Eukaryotes

• Eukaryote


  An organism whose cells contain complex structures enclosed within membranes
• Nucleus


  The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells, within which the genetic material is carried
• Protista


  The kingdom that single-celled eukaryotes are classified under, a paraphyletic group
• Organisms classified under Protista

  • Protozoa
  • Some unicellular algae
  • Phycomycetes
  • Myxomycetes
  • Yeasts
• Protists


  • Microscopical, unicellular eukaryotes
  • Unicellular or colonial forms without distinct division of labor
  • Exhibit all symmetries
  • No germ layer, no organs or tissues, but possess specialized organelles
  • Free-living, mutualism, commensalism, parasitism
  • Generally live in water
  • May be heterotrophic, autotrophic or saprozoic
  • May use pseudopodia, flagella or cilia for locomotion
  • Some have simple endoskeleton or exoskeleton, but most are naked
  • Reproduce asexually by fission, budding, and cysts, and sexually by conjugation or by syngamy
• Phyla of Animal-like Protists classified by how they move

  • Zooflagellates - flagella
  • Sarcodines - extensions of cytoplasm (pseudopodia)
  • Ciliates - cilia
  • Sporozoans - do not move
• Leishmania


  Moves using one or two flagella, absorbs food across membrane
• Amoeba


  Moves using pseudopodia (false feet), which are extensions of the cytoplasm - ameboid movement; ingests food by surrounding and engulfing it (endocytosis), creating a food vacuole; reproduces by binary fission; has a contractile vacuole that removes excess water
• Paramecium


  Moves using cilia; has two nuclei: macronucleus, micronucleus; food is gathered through food vacuole; has an anal pore for removing waste; has a contractile vacuole that removes excess water; reproduces asexually (binary fission) or sexually (conjugation); always the same shoe-like shape
• Plasmodium


  Does not move on its own, is parasitic; Plasmodium falciparum and Plasmodium vivax are sporozoans that infect the liver and blood and cause malaria
• Phyla of Photosynthetic Protists

  • Euglenophytes
  • Chrysophytes
  • Diatoms
  • Dinoflagellates
• Euglena


  Lives in water, has 2 flagella for movement, uses chloroplasts for photosynthesis but can turn into a heterotroph if kept in the dark, has an eyespot to sense light and dark, has a pellicle-like cell wall to maintain its shape
• Photosynthetic Protists


  • Chrysophytes - yellow-green algae, "golden plants"
  • Diatoms - produce thin cell walls of silicon
  • Dinoflagellates - often have two flagella, can be luminescent
• Yeasts


  Eukaryotic, mostly unicellular microorganisms; most reproduce asexually by budding, a few by mitosis; phylogenetically diverse, placed under phyla Ascomycota and Basidiomycota; chemorganotrophs, usually reproduce by budding or meiosis and spore formation
• Nutrition in Protists


  • Flagellates may filter feed using their flagella
  • Some can engulf and digest bacteria internally by extending their cell membrane around the food to form a food vacuole, usually by phagocytosis or pinocytosis
• Nutritional types of Protists

  • Phototrophs - use sunlight and organic compounds or carbon fixation as energy and carbon sources (e.g. algae, dinoflagellates, Euglena)
  • Organotrophs - use organic compounds as energy and carbon sources (e.g. Apicomplexa, Trypanosomes, Amoebae)
• Some protists reproduce sexually (conjugation), while others reproduce asexually (binary fission); some species like Plasmodium falciparum have complex life cycles involving both sexual and asexual reproduction
• Protists form a broad base across the bottom of the food chain and supply approximately one-half of the world's oxygen
• Protists, along with bacteria and fungi, are responsible for decomposing and recycling nutrients
• Euglena are used to help treat sewage because of their unique ability to switch from an autotrophic to a heterotrophic nutritional mode, helping to maintain oxygen levels
• Trichonympha which lives in the digestive system of termites produces cellulase, an enzyme that enables termites to digest wood
• Products derived from protists are used in treatment of ulcers, high blood pressure and arthritis
• Some protists are significant pathogens of both animals and plants, e.g. Plasmodium falciparum and P. vivax which cause malaria, Phytophthora infestans which causes potato blight, Balantidium Coli and Entamoeba Histolytica which cause severe dysentery, and Trypanosoma which causes African Sleeping Sickness