Protists
Chapter 35
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Endosymbiosis
•
Theory of endosymbiosis
proposes mitochondria
originated as symbiotic,
aerobic eubacteria.
 Each mitochondrian still
has its own genome in a
circular, closed molecule
of DNA.
- Divide by simple
fission.
 Directed by
nuclear genes.
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Classifying Protists
•
Protists are the most diverse of the four
kingdoms in the domain Eukarya.
 Artificial group of convenience.
- Single-celled organisms.
 Little consensus about protist
classification.
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General Biology of the Protists
Cell Surface
- Possess varied array of
cell surfaces.
Locomotor Organelles
- flagellular rotation
- pseudopodial movement
- Cilia (short hairs
covering the surface)
Cyst Formation
- Dormant form of a cell
with resistant outer
covering in which
metabolism is
essentially shut down.
Nutrition
Employ all forms but
chemoautotrophic.
-Phototrophs
-Heterotrophs
--Phagotrophs - Visible
food particles.
--Osmotrophs - Food
in soluble form.
Reproduction
Typically reproduce
asexually.
Sexual reproduction in
times of stress.
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Five Groups of Protists
•
Group according to shared characteristics:
 Presence/Absence of cilia or flagella.
 Presence and kinds of pigments.
 Type of Mitosis.
 Kinds of cristae in mitochondria.
 Molecular genetics of ribosomal S subunit.
 Inclusions
 Overall body form.
 Armor
 Modes of nutrition and movement.
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Heterotrophs with No Permanent Locomotion
•
•
Largest of the five general groups.
Three Principal Phyla
 Rhizopoda: Amoebas
- Move by pseudopods.
 Actinopoda: Radiolarians
- Secrete glassy exoskeletons.
 Foraminifera: Forams
- Pore-studded shells
 Cytoplasmic projections (podia)
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Photosynthetic Protists
•
Pyrrhophyta: Dinoflagellates
 Mostly unicellular photosynthetic organisms.
 Distinctive flagella, protective coats, and
biochemistry.
 Zooxanthellae
- Grow as symbionts within other cells
lacking characteristic cellulose plates and
flagella.
 Produce primarily by asexual cell division.
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Dinoflagellates
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Photosynthetic Protists
•
Euglenophyta: Euglenoids
 Most are freshwater.
 About one-third are autotrophic.
 Pellicle lies within membrane.
- Stigma - Light sensitive organ that aids in
orienting towards light.
 Euglena
- Two flagella attached to reservoir.
- Contain numerous chloroplasts.
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Photosynthetic Protists
•
Chrysophyta: Diatoms and Golden Algae
 Diatoms - Photosynthetic,unicellular
organisms with double shells of opaline
silica.
- Divided into radial and bilateral symmetry.
 Golden Algae - Named for yellow and brown
carotenoid and xanthophyll accessory
pigments in chloroplasts.
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Photosynthetic Protists
•
•
Rhodophyta: Red Algae
 Colors results from phycobilin pigment,
phycoerythrin.
- Great majority of species occur in sea.
- Interwoven filaments of cells.
Phaeophyta: Brown Algae
 Multicellular protists, almost exclusively
marine.
- Kelp forests.
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Photosynthetic Protists
•
Chlorophyta: Green Algae
 Extensive fossil record dating back 900
million years.
 Mostly aquatic
 Chlamydomonas is well-known genus.
- Probably represents primitive state.
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Heterotrophs with Flagella
•
•
Zoomastigophora: Zoomastigotes
 Unicellular, heterotrophic organisms highly
variable in form.
- Each has at least one flagellum.
 Includes genera Trypanosoma (African
Sleeping Sickness) and Crithidia, pathogens
of human and domestic animals.
Giardia lamblia - Hiker’s Diarrhea.
 Lives in upper intestine of host.
- Spread by infected fecal matter.
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Heterotrophs with Flagella
•
Ciliophora: Ciliates
 Most members have large numbers of cilia.
- Usually arranged in longitudinal rows or in
spirals around the body.
 Micronuclei (mutligene chromosomes) or
macronuclei (multiple copies of a certain
gene).
 Form vacuoles for ingesting food and
regulating water balance.
 Usually reproduce via transverse fission.
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Nonmotile Spore-Formers
•
Apiocomplexa: Sporozoans
 Nonmotile, spore-forming animal parasites.
 Complex life cycles that involve both
asexual and sexual phases.
 Malaria is caused by infection by sporozoan
Plasmodium.
- Three different stages of the Plasmodium
life cycle each produce different antigens,
and are sensitive to different antibodies.
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Heterotrophs With Restricted Mobility
•
Oomycota
 Comprise water molds, white rusts, and
downy mildews.
 All are parasites or saprobes.
 Life cycles characterized by gametic
meiosis and a diploid phase.
- Motile spores, zoospores, bear two
unequal flagella.
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Heterotrophs With Restricted Mobility
•
•
Acrasiomycota: Cellular Slime Molds
Individual organisms behave as separate
amobeas, moving through soil or other
substrate and ingesting bacteria.
 Individual organisms aggregate and form
moving mass “slug”, that eventually
transforms into a spore-containing mass
sorocarp.
- Develops stalk and releases spores.
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Heterotrophs With Restricted Mobility
•
Myxomycota: Plasmodial Slime Molds
 Stream along as a non-walled,
multinucleate mass of cytoplasm,
plasmodium.
- Produces sporangium during times of
resource shortage.
- Forms spores that quickly undergo
meiosis.
 Multiple nuclei in each spore
disintegrate, leaving each spore with a
single haploid nucleus.
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Copyright © McGraw-Hill Companies Permission required for reproduction or display
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