Protists

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Protists

• Chapter 29

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Protists

• Protists are the most diverse of the four
  eukaryotic kingdoms
• -Unicellular, colonial and multicellular groups
• The kingdom Protista is paraphyletic and grouped
  for convenience
• The 15 major protist phyla are grouped into seven
  major monophyletic groups
• -However, 60 lineages cannot be placed with
  confidence

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Protists
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Protists (Cont.)
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Eukaryotic Origins

• Eukaryotic cells differ from prokaryotes by the
  presence of a cytoskeleton and organelles
• Appearance of eukaryotes in microfossils occurred
  about 1.5 BYA

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Eukaryotic Origins

• The nucleus and endoplasmic reticulum arose from
  infoldings of prokaryotic cell membrane

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Eukaryotic Origins

• Many organelles evolved via endosymbiosis between
  an ancestral eukaryote and a bacterial cell
• -Mitochondria Aerobic bacteria
• Organisms that host chloroplasts are not
  monophyletic
• -Red and green algae engulfed cyanobacteria
• -Brown algae engulfed red algae
• -Secondary endosymbiosis

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Eukaryotic Origins

• Over time, most organellar genes moved into the
  nucleus
• -Therefore, these organelles cannot be grown in
  pure culture
• Mitosis and cytokinesis did not evolve in
  eukaryotes all at once
• -Intermediate mechanisms survive today
• -Fungal nuclear membranes do not dissolve

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General Biology of the Protists

• Cell surface
• -Plasma membrane
• -Extracellular material (ECM), in some
• -Diatoms Silica shells
• Cysts
• -Dormant cell with resistant outer covering
• -Used for disease transmission

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General Biology of the Protists

• Locomotion
• -Flagella
• -Cilia
• -Pseudopodia (false feet)
• -Lobopods Large, blunt
• -Filopods Thin, branching
• -Axopods Thin, long

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General Biology of the Protists

• Nutrition
• -Phototrophs
• -Heterotrophs
• -Phagotrophs Particulate food matter
• -Osmotrophs Soluble food matter
• -Mixotrophs are both phototrophic and
  heterotrophic

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General Biology of the Protists

• Asexual reproduction
• -Typical mode of reproduction
• -Some species have an unusual mitosis
• -Binary fission Equal cells
• -Budding Progeny cell smaller
• -Schizogony Multiple fission
• Sexual reproduction
• -Union of haploid gametes which are produced by
  meiosis

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Diplomonads and Parabasalids

• Are closely related to the early, now extinct
  eukaryotic cell
• -Flagellated

-Lack mitochondria
-May have lost their mitochondria, rather than
never acquired them
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Diplomonads and Parabasalids

• Diplomonads
• -Have two nuclei
• -Giardia intestinalis

Parabasalids -Have undulating membranes -Trichom
onas vaginalis
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Euglenozoa

• Euglenoids were among the earliest eukaryotes to
  possess mitochondria
• -1/3rd have chloroplasts

-All have a flexible pellicle
-None have sexual reproduction
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Euglenozoa

• Euglena
• -Two anterior (and unequal) flagella
• -Contractile vacuoles Collect excess water
• -Stigma Movement towards light
• -Numerous small chloroplasts
• -The concept of a single Euglena genus is now
  being debated

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Euglenozoa
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Euglenozoa

• Kinetoplastids
• -Unique, single mitochondrion with DNA
  maxicircles and minicircles (RNA editing)
• -Trypanosomes cause human diseases
• -African sleeping sickness Tsetse fly
• -Leishmaniasis Sand fly
• -Difficult to control because organisms
  repeatedly change their protective coat

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Euglenozoa
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Alveolata

• Alveolata have flattened vesicles called alveoli
• -These function like Golgi bodies below the cell
  membrane

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Alveolata

• Dinoflagellates
• -Unicellular with two unequal flagella
• -Live in aquatic environments

-Most are photosynthetic -Do not appear to be
directly related to any other phylum
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Alveolata

• Dinoflagellates
• -Reproduction is primarily asexual
• -DNA is not complexed with histones
• -About 20 species produce powerful toxins that
  harm vertebrates
• -Blooms are responsible for red tide

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Alveolata

• Apicomplexans
• -Spore-forming animal parasites

-Apical complex is a unique arrangement of
organelles at one end of the cell -Enables the
cell to invade its host
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Alveolata

• Plasmodium
• -An apicomplexan that causes malaria
• -Eradication of malaria
• 1. Elimination of mosquito vectors
• 2. Development of drugs
• 3. Development of vaccines
• -Organism has a very complex life cycle

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Alveolata

• Other apicomplexans
• -Gregarines
• -Found in the intestines of arthropods,
  annelids and mollusks

-Toxoplasma gondii -Causes infections in
humans with immunosuppression
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Alveolata

• Ciliates
• -Feature large numbers of cilia arranged in
  longtitudinal rows or spirals around the cell
• -Have two types of vacuoles
• -Food vacuoles Digestion of food
• -Contractile vacuoles Regulation of water
  balance

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Alveolata

• Ciliates
• -Have two types of nuclei
• -Macronucleus Divides by mitosis
• -Responsible for physiological functions
• -Micronucleus Divides by meiosis
• -Involved in conjugation
• -Fusion of two cells of different mating
  types

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Stramenopila

• Stramenopiles have very fine hairs on their
  flagella

-A few species have lost their hairs during
evolution
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Stramenopila

• Brown algae
• -Kelps
• -Grow in relatively shallow waters throughout
  the world

-Life cycle involves alternation of generations
-Sporophyte Multicellular and
diploid -Gametophyte Multicellular and haploid
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Stramenopila

• Diatoms (Phylum Chrysophyta)
• -Unicellular organisms
• -Have unique double shells made of silica
• -Some move using raphes
• -Two long grooves lined with vibrating fibrils

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Stramenopila
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Stramenopila

• Oomycetes (water molds)
• -Were once considered fungi
• -Motile zoospores with two unequal flagella
• -Undergo sexual reproduction
• -Either parasites or saprobes
• -Phytophthora infestans
• -Irish potato famine (1845-1847)

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Rhodophyta

• Rhodophyta, or red algae, range from microscopic
  to very large sizes
• -Lack flagella and centrioles
• -Have accessory photosynthetic pigments within
  phycobilisomes
• -Origin has been a source of controversy
• -Tentatively, treated as a sister clade of
  Chlorophyta (green algae)

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Rhodophyta
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Choanoflagellida

• Choanoflagellates are most like the common
  ancestor of all animals
• -Single emergent flagellum, surrounded by
  funnel-shaped contractile collar
• -Use collar to feed on bacteria
• -Have a surface tyrosine kinase receptor found
  in sponges

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Choanoflagellida
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Protists Without a Clade

• Amoebas are paraphyletic
• -Rhizopoda (True amoebas)
• -Move by means of cytoplasmic projections
  called pseudopods
• -Actinopoda (Radiolarians)
• -Glassy exoskeletons made of silica
• -Needlelike pseudopods

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Protists Without a Clade
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Protists Without a Clade

• Foraminifera are heterotrophic marine protists
• -Have pore-studded shells called tests, through
  which thin podia emerge
• -Use podia for swimming and feeding
• -Have complex life cycles with haploid and
  diploid generations
• -Limestones are rich in forams
• -White cliffs of Dover

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Protists Without a Clade
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Protists Without a Clade

• Slime molds
• -Were once considered fungi
• -Include two lineages
• 1. Plasmodial slime molds
• 2. Cellular slime molds

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Protists Without a Clade

• 1. Plasmodial slime molds
• -Stream along as a plasmodium, a nonwalled,
  multinucleate mass of cytoplasm
• -Ingests bacteria and other organic material
• -When food or moisture is scarce, organism forms
  sporangia, where spores are produced

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Protists Without a Clade
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Protists Without a Clade

• 2. Cellular slime molds
• -Individual organisms behave as separate amoebas
• -Move through soil ingesting bacteria
• -When food is scarce, organisms aggregate to
  form a slug
• -Slug differentiates into a sorocarp

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Protists Without a Clade