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Title: Henry Hsieh


1
Chapter 28The Origins of Eukaryotic Diversity
  • By
  • Henry Hsieh
  • Perry Huang
  • Kevin Kim
  • Joon Park
  • Period 6

2
(No Transcript)
3
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

4
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

5
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)?

6
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)?

7
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

8
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

9
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

10
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.

11
Fig 28-1. Too diverse for one kingdom a small
sample of protists.
12
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

13
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.

14
Giardia lamblia
15
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.

16
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
17
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

18
Fig 28-13. The two-host life history of
Plasmodium , the apicomplexan that causes
malaria. (Colors are not true to life.)?
19
Ciliophora (Ciliates)?
  • This diverse group of protists is named for their
    use of cilia to move and feed

20
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

21
Fig 28-15. Conjugation and genetic recombination
in Paramecium caudatum .
22
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.

23
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)?

24
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

25
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

26
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)?

27
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

28
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

29
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
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