Evolution of Protists


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Evolution of Protists

  1. 1. Chapter 17Evolution of Protists Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. Protists May Represent the Oldest Eukaryotic Cells 17-2
  3. 3. 17.1 Eukaryotic organellesprobably arose by endosymbiosis Protists (kingdom Protista) are eukaryotes  Endosymbiotic theory - at least mitochondria and chloroplasts are derived from independent prokaryotic cells 17-3
  4. 4. Figure 17.1 Origin of mitochondria (above) and chloroplasts(below) 17-4
  5. 5. 17.2 Protists are a diverse group Protists vary in size from microscopic to macroscopic exceeding 200 m in length  Most protists are unicellular, but they have attained a high level of complexity Asexual reproduction by mitosis is the norm in protists  Sexual reproduction generally occurs only in a hostile environment They are of enormous ecological importance  They are a major component of plankton  Organisms suspended in the water and are food for animals  Protists have symbiotic relationships from parasitism to mutualism 17-5
  6. 6. Figure 17.2 Protist diversity 17-6
  7. 7. APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES 17.3 How can the protists be classified? Lumping all the single-celled eukaryotes (protists) into a single kingdom is artificial  Does not represent evolutionary history 17-7
  8. 8. Figure 17.3 Proposedevolutionary tree ofprotists (blue branches)based on DNA and RNAsequencing 17-8
  9. 9. Protozoans AreHeterotrophic Protists with Various Means of Locomotion 17-9
  10. 10. 17.4 Protozoans called flagellates move by flagella Zooflagellates - thousands of species of mostly unicellular, heterotrophic protozoans that move with a flagellum  Many zooflagellates are symbiotic and some are parasitic Euglenoids include about 1,000 species of small (10–500 μm) freshwater unicellular organisms  One-third of all genera have chloroplasts; the rest do not  Those that lack chloroplasts ingest or absorb their food  Some do both  Euglena deces, an inhabitant of freshwater ditches and ponds can undergo photosynthesis as well as to ingest food 17-10
  11. 11. Figure 17.4Euglena, aflagellate 17-11
  12. 12. 17.5 Protozoans called amoeboids move by pseudopods Pseudopods - extensions that form when cytoplasm streams in a particular direction  May be zooplankton, microscopic suspended organisms that feed on other organisms Feed by phagocytosis, surrounding prey with pseudopods and digesting it in a food vacuole Foraminiferans and Radiolarians have shells called tests  Intriguing and beautiful  In foraminiferans the test is often multichambered  Deposits of foraminiferans formed the White Cliffs of Dover 17-12
  13. 13. Figure 17.5A Amoeba proteus, an amoeboid 17-13
  14. 14. Figure 17.5B Foraminiferans, such as Globigerina, built the WhiteCliffs of Dover, England 17-14
  15. 15. Figure 17.5C Radiolarian tests 17-15
  16. 16. 17.6 Protozoans called ciliates move by cilia Ciliates - approximately 8,000 species of unicellular protists  Range from 10 to 3,000 μm in size The most structurally complex and specialized of all protozoans  The majority are free-living  Several parasitic, sessile, and colonial forms exist When a paramecium feeds, food particles are swept down a gullet into food vacuoles Asexual reproduction  Ciliates divide by transverse binary fission Sexual reproduction involves conjugation 17-16
  17. 17. Figure 17.6A Paramecium, a ciliate 17-17
  18. 18. Figure 17.6B During conjugation, two paramecia first unite at oralareas 17-18
  19. 19. Figure 17.6C Stentor, a ciliate 17-19
  20. 20. 17.7 Protozoans called sporozoans are not motile Sporozoans - nearly 3,900 species  nonmotile, parasitic, spore-forming  Many sporozoans have multiple hosts One million people die each year from malaria  Widespread disease caused by four types of sporozoan parasites in the genus Plasmodium 17-20
  21. 21. Figure 17.7 Life cycle of Plasmodium vivax, the cause of one typeof malaria 17-21
  22. 22. Some Protists HaveMoldlike Characteristics 17-22
  23. 23. 17.8 The diversity of protists includes slime molds and water molds The Plasmodial Slime Molds  Exist as a plasmodium, a diploid, multinucleated, cytoplasmic mass  Enveloped by a slimy sheath creeping along, phagocytizing decaying plant material  During droughts, plasmodium develops many sporangia, spore producing reproductive structures  An aggregate of sporangia is called a fruiting body 17-23
  24. 24. Cellular Slime Molds Exist as individual amoeboid cells and are too small to be seen  Common in soil, feeding on bacteria and yeasts As the food supply runs out cells release a chemical that causes them to aggregate into a pseudoplasmodium  Eventually gives rise to a fruiting body 17-24
  25. 25. Figure 17.8 Lifecycle of plasmodialslime molds 17-25
  26. 26. Water Molds Water Molds  Usually live in water, where they form furry growths when they parasitize fishes or insects and decompose remains  Water molds have a filamentous body as do fungi, but their cell walls are largely composed of cellulose 17-26
  27. 27. 17-27
  28. 28. Algae Are Photosynthetic Protists of Environmental Importance 17-28
  29. 29. 17.9 The diatoms and dinoflagellates are significant algae in the oceans Diatoms (approximately 11,000 species) are free-living photosynthetic cells in aquatic and marine environments  Most numerous unicellular algae in the oceans and freshwater environments  Significant part of the phytoplankton, photosynthetic organisms suspended in the water  Serve as an important source of food and oxygen for heterotrophs Diatom Structure  Often compared to a hat box  Cell wall has two halves, or valves, with the larger valve acting as a “lid” that fits over the smaller valve 17-29
  30. 30. Figure 17.9A Cyclotella, a diatom. Diatoms live in “glass houses”because the outer visible valve, which fits over the smaller innervalve, contains silica 17-30
  31. 31. Dinoflagellates Dinoflagellates (about 4,000 species) are usually bounded by protective cellulose plates impregnated with silicates  Typically, the organism has two flagella:  One in a longitudinal groove with its distal end free  One in a transverse groove that encircles the organism  Important source of food for small animals in the ocean  Some are symbionts in the bodies of invertebrates  Corals usually contain large numbers of zooxanthellae  Some undergo a population explosion and cause “red tides” 17-31
  32. 32. Figure 17.9B Gonyaulax, a dinoflagellate. This dinoflagellate isresponsible for the poisonous “red tide” that sometimes occursalong the coasts 17-32
  33. 33. 17.10 Red algae and brown algae are multicellular Red algae (>5,000 multicellular species) living primarily in warm seawater  Some grow attached to rocks in the intertidal zone  Others can grow at depths exceeding 200 m  economically important  Produce agar, a gelatin-like product made primarily from the algae Gelidium and Gracilaria, used commercially and in the laboratory Brown algae (>1,500 species of seaweeds)  Range from small forms with simple filaments to large, multicellular forms that may reach 100 m in length  Majority of brown algae, like Fucus, live in cold ocean waters Multicellular forms of green, red, and brown algae are called seaweeds, a common term for any large, complex alga 17-33
  34. 34. Figure 17.10A Chondrus crispus, a red alga 17-34
  35. 35. Figure 17.10BRockweed, Fucus, abrown alga 17-35
  36. 36. 17.11 Green algae are ancestral to plants Green algae (Approximately 7,500 species)  Not always green  Some have an orange, red, or rust color  Inhabit a variety of environments  Oceans, freshwater, snowbanks, bark of trees, backs of turtles Lichen-symbiotic algal relationship with fungi Filaments - end-to-end chains of cells that form after cell division in only one plane  In some algae, the filaments are branched, and in others the filaments are unbranched Asexual Reproduction  Chlamydomonas produces 16 daughter cells still within the parent cell Sexual reproduction  Spirogyra undergoes conjugation, temporary union, during which cells exchange genetic material 17-36
  37. 37. Figure 17.11A Reproduction in Chlamydomonas, a motile green alga 17-37
  38. 38. Figure 17.11B Cell anatomy and conjugation in Spirogyra, afilamentous green alga 17-38
  39. 39. Figure 17.11C Volvox, a colonial green alga 17-39
  40. 40. Figure 17.11D Ulva, a multicellular alga 17-40
  41. 41. Figure 17.11E Chara, a stonewort 17-41
  42. 42. APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES 17.12 Life cycles among the algae have many variations Asexual Reproduction  When environment is favorable to growth, asexual reproduction is a frequent mode of reproduction among protists  Offspring are identical to parent Sexual Reproduction  More likely to occur among protists when the environment is changing and is unfavorable to growth  May produce individuals more likely to survive extreme environments Haploid life cycle  The zygote divides by meiosis to form haploid spores that develop into haploid individuals Alternation of generations  Diploid sporophyte produces haploid spores  Spore develops into a haploid gametophyte that produces gametes  Gametes fuse to form a diploid zygote that develops into sporophyte Diploid life cycle  Diploid individual produces haploid gametes by meiosis  Gametes fuse to form a diploid zygote 17-42
  43. 43. Figure 17.12A Haploid life cycle 17-43
  44. 44. Figure 17.12B Alternation of generations 17-44
  45. 45. Figure 17.12C Diploid life cycle 17-45
  46. 46. Connecting the Concepts: Chapter 17 Protists we study today are not expected to include the direct ancestors to fungi, plants, and animals  They may be related to the other eukaryotic groups by way of common ancestors that have not been discovered in the fossil record  May represent an adaptive radiation experienced by the first eukaryotic cell Mutualism is a powerful force that shaped the eukaryotic cell and also shapes all sorts of relationships in the living world All possible forms of reproduction and nutrition are present among the protists  Each of the other eukaryotic groups specializes in a particular type of reproduction and a particular method of acquiring needed nutrients 17-46