CHAPTER 11
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Transcript of CHAPTER 11
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CHAPTER 11
Unicellular Eukaryotes:Protozoan
Groups
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EMERGENCE OF EUKARYOTESCellular Symbiosis First evidence of life
Dates to 3.5 billion years agoFirst cells were bacteria-like
Origin of complex eukaryote cellsMost likely symbiosis among prokaryotic cells
Changed the prokaryote that was “eaten” into an organelle: Primary endosymbiosis
Aerobic bacteria “eaten” by bacteria May have become mitochondria found in most
modern eukaryotic cells “Eaten” photosynthetic bacteria evolved into
chloroplasts Descendants in green algae lineage gave rise to
multicellular plants
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EMERGENCE OF EUKARYOTES Protozoa
Lack a cell wallHave at least one motile stage in life cycleMotile- moving
Most ingest (eat) their food Other groups originated by
Secondary endosymbiosis One eukaryotic cell “ate” another eukaryotic cell
Latter became transformed into an organelle
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EMERGENCE OF EUKARYOTES Protozoans
Carry on all life activities within a single cell
Can survive only within narrow environmental ranges
Very important ecologicallyAt least 10,000 species of protozoa
are symbiotic in or on other plants or animalsRelationships may be mutualistic, commensalistic, or parasitic
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HOW DO WE DEFINE PROTOZOAN GROUPS? Heterotrophic protozoa obtain organic
molecules synthesized by other organismsPhagotrophs (holozoic feeders)
Feed on visible particlesOsmotrophs (saprozoic feeder)
Feed on soluble food Mode of nutrition employed by
unicellular organismsOften variable and opportunistic
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HOW DO WE DEFINE PROTOZOAN GROUPS? Mode of locomotion
Used in the past to distinguish three of the four classes of the phylum Protozoa
Society of Protozoologists (1980) published a new classification with seven separate phyla
Molecular analyses have given scientists new insight into protozoan relationships.
There may be 250,000 protozoan species
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FORM AND FUNCTION
LocomotionCilia and flagella
Both called undulipodiaCilia : Propel water parallel
to the cell surface Flagella : Propel water parallel
to the flagellum axis
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11-11
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FORM AND FUNCTION 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 FormWhole body moves rather than sending out arms
Filopodia Thin extensions containing only ectoplasm
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FORM AND FUNCTION How Pseudopodia Work
EndoplasmContains nucleus and cytoplasmic organelles
EctoplasmMore transparent (hyaline)Contains bases of cilia or flagellaOften more rigid Appears granular
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FORM AND FUNCTIONA lobopodium forms by extending
ectoplasm (hyaline cap)Endoplasm flows into hyaline cap
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FORM AND FUNCTIONFunctional Components of Protozoan Cells Nucleus
Membrane bound organelleContains DNA in the form of
chromosomesChromatin often clumps leaving
clear areasNucleoli are often present
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FORM AND FUNCTIONNutrition Holozoic nutrition implies phagocytosis
In folding of cell membrane surrounds food particle
Then pinches offFood particle contained in
intracellular vesicleFood vacuole (phagosome)
Lysosomes fuse (binds) with phagosome and release enzymes
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FORM AND FUNCTION Digested products absorbed across vacuole
membrane Undigestible material released to outside by
exocytosis
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FORM AND FUNCTIONExcretion and Osmoregulation Excretion of metabolic wastes is by
diffusion Primary end product of nitrogen
metabolism Ammonia
Contractile vacuoles fill and empty to maintain osmotic balanceWater enters by osmosis
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FORM AND FUNCTIONReproduction 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
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FORM AND FUNCTIONMultiple fission (schizogony)
Cytokinesis (part of mitosis) preceded by several nuclear divisions
May individuals formed simultaneously If union of gametes precedes multiple fission Called sporogony
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FORM AND FUNCTION All of above accompanied by some
form of mitosisMitosis in protozoa divisions varies
from other mitosis Nuclear membrane often persistsCentrioles not observed in ciliates
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FORM AND FUNCTION Sexual Processes
All protozoa reproduce asexuallySome exclusively
Sexual reproduction also occurs widely among protozoaMay precede phases of asexual reproduction
Isogametes Gametes look alike
AnisogametesGametes are dissimilarCharacteristic of most species
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FORM AND FUNCTIONMeiosis
May occur during or just before gamete formation
In other groups, meiosis occurs after fertilization (zygotic meiosis)
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FORM AND FUNCTION Fertilization of one gamete by another
Syngamy Some sexual phenomena do not involve
syngamyAutogamy
Gamete nuclei form by meiosis Fuse to form a zygote inside the parent organism
ConjugationGamete nuclei exchanged between paired organisms
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MAJOR PROTOZOAN TAXA Phyla Retortamonada and Diplomonads
Divided into 2 exclusive clades: Retortamonds and Diplomonads
Retortamonds Include commensal and parasitic unicellsLack mitochondria and Golgi bodies
Diplomonads Lack mitochondria
Mitochondrial genes occur in the cell nucleus
Absence of mitochondria may be a secondary change
Giardia inhabit the digestive tract of humans, birds, and amphibians
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MAJOR PROTOZOAN TAXAPhylum Euglenozoa
Generally considered as monophyletic
Have a series of longitudinal microtubules Stiffen the cell membrane into a pellicle
Two subphylumsSubphylum Euglenida
Chloroplasts surrounded by a double membrane
Secondary endosymbiosis
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MAJOR PROTOZOAN TAXASubphylum Kinetoplasta Have kinetoplastids: round DNA Zooflagellates
Lack chromoplastsHolozoic or saprozoic nutritionMost are symbioticTrypanosoma
Important genus of protozoan parasitesSome not pathogenic*Affects birds, fish, amphibians, mammals. Can be passed by insects to humans.
• African sleeping sickness
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MAJOR PROTOZOAN TAXAPhylum Ciliophora
Ciliates are the most diverse and specialized protozoans
Larger than most other protozoaMost free-living, some commensal
and parasiticUsually solitaire and motileMost free-living in freshwater or
marine habitats
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Phylum CilliophoraCilia
Arranged in rowsPropel food to the cytopharynxFused cilia (cirri) used in locomotion
Most are holozoic
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MAJOR PROTOZOAN TAXA Suctorians
Ciliates that paralyze their prey and
Ingest contents through tube-like tentacles
Trichocysts and toxicysts in someExpel long thread-like structures when stimulated
Believed to be defensive mechanism
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EndoparasitesHosts are in many animal phylaGametes may be flagellated
The life cycle usually includes both sexual and asexual stagesInvertebrate may be an intermediate
host During life cycle
Form a spore (oocyst) Infective in the next host Protected by a resistant coat
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MAJOR PROTOZOAN TAXA Plasmodium: The Malarial Organism
Most important infectious disease of humans
Four species infect humansEach produces different clinical symptoms
Anopheles mosquitoes carry all forms
Female injects the Plasmodium present in her saliva