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
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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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Proposal of Endosymbiosis
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Endosymbiotic origins of chloroplasts in red and
brown algae
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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
• Trichomonas 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