2421ch25 20Protozoan 20characteristics 20webnotes by A6524fjQ

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									Chapter 25
The Protozoa
Protozoa
•   unicellular, usually motile
    – lack cell wall
•   chemoorganoheterotrophs
•   protozoology
    – study of protozoa
Distribution
•   primarily in moist habitats
•   most are free-living in aquatic environments
•   terrestrial protozoa usually found in decaying organic matter and soil
•   some parasitic in plants and animals

Importance
• important link in food chains and food webs
    – food chains – series of organisms, each feeding on the preceding one
    – food web – complex interlocking series of food chains
    – make up large part of plankton in aquatic habitats
•   research
    – model organisms because have same metabolic pathways as multicellular
        eucaryotes
•   causative agents of some important diseases in humans and other animals

Morphology
•   similar to cells of multicellular eucaryotes
•   have some unique features because are unicellular

    Vacuoles
    •   contractile vacuoles
        – osmoregulatory
        – expel water
    •   phagocytic vacuoles
        – site of food digestion
    •   secretory vacuoles
        – contain enzymes for specific functions (e.g., excystation)
    Hydrogenosomes
    •   observed in some anaerobic protozoa
    •   small, membrane-delimited organelles that contain a unique electron transfer
        system
        – uses protons as terminal electron acceptors
    Ectoplasm & Endoplasm
        ectoplasm – semisolid or gelatinous cytoplasm directly under the plasma
          membrane
        endoplasm – fluid, granular cytoplasm which lyes inside of the ectoplasm,
          contains most of the organeles

    Pellicle
        plasma membrane and all the structures immediately beneath it

Nutrition
•   chemoheterotrophic
•   two types of nutrition
    – holozoic nutrition
       • nutrients acquired by phagocytosis
       • cytostome – used by some ciliates for phagocytosis
    – saprozoic nutrition
       • nutrients acquired by pinocytosis, diffusion, or carrier-mediated transport
Encystment and Excystment
•   formation and germination of cysts

Encystation
•   formation of a cyst
    – resting state with a wall and low metabolic activity
    – function of cysts
       • protection from changes in environment
       • sites for nuclear reorganization and cell division
           • transfer from one host to another
Excystation
•   escape of vegetative form from cyst
•   usually triggered by return to favorable environment
•   trophozoite
    – vegetative form released by parasitic species
–   excystation often triggered by entry into new host

Locomotory Organelles
•   some protozoa are nonmotile
•   motile species use one of following:
    – cilia
    – flagella
    – pseudopodia (s., pseudopodium)
       • cytoplasmic extensions

Reproduction
•   asexual
    – usually by binary fission
       • mitosis followed by cytokinesis
•   sexual
    – usually by conjugation
       • exchange of gametic nuclei between paired protozoa of opposite mating types


Classification
    •   Protist Classification
    •   subject of much work and debate
    •   scheme used here is that of the International Society of Protistologists
            • Super-Group Excavata
    •   includes Fornicata, the Parabasilia and the Euglenozoa
    •   includes some of most primitive, or deeply branching eucaryotes
            • most have a cytostome
                   • characterized by a suspension-feeding groove
                   • plays role in capturing particles from a feeding current
            • Fornicata
    •   members are flagellated and lack mitochondria
•   reproduction by binary fission
•   most are harmless symbionts with the following exceptions
        • Giardia – causes diarrhea
        • Hexamida salmonis – fish parasite
        • H. meleagridis – turkey pathogen
•   Parabasila
•   most are flagellated endosymbionts of animals
•   lack a distinct cytosome, use phagocytosis to engulf food
•   two subgroups
        • Trichonymphida – obligate mutuals of wood-eating insects such as
            termites
        • Trichomonadida – symbionts of digestive, reproductive and
            respiratory traits of many vertebrates, including humans
                • some strains are human pathogens
•   Euglenozoa
•   commonly found in fresh water
•   ~ one third are photoautotrophic, rest are chemoorganotrophs
•   Euglena is the representative genus
        • cell bounded by plasmalemma
        • pellicle consists of proteinaceous strips and microtubules
        • red eye spot or stigma helps organism orient to light
•   Pathogens Among the Euglenozoa
•   trypanosomes
        • parasites of plants and animals
        • leishmaniasis
                • caused by members of genus Leishmania
                • includes systemic and skin/membrane damage
        • Trypanosoma cruzi
                • causes Chagas disease
                • transmitted by “kissing bugs”
                • causes damage to nervous system
        • T. gambiense and T. rhodesiense
                • cause African sleeping sickness
•   Super-Group Amoebozoa
•   amoeboid motility involves the use of pseudopodia for locomotion and
    feeding
        • terms for shape of pseudopods
                • lobopodia – rounded
                • filopodia – long and narrow
                • reticulopodia – form a netlike mesh
•   naked amoebae are surrounded only by a plasma membrane
•   testate amoebae
        • plasma membrane covered by material made by amoebe or obtained
            from the environment
•   most amoebae reproduce by asexual division
•   Tubulinea
•   members inhabit moist environments
•   free-living, endosymbiotic, commensal and parasitic forms
•   Amoeba proteus
        • present in this phylum
        • commonly used in student laboratories
        • Entamoebida
•   Entamoeba histolytica
        • causes amoebic dysentery
        • major parasitic disease
•   Eumycetozoa
    “Slime Molds”
•   have been classified as plants, animals or fungi
•   include the Myxogastria (the acellular slime mold) and Dictyostelia (the
    cellular slime mold)
•   Myxogastria
    Acellular Slime Molds
•   Dictyostelia
    Cellular Slime Molds
•   Super-Group Rhizaria
•   amoeboid in morphology
        • can be distinguished by fine pseudopodia (filopodia)
                • may be simple, branched or connected
        • axopodia
                • filopodia supported by microtubules
                • protrude from the axoplast
                • primarily used in feeding
        • Radiolaria
•   most have internal skeleton made of siliceous material
•   feed by endocytosis using mucous coated filopodia to entrap prey
•   sexual and asexual reproduction used
•   Foraminifera
•   called forams
•   ~20mm – several centimeter size range
•   filopodia are arranged in branching network (reticulopodia)
•   have characteristics tests arranged in multiple chambers that are
    sequentially added as organism grows
•   More About Forams
•   complex life cycle
•   found in marine and estuarine habitats
•   foram tests make up most modern-day chalk, limestone, and marble
•   Super-Group Chromoaveolata
•   a diverse group including autotrophic, mixotrophic and heterotrophic
    protists
•   three subgroups
        • Alveolata
        • Stremenopiles
        • Haptophyta
        • Alveolata
•   large group including
        • Apicomplexa
        • Dinoflagellata (dinoflagellates)
        • Ciliophora
•   Apicomplexans
•   distinguished by the apical complex, located at one end of the cell
•   parasitic with complex life cycles
        • life cycle has both sexual and asexual phases
               • clonal and sexual stages are haploid, except for zygotes
               • sporozoite is the motile, infective stage
•   most important member is Plasmodium, the cause of malaria
•   Other pathogens…
•   Eimera
        • causative agent of cecal coccidiosis in chicken
•   Toxoplasma
        • cause of toxoplasmosis
•   Cryptosporidia
        • cause of cryptosporidiosis
•   Dinoflagellates
•   large group found in marine plankton
        • cause phosphorescence and toxic blooms
•   nutritionally complex
•   symbiotic forms live in association with reef building corals
•   Ciliophora
•   chemoorganotrophic
•   found in both benthic and planktonic communities in water and soil systems
•   use many cilia as locomotory and feeding organelles
•   reproduction
        • asexual by transverse binary fission
        • sexual by conjugation
•   Stramenopiles
•   a Chromalveolata subgroup
•   extremely diverse including
        • diatoms
               • found in marine plankton
                      – produce 40% to 50% of organic carbon in ocean
        • golden and brown algae
        • öomycetes and labyrinthulids
               • previously thought to be fungi
        • haptophytes
•   More on Stramenopiles
•   haptophytes include
        • planktonic photosynthetic protists such as Cocclithales
•   coccolithophores and the Foraminifera precipitate calcium carbonate in the
    open ocean for their ornate calcite scales called coccoliths
        • has influence on Earth’s carbon budget
                • Super-Group Archaeplastida
•   includes organisms containing a photosynthetic plastid that arose through an
    ancient endosymbiosis with a cyanobacterium
        • all higher plants and many algal species are included
•   Chloroplastida
•   often referred to as green algae
•   have chlorophylls a and b and specific carotenoids
•   many have cellulose cell walls
•   exhibit a diverse morphology
        • Chlamydomonas
•   Member of subgroup Chlorophyta
        • cells have a haploid nucleus, large chloroplast, conspicuous pyrenoid,
            and a stigma (eyespot) which plays role in phototaxis
        • osmoregulation controlled by two small contractile vacuoles at
            flagella base
        • reproduces by sexual and asexual reproduction
•   Chlorella
•   also a Chlorophyta
•   widespread in water and soil
•   asexual reproduction only
•   lacks flagella, eyespots, contractile vacuoles; nucleus is small
•   Prototheca moriformis
•   a pathogenic chlorophyte
•   causes protothecosis in humans and animals

								
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