Chapter 28

1. Chapter 28 Protists

2. Explain the process of endosymbiosis and state what living organisms are likely relatives of mitochondria and plastids Endosymbiosis is the process in which certain unicellular organisms engulf other cells which becomes endosymbionts and ultimately organelles in the host cell. For example: • The first eukaryotes acquired mitochondria by engulfing an aerobic prokaryote (alpha proteobacterium) that evolved into mitochondria • Later heterotrophic eukaryotes acquired an additional endosymbiont (photosynthetic cyanobacterium) that evolved into plastids

3. Overview: Living Small • Even a low-power microscope can reveal a great variety of organisms in a drop of pond water • Protist is the informal name of the kingdom of mostly unicellular eukaryotes • Advances in eukaryotic systematics have caused the classification of protists to change significantly • Protists constitute a paraphyletic group, and Protista is no longer valid as a kingdom

5. Fig. 28-01 1 µm

6. Concept 28.1: Most eukaryotes are single-celled organisms • Protists are eukaryotes and thus have organelles and are more complex than prokaryotes • Most protists are unicellular, but there are some colonial and multicellular species

7. Structural and Functional Diversity in Protists • Protists exhibit more structural and functional diversity than any other group of eukaryotes • Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell

8. Protists, the most nutritionally diverse of all eukaryotes, include: • Photoautotrophs, which contain chloroplasts • Heterotrophs, which absorb organic molecules or ingest larger food particles • Mixotrophs, which combine photosynthesis and heterotrophic nutrition • Protists can reproduce asexually or sexually, or by the sexual processes of meiosis and syngamy(conjugation and an alternation of generations)

9. Endosymbiosis in Eukaryotic Evolution • There is now considerable evidence that much protist diversity has its origins in endosymbiosis • Mitochondria evolved by endosymbiosis of an aerobic prokaryote • Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium

10. Fig. 28-02-2 Plastid Dinoflagellates Secondary endosymbiosis Apicomplexans Red alga Cyanobacterium Primary endosymbiosis Stramenopiles Plastid Heterotrophic eukaryote Secondary endosymbiosis Over the course of evolution, this membrane was lost. Euglenids Secondary endosymbiosis Green alga Chlorarachniophytes

11. The plastid-bearing lineage of protists evolved into red algae and green algae • On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote

12. Five Supergroups of Eukaryotes • It is no longer thought that amitochondriates (lacking mitochondria) are the oldest lineage of eukaryotes • Our understanding of the relationships among protist groups continues to change rapidly • One hypothesis divides all eukaryotes (including protists) into five supergroups

13. Fig. 28-03a Diplomonads Excavata Parabasalids Euglenozoans Dinoflagellates Apicomplexans Alveolates Ciliates Chromalveolata Diatoms Golden algae Brown algae Stramenopiles Oomycetes Chlorarachniophytes Rhizaria Forams Radiolarians Red algae Chlorophytes Archaeplastida Green algae Charophyceans Land plants Slime molds Gymnamoebas Amoebozoans Entamoebas Nucleariids Unikonta Fungi Opisthokonts Choanoflagellates Animals

14. Fig. 28-UN6

15. Giardia intestinalis

16. Diatom diversity

17. Globigerina

18. Volvox (green alga)

19. Amoeba

20. Fig. 28-16-2 Sporangia 10 cm MEIOSIS Sporophyte (2n) Zoospore Female Developing sporophyte Gametophytes (n) Zygote (2n) Mature female gemetophyte (n) Male Egg FERTILIZATION Sperm Key Haploid (n) Diploid (2n)

21. Concept 28.7: Protists play key roles in ecological relationships • Protists are found in diverse aquatic environments • Protists often play the role of symbiont or producer

22. Symbiotic Protists • Some protist symbionts benefit their hosts • Dinoflagellates (Alveolates) nourish coral polyps that build reefs • Hypermastigotes (Parabasalids)digest cellulose in the gut of termites

23. Some protists are parasitic • Plasmodium is a dinoflagellate that causes malaria • Pfesteria shumwayae is a dinoflagellate that causes fish kills • Phytophthora ramorum is a oomycete that causes sudden oak death

24. Photosynthetic Protists • Many protists are important producers that obtain energy from the sun • In aquatic environments, photosynthetic protists and prokaryotes are the main producers • The availability of nutrients can affect the concentration of protists

25. Fig. 28-28 Other consumers Herbivorous plankton Carnivorous plankton Bacteria absorbed by Soluble organic matter Protistan producers secrete

26. You should now be able to: • Explain why the kingdom Protista is no longer considered a legitimate taxon • Explain the process of endosymbiosis and state what living organisms are likely relatives of mitochondria and plastids • Distinguish between endosymbiosis and secondary endosymbiosis • Name the five supergroups, list their key characteristics, and describe some representative taxa