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Unicellular Eukaryotes:
CHAPTER 11 Unicellular Eukaryotes: Protozoan Groups
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Emergence of Eukaryotes
Cellular Symbiosis First evidence of life Dates to 3.5 billion years ago First cells were bacteria-like Origin of complex eukaryote cells Most 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 wall Have at least one motile stage in life cycle Motile- 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 ecologically At least 10,000 species of protozoa are symbiotic in or on other plants or animals Relationships may be mutualistic, commensalistic, or parasitic
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How do we define protozoan groups?
Heterotrophic protozoa obtain organic molecules synthesized by other organisms Phagotrophs (holozoic feeders) Feed on visible particles Osmotrophs (saprozoic feeder) Feed on soluble food Mode of nutrition employed by unicellular organisms Often 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 Cilia and flagella Both called undulipodia
Locomotion Cilia and flagella Both called undulipodia Cilia : Propel water parallel to the cell surface Flagella : Propel water parallel to the flagellum axis
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Form and Function Pseudopodia Lobopodia Limax Form Filopodia
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
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Form and Function Endoplasm
How Pseudopodia Work Endoplasm Contains nucleus and cytoplasmic organelles Ectoplasm More transparent (hyaline) Contains bases of cilia or flagella Often more rigid Appears granular
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Form and Function A lobopodium forms by extending ectoplasm (hyaline cap) Endoplasm flows into hyaline cap
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Form and Function Nucleus Membrane bound organelle
Functional Components of Protozoan Cells Nucleus Membrane bound organelle Contains DNA in the form of chromosomes Chromatin often clumps leaving clear areas Nucleoli are often present
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Holozoic nutrition implies phagocytosis
Form and Function Nutrition Holozoic nutrition implies phagocytosis In folding of cell membrane surrounds food particle Then pinches off Food particle contained in intracellular vesicle Food 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 Function Excretion of metabolic wastes is by diffusion
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
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Form and Function Asexual Processes Fission Budding Reproduction
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 Function Multiple 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 mitosis
Mitosis in protozoa divisions varies from other mitosis Nuclear membrane often persists Centrioles not observed in ciliates
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Form and Function All protozoa reproduce asexually
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
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Form and Function Meiosis
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 syngamy Autogamy Gamete nuclei form by meiosis Fuse to form a zygote inside the parent organism Conjugation Gamete 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 unicells Lack 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 Taxa Two subphylums
Phylum Euglenozoa Generally considered as monophyletic Have a series of longitudinal microtubules Stiffen the cell membrane into a pellicle Two subphylums Subphylum Euglenida Chloroplasts surrounded by a double membrane Secondary endosymbiosis
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Major Protozoan Taxa Have kinetoplastids: round DNA Zooflagellates
Subphylum Kinetoplasta Have kinetoplastids: round DNA Zooflagellates Lack chromoplasts Holozoic or saprozoic nutrition Most are symbiotic Trypanosoma Important genus of protozoan parasites Some not pathogenic *Affects birds, fish, amphibians, mammals. Can be passed by insects to humans. African sleeping sickness
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Major Protozoan Taxa Phylum Ciliophora Ciliates are the most diverse and specialized protozoans Larger than most other protozoa Most free-living, some commensal and parasitic Usually solitaire and motile Most free-living in freshwater or marine habitats
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Propel food to the cytopharynx Fused cilia (cirri) used in locomotion
Phylum Cilliophora Cilia Arranged in rows Propel food to the cytopharynx Fused cilia (cirri) used in locomotion Most are holozoic
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Major Protozoan Taxa Ciliates that paralyze their prey and
Suctorians Ciliates that paralyze their prey and Ingest contents through tube-like tentacles Trichocysts and toxicysts in some Expel long thread-like structures when stimulated Believed to be defensive mechanism
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Endoparasites Hosts are in many animal phyla Gametes may be flagellated The life cycle usually includes both sexual and asexual stages Invertebrate 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 Most important infectious disease of humans
Plasmodium: The Malarial Organism Most important infectious disease of humans Four species infect humans Each produces different clinical symptoms Anopheles mosquitoes carry all forms Female injects the Plasmodium present in her saliva
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