• 1) Protists exhibit a remarkable variety of 'feeding' modes

  • a) autotrophic: photosynthesis in chloroplasts (phytoflagellates only)
  • b) heterotrophic:
    • phagocytosis (e.g., capture and ingestion by amoeba)
    • filtration (e.g., particle capture by sieving with microvilli of choanoflagellates or direct interception by cilia of ciliates)
    • engulfing (e.g., swallowing other protists whole by ciliates)

• 2) How does multicellularity differ from coloniality?

  • a) differentiation (identifiable cells perform specific functions)
  • b) interdependence (all cell types required for organism to work)
  • c) coordination (different cell types must work together)
  • d) multicellular organisms exhibit two distinct cell layers

• 3) Examples of 'colonial' protists (some appear multicellular) include:

  • a) some choanoflagellates
  • b)Volvox (hollow spherical 'colonies')
  • c) swarming ciliates & sarcodines (slime molds) that alternate between isolated cells and complex stalked sporocarps
  • d) true multicellularity has evolved at least 5 times (green plants, red algae, brown algae, fungi , animals)

• 4) The difference between 'colonial unicellular' & 'multicellular' is not discrete:

  Taxon	Cell differentiation?	Cell interdependence?	Cell coordination?	Two cell layes?
  Colonial choanoflagellates	no	no	no	no
  Volvox	yes	no?	yes	no?
  Swarming ciliates & sarcodines	yes	yes	yes	no
  Porifera (sponges)	yes	yes	yes	yes

• 5) Taxa important to understanding the Tree of Life:

  • a) Phylum Metamonadida- amitochondrial, bilaterally symmetrical flagellated cell; possible sister group to mitochondrial eukaryotes
  • b) Phylum Ciliophora- good monophyletic group of structurally complex protists; possess two nuclei: micro- & macronucleus
  • c) Phylum Choanoflagellata- a likely sister group to higher animals because they share two key characters with primitive Metazoa:
    • i) common cell type (choanocyte)- a single flagellum, (=monociliated) with a distinctive flagellar vane, surrounded by a ring of microvilli (clearly rejects ciliates as ancestor of Metazoa)
    • ii) diplosome- odd anchor structure to flagellum (2 basal bodies)

    • Also, a pelagic colonial form of choanoflagellate has a skeletal matrix & amoebocytes!

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