1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 17 Evolution of Protists

2. Protists May Represent the Oldest Eukaryotic Cells 17-2

3. 17.1 Eukaryotic organelles probably arose by endosymbiosis  Protists (kingdom Protista) are eukaryotes  Endosymbiotic theory - at least mitochondria and chloroplasts are derived from independent prokaryotic cells 17-3

4. Figure 17.1 Origin of mitochondria (above) and chloroplasts (below) 17-4

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. Figure 17.2 Protist diversity 17-6

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. Figure 17.3 Proposed evolutionary tree of protists (blue branches) based on DNA and RNA sequencing 17-8

9. Protozoans Are Heterotrophic Protists with Various Means of Locomotion 17-9

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. Figure 17.4 Euglena, a flagellate 17-11

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. Figure 17.5A Amoeba proteus, an amoeboid 17-13

14. Figure 17.5B Foraminiferans, such as Globigerina, built the White Cliffs of Dover, England 17-14

15. Figure 17.5C Radiolarian tests 17-15

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. Figure 17.6A Paramecium, a ciliate 17-17

18. Figure 17.6B During conjugation, two paramecia first unite at oral areas 17-18

19. Figure 17.6C Stentor, a ciliate 17-19

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. Figure 17.7 Life cycle of Plasmodium vivax, the cause of one type of malaria 17-21

22. Some Protists Have Moldlike Characteristics 17-22

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. 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. Figure 17.8 Life cycle of plasmodial slime molds 17-25

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. 17-27

28. Algae Are Photosynthetic Protists of Environmental Importance 17-28

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. Figure 17.9A Cyclotella, a diatom. Diatoms live in “glass houses” because the outer visible valve, which fits over the smaller inner valve, contains silica 17-30

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. Figure 17.9B Gonyaulax, a dinoflagellate. This dinoflagellate is responsible for the poisonous “red tide” that sometimes occurs along the coasts 17-32

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. Figure 17.10A Chondrus crispus, a red alga 17-34

35. Figure 17.10B Rockweed, Fucus, a brown alga 17-35

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. Figure 17.11A Reproduction in Chlamydomonas, a motile green alga 17-37

38. Figure 17.11B Cell anatomy and conjugation in Spirogyra, a filamentous green alga 17-38

39. Figure 17.11C Volvox, a colonial green alga 17-39

40. Figure 17.11D Ulva, a multicellular alga 17-40

41. Figure 17.11E Chara, a stonewort 17-41

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. Figure 17.12A Haploid life cycle 17-43

44. Figure 17.12B Alternation of generations 17-44

45. Figure 17.12C Diploid life cycle 17-45

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