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Algae alternation of generations. The multicellular, diploid sporophyte produces haploid spores by meiosis. The spores develop into multicellular, haploid gametophytes by mitosis. The gametophytes release gametes, which may fuse to yield diploid zygotes. A zygote develops into a multicellular, diploid sporophyte.

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An amoeba moves by extending a pseudopodium, where the cytoplasm switches between a liquid sol state (endoplasm) and a gel-like state (ectoplasm). The pseudopodium can also be used to capture prey into a food vacuole. _Vid_Johnson4e/Wmv/Amoeboid_Protists.wmv

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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.

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Conjugation in Paramecium.

1. Meiosis of micronucleus produces 4 haploid micronuclei.
2. Three micronuclei disintegrate; the remaining one divides by mitosis.
3. The cells exchange one micronucleus; micronuclei then fuse, becoming diploid.
4. Three rounds of mitosis without cytokinesis produce eight micronuclei.
5. The original macronucleus disintegrates. Four micronuclei become macronuclei.
6. Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of 4 daughter cells.

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Diatoms are unicellular algae which make up a major component of phytoplankton (drifting photosynthetic organisms). This diverse group has a two-part, glass-like wall of hydrated silica. _Vid_Campbell7e/DiatomsMoving-V.swf

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Massive accumulations of fossilized diatom walls form sediments known as diatomaceous earth, which is mined as a filtering and absorbing medium and as an abrasive control of crawling invertebrate pests.

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Pfiesteria shumwayae, a dinoflagellate. A spiral flagellum lies in a groove around the cell, which is reinforced by internal plates of cellulose. Some of these photosynthetic species can undergo explosive growth and cause red tides. Their toxins can accumulate in molluscs and result in shellfish poisoning.

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Like most Euglenozoa, the freshwater protist Euglena has a 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. Bands of protein pellicle beneath the plasma membrane provides protection.

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Euglenozoan flagellum.
Most euglenozoans have a crystalline rod inside one of their flagella. The rod lies alongside the 9 + 2 ring of microtubules found in all eukaryotic flagella.

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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 kimgdoms than to other protists.

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Dinobryon, a fresh water colonial golden alga. Golden algae, or chrysophytes, are named for their color, which results from their carotenoid pigments. Their flagella can trap food particles and digest them by phagocytosis, thus they are mixotrophic: both photosynthetic and heterotrophic.

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Chlorophytes (Green algae).

1. Ulva, or sea lettuce, is an edible seaweed with a multicellular thallus differentiated into leaflike blades and a rootlike holdfast that anchors the alga against waves and tides.
2. Caulerpa lacks cross-walls; the thallus is one multi-nucleate “supercell.”

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A kelp forest. The great kelp beds of temperate coastal waters provide habitat and food for a variety of organisms, including many fish species caught by humans. Macrocystis, a kelp common along the Pacific coast of the United States, can grow more than 60 m in a single season, the fastest linear growth recorded in any organism.

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The dinoflagellate Gymnodinium is mixotrophic: after feeding on the golden alga Rhodomonas salina, it retains the functional chloroplasts of the prey for a few days.

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Ciliates such as Paramecium have a large macronucleus and a small micronucleus. They use cilia to move and feed. Contractile vacuoles perdiodically pump out excess water which had entered the cell by osmosis from the hypotonic environment. _Vid_MicroscopyU/paramecium17df40x.rm

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Acellular (Plasmodial) Slime Mold. _Vid_Campbell7e/SlimeMoldZoom-V.swf Physarum polycephalum forms one large cell (plasmodium) in the diploid stage with thousands of nuclei during the diploid stage of its life cycle. _Vid_Campbell7e/ch28/28_26SlimeMoldStreaming_VT.swf Note: Plasmodium is a different protozoan which causes malaria.

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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 gametes, causing periodic fevers and chills.

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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). Some of these plastids may contain a small nucleus.

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

1. Some are unicellular, such as the various diatoms.
2. Volvox is a colonial protist with some specialization among the cells.
3. The sea lettuce, Ulva, is multicellular with differentiated structures that resemble leaves and roots.

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

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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 (Palmaria palmata) are “leafy” and edible.

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Brown algae (Phaeophyta). Many brown algae are multicellular "seaweeds". The sea palm (Postelsia) lives on rocks 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.

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

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Ulva, or sea lettuce. This edible seaweed has a multicellular thallus differentiated into leaflike blades and a rootlike holdfast that anchors the alga against turbulent waves and tides.

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Volvox, a colonial freshwater chlorophyte. The colony wall is composed of biflagellated cells that cannot reproduce if isolated. _Vid_Campbell7e/VolvoxColony-V.swf The colony also contains 16 asexual reproductive cells called gonidia which divide to form “daughter” colonies. _Vid_Campbell7e/VolvoxDaughter-V.swf