Protists

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Protists

• Chapter 21 (In part)

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Characteristics of Protists

• Diverse group
• Include plant-like, animal-like, and fungus-like
  forms
• All are eukaryotic
• Nucleus
• Membrane bound organelles
• Most have mitochondria, chromosomes
• Reproduce asexually and sexually

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Diversity of Protists

• Some autotrophic, Some heterotrophic
• Some have shells (testa)
• Some parasitic, some free-living
• Some single-celled, some multicellular
• Some float (plankton), others mobile using
• Cilia, flagella, pseudopodia

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Difficulty in classifying

• Early classifications into plant or animal split
  the protists
• Euglena has characteristics of both
• can use sunlight for photosynthesis
• can also eat smaller protists
• Protists are defined by what they are not (fungi,
  plants, animals)

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Modern classification of protists

• 27 phyla
• Can be separated into
• plant-like (algae)
• animal-like (protozoa)
• fungus-like protists (slime molds)
• Reproductive cycle important in classification
• Some undergo alternation of generations

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Plantlike protists (algae)

• Most are photoautotrophs
• Some can also be heterotrophic when needed
  (Euglena)
• Use chlorophyll like plants, but most have
  different forms of chlorophyll
• Plants use chlorophyll a and b, algae use mostly
  a
• Different cell walls and flagella arrangement

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Plantlike protists (algae)

• Dinoflagellates
• Chrysophytes (Golden algae, diatoms)
• Euglenophytes (Euglena)
• Phaeophytes (Brown algae)
• Rhodophytes (Red algae)
• Chlorophytes (Green algae)

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Dinoflagellates (570 mya)

• Free-floating plankton, warm oceans
• Single-celled or colonies, some symbiotic
• Cause red tides (toxins), some bioluminesce
• Have a rigid wall (testa) of cellulose and silica
• Two grooves in testa with flagella
• Unusual chromosomes and no sexual reproduction

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Dinoflagellate
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Chrysophytes (Golden Algae and Diatoms)

• Golden-yellow pigments
• Form hard tests of silica
• Single-celled and colonial forms
• Plankton in temperate lakes and ponds, a few in
  ocean
• Reproduce asexually or sexually (diatoms)
• Diatoms most numerous group of chrysophytes

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Diatoms
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Euglenophytes

• Mix of plant and animal features
• In dark, live like heterotroph (eat organisms)
• In sunlight, live like a plant (autotrophic)
• Use both chlorophyll a and b
• Store food differently from plants (no starch)
• Reproduce asexually

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Euglena
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Phaeophytes (Brown Algae)

• All multicellular, large protists
• Cold oceans
• Sexual reproduction occurs, spores produced
• First alternation of generations occurs in this
  group
• Use chlorophyll a and c, do not produce starch

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Phaeophyta (Brown Algae)
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Rhodophytes (Red Algae-500 mya)

• Seaweeds (4000 species)
• Warm oceans
• Cells have agar and carrageen (slippery)
• Sexual reproduction, complex life-cycles

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Rhodophyta-Red Algae
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Chlorophytes (Green Algae)

• Most like plants of plant-like protists
• Use chlorophyll a and b, store food as starch
• single, colonial, multicellular forms
• free-living, mostly aquatic
• some symbiotic, live inside other organisms

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Chorophyta
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Chlorophyta
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Animal-like Protists (Protozoa)

• All heterotrophic
• Rhizopoda (Amoebas)
• Foraminifera
• Sporozoans
• Ciliaphora (Ciliates)
• Zoomastigna (Flagellates)

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Rhizopods (Amoebas)

• Worldwide
• Free-living or parasitic
• Terrestrial and aquatic
• Move using pseudopodia
• Reproduce asexually

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Foraminifera (230 mya)

• Marine organisms
• Hard shell (testa)
• Live in sand or free-floating plankton
• True alternation of generations (Sexual
  reproduction)

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Sporozoans

• All parasitic
• Reproduce asexually and sexually
• Complex life-cycles, multiple hosts
• Cause malaria (Plasmodium)

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Ciliophora (Ciliates-100 mya)

• 8000 species
• Free-living, aquatic (fresh and salt)
• Move by cilia on outer membrane

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Zoomastigna (Flagellates)

• Diverse group
• Single-celled
• Have at least 1 large flagella
• Free living in water or parastic
• Mostly asexual reproduction (some sexual)

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Fungus-like Protists

• Acrasiomycota (Cellular Slime Molds)
• Myxomycota (Plasmodial Slime Molds)
• Oomycota (Water molds, blights)

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Acrasiomycota (Cellular Slime Molds)

• Fresh water or damp soil
• Ameoba-like when food is plentiful (phagocytosis)
• Food is scarce, adopt wandering life-cycle
• Finds food, produces fruiting body that produces
  spores
• Spores develop into amoebas
• Asexual reproduction

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Cellular Slime Mold
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Myxomycota (Plasmodial Slime Molds)

• Similar in shape and life-cycle to acrasiomycota
• Different migrating form
• Forms a plasmodium (many cells with nuclei, no
  cell boundary)
• Plasmodium has a sexual form

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Oomycota (Water molds, blights)

• Either parasitic or saprophytic
• Extend bodies into host or dead organism
• Release digestive enzymes and absorb nutrients
• Have flagellated spores unlike fungi
• Sexual reproduction (haploid and diploid)

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Oomycota (Water Mold)
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DNA evidence about evolution of protists

• Diversity greater than expected based on
  morphology
• DNA shows evidence of endosymbiosis

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Endosymbiosis