protozoan groups unicellular...
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CHAPTER 11
Protozoan Groups Unicellular Eukaryotes
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Cellular Symbiosis Origin of complex eukaryote cells
Most likely symbiosis among prokaryotic cells Modification of engulfed prokaryote into an organelle:
Primary endosymbiosis Aerobic bacteria engulfed by bacteria May have become mitochondria found in most modern
eukaryotic cells Engulfed photosynthetic bacteria evolved into
chloroplasts Descendants in green algae lineage gave rise to
multicellular plants
Emergence of Eukaryotes
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Protozoa Lack a cell wall Have at least one motile stage in life cycle Most ingest their food
Other groups apparently originated bySecondary endosymbiosis
One eukaryotic cell engulfed another eukaryotic cell
Latter became transformed into an organelle
Emergence of Eukaryotes
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Protozoans Carry on all life activities within a single
cell Can survive only within narrow
environmental ranges Very important ecologically At least 10,000 species of protozoa are
symbiotic in or on other plants or animalsRelationships may be mutualistic,
commensalistic, or parasitic
Emergence of Eukaryotes
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Heterotrophic protozoaobtain organic molecules synthesized by other organisms Phagotrophs (holozoic
feeders)Feed on visible
particles Osmotrophs (saprozoic
feeder)Feed on soluble food
How do we define protozoan groups?
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Mode of locomotion Used in the past to distinguish
three of the four classes of the phylum Protozoa
Cilia and flagellaBoth called undulipodiaCilia
Propel water parallel to the cell surface
Flagella Propel water parallel to
the flagellum axis
How do we define protozoan groups?
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Morphologically the same
Contain 9 pairs of microtubules arranged around a central pair Arrangement called
an axoneme Covered by
plasma membrane
Found in all motile flagella and cilia in animal kingdom
Form and Function
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Pseudopodia Primary means of locomotion in
Sarcodina, many flagellates and ameboid cells of many invertebrates and vertebrates
Lobopodia Large blunt extensions of the
cell body Contains both endoplasm and
ectoplasm Limax Form
Whole body moves rather than sending out arms
Filopodia Thin extensions containing
only ectoplasm Reticulopodia
Repeatedly rejoin to form a netlike mesh
Form and Function
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How Pseudopodia Work Endoplasm
Contains nucleus and cytoplasmic organelles
EctoplasmMore transparent (hyaline)Contains the base for each cilia or
flagellaOften more rigid Most appears granular (except hyline
cap)
Form and Function
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A lobopodium forms by extending ectoplasm (hyaline cap)
Endoplasm flows into hyaline cap Flowing endoplasm contains actin
subunits with proteins that prevent actin from polymerizing
Lipids release the actin to polymerize Actin filaments cross-link by another actin-
binding protein to form semisolid gel
Form and Function
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Functional Components of Protozoan Cells
Nucleus Membrane bound organelle Contains DNA in the form of
chromosomes Chromatin often clumps
irregularly leaving clear areas Imparts a vesicular
appearance Nucleoli are often present Macronuclei of ciliates
Compact or condensed with no clear areas
Form and Function
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Mitochondria Involved in energy production
Golgi apparatus Part of the secretory system of the endoplasmic reticulum
Plastids Organelles containing a variety of photosynthetic pigments Perhaps added when a cyanobacterium was engulfed but not
digested Chloroplasts contain different types of chlorophylls
Extrusomes General term applied to membrane-bound organelles used to
extrude material from cell
Form and Function
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Nutrition Holozoic nutrition implies phagocytosis
Infolding of cell membrane surrounds food particle
Invagination pinches off Food particle contained in intracellular
vesicleFood vacuole (phagosome)
Lysosomes fuse with phagosome and release enzymes
Undigestible material released to outside by exocytosis
Form and Function
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In ciliates, site of phagocytosis called a cytostome Many have a point
for expulsion of wastes Cytopyge or
cytoproct Saprozoic feeding may
be by Pinocytosis Transport of solutes
across cell membrane
Form and Function
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Excretion and Osmoregulation
Excretion of metabolic wastes is by diffusion
Primary end product of nitrogen metabolism Ammonia
Contractile vacuoles fill and empty to maintain osmotic balance Water enters by
osmosis
Form and Function
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Reproduction Asexual Processes
Fission Produces more
individuals than other forms of reproduction
Binary fission is most common
Two identical individuals produced
Budding Occurs when a small
progeny cell (bud)pinches off from parent cell
Bud grows to adult size
Form and Function
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Multiple fission (schizogony) Cytokinesis preceded by several nuclear
divisions Many individuals formed simultaneously If union of gametes precedes multiple fission
Called sporogony
Form and Function
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Sexual Processes All protozoa reproduce asexually
Some exclusively Sexual reproduction also occurs widely
among protozoa May precede phases of asexual reproduction
Isogametes Gametes look alike
Anisogametes Gametes are dissimilar Characteristic of most species
Form and Function
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Fertilization Fertilization of one gamete by another
Syngamy Some sexual phenomena do not
involve syngamy Autogamy
Gamete nuclei form by meiosis Fuse to form a zygote inside the
parent organism Conjugation
Gamete nuclei exchanged between paired organisms
Form and Function
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Encystment and Excystment Unicellular forms amazingly successful in
extremely harsh conditions Related to the ability to form cysts
Dormant forms that shut down metabolism and have a resistant external covering (secreted by Golgi apparatus)
ExcystmentEscape from cysts when environmental
conditions are favorable
Form and Function
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Phylum Chlorophyta Flagellated, autotrophic,
single-celled algae such as Chlamydomonas, as well as colonial forms like Gonium and Volvox
Hollow ball of cells Each organism contains
thousands of cells Cells resembles a
euglenid: Nucleus, pair of
flagella, large chloroplast, and stigma
Most cells are somatic concerned with nutrition and locomotion
Major Protozoan Taxa
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Reproduction Asexual Reproduction
Repeated mitotic division form daughter colonies inside parent colony Rupture through wall to escape
Sexual Reproduction Cells differentiate into macrogametes and
microgametes Macrogametes (a.k.a egg)
Larger, fewer, and store food for nourishment of young organisms
Microgametes (a.k.a. sperm)Smaller and form bundles of flagellated
sperm that swim freely until they find an ovum
Major Protozoan Taxa
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Zygote Secretes a hard, spiny, protective shell and
overwinters In spring, repeated divisions allow it to break
out Asexual reproduction occur in the summer
Major Protozoan Taxa
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Phylum Euglenozoa Cell membrane is
stiffened into a pellicle Freshwater with
abundant vegetation Flagellum extends
anterior end Oval chloroplasts Stigma functions in
orientation to light Normally autotrophic, but
can make use of saprozoic nutrition
Major Protozoan Taxa
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Phylum Ciliophora Ciliates are the most
diverse and specializedprotozoans
Larger than most other protozoa
Most free-living, some commensal and parasitic
Usually solitaire and motile
Most free-living in freshwater or marine habitats
Major Protozoan Taxa
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Slipper shaped - Multinucleate At least one macronucleus and a
micronucleus Macronuclei
Metabolic and developmental functions
Micronuclei Involved in sexual
reproduction and give rise to macronuclei afterwards
Pellicle varies from a simple membrane to thickened armor
Cilia Arranged in rows Propel food to the
cytopharynx Fused cilia (cirri) used in
locomotion Most are holozoic
Major Protozoan Taxa
StentorVorticella
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Paramecium may be studied as a typical free-living ciliate Trichocysts present Cytostome leads to a tubular cytopharynx Fecal material discharged from the cytoproct 2 contractile vacuoles Body is elastic Binary fission Conjugation
Major Protozoan Taxa
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Amebas Found in fresh and salt water, and
moist soils Some planktonic, some require a
substratum Most reproduce by binary fission
Sporulation and budding are also seen
Nutrition is holozoic May form lobopodia, filopodia, or
rhizopodia Slow streams and ponds of clear
water Require a substratum
Major Protozoan Taxa
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