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Chapter 22
The Protists
The Protists
Protist Biology
Protist Diversity, cont.
Protist Evolution
Protist Diversity
Green Algae
Red Algae
Brown Algae
Slime Molds
Water Molds
The Protists
General Biology of the Protists
Classified into the Domain Eukarya & the
Kingdom Protista
Most unicellular
Many with amazingly high level of strucrural and
functional complexity
Life cycles:
Asexual reproduction common
Sexual reproduction may occur when conditions
Some life cycles simple, many extremely complex
Origin of the Eukaryotic Cell
The Protists
Ecology of Protists
Protists are of enormous eco-logical importance
Photoautotrophic forms:
Produce oxygen
Function as producers in both freshwater and saltwater
Major component of plankton
- Organisms that are suspended in the water
- Serve as food for heterotrophic protists and animals
Many protists are symbionts
Ranges from strict parasitism to mutualism
Coral reefs greatly aided by symbiotic photoautotrophic
protists in tissues of corals
The Protists
Evolution of Protists
Complexity and diversity of protists makes them
difficult to classify
Many classification schemes proposed
None has broad support
Cannot be classified as plants, animals, or fungi
Could be split into as many as a dozen kingdoms
The scheme chosen for this discussion is based
on modes of nutrition
Protist Diversity
The Protists
Diversity of Protists:
Green Algae – The Chlorophyta
Phylum Chlorophyta
Approximately 7,500 species
Inhabit a variety of environments including oceans,
freshwater, snowbanks, tree bark, and turtles backs
Many are symbionts with fungi, plants, or animals
Morphology varied
Majority unicellular, but many are filamentous or colonial
Some are multicellular and resemble leaves of lettuce
Plants thought to be derived from Chlorophyta because
both groups:
Have a cell wall that contains cellulose
Possess chlorophylls a and b, and
Store excess food as starch
Green Algae:
The Protists
A minute (<25 μ m), actively moving flagellate
Inhabits still, freshwater pools
Fossil ancestors date back over a billion years
Definite cell wall
Single, large, cup-shaped chloroplast
Chloroplast with a pyrenoid where starch is synthesized
Many with a bright red eyespot, or stigma on chloroplast
Two long, whip-like flagella
- Project from the anterior end
- Operate with a breaststroke motion
Electron Micrograph of Chlamydomonas 10
Green Algae:
The Protists
Most often reproduces asexually
As many as 16 daughter cells within parent cell
Escape by digesting the parent cell
Occasionally reproduces sexually
Gametes fuse to form a zygote
Becomes a heavy-walled, resistant zygospore
- Goes into a period of dormancy
- Upon germination produces four zoospores by meiosis
“Spore” - a reproductive cell that develops into a new organism
without fusing with another cell
“Zoospore” - flagellated spores, typical of aquatic species
Reproduction in Chlamydomonas
Green Algae:
The Protists
Filamentous green algae
Found in green masses on the surfaces of ponds and
Has ribbon-like, spiraled chloroplasts
Sexual reproduction by conjugation:
A temporary union during which the cells exchange
genetic material
Two filaments line up parallel to each other
- Cell contents of one filament move into the cells of the other
- Forms diploid zygospores
- In spring, undergo meiosis to produce new haploid filaments
Green Algae:
Multicellular Forms
The Protists
Multicellular green alga
Commonly called sea lettuce
Thallus (body) is two cells thick
Can be as much as a meter long
Sexual cycle involves alternation of generations
Similar to higher plants, except
- Both generations look exactly alike, and
- The gametes all look the same
Multicellular Green Algae
Green Algae:
Colonial Forms
The Protists
A colony is a loose association of independent cells
A Volvox colony:
A hollow sphere
Thousands of cells arranged in a single layer surrounding
a watery interior
Each cell of colony resembles a Chlamydomonas cell
Flagella beat in a coordinated fashion
Some cells are specialized for reproduction
- Each can divide asexually to form a new daughter colony
within the parental colony
- Leaves parental colony by releasing an enzyme that
dissolves away a portion of the parental colony
The Protists
Diversity of Protists:
Red Algae – The Rhodophyta
About 5,000 species
Live mostly in warmer seawater, some as deep as 200
Economic Importance
Agar - capsules; dental impressions; cosmetics; culture
medium; electrophoresis; food prep.
Carrageen - an emulsifying agent used in chocolate, lowfat foods, & cosmetics
The reddish-black wrappings around sushi rolls consist of
processed Porphyra blades
Red Algae
The Protists
Diversity of Protists:
Brown Algae – The Phaeophyta
About 1,500 species
Most live in colder ocean waters along rocky coasts
No unicellular or colonial brown forms
Some small forms with simple filaments
Others large multicellular forms that may exceed 200 m
in length
Chlorophylls a and c
Fucoxanthin (a type of carotinoid pigment) gives them
their color
Excess food stored as a carbohydrate called laminarin
Brown Algae
The Protists
The Phaeophyta
Multicellular forms of green, red, and brown
algae are called seaweeds
Laminaria (a kelp), and Fucus, (rockweed), are
common intertidal seaweeds
Nereocystis and Macrocystis often form forestlike thickets in deeper waters
Sargassum forms floating masses where other
organisms find shelter
Harvested for food and fertilizer
Macrocystis is source of algin, a thickener for
The Protists
The Phaeophyta
Laminaria shows tissue differentiation
Transport organic nutrients in a tissue resembling
Life cycle
Most brown algae have alternation of generations
In some species of Fucus
- Meiosis produces gametes instead of spores
- The adult is always diploid, as in animals
The Protists
Diversity of Protists:
Yellow-green Algae – The Chrysophyta
Diatoms (formerly Bacillariophyta) are the most
numerous unicellular algae in the oceans
Significant portion of phytoplankton
Cell wall
Two valves, with the larger valve acting as a lid (like a
mint tin)
Contains silica
Diatomaceous earth used as
Filtering agents
Sound-proofing materials
Polishing abrasives
The Protists
Diversity of Protists:
Dinoflagellates – The Pyrrophyta
About 4,000 species of unicellular aquatic and marine organisms
 Cell is usually bounded by protective cellulose plates impregnated
with silicates
 Typically with two flagella
- One in a longitudinal groove with its distal end free
- The other lies in a transverse groove that encircles the organism
Symbiotic dinoflagellates in corals called zooxanthellae
 Dinoflagellates provide their host with organic nutrients
 Corals provide wastes that fertilize the algae
 Some lack chloroplasts and are parasitic
Gymnodinium brevis may cause “red tide”
 Produce a powerful neurotoxin that has caused massive fish kills
 Consume shellfish during outbreak can cause respiratory paralysis
Diatoms and Dinoflagellates
Fish Kill and Dinoflagellate Bloom
The Protists
Diversity of Protists:
The Euglenoids – Phylum Euglenophyta
Small freshwater unicellular organisms
Difficult to classify
Have two flagella and an eyespot (shades a
One flagellum much longer than the other
- Projects out of an anterior, vase-shaped invagination
- Called a tinsel flagellum because of hair-like projections
Cell bounded by flexible pellicle
Surrounded by three rather than two membranes
With a pyrenoid which produces an unusual type of
carbohydrate called paramylon
The Protists
Diversity of Protists:
Zooflagellates – Phylum Zoomastigophora
Colorless heterotrophs
Most symbiotic and many parasitic
Well known for causing various diseases in humans
 Trypanosoma
- African sleeping sickness - Tsetse fly
- Chagas disease – Kissing bug
 Giardia lamblia
Most common flagellate in human digestive tract
Causes severe diarrhea
Cysts are transmitted in contaminated water
Beavers are important reservoir hosts
 Trichomonas vaginalis
- Sexually transmitted protist,
- Infects urogenital organs; a common cause of vaginitis
Giardia lamblia
Diversity of Protists:
Protists with Pseudopods
The Protists
Pseudopods form when cytoplasm streams forward in a
particular direction
Amoeboids (phylum Rhizopoda) are protists that move
and ingest their food with pseudopods
Phagocytize food
 Entamoeba histolytica - a parasite of the human colon;
- Causes amoebic dysentery
- Can be fatal
Foraminiferans (phylum Foraminifera) and radiolarians
(phlyum Actinopoda)
Both have a skeleton (test) of either calcite or silica
Protists with Pseudopods
The Protists
Diversity of Protists:
The Ciliates – Phylum Ciliophora
Ciliates (phylum Ciliophora) are among the most
complex of the protozoans
Hundreds of cilia beat in coordinated rhythm
Most are holozoic, swallowing food whole
Divide by transverse binary fission during asexual
Two nuclei of differing types
- Micronucleus – Heredity
- Macronucleus – Metabolism
The Protists
Diversity of Protists:
The Sporozoans – Phylum Apicomplexa
Nonmotile obligate parasites
Most serious parasitic disease of human is
Plasmodium spp
- Kills 3,000,000 people each year
- Transmitted by mosquito
- Humans get from cats
- Causes birth defects and mental retardation when
pregnant mom exposed
Life Cycle of Plasmodium vivax
Diversity of Protists:
Slime Molds
The Protists
Plasmodial Slime Molds - Phylum Myxomycota
Body in the form of a plasmodium
- Diploid, multinucleated, cytoplasmic mass
- Enveloped by a slimy sheath
Eventually produces sporangium which in turn
produces spores
Cellular Slime Mold - Phylum Acrasiomycota
Body in the form of individual amoeboid cells
Later aggregate into pseudoplasmodium which
then forms sporangium & spores
Plasmodial Slime Molds
The Protists
Diversity of Protists:
Water Molds - Phylum Oomycota
Most live in the water
Phylum name refers to the enlarged tips (called
oogonia) where eggs are produced
Body filamentous, appearing like true Fungi
Cell walls largely of cellulose rather than chitin
The organism is diploid (not haploid as in the
Phytophthora infestans caused the 1840’s potato
famine in Ireland
Saprolegnia is often seen as a white, cotton-like
coating on dead aquarium fish
Water Mold
The Protists
Protist Biology
Protist Diversity, cont.
Protist Evolution
Protist Diversity
Green Algae
Red Algae
Brown Algae
Slime Molds
Water Molds
Ending Slide Chapter 22
The Protists