Eukaryotes (27)

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Eukaryotes (27)
2012-02-13 17:03:20

Biology test 1
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  1. protists
    Eukaryotes that are neither plants, animals, or fungi

    do not constitute a clade, they are paraphyletic
  2. paraphyletic
    group contains its most recent common ancestor but does not contain all the descendants of that ancestor
  3. Monophyletic
    contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group
  4. Polyphyletic
    group is one whose members' last common ancestor is not a member of the group.
  5. 5 steps preceded the origin of eukaryotic cells:
    1. Development of a flexible cell surface (loss of protective cell wall).

    2. Origin of a cytoskeleton through infolding of the cell membrane.

    3. Origin of a nuclear envelope as DNA attaches to the membrane of an infolded vesicle.

    4. Appearance of digestive vesicles or vacuoles.

    5. Acquisition of some organelles by endosymbiosis (e.g., mitochondria from a proteobacterium, chloroplasts from cyanobacteria).
  6. Primary endosymbiosis
    First, one eukaryote engulfed a cyanobacterium, gave rise to the first photosynthetic eukaryotes
  7. Secondary and tertiary endosymbiosis
    occurred multiple times; leading to other photosynthetic microbial eukaryote groups.
  8. Protozoans
    convenience term, protists formerly classified as animals; many are ingestive heterotrophs
  9. Algae
    convenience term, photosynthetic protists
  10. eukaryotes can be divided into five hypothesized clades
    Chromalveolates, Plantae, and some Excavates contain at least some photosynthetic species;

    Rhizaria and Unikonts do not.
  11. Chromalveolates:
    2 main groups: Alveolates and Stramenopiles

    •Include common groups of algae (Dinoflagellates, Diatoms) and “seaweeds” (Brown algae).

    Haptophytes are unicellular, marine, flagellates, mostly armored
  12. Alveolates
    • subgroup of Chromalveolates
    • synapomorphy = presence of alveoli (sacs beneath surface of plasma membrane )

    Broken into 3 groups: Apicomplexans, Dinoflagellates, Ciliates
  13. Apicomplexans
    subgroup of alveolates

    all parasites whose infectious stages have an apical complex of organelles that penetrate host cells
  14. Dinoflagellates
    subgroup of alveolates

    have 2 flagella that arise from grooves formed by internal cellulose plates. They are free-living and common in both freshwater and marine habitats. Responsible for toxic “red tides” and fishy odors; also endosymbionts in corals
  15. Ciliates
    subgroup of alveolates

    have two types of nuclei and use cilia (structure identical to flagella) for motility and feeding (e.g., Paramecium); they are heterotrophic. Some also have Trichocysts, like sharp darts on filament tip.
  16. Stramenopiles
    Synapomorphy are rows of tubular hairs on the longer of the two flagella.

    • Includes diatoms, brown algae, oomycetes, and
    • slime nets.
  17. Diatoms
    Subgroup of Stramenopiles

    •live in a petri-dish-like silica shell called a frustule; abundant primary producers in both freshwater and marine environments.

    •They are either bilaterally or radially symmetrical. Asexual reproduction is by binary fission. Both top and bottom of the “petri plate” become the tops of the new daughter cells.
  18. Brown algae
    Subgroup of Stramenopiles

    •multicelluar; some get very large, includes large seaweeds and kelps; mostly marine.

    •The carotenoid fucoxanthin imparts the brown color.

    •Sargassum forms dense mats in the Sargasso Sea in the mid-Atlantic.

    •Most brown algae attach to rocks by a holdfast that glues it to the rock. The “glue” is alginic acid—a gummy polymer of sugars. It is harvested and used as an emulsifier in ice cream, cosmetics, and other products.
  19. Oomycetes
    Subgroup of Stramenop•water molds and downy mildews, nonphotosynthetic. Diploid throughout most of their life cycle, have flagellated reproductive cells. Responsible for Irish potato famine.

    •Water molds are absorptive heterotrophs or saprobic (feed on dead organic matter)(e.g. Saprolegnia). Once were classed as fungi, but are now known to be unrelated.

    •Some are coenocytes- many nuclei enclosed in one plasma membrane.
  20. Plantae
    •Divided into 5 main groups, 4 of which are entirely aquatic or marine; the 5th group being the land plants.

    Glaucophytes, Red algae, Chlorophytes, Land Plants, Charophytes

    all chloroplasts trace back to a single incidence of endosymbiosis of a cyanobacterium
  21. Glaucophytes
    Subgroup of plantae

    unicellular, freshwater organisms. Likely first group to diverge. Chloroplasts retain bit of peptidoglycan, between inner and outer membrane, normally only in prokaryotes (e.g. cyanobacteria). Feature has been lost in other groups
  22. Red algae
    Subgroup of plantae

    •include multicellular marine forms that often accumulate large amounts of the red pigment phycoerythrin. Mucilaginous polysaccharides are source of agar.
  23. Chlorophytes, Charophytes and Land Plants
    Subgroups of plantae

    • Synapomorphies of the 3 groups include
    • chlorophyll a and b in chloroplasts, and have starch as a storage product
  24. Charophytes
    •are most closely related to higher plants.

    •More than 17,000 species; marine, freshwater, and terrestrial. Unicellular to large multicellular forms.

    •Some chlorophytes form colonies of cells that show the possible first step for cell and tissue differentiation. (e.g. Volvox colonies have cells for reproduction.
  25. Excavates
    several clades lack mitochondria—a derived condition (in the Diplomonads and Parabasalids).

    •All are single celled.

    •Non-photosynthetic except for some Euglenids.

    •Some groups are very important medically (e.g., Kinetoplastids); with several groups that cause human disease
  26. •Heteroloboseans
    have both amoeboid and flagellated life stages. Sometimes infect humans from under- chlorinated pool water.
  27. Diplomonads
    Trichomonas vaginalis is responsible for a sexually transmitted disease in humans.

    unicellular; lack mitochondria.
  28. parabasalids
    Subgroup of Excavates. unicellular; lack mitochondria.

    Trichomonas vaginalis is responsible for a sexually transmitted disease in humans.
  29. Euglenids
    include autotrophic and heterotrophic flagellates.

    •Have an anterior chamber from which 1 or 2 flagella emerge, typically free-living.

    •Some species with chloroplasts, others without; some species produce them only when needed.
  30. Kinetoplastids
    •unicellular parasites with two flagella and a single mitochondrion.

    •They have a single large mitochondrion associated with a kinetoplast, a unique organelle that houses extranuclear circular DNA and proteins.

    •All are symbiotic and some are pathogenic to their hosts.

    •Trypanosomes are kinetoplastids; including African Sleeping Sickness (caused by T. brucei), Chagas’ disease (caused by T. cruzi), and Leishmaniasis (caused by Leishmania). They can change their cell surface molecules frequently, making them diffucult to control.
  31. Rhizaria
    3 subgroups: Cercozoans, Foraminiferans, Radiolarians

    Unicellular, aquatic, amoeboid and use long thin pseudopodia for locomotion.
  32. Cercozoans
    Subgroup of Rhizaria

    •Diverse with some amoeboid and some flagellated forms; found in freshwater and soil.

    •One group has chloroplasts derived from a green alga by secondary endosymbiosis.
  33. Foraminiferans
    Subgroup of Rhizaria

    •Foraminiferans- secrete shells of calcium carbonate.

    •Feed and move with thread-like branched pseudopods extending through numerous pores in the shell; form sticky net capturing smaller plankton.

    •All marine; some plankton, some benthic, 90% spp. known from fossils.

    •Responsible for calcium deposits such as the “white cliffs of Dover.”
  34. Radiolarians
    Subgroup of Rhizaria

    •Secrete a glassy internal endoskeleton that can be remarkably ornate; among the most beautiful of all microbial eukaryotes.

    •Exclusively marine.

    •Have thin, stiff pseudopods reinforced by microtubules; pseudopods increase surface area for exchange of materials; and help them float.
  35. Unikonts
    fungi and animals, have single flagellum (if present)

    2 subgroups: Opisthokonts and Amoebozoans
  36. Opisthokonts
    Subgroup of Unikonts

    posterior flagellum (e.g. human sperm)

    –Includes Fungi, Choanoflagellates, and Animals
  37. Amoebozoans
    subgroup of Unikonts

    amoeboid in form, lobe-shaped pseudopods
  38. Loboseans
    Subgroup of Amoebozoans

    unicellular, cells live independently, do not aggregate. Includes Entamoeba histolytica, responsible for amoebic dysentery and amoebic liver abscess in humans.
  39. Slimemolds
    Subgroup of Amoebozoans

    All are motile by “cytoplasmic streaming”, ingest food by endocytosis, and form spores on stalks called fruiting bodies. Slime molds are found in cool, moist habitats, primarily forests.
  40. Animals and fungi arose from a common ancestor within the ___________ clade
  41. Multicellular life probably evolved from stalked colonial forms such as this ______. They resemble a type of cell found in sponges.

    Therefore, ________ may represent a connection between unicellular and multicellular animals