2. Unicellular Eukaryotes (protozoans)
Origins of eukaryotes
- First evidence for life 3.5 bya
- These organisms were prokaryotes
- Eukaryotes arose by symbiogenesis (aka, endosymbiosis)
- whereby, one cell engulfed another
- Alpha-protobacterium derived energy from carbon compounds
became mitochondria
- Cyanobacterium derived energy from sunlight became plastid,
specifically chloroplast
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3. Unicellular Eukaryotes (protozoans)
Protozoan
- Literally “first animal-like organisms in time”
- Not animals, but with animal features
- Lack cell wall
- At least one motile stage during life
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6. Unicellular Eukaryotes (protozoa)
General characteristics
- Many species are symbiotic (living with other species)
- Mutualistic, commensalistic, or parasitic
- Movement - once used for classification; no longer
- Flagella, cilia, and pseudopodia
- No germ layers, tissues, or organs present
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7. Unicellular Eukaryotes (protozoa)
- Movement - once used for
classification; no longer
- Flagella, cilia, and pseudopodia
- Flagella - generally few, long,
and propel water parallel to the
main axis of the flagella
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8. Unicellular Eukaryotes (protozoa)
- Movement - once used for
classification; no longer
- Flagella, cilia, and pseudopodia
- Cilia - many, short, and propel
water parallel to surface on
which its attached
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9. Unicellular Eukaryotes (protozoa)
- Movement - once used for
classification; no longer
- Flagella, cilia, and pseudopodia
- Pseudopodia - extensions of
the cytoplasm
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10. Unicellular Eukaryotes (protozoa)
Microstructure of cilia and flagella
- 9+2 arrangement of microtubules (= axoneme)
- Where axoneme enters body, a plate of 9 microtubules triplets (= kinetosome)
- Identical to centrioles that organize the mitotic spindle
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11. Unicellular Eukaryotes (protozoa)
Functional components
- Nucleus
- Genetic material on chromosomes; communicates with cells via pores; nucleoli present,
ciliates with two nuclei (macro and micro)
- Mitochondria
- Recovers energy from carbon bonds
- Golgi complex
- Participates in intracellular digestion
- Plastids
- Photosynthetic elements
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12. Unicellular Eukaryotes (protozoa)
Nutrition
- Phagocytosis - food particle enveloped by cell
- Creates a food vacuole; lysosomes will fuse with vacuole and excrete digestive enzymes
- Digested products are absorbed across vacuole membrane
- In some groups the cite of phagocytosis is fixed; not in others.
- Saprozoic feeding - absorb foods from the environment
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13. Unicellular Eukaryotes (protozoas)
Homeostatic functions and structures
- No circulatory, respiratory, or
excretory system present
- Diffusion in all cases is sufficient
- No temperature regulation
- Osmoregulation by contractile
vacuole
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14. Unicellular Eukaryotes (protozoa)
Reproduction
- Sexual reproduction in most; no
embryological development
- Both syngamy and autogamy are
known
- Asexual reproduction common
- Binary fission
- Schizogony
- Budding
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15. Unicellular Eukaryotes (protozoa)
Phylum Parabasala
- Approximately 400 species
- Presence of axostyle is diagnostic
- Have many flagella
- Some are of medical and veterinary importance
- E.g., Trichomonas, Tritrichomonas
- Trichomonas vaginalis STD - in humans
- Tritrichomonas foetus infertility and spontaneous abortion in cattle
- Trichomonas gallinae parasite of pigeons/doves and other birds
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17. Unicellular Eukaryotes (protozoa)
Phylum Euglenozoa
- Pellicle is present
- Divided into two subphyla -
Euglenida and Kinetoplasta
- Euglenida are free-living; Kinetoplasta
are parasitic
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18. Unicellular Eukaryotes (protozoa)
Phylum Euglenozoa
- Euglenida
- Chloroplasts with chlorophyll b
- Live in freshwater
- Single, long flagellum
- Often with red stigma (i.e., eyespot)
- Normally autotrophic, but can become
saprozoic if held in darkness
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19. Unicellular Eukaryotes (protozoa)
Phylum Euglenozoa
- Kinetoplasta
- Some important parasites
- Flagella and undulating membrane for locomotion
- Trypanosoma brucei, transmitted by tsetse fly causes African sleeping sickness
- T. cruzi, transmitted by Triatoma, causes Chagas disease
- Leishmania spp., transmitted by sand flies, causes leishmaniasis
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20. Unicellular Eukaryotes (protozoa)
Phylum Ciliophora
- Many species have bodies entirely covered with cilia
- Others have cilia near oral region only
- Generally much larger than other protozoans
- Most are free-living, some commensals, some
parasitic
- Great variation in body form
- Always multinucleate (macro and micronucleus)
- May possess trichocysts or toxocysts
- Defense and offense
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22. Unicellular Eukaryotes (protozoa)
Phylum Dinoflagellata
- Important primary producers in marine
ecosystems
- About half are autotrophic
- Typically with two flagella
- Found in grooves
- Body often covered in plates
- Important mutualism with corals as
zooxanthellae
- Without zooxanthellae, corals don’t thrive
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24. Unicellular Eukaryotes (protozoa)
Phylum Apicomplexa
- Almost all are endoparasitic
- Presence of unique organelles, the apical complex, is diagnostic
- Hypothesized to be useful for penetrating host’s cells and tissues
- Locomotor organelles are less known; pseudopodia is some reproductive
stages.
- Plasmodium spp. responsible for causing malaria
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26. Unicellular Eukaryotes (protozoa)
Phylum Foraminifera
- Testate amoebas
- Pseupodia as reticulopodia
- Most are benthic
- Tests are chambered and made of calcium carbonate (most)
- Dead individuals make up ocean floor ooze
- Important for limestone and chalk
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29. Unicellular Eukaryotes (protozoa)
Phylum “Radiolaria”
- Testate amoebas
- Pseudopodia as axopodia
- Inhabit surface waters
- Tests may be silicate
- Form into chert
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30. Unicellular Eukaryotes (protozoa)
Phylum Viridiplantae
- Belongs in clade Plantae with familiar green
plants and algaes
- Unicellular, colonial, and multicellualr
- Multicellular implies cellular division of labor
- Members are photosynthetic
- Use flagella to move
- Cells either zooids or daughter colonies
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31. Unicellular Eukaryotes (protozoa)
Phylum Amoebozoa
- Naked and testate forms
- Some notable disease causing
species
- Acanthamoeba castellanii - kills cells of
cornea, spread through improperly
disinfected contact lenses.
- Entamoeba histolytica - amoebic
dysentery
- Naegleria fowleri - brain-eating amoeba
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32. Unicellular Eukaryotes (protozoa)
Phylum Opisthokonta
- Also a clade which contains
animals, fungi, and some
unicellular eukaryotes
- Choanoflagellates are solitary or
colonial
- Choanoflagellate morphology is similar
to the collar cells of sponges
- Thus, they are hypothesized to
represent a sister taxa to the
animals.
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