Henry Hsieh

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Chapter 28The Origins of Eukaryotic Diversity

• By
• Henry Hsieh
• Perry Huang
• Kevin Kim
• Joon Park
• Period 6

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(No Transcript)
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Introduction to the Protists

• Protists existed at least a billion years ago,
  before the origin of plants, fungi, and animals
• They were the earliest descendants of prokaryotes
• Oldest fossils called acritarchs Precambrian
  objects about 2.1 billion years old

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Protists are the most diverse of all eukaryotes

• All protists are eukaryotes
• About 60,000 known species of unicellular
  protists, few colonial and multicellular species
• Incredibly complex at cellular level because a
  single cell would have to perform many functions

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Protists are the most diverse of all eukaryotes
(cont.)?

• Protists are metabolically diverse
• Most are aerobic in their metabolism and use
  mitochondria for cellular respiration
• 3 categories of nutritional diversity1.
  protozoa (animal-like protists)2. absorptive
  (funguslike) protists3. algae (photosynthetic
  plantlike protists)?

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Protists are the most diverse of all eukaryotes
(cont.)?

• Most protists are motile, can have flagella or
  cilia- Eukaryotic flagella and cilia are
  extensions of the cytoplasm, with bundles of
  microtubules covered by the plasma membrane
• Some protists are asexual, others can reproduce
  sexually with meiosis and syngamy (the union of 2
  gametes)?

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Protists are the most diverse of all eukaryotes
(cont.)?

• Resistant cells called cysts are formed at some
  point in life cycle
• Protists can be found almost anywhere with water
• Important constituents of plankton the
  communities of organisms that drift near water
  surface that are the bases of most marine and
  freshwater food webs

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Symbiosis was involved in the genesis of
eukaryotes from prokaryotes

• The endomembrane system of eukaryotic cells the
  nuclear envelope, endoplasmic reticulum, Golgi
  apparatus, and related structures-- may have
  evolved from infoldings of the plasma membrane of
  an ancestral prokaryote
• Endosymbiosis led to mitochondria, chloroplasts,
  and other features of eukaryotic cells

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Symbiosis was involved in the genesis of
eukaryotes from prokaryotes (cont.)?

• Serial endosymbiosis proposes that mitochondria
  and chloroplasts were formerly small prokaryotes
  living within larger cells.
• All eukaryotes have mitochrondria
• Only photosynthetic eukaryotes have chloroplasts
• Mitochondria is proposed to have evolved before
  chloroplasts

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Protist Systematics and PhylogenyMonophyletic
taxa are emerging from modern research in protist
schematics

• Unicellular eukaryotes assigned to Kingdom
  Protista
• Later included some multicellular organisms, such
  as seaweeds
• Kingdom Protista is polyphyletic (members derived
  from two or more ancestral forms not common to
  all members)?
• For now, divide into 5 groups of Protists
  Archaezoa, Euglenozoa, Alveolata, Stramenopila,
  Rhodophyta.

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Fig 28-1. Too diverse for one kingdom a small
sample of protists.
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Members of candidate kingdom Archaezoa lack
mitochondria and may represent early eukaryotic
lineages

• Several protists lack mitrochondria, leads to the
  hypothesis that the lineages of these organisms
  diverged before the endosymbiotic event that gave
  rise to mitochondria
• Protists that lack mitochondria located in
  Kingdom Archaezoa
• Diplomonads subgroup of archaezoans have
  flagella, two separate nuclei, no mitochondria,
  no plastids, and a simple cytoskeleton

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Members of candidate kingdom Archaezoa lack
mitochondria and may represent early eukaryotic
lineages (cont.)?

• A diplomonad parasite called Giardia lamblia
  infects human intestines
• Giardia and others are living relics of an early
  lineage of eukaryotes evidence indicates that
  their genes once coded for mitochondria. This
  indicates that their ancestors once possessed
  mitrochondria, but have lost them over
  evolutionary history.

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Giardia lamblia
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Candidate kingdom Euglenozoa includes both
autotrophic and heterotrophic flagellates

• Flagellates- A term that is not used in formal
  taxonomy.
• -Molecular indicates that two groups of
  flagllates
• euglenoids and kinetoplastids make up the
  monophyletic candidate kingdom Euglenozoa.
• Euglenoids-(Englena and its close relatives) are
  characterized by an anterior pocket, or chamber,
  from which one or two flagella emerge.
• Paramylum, a glucose ploymer that functions as a
  storage molecule, is also characteristic of
  euglenoids.
• Euglena is chiefy autotrophic, absorbing organic
  molecules from their surroundings or engulfing
  prey by phagocytosis.
• The kinetoplastids have a single large
  mitochondrion associated with unique organelle,
  the kinetoplast, that houses extranulear DNA.

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Subsurface cavities(alveoli) are diagnostic of
candidate kingdom Alveolata
Another monophyletic candidate kingdom that is
emerging from molecular systematics, -The
Alveolata, -draws together a group of
photosynthetic flagellates ( the
dinoflagellates), -a group of parasites
(apicomplexans), -and a a distinctive group of
eukaryotes that move by means of cilia( the
cilates). -Alveolates have a small
membrane-bounded cavities (alveoli) under their
cell surfaces, functions are unknown may help
stabilize the cell surface and regulate the
cells water and ion content
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Dinoflagellata (Dinoflagellates) Apicomplexa
(Apicomplexans)?

• Dinoflagellates are abundant components of the
  vast aquatic pastures of phytoplankton that are
  suspended near the water surface and provide the
  foundation of most marine and many freshwater
  food webs. There are also heterotrophic species
  of dinoflagellates.
• Apicomplexans are parasites of animals,
• Some cause serious human diseases
• The parasites disseminate as tiny infectious
  cells called sporozoite

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Fig 28-13. The two-host life history of
Plasmodium , the apicomplexan that causes
malaria. (Colors are not true to life.)?
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Ciliophora (Ciliates)?

• This diverse group of protists is named for their
  use of cilia to move and feed

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Ciliophora (Ciliates) Con.

• Most ciliates live as solitary cells in fresh
  water. In contrast to most flagella, cilia are
  relatively short. They are associated with a
  submembrane system of microtubules that may
  coordinate the movement of the thousands of
  cilia.
• Some ciliates are completely covered by rows of
  cilia, whereas others have their cilia clustered
  into fewer rows or tufts.
• The specific arrangements adapt the ciliates for
  their diverse lifestyles. Some species, for
  instance, scurry about on leglike structures
  constructed from many cilia bonded together.
• A unique feature of ciliate genetics is the
  presence of two types of nuclei,
• a large macronucleus and usually several tiny
  micronuclei.
• The genes are not distributed in typical
  chromosomes but are instead packaged into a much
  larger number of small units, each with hundreds
  of copies of just a few genes.
• The macronucleus controls the everyday functions
  of the cell by synthesizing RNA and is also
  necessary for asexual reproduction.
• Ciliates generally reproduce by binary fission,
• The sexual shuffling of genes occurs during the
  process known as conjugation

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Fig 28-15. Conjugation and genetic recombination
in Paramecium caudatum .
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A diverse assemblage of unicellular eukaryotes
move by means of pseudodia

• The three gropus we discuss in this section
  represent some of the immense diversity of
  unicellular eukaryotes that move and often feed
  by means of cellular extensions called
  pseudpopdia.
• Most of these organisms are heterotrophs that
  actively seek and consume bacteria, other
  protists, and detritus (dead organic matter).
  There are also symbiotic species, including some
  parasites cause human diseases.
• Little is known about their phylogeny.

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Rhizopods (Amoebas)?

• Are all unicellular and use pseudopodia to move
  to feed.
• The cytoskeleton, consisting of microtibules and
  microfilaments
• Functions in amoeboid movement
• Meiosis sex are NOT known to occur in amoebas.
• Reproduce asexually by various mechanisms of cell
  division.
• Inhabit both freshwater marine environments and
  are also abundant in soils
• The majority of amoebas are free-living, but some
  are important parasites, including Entamoeba
  histolytica
• Cause amoebic dysentery in humans
• (These organisms spread via contaminated drinking
  water, food, or eating utensils)?

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Actinopods (Heliozoans Radiolarians)?

• Means ray foot
• A reference to the slender pseudopodia called
  axopodia that radiate from these exceptionally
  beautiful protists.
• Each axopodium is reinforced by a bundle of
  microtubules cover by thin layer of cytoplasm
• Most actinpods are planktonic
• Their projections place an extensive area of
  cellular surface in contact with the surrounding
  water, help the organism float and feed

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Actinopods (Heliozoans Radiolarians) con.

• Heliozoan(sun animals)- living in freshwater.
• Skeletons consist of siliceous(glassy) or
  chitnous unfused plates.
• Radiolarian(not used in formal taxonomy)-refers
  to several groups of mostly marine actinopods
  w/skeleton fused into one delcate piece-commonly
  made of silica
• After actinopods die, their skeletons settle
  settle to the seafloor, where they have
  accumlated as an ooze that is hundreds of meters
  thick in some locations

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Foraminiferans (Forams)?

• Are almost all marine.
• Most live in sand or attach themselves to rocks
  algae, but some are abundant in plankton
• Named for their poruous shells
• The shells generally multichambered and consist
  of organic material hardened w/calcium carbonate.
• Strands of cytoplasm(pseudopodia) extend through
  the pores
• Functioning-swimming, shell formation, and
  feeding.
• (Many also derive nourishment from the
  photosynthesis of symbiotic algae that live w/in
  the shells)?

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Slime molds have structural adaptations and life
cycles that enhance their ecological role as
decomposers

• 2 groups of protists called slime molds
• Resemble fungi in appearance and lifestyle
• Similarities are convergence
• In their cellular organization, reproduction and
  life cycles
• Slime molds depart from the true fungi is partly
  due to convergent evolution of filamentous body
  structure
• A morphological adaptation that increase exposure
  to the environment and enhances the ecological
  role of these organisms as decomposers
• Slime molds have complex life cycles that are
  adaptations that contribute to survival in
  changing habitats and facilitate dispersat to new
  food sources

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Plasmodial Slime Molds (Myxomycota)?

• Are more attractive than their name implies.
• Many brightly pigmented, usually yellow or
  orange, but all are heterotrophic.
• The feeding stage of the cycle is an amoeboid
  mass called a plasmodium
• Plasmodium are not multicellular
• The cytoplasmic streaming apparently helps
  distribute nutrients oxygen
• The plasmodium engulfs food particles by
  phagocytosis as it grows by extending pseudopodia
  through moist soil, leaf mulch, or rotting logs.
• If the habitat of slime mold dried out or no food
  left, the plasmodium ceases growth and
  differentiates into a stage of the life cycle
  that function in sexual reproduction

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Cellular Slime Molds(Acrasiomycota)?

• Pose a semantic question what it means to be an
  individual organism.
• Although the feeding stage of the life cycle
  consists of solitary cells that function
  individually
• When food is depleted the cells form an aggregate
  that function as a unit
• Though the mass of cells resembles a plasmodial
  slime mold
• The distinction is that the cells of a cellular
  slime mold maintain their identity and remain
  separated by their membranes.
• Cellular Slime molds also differ from Plas. Slime
  molds in being haploid organisms
• Cellular Slime molds have fruiting bodies that
  function in asexual reproduction.
• Most of Cell. Slime mold have no flagellated
  stages