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AP BIOLOGY 11
13. The Protists
Classification
• The protists are by far the most difficult group of organisms to classify.
• It is the most artificial and disagreed upon by biologists.
• We will not focus so much on the taxonomy as the diversity within this group.
• We will divide them into three groups based upon their nutrition method.
Classification
1. Ingestive Protists • These are animal
like protists that bring food into cells (ingest) and digest it.
• Examples include the Protozoa.
A Paramecium
Classification 2. Absorptive Protists • Fungus like protists that
use extracellular digestion, ie. They secrete enzymes onto a food source, digest it, then absorb the digested products.
• Ex: Water and slime molds.
A plasmodial slime mold
Classification
3. Photosynthetic Protists
• Plant like protists that do photosynthesis.
• Include most of the unicellular, colonial, and multicellular algae.
Evolution
• Protists represent the first eukaryotes. • Probably evolved from prokaryotes that didn’t
have a cell wall (therefore flexible). • Maintained shape with their cytoskeleton. • This could also “pull” is some plasma
membrane to surround their nuclear material - forming a nucleus (by process like phagocytosis).
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Evolution
• This started cytoplasmic compartmentalization which allows for internal specialization.
• Cytoskeleton also allowed for new mode of cell division - mitosis.
• This removed the restriction of one circular chromosome, allowing many linear chromosomes - this produces more genetic information and more complexity.
Evolution
• This also allowed for true sexual reproduction to occur with meiosis and fertilization - increasing variations!
• The evolution of mitochondria and chloroplasts probably involved the evolution of a symbiotic relationship between a prokaryote and the evolving eukaryote.
• Protist evolution is still quite obscure.
Ingestive Protists
1. Archeozoa • “ancient protists” • Lack mitochondria
(primitive feature), often flagellated.
• Ex. Giardia sp.(Beaver Fever)
Ingestive Protists
2. The Flagellates • Move by flagella. • Contain both photosynthetic and
heterotrophic varieties. • Also contains parasitic forms. • Three main subgroups:
Ingestive Protists A. Dinoflagellates • Photosynthetic. • Major component of
phytoplankton in the ocean.
• Cause “Red Tides” which can cause paralytic poisoning when eating shellfish.
Ingestive Protists B. Sporozoans • Form spores at one
stage of life cycle, other stage moves by flagella.
• Ex. Plasmodium vivax parasite that causes malaria.
• Learn its life cycle and vector.
P. vivax in human blood smear
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Ingestive Protists
C. Euglenophyta • Contains Euglena and
related organisms. • Combine auto and
heterotroph character. • Shows why protists are
so difficult to classify. • Moves by flagellum.
Ingestive Protists 3. Ciliates • Among most complex of
protozoans - show high degree of intracellular specialization.
• Have body “systems” like animals.
• Reproduce sexually by conjugation.
Paramecia
Ingestive Protists 4. Rhizopoids • Move by pseudopods
with cytoplasmic streaming - demonstrates “sol--gel” phase reversal.
• Includes largest eukaryotic cells - the amoeba.
Ingestive Protists
Ingestive Protists 5. Radiolaria • Secrete a “glass” skeleton. • Major component of fresh and salt water plankton. • Basis of aquatic food chains.
Ingestive Protists
6. Forminifera • Have CaCO3 skeleton (chalk) form large
deposits on ocean floors. • Mostly marine, have pseudopods. • Major source of chalk (white Cliffs of
Dover).
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Absorptive Protists
Slime Molds • Fungus like protist
that also has stage that resembles ameba.
• Most common stage resembles a mass of gooey fungus called the “Plasmodium”.
Absorptive Protists • The plasmodium
forms an upright sporangium that produces and releases haploid spores.
• These germinate to form the haploid ameba like and flagellated stages.
Absorptive Protists
• These synapse to form a zygote which grows back to the plasmodium.
• The zygotes all merge together to form the plasmodium which is the feeding stage.
• The asexual (spore) stage is environmentally resistant to survive winters.
Plant Like Protists: Algae
• Most diverse group. • Not all agree should be classified as protists • All are photosynthetic. • May be unicellular, colonial, or
multicellular (some classify these in the plants).
Plant Like Protists: Algae
A) The Diatoms • Classified as “Golden
- Brown Algae”. • Produce glass-like
(silica based) cell walls in “box and lid”.
• Compose a large part of fresh and salt water plankton.
Plant Like Protists: Algae B) Brown Algae • Phylum Phaeophyta. • Contains brown
pigment “fucoxanthin” as accessory light pigment (masks chlorophyll color).
• Mostly marine and temperate.
Kelp
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Plant Like Protists: Algae • Kelp such as Macrocystis sp.
shows basic adaptation to living near land and was necessary precursor to evolution of plants to land.
• Show specialized regions: blades for photosynthesis and reproduction, stipe to hold and suspend blades, air bladders to float plant, and...
Plant Like Protists: Algae
• Holdfasts to enable plant to stay anchored in nutrient rich continental shelf area.
• Kelp beds provide foundation of a major marine ecosystem.
• Show “Alternation of Generations”
Holdfast of Macrocytis sp. From Bamfield BC
Plant Like Protists: Algae
C) Red Algae • Phylum Rhodophyta. • Red due to red
accessory pigment (phycoerythricin).
• Most common in warmer tropical waters.
• In temperate zones, found in deeper water.
Plant Like Protists: Algae
D) Green Algae • Phylum Chlorophyta. • Very diverse group. • Include unicellular,
colonial, and multicellular forms.
• Live in all environments: fresh and salt water, soil.
Ulva sp. Sea lettuce
Plant Like Protists: Algae
1. Unicellular Green Algae
• Very common in fresh water as part of phytoplankton.
• Ex. Chlamydomonas sp.
Plant Like Protists: Algae
2. Colonial Green Algae • Live in long filaments or as
colonial spheres.
Volvox, spherical colonial
Filamentous green algae
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Plant Like Protists: Algae 3. Multicellular Green Algae • Mostly marine. • Likely ancestors of land
plants. • Show equal Alternation of
Generations (a pre-adaption to land) with equal Sporophyte and Gametophyte.
• (end show)