Bio1151 Chapter 28 Protists
  1. The kingdom formerly known as           is crumbling. Protists are more diverse than any other eukaryote group.

    Protists are eukaryotes, and comprise a wide diversity of forms.

  2. Some are unicellular, such as the various diatoms.
  3. Volvox is a colonial protist with some specialization among the cells.
  4. The sea lettuce, Ulva, is multicellular with differentiated structures that resemble leaves and roots.
  5. Much of protist diversity has its origins in serial                .

    Domain Eukarya can be divided into five supergroups. Organisms in kingdom Protista are scattered among the supergroups, and certain groups within Protista are more closely related to the other 3 eukaryote kingdoms than to other protists.

    Serial endosymbiosis. Plastids (pigment-bearing organelles such as chloroplasts) evolved from a cyanobacterium that was engulfed by a heterotrophic eukaryote (primary endosymbiosis). That ancestral eukaryote diversified into red algae and green algae, some of which were subsequently engulfed by other eukaryotes (secondary endosymbiosis); these plastids may retain their own nucleus.
  6. Unicellular protists:
    • Euglenozoa

      Euglenozoa are photosynthetic. Most Euglenozoa such as Euglena have a crystalline rod inside one of their flagella. The rod lies alongside the 9 + 2 ring of microtubules found in all eukaryotic flagella.

        Like most Euglenozoa, the freshwater protist Euglena has bands of protein pellicle under the plasma membrane for protection, flagella, an eyespot for directing light to the light detector that detects light, and chloroplasts that perform photosynthesis. Euglena motion:
    • Trypanosoma

      Trypanosoma is a parasite transmitted by the tsetse fly and causes the neurological disorder sleeping sickness in humans.
    • Plasmodium

      Plasmodium is a parasite transmitted by the Anopheles mosquito and causes malaria in humans.

      After a stage in the liver, merozoites use their apex to penetrate and reproduce in red blood cells.

      Eventually the host cells rupture to release gametocytes, causing periodic fevers and chills.

    • Dinoflagellates


      Spiral flagella lie in a groove around the cell, which is reinforced by internal plates of cellulose.

      Some of the photosynthetic species can undergo explosive growth and cause red tides.

      Their toxins can accumulate in molluscs and result in shellfish poisoning.

      Dinoflagellate spinning:

        Excess nutrients in the water can cause red tides, an explosive growth of Dinoflagellate populations. The color is due to the presence of carotenoids in their plastids.
    • Ciliates

      Ciliates such as Paramecium are non-photosynthetic and use cilia to move and feed. They have a large macronucleus that performs everyday functions, and a small micronucleus used in conjugation. Contractile vacuoles pump out excess water which had entered the cell from the hypotonic environment. Movie:
    • Amoebozoans


    • Amoeba
    • plasmodial slime mold
    • cellular slime mold

        A unicellular amoeba moves by extending pseudopodia, where the cytoplasm switches between a liquid sol state (endoplasm) and a gel-like state (ectoplasm).

        The pseudopodia can also be used to capture prey into a food vacuole.

        Pseudopodia diversity:

        Plasmodial slime mold.

        One large cell (plasmodium) with thousands of nuclei is formed during the diploid, feeding stage of the life cycle.

        The plasmodium moves slowly as an amoeboid mass by "streaming" its cytoplasm.

        Note: Plasmodium is a different protozoan which causes malaria.


        A cellular slime mold can live as unicellular amoebae, but can aggregate to form a multicellular pseudoplasmodium, or "slug", in the haploid stage.

        The "slug" migrates to a new location, then forms a stalked fruiting body that releases spores which develop into new amoebae.

    • Diatoms

    Diatoms make up a major component of phytoplankton (drifting photosynthetic organisms). They have a two-part, glass-like wall made of silica which can be harvested as diatomaceous earth. Diatoms video:

      Massive accumulations of fossilized diatom walls form sediments known as diatomaceous earth,

      This is mined as a filtering and absorbing medium and as an abrasive control of crawling invertebrate pests.

  7. Multicellular protists:
    • Golden algae (              ) can be unicellular or colonial and contain yellow and brown              for photosynthesis.

      Golden algae (Chrysophyta) are named for their color, which results from their carotenoid pigments.

      The flagella of the colonial Postelsia can trap food particles and digest them by phagocytosis.

      Thus they are mixotrophic: both photosynthetic and heterotrophic.

    • Brown algae (             ), are multicellular "seaweeds" that can grow to great heights.

      Brown algae (Phaeophyta).

      Many brown algae are multicellular "seaweeds".

      The sea palm lives along the Pacific coast of north America.

      The thallus (undifferentiated tissue) is composed of

    • photosynthetic blades,
    • a stipe that provides structural support, and
    • a holdfast anchors the organism to the sea floor.
    •      algae and        algae are the closest relatives of land plants.
      • Red algae (             ) are multicellular "seaweeds" that contain red pigments.

        Red algae (Rhodophyta).

        Red algae contain the pigment phycoerythrin, which masks the green of chlorophyll.

        Some, such as Bonnemaisonia hamifera, have a filamentous form, while Dulse are "leafy" and edible.

          Edible red algae.

          Nori is a traditional Japanese food made from the "seaweed" Porphyra.

      • Green algae (              ) contain               that give them their green color.

      Chlorophytes (Green algae).

    • Ulva (sea lettuce) has a multicellular thallus differentiated into leaf-like blades and a root-like holdfast that anchors the alga against waves and tides.
    • Caulerpa has a thallus that is one multi-nucleate "supercell".

      Volvox is a colonial form.

        Volvox, a colonial chlorophyte.

        The colony wall is composed of biflagellated cells that cannot reproduce if isolated.

        Within are asexual reproductive cells called gonidia which divide to form "daughter" colonies.

        Releasing daughter colony:

    • An innovation among the multicellular algae is the              of generations.

    Algae alternation of generations.

    The multicellular, diploid sporophyte produces unicellular haploid spores by meiosis.

    The spores develop into multicellular, haploid male or female gametophytes by mitosis.

    The gametophytes produce gametes; fertilization yields a diploid zygote.

    A zygote develops into a multicellular, diploid sporophyte by mitosis.