CHAPTER 11

1. CHAPTER 11 Unicellular Eukaryotes: Protozoan Groups

3. 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: Primaryendosymbiosis • 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

4. 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

5. 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

7. 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

9. 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 classificationwith seven separate phyla • Molecular analyses have given scientists new insight into protozoan relationships. • There may be 250,000 protozoan species

10. Form and Function Locomotion Cilia and flagella Both called undulipodia Cilia : Propel water parallel to the cell surface Flagella : Propel water parallel to the flagellum axis

13. 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 Form • Whole body moves rather than sending out arms • Filopodia • Thin extensions containing only ectoplasm

14. Form and Function • How Pseudopodia Work • Endoplasm • Contains nucleus and cytoplasmic organelles • Ectoplasm • More transparent (hyaline) • Contains bases of cilia or flagella • Often more rigid • Appears granular

15. Form and Function • A lobopodium forms by extending ectoplasm (hyaline cap) • Endoplasm flows into hyaline cap

16. Form and Function Functional Components of Protozoan Cells • Nucleus • Membrane bound organelle • Contains DNA in the form of chromosomes • Chromatin often clumpsleaving clear areas • Nucleoliare often present

17. 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

18. Form and Function • Digested products absorbed across vacuole membrane • Undigestible material released to outside by exocytosis

19. Form and Function 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

21. Form and Function 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

24. 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

25. 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

26. Form and Function • 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

27. Form and Function • Meiosis • May occur during or just before gamete formation • In other groups, meiosis occurs after fertilization (zygotic meiosis)

28. 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

29. 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 inhabitthe digestive tract of humans, birds, and amphibians

31. Major Protozoan Taxa 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

32. Major Protozoan Taxa 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

33. 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

34. Phylum Cilliophora • Cilia • Arranged in rows • Propel food to the cytopharynx • Fused cilia (cirri) used in locomotion • Most are holozoic

35. Major Protozoan Taxa • 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

36. 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

37. Major Protozoan Taxa • 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