Transcript A diversity of protists use pseudopodia for movement and feeding

Lecture 2 Biology 1002
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Objectives
1)
Examine an example of a heterotrophic protist , Amoeba, that
use pseudopodia for movement and feeding.
2)
Examine the plasmodial slime molds (Myxogastrida) and their
relation between their biology and their ecology.
A diversity of protists use pseudopodia for
movement and feeding
• Three groups of protists use pseudopodia,
cellular extensions, to move and often to
feed.
– Most species are heterotrophs that actively
hunt bacteria, other protists, and detritus.
– Other species are symbiotic, including some
human parasites.
– Little is known of their phylogenetic
relationships to other protists and they
themselves are distinct eukaryotic lineages.
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• Rhizopoda are all unicellular and use
pseudopodia to move and to feed.
• Pseudopodium emerge from anywhere in
the cell surface.
– To move, an amoeba extends a pseudopod,
anchors its tip, and then streams more
cytoplasm into the pseudopodium.
Amoeba sp.
Fig. 28.26
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• Amoeboid movement is driven by changes
in microtubules and microfilaments in the
cytoskeleton.
• Pseudopodia activity is not random but in
fact directed toward food.
• In some species pseudopodia extend out
through openings in a protein shell around
the organism.
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• Amoebas inhabit freshwater and marine
environments and maybe also abundant in
soils
• Most species are free-living heterotrophs.
• Some are important parasites.
– These include Entamoeba histolytica which
causes amoeboid dysentery in humans.
• These organisms spread via contaminated drinking
water, food, and eating utensils.
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• The plasmodial slime molds (Myxogastrida) are
brightly pigmented, heterotrophic organisms.
• The feeding stage is an amoeboid mass, the
plasmodium, that may be several centimeters in
diameter.
• The plasmodium is
not multicellular,
but a single mass
of cytoplasm with
multiple nuclei.
Fig. 28.29
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• The diploid nuclei undergo synchronous mitotic
divisions, perhaps thousands at a time.
• Within the cytoplasm, cytoplasmic streaming
distributes nutrients and oxygen throughout the
plasmodium.
• The plasmodium phagocytises food particles from
moist soil, leaf mulch, or rotting logs.
• If the habitat begins to dry or if food levels drop,
the plasmodium differentiates into stages that lead
to sexual reproduction.
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• The cellular slime molds (Dictyostelida) straddle
the line between individuality and multicellularity.
• The feeding stage consists of solitary cells.
• When food is scarce, the cells form an aggregate
(“slug”) that functions as a unit.
• Each cell retains its identity in the aggregate.
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Fig. 28.30
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The dominant stage in a cellular slime mold is the
haploid stage.
• Aggregates of amoebas form fruiting bodies that
produce spores in asexual reproduction.
• Most cellular slime molds lack flagellated stages.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Slime molds and water molds maybe thought to resemble
fungi, but they are not closely related.
Any resemble is analogous not homologous.
What does this mean?