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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)