• Symptoms subside, but can reoccur
• Transmitted to humans by mosquitoes
• Females of genus Anopheles

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MALARIA

• Salivary gland ? blood delivery of sporozoites
• Sporozoites travel to liver
• Asexual reproduction produces merozoites
• Some merozoites divide mitotically in RBCs
• Other merozoites develop into gametocytes
• Male and female gametocytes develop into gametes
• Occurs within mosquito, not human (too warm, O2
  poor)
• Gametes fuse to form zygotes
• Zygotes divide to form sporozoites

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PLASMODIUM LIFE CYCLE
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PLASMODIUM LIFE CYCLE
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MALARIA

• Malaria has been and still is prevalent in
  portions of Africa, Asia, and the Middle East
• Malaria has infected gt 100 million people
• 1 million die yearly in Africa alone

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SICKLE-CELL ANEMIA

• The prevalence of sickle-cell anemia roughly
  parallels that of malaria
• Is there a connection?

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SICKLE-CELL ANEMIA

• Genetically determined
• Aberrant b-globin allele (HbS)
• Glutamic acid (HbA) ? valine (HbS)
• Cells sickle under low oxygen conditions
• Multiple deleterious effects

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SICKLE-CELL ANEMIA
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SLAVE TRADE

• Many of the African slaves transported to the
  Americas came from regions where malaria and
  sickle-cell anemia were prevalent
• As a result, 0.25 of African-Americans have
  sickle-cell anemia
• 10 are carriers of the sickle-cell allele

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SICKLE-CELL ANEMIA

• If the HbS allele is bad, why is its frequency so
  high in certain populations?
• Shouldnt natural selection weed it out?

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SICKLE-CELL ANEMIA

• Though having sickle-cell anemia is harmful,
  possession of a single HbS allele is beneficial
• Individuals possessing a single HbS allele
  possess an innate resistance to the malaria
  parasite
• Thus, natural selection preserves this allele in
  populations due to this beneficial effect
• How does this work?

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SSA MALARIA

• HbS/HbS individuals have sickle-cell anemia
• HbA/HbS individuals are only mildly anemic
• HbA/HbA individuals are normal
• Who gets killed by sickle-cell anemia?
• Who gets killed by malaria?

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DINOFLAGELLATES

• Pyrrhophyta, another branch of alveolates
• gt 1,200 species
• Most are unicellular and photosynthetic
• Some are symbionts with coral
• Two flagella
• One occupies groove around cell body
• Cellulose plates surround body
• Yellow-green, green, blue, brown, or red
• Different pigments

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DINOFLAGELLATES

• Dinoflagellates periodically experience huge
  increases in population size
• Algal blooms cause red tides
• Toxins produced by dinoflagellates accumulate
• Toxins kill fish feeding on these phytoplankton
• Birds feeding on such fish can die
• Humans feeding on shellfish having eaten these
  dinoflagellates can experience paralytic
  shellfish poisoning

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STRAMENOPHILES

• Three groups
• Oomycotes
• Chrysophytes
• Brown algae
• Possess two flagella
• One has thin filaments projecting from it and
  resembles a feather

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OOMYCOTES

• Ancient stramenophiles
• Main groups
• Water molds
• Downy mildews white rusts

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OOMYCOTES

• Water Molds
• 580 known species
• Non-photosynthetic
• Saprobic decomposers of aquatic habitats
• Some are parasites
• e.g., Saprolegnia commonly attacks damaged tissue
  in aquarium fish

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OOMYCOTES

• Downy Mildews
• Non-photosynthetic major pathogens
• e.g., Plasmopara viticola molds grapevines
  fruits
• e.g., Phytophthora infestans caused the Irish
  potato blight
• 1/3 of Irish population lost from 1845 1860
• Starvation
• Cholera
• Emigration

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CHRYSOPHYTES

• One photosynthetic group of stramenophiles
• Possess chlorophylls a, c1, and c2
• Most are free-living
• Various groups
• Golden algae
• Yellow-green algae
• Diatoms
• Coccolithophores

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CHRYSOPHYTES

• Golden Algae
• 500 known species
• Covered by silica scales or other hard parts
• Possess accessory pigment fucoxanthin
• Golden-brown pigment
• Can form colonies in phytoplankton
• Some species resemble true amoebas
• (With chloroplasts)

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CHRYSOPHYTES

• Yellow-green Algae
• 600 known species
• Common components of aquatic phytoplankton
• Can form colonies
• Lack fucoxanthin
• Golden-brown carotenoid pigment
• Most are non-motile
• All produce flagellated gametes

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CHRYSOPHYTES

• Diatoms
• 5,600 species currently exist
• 35,000 extinct species
• Possess a silica shell
• Two parts overlap like a Petri plate
• Very diverse shapes
• Finely crushed shells accumulate at the bottom of
  lakes and seas
• Used as fine abrasives, filters, and insulation

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CHRYSOPHYTES

• Coccolithophores
• 500 species currently exist
• Most are unicellular marine organisms
• Protected by calcium carbonate plates
• Accumulations of plates helped form marine
  sediments, chalk and limestone deposits
• Mucus around cells can clog fish gills during
  algal blooms

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BROWN ALGAE

• Another group of photosynthetic stramenophiles
• 1,500 species currently exist
• Most live in cool or temperate seawater
• Possess chlorophylls a, c1, and c2
• Possess fucoxanthin and/or other accessory
  pigments
• Appear olive-green, golden, dark brown, etc.
• Microscopic to very macroscopic
• Diverse life cycles
• Asexual and sexual phases

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BROWN ALGAE

• Giant kelps are largest, most complex protistans
• Complex multicelled sporophytes
• Stipes (stemlike parts)
• Blades (leaflike parts)
• Holdfasts (anchoring structures)
• Buoyancy provided by hollow, gas-filled bladders
• Why do you think this is important?
• Tubelike arrays in blades carry sugars to rest of
  body
• Evolved in parallel in vascular plants

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BROWN ALGAE

• Giant kelp beds function as productive ecosystems
• Homes to diverse bacteria, protozoans, animals
• Some species commercially harvested
• Food or fertilizer
• Extracts are components of ice cream, pudding,
  jelly beans, salad dressings, etc.
• Alginic acids from cell wall useful as a
  thickening agent

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PLANT LINEAGE

• The monophyletic group containing green algae and
  their closest relatives also contains plants
• These groups are sometimes classified in the
  plant kingdom
• Green algae (Chlorophyta)
• Zygophyta
• Charophyta
• Plants

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GREEN ALGAE

• gt7,000 known species
• Share many features with plants
• All are photosynthetic (oxygenic)
• Possess chlorophylls a b
• Store carbohydrates as starch inside chloroplasts
• Some have cell walls composed of cellulose,
  pectins, and other polysaccharides
• Single-celled, sheetlike, tubular, or colonial
• Most are microscopic
• Generally possess two anterior flagella

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GREEN ALGAE

• Most live in freshwater
• Some grow elsewhere
• Ocean surface
• Marine sediments
• Below soil surface
• On various substrates (rocks, snow, organisms,
  etc)
• Some are symbionts with fungi, protozoans, or
  marine animals

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GREEN ALGAE

• Diverse modes of reproduction
• e.g., Chlamydomonas sexual asexual cycles

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RED ALGAE (Rhodophyta)

• 4,100 species
• 95 saltwater / 5 freshwater
• Mucous material in cell wall imparts slippery
  texture
• Agar is made from cell wall extracts
• Culture media, cosmetics, jellies, etc.
• Nutritious food source
• Wrapping for sushi

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RED ALGAE (Rhodophyta)

• Most abundant in tropical seas warm currents
• Some grow at great depths
• Up to 265 meters in clear water
• Chlorophyll a plus accessory pigments
• Typically appear red, green, purple, or black
• Phycobilins are accessory pigments that absorb
  green and blue-green wavelengths that penetrate
  deep waters

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RED ALGAE (Rhodophyta)

• Life cycles of most species include multicelled
  stages lacking tissues and organs
• Asexual and sexual phases in life cycle

Diploid (2n) Stage
event?
event?
Haploid (n) Stage
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CHLOROPLASTS
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SLIME MOLDS

• Free-living amoeba-like cells part of life cycle
• Two main types
• Cellular slime molds (Acrasiomycota)
• 70 different species
• Plasmodial slime molds (Myxomycota)
• 500 different species
• Predators
• Eat organic compounds and microorganisms
• Asexual reproduction involves colonies
• Sexual reproduction also exists

Plasmodial slime mold
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SLIME MOLDS
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CELLULAR SLIME MOLD LIFE CYCLE
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PLASMODIAL SLIME MOLD LIFE CYCLE