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Chapter 24

Chapter 24. Protists. Kingdom Protista “Simple” eukaryotes Mostly unicellular Some form colonies Some are coenocytic Multiple nuclei in one mass of cytoplasm A few are multicellular. Most protists live in aquatic environments Sixty major groups of protists Important in the biosphere

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Chapter 24

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  1. Chapter 24 Protists

  2. Kingdom Protista • “Simple” eukaryotes • Mostly unicellular • Some form colonies • Some are coenocytic • Multiple nuclei in one mass of cytoplasm • A few are multicellular

  3. Most protists live in aquatic environments • Sixty major groups of protists • Important in the biosphere • Food for other organisms • Photosynthetic protists supply oxygen

  4. Locomotion • Pseudopodia • Flagella • Cilia • A few are nonmotile • Modes of nutrition • Autotrophs • Heterotrophs

  5. Chlamydomonas

  6. Interactions with other organisms • Free-living • Mutualism • Commensalism • Parasitism • Habitats • Most live in the ocean or freshwater ponds, lakes, and streams • Parasites live in host’s bodily fluids

  7. Modes of reproduction • Many protists reproduce both sexually and asexually • Syngamy (union of gametes) • Some protists are solely asexual

  8. Endosymbiont theory • Certain organelles arose from symbiosis with prokaryotes • Mitochondria arose from aerobic eubacteria • Chloroplasts arose from cyanobacteria

  9. Primary and secondary endosymbiosis

  10. Classifying eukaryotes • Ultrastructure • Fine details of cell structure • Molecular data • Ribosomal RNA • Nuclear genes • The protist kingdom is probably paraphyletic

  11. Eight monophyletic groups of eukaryotes

  12. Zooflagellates • Mostly unicellular heterotrophs • Move using flagella • Now separated into several monophyletic groups • Excavates • Discicristates

  13. Excavates live in oxygen-free environments • Diplomonads • No mitochondria • No Golgi complex • One or two nuclei • Up to eight flagella • Giardia is a parasite

  14. Giardia

  15. Discicristates have disc-shaped mitochondrial cristae • Euglenoids • About 1/3 are photosynthetic • Inhabit freshwater ponds and puddles • Trypanosoma causes African sleeping sickness

  16. Euglena gracilis

  17. Alveolates have flattened vesicles under the plasma membrane • Ciliates • Move by hairlike cilia • Micronuclei for sexual reproduction • Macronuclei control metabolism • Reproduce sexually by conjugation

  18. Paramecium, a ciliate

  19. Alveolates • Dinoflagellates • Mostly unicellular with two flagella • Mostly photosynthetic • Apicomplexans • Parasitic • Spore-forming • Plasmodium causes malaria

  20. Dinoflagellates

  21. Heterokonts are motile with two different kind of flagella • Water molds • Mycelium absorbs organic material • Reproduce asexually with biflagellate zoospores • Reproduce sexually with oospores • Phytophthora causes plant diseases

  22. Mycelium around a dead insect Saprolegnia

  23. Heterokonts • Diatoms • Mostly unicellular with shells containing silica • Some diatoms are part of plankton • Golden algae • Mostly unicellular, biflagellate algae • Both freshwater and marine

  24. Diatoms

  25. Heterokonts • Brown algae • Multicellular seaweed • Ecologically important in cooler ocean waters • Kelps have leaflike blades, stemlike stipes, anchoring holdfasts, gas-filled bladders

  26. Brown algae

  27. Cercozoa are amoeboid cells that often have hard outer shells, called tests, through which cytoplasmic projections extend

  28. Cercozoa • Foraminferans • Many-chambered tests with pores • Cytoplasmic extensions to move and obtain food • Actinopods • Mostly marine plankton • Axopods to obtain food

  29. An actinipod

  30. Plants have chloroplasts bounded by inner and outer membranes • Land plants, red algae, and green algae are monophyletic • Red algae and green algae are in kingdom Protista

  31. Red algae are mostly multicellular seaweeds • Ecologically important in warm tropical waters • Red algae with calcium carbonate in their cell walls are important for reef building

  32. Red algae

  33. Green algae are diverse in size, structural complexity, and reproduction • May be the ancestors of land plants • Multicellular forms do not have cells differentiated into tissues, unlike plants

  34. Green algae

  35. Amoebas move and obtain food using cytoplasmic extensions called pseudopodia • Capture and engulf food by surrounding it and forming a vacuole around it • Entamoeba histolytica causes amoebic dysentery

  36. Plasmoidal slime mold • Feeding stage is a multinucleate plasmodium that extends up to one foot in diameter • In the reproductive stage, stalks called sporangia produce haploid spores

  37. Plasmoidal slime mold

  38. Cellular slime molds • Feeding stage is individual amoeboid cells • During moisture or food shortage, they aggregate into a migrating pseudoplasmodium • Forms stalked fruiting body containing spores

  39. Cellular slime mold

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