protist characteristics

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					AP BIOLOGY UNIT 10 (CH. 28)

1) General Characteristics of Protists.
   a) Constituents of plankton (passive drifters in water); foundation for aquatic food chains.
   b) Free-living and parasitic forms.
   c) Eukaryotic (9+2 flagella, membranous organelles, nuclei)
   d) Primarily unicellular (eg. Paramecium, Euglena); some colonial (Volvox) some multicellular
   e) Aerobic
   f) Cilia or flagella at some time in life cycle.
   g) Sexual (syngamy- meiosis and union of gametes) and asexually reproducing.
   h) Grouped into three categories (representing different phylogeny and nutritional modes)
      i) Animal-like (protozoa): ingestive; chemoheterotrophs
      ii) Fungus-like, absorptive; chemoheterotrophs
      iii) Plant-like (algae): photosynthetic autotrophs
           (1) Chlorophyll a and accessory pigments (carotene, xanthophylls, phycobilins)

2) Origin of Eukaryotes
   Increasing multicellularity found in prokaryotes. Allows for division of labor, specialization of
   functions and compartmentalization.

                                  How did these characteristics evolve?
    a) Autogenous model of membrane development.
    b) Endosymbiotic hypothesis (serial endosymbiosis) for origin of mitochondria and chloroplasts.
       i) Proposed by Lynn Margulis
       ii) Heterotrophic and photosynthetic prokaryotes become endosymbionts.
       iii) Similar size
       iv) Inner membrane transport proteins and enzymes similar
       v) Divide by “binary fission”
       vi) Circular DNA without histones
       vii) Transcription/translation machinery
    c) Evolution of eukaryotic flagella/cilia unknown.

3) Phylogeny of Protista
              Many biologists propose different phylogeny. Highly diverse and dynamic.
   a) Kingdom is polyphyletic (members of taxon from two or more ancestral forms)
   b) Nucleic acid sequencing, cell structure attempting to create monophyletic groups.
   c) Have enabled systematists to create additional kingdom-level groupings.
   d) Splitting Kingdom Protista into 3 separate kingdoms (Archaezoa, Protista/Protozoa, Chromista)
      or 5 “candidate kingdoms” (Archaezoa, Euglenozoa, Alveolata, Stramenopila, Rhodophyta)

1                                                           Knight/2002/Origins of Eukaryotic Diversity (Ch. 28)
                                               Phylogeny of Protista

Candidate Kingdom: Archaezoa
    •    Lack mitochondria. Thought to have diverged prior to endosymbiosis event forming mitochondria.
    •    Ribosomes similar to prokaryotes

Ex. Diplomonadida
Diplomonads are small heterotrophic protists with no mitochondria.
Some diplomonads are free-living and may be common in stagnant
fresh water, but most are commensal in the intestines of animals (they
attach to the duodenum by a sucker. In a test tube they take up
glucose and certain lipids (anaerobic respiration) but their nutrition in
vivo is unknown. Some are parasitic and cause disease; in humans,
the diplomonad Giardia infects the intestine and can cause diarrhea (a
disease known as giardiasis, or "hiker's diarrhea"). Individuals may
be infected and show no disease, some have acute diarrheal disease
periodically. They have two haploid nuclei. Outbreaks have occurred
among travelers to Russia, skiers in Rocky Mountain resorts, and
parts of Pennsylvania. Cysts are the infective stage. They are passed
periodically in solid stools. The wall of the cyst resists the deleterious
effects of various physical and chemical agents such as chlorine. The only sure methods to render contaminated water safe
are boiling water or the physical removal of the cysts by filtration.

Candidate Kingdom: Euglenozoa.
•   Flagellates (have flagella)

Euglenozoa (Euglena)
Euglenid protists are generally elongated cells that possess one or two
flagella; there are about 1000 species. While many are photosynthetic
and have chloroplasts (chlorophyll a and b), some euglenids lack
chloroplasts and are colorless. The euglenid cell is covered by a flexible
coat, the pellicle, that allows the cell to change shape. Exhibit positive
phototaxis. Most known euglenids live in shallow freshwater habitats
enriched in organic matter, but some live in marine or brackish waters,
and a few are parasitic in animals. Store polysaccharide as paramylon.

                                              Relatives of the Euglenida, kinetoplastids include two main groups of small,
                                              flagellated protists: which includes the parasitic trypanosomes. The best-
                                              known trypanosomes are those in the genus Trypanosoma that cause human
                                              diseases such as sleeping sickness (in equatorial Africa) and Chagas' disease (in
                                              South America; Darwin was thought to have contracted Chagas’ disease on his
                                              voyage). These trypanosomes are transmitted by biting flies (tsetse), and are a
                                              serious public health problem in much of the world.

2                                                                        Knight/2002/Origins of Eukaryotic Diversity (Ch. 28)
Candidate Kingdom: Alveolata.
•   Includes photosynthetic flagellates (dinoflagellates), parasites (apicomplexans) and ciliates.
•   All have small cavities (alveoli) under cell surfaces (stabilize cell surface, regulate water and ion transport).

A. Dinoflagellates:
    •   Most unicellular, some colonial.
    •   Some live symbiotically with cnidarians (corals)
    •   May cause Red Tides.
            These species reproduce in such great numbers that the water may appear golden or red, producing a
            "red tide". When this happens many kinds of marine life suffer, for the dinoflagellates produce a
            neurotoxin which affects muscle function in susceptible organisms. Humans may also be affected by
            eating fish or shellfish containing the toxins. The resulting diseases include paralytic shellfish
            poisoning or PSP (from eating affected shellfish, such as clams, mussels, and oysters); they can be
            serious but are not usually fatal.
    •   Storage polysaccharide as starch.
    •   Cellulose plates reinforce cell surface. Flagella beat perpendicular to each other causing spinning motion.
    •   Some species are capable of producing their own light through bioluminescence.

B. Apicomplexans:
    •   Also known (formally) as sporozoans.
    •   There are about 4,000 known species, but this is probably a very low estimation.
    •   Sporozoites are infectious cells of organism and are able to penetrate host cells and tissues.
    •   Complex life cycle often involves more than one host.
    •   Are parasites of animals.
    •   Responsible for malaria (Plasmodium) and toxoplasmosis.
    •   Species in the genus Plasmodium cause malaria in humans and other animals an estimated 300 million people in
        over 90 countries are infected with malaria, and over 1 million die from it each year.
    •   Have been used experimentally to control populations of insect pests.

C. Ciliates:
    •   The Ciliata “eyelash”, or Ciliophora, includes
        about 7000 known species of some of the most
        complex single-celled organisms ever. Use cilia
        for locomotion and to draw water in for feeding.
        (Stentor, Didinium, Paramecium, Vorticella)
    •   Most are solitary.
    •   Ciliates include some of the largest free-living
        protists; a few genera may reach two millimeters in length (Stentor). Ciliates are classified on the basis of cilia
        arrangement, position, and ultrastructure
    •   abundant in almost every environment with liquid water: ocean waters, marine sediments, lakes, ponds, and rivers,
        and even soils.
    •   vary greatly in their tolerance of pollution, the ciliates found in a body of water can be used to gauge the degree of
        pollution quickly.
    •   Possess two types of nuclei:
        • The micronucleus contains chromosomes, with two copies of each chromosome; hence this nucleus is diploid,
             as is common in eukaryotes. A ciliate may have one or several micronuclei. In the much larger macronucleus
             (n), the genetic material is in the form of short pieces of DNA, each of which may exist in tens of thousands of
             copies. Macronucleus controls everyday functions of cell. At cell division, the micronuclei divide through
             mitosis, while in most ciliates the macronucleus simply pinches apart into two.
    •   ciliates also reproduce sexually, through a process known as conjugation; induced by lack of food. Generates
        genetic variation. After conjugation, each ciliate partner has acquired new genetic material, and divides to give rise
        to progeny with a new combination of genes.

3                                                                         Knight/2002/Origins of Eukaryotic Diversity (Ch. 28)
Protists with locomotion via pseudopodia.
•   Pseudopodia “false-feet”: Cellular extensions that function in feeding and movement.
•   Pseudopods form and reform as microtubules and microfilaments extend the pseudopods.
•   Heterotrophic. Feed on algae, bacteria and other protozoa. Detritivores: feed on dead organic matter. Parasitic forms
    cause disease (amoebic dysentery)

1. Rhizopods (formerly Rhizopoda phylum)
• Amoeba
• Unicellular
• Asexual reproduction (binary fission) only, no meiosis.
• Free-living and parasitic forms (Entamoeba histolytica). Passed through
    contaminated water via cyst.
• Freshwater, marine and soil habitats.

2. Actinopods (Heliozoans and Radiozoans) (formerly Actinopoda phylum)
    Posses axopodia. Thinner extension of cytoplasm made of cytoskeleton
    Component of plankton.
        Two groups:
            • Primarily freshwater species.
            • Tests made of silica or chitinous plates.
            Radiozoans (commonly called Radiolarian)
            • Marine and freshwater forms.
            • Silica test that is fused.
            • Tests accumulate on ocean floor as silica ooze.

3. Foraminifera (Forams) (formerly Foraminifera phylum)
• Calcium carbonate shells (tests); built of hollow chambers separated by
    partitions, with small openings called foramina that connect the chambers (they get their name from these foramina)
• Primarily marine.
• Pseduopodia for feeding, shell formation and movement.
• Symbiotic algae provide nutrients.
• CaCO3 shells form sedimentary layers (White Cliffs of Dover)

Candidate Kingdom: Stramenopila (aka. Chromista in 8 Kingdom system)
•   Primarily algae but also includes heterotrophic water molds.
•   Chlorophyll c found in this kingdom (not found in any plants); Most also contain carotenoid pigments, such as the
    brown pigment fucoxanthin, that give the cells a yellow, orange, or brown color.
•   Storage of energy as leucosin or the polysaccharide laminarin; do not manufacture the same type of starch as plants.

    Phylum: Bacillariophyta (Diatoms)
    • Olive-brown color due to plastids.
    • Primarily unicellular with 2-piece test made of silica.
    • Planktonic; Leucosin storage lipid.
    • Sperm and egg are only flagellated structures.
    • Microfossils form diatomaceous earth. (Lompoc)

    Phylum: Chrysophyta. (Golden algae)
    • Chlorophyll a and c, yellow & brown carotenoids, xanthophyll.
    • Unicellular and colonial forms.
    • Storage carbohydrate as Laminarian.
    • Related to bacillariophyta.

    Phylum: Phaeophyta (Brown algae)
    • Largest protist organisms (60 m). All multicellular. Some used as food.
    • Chlorophyll a & c, carotenoid (fucoxanthin)

4                                                                     Knight/2002/Origins of Eukaryotic Diversity (Ch. 28)
    •   Polysaccharide stored as laminarin.
    •   Cell wall of cellulose and algin (protects against damage in waves and exposure to air; used to ensure uniform
        melting and freezing in foods)
    •   Common forms (Laminaria and Macrocystis) the kelps.

    Phylum: Oomycota. (Water molds, rusts and mildew)
    • Coenocytic hyphae (multinucleated cells)
    • Cell wall of cellulose. (fungi have chitin)
    • 2n dominant throughout life cycle.
    • Flagellated cells which are absent in true fungi.
    • Parasitic of fish and dead organisms (water molds) and terrestrial plants (downy mildews); absorptive nutrition.
    • Phytophthora infestans (cause of Irish Potato Famine 1840’s)); a particular Downy mildew almost eliminated entire
       French grape crop in 1870’s.

Candidate Kingdom: Rhodophyta. (Red algae)
•   No flagella at any time. All have sexual reproducing forms.
•   Chlorophyll a and d (some species), carotenoids, phycobilins (phycoerythrin = red color/absorbs blue, present only in
    algae). Blue light penetrates into seawater deeper so able to grow at greater depths. Pigments similar to those in
•   Cell wall of cellulose with agar and carageenan (protects). Both are used as food additive (thickener). Agar used in
    petri dishes. Some coralline algaes have hard calcareous (CaCO3) cell walls; helps to protect from grazing invertebrates.
•   Store products of photosynthesis as Floridean starch (similar to starch)
•   Primarily tropical species but some temperate. Encrusted on coral or shellfish, also filamentous forms. Some used as
    food (Nori)

Algae structure and reproduction.
                                                                                                Have differentiated cells.
                                                                                                Many algae show
                                                                                                Alternation of
                                                                                                Alternate between
                                                                                                multicellular haploid and
                                                                                                diploid forms.
                                                                                                Multicellular Sporophyte
                                                                                                (2n) produces spores (n)
                                                                                                which are released from
                                                                                                organism and develop
                                                                                                into multicellular
                                                                                                gametophyte (n).
                                                                                                Gametophyte is haploid
                                                                                                and produces gametes that
                                                                                                fuse to form 2n
                                                                                                Seaweeds primarily found
                                                                                                in intertidal zones.
                                                                                                Structures are analogous
                                                                                                to plant structures.
                                                                                                Root-like holdfast
                                                                                                anchors structure to
        substrate. Blades and held off of thallus by stipe. Thallus cushioned from wave action by algin (brown algae)or
        carageenan (red algae)
        Floats help suspend blades at surface.

5                                                                      Knight/2002/Origins of Eukaryotic Diversity (Ch. 28)
Chlorophyta Green Algaes.
• Ex. Volvox, Spirogyra, Ulva,
   Chlamydomonas; more than 7000 species.
• Thought to be ancestors of modern plants,
   sometimes included in plant kingdom.
• Contain chlorophyll a and b, carotenoids.
   Storage polysaccharide as starch.
• Mostly freshwater, inhabit many areas.
• Mutualistic relationship with fungi forming

Fungi-Like Protists.
•   Analogous to fungi in that they have filamentous structure to increase surface area for decomposition.
•   Two phyla: Plasmodial Slime Mold (Myxomycota) and
    Cellular Slime Mold (Acrasiomycota)
•   Amoebalike cells used for feeding in both phyla.

    1.    Phylum Myxomycota (Plasmodial Slime Mold):
    •     Heterotrophic.
    •     Feeding stage is mulitnucleated plasmodium (2n) that
          feeds on organic waste. Single mass of cytoplasm with
          many nuclei (coenocytic). Looks like a multinucleated
    •     Cytoplasmic streaming moves mass of cells and distributes
          O2 and nutrients throughout mass.
    •     When food supply depleted, forms a sporangium (str. That
          produces n spores) within which meiosis takes place
          forming spores (n). Spores germinate under favorable
          conditions forming both flagellated and amoeboid-type
          cells that fuse (undergo                               )
          forming a 2n zygote. The zygote nucleus divides
                                                but the cytoplasm fails
          to undergo
    •     Brightly colored pigments.
    2.   Phylum Acrasiomycota (Cellular Slime Mold):
    •     Ameobalike cells consume bacteria.
    •     Individual cells (n) aggregate to form mass of cells that produce fruiting bodies. Use cAMP to communicate
          between cell to form fruiting bodies. Used in studies of cell communication.
    •     Fruiting bodies (n) are asexual reproducing form that releases cells that function as spores (n) after they have dried
          up for protection.
    •     Sexual reproduction occurs.
    •     Haploid cells undergo (                                ) to form diploid zygote that becomes surrounded by wall to
          form cyst. Meiosis within cyst forms haploid cells that are then released to form other amoebalike cells.

6                                                                         Knight/2002/Origins of Eukaryotic Diversity (Ch. 28)

7                             Knight/2002/Origins of Eukaryotic Diversity (Ch. 28)