The Protists. Copyright McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

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1 25 The Protists Copyright McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display. 1

2 Outlines 25.1 Overview of Protists 25.2 Supergroup Excavata 25.3 Supergroup Amoebozoa 25.4 Supergroup SAR 25.5 Supergroup Archaeplastida 2

3 25.1 Overview of Protists 3

4 What are Protists? Eukaryotes with the taxonomic classification in flux Eukaryotes that are not plants, animals or fungi Kingdom Protists is artificial grouping of over 65,000 different single-celled life forms A polyphyletic collection of organisms Most are unicellular; some are multicellular Lack the level of tissue organization present in higher eukaryotes 4

5 Distribution of Protists Grow in a wide variety of moist habitats; most are free living Chemoorganotrophic forms play role in recycling nitrogen and phosphorus Terrestrial and planktonic forms Parasitic forms cause disease in humans and domesticated animals 5

6 Nutrition in Protists: organotroph and phototroph Chemoheterotrophic protists saprophytes nutrients obtained from dead organic matter through enzymatic degradation osmotrophy absorb soluble products holozoic nutrition solid nutrients acquired by phagocytosis Photoautotrophic protists strict aerobes, use photosystems I and II for oxygenic photosynthesis Mixotrophic protists use organic and inorganic carbon compounds simultaneously 6

Morphology-1 Outer gelatinous ectoplasm just underneath plasma

7 Plasma membrane structure similar to multicellular plants/animals Cytoplasm sometimes subdivided into Protist Morphology-1 Outer gelatinous ectoplasm just underneath plasma membrane Inner fluid region termed endoplasm Pellicle structure provides support 7

8 Protist Morphology-2 Vacuoles commonly present in protists contractile vacuoles help maintain osmoregulation phagocytic vacuoles allow some protists to ingest food Energy production through mitochondria in aerobic chemoorganotrophic protists chloroplasts and mitochondria in photosynthetic protists hydrogenosomes in anaerobic chemoorganotrophs Cilia/flagella may be present for motility/feeding 8

9 Encystment and Excystment Encystment protists simplify in structure and become dormant (cyst) with a cell wall and very low metabolic activity protects against environmental changes can assist in nuclear reorganization/reproduction serve as a means of host to host transfer for parasitic species 9

10 Encystment and Excystment Excystment A return to favorable conditions may stimulate a cyst form to return to its original state In parasitic protists, this may occur following ingestion of a cyst by a new host organism 10

gametes in syngamy process This can occur within a single

11 Reproduction of Protists: Sexual, Asexual, Both Asexual stage usually binary fission Sexual stages use fusion of gametes in syngamy process This can occur within a single individual (autogamy) or between individuals (conjugation) 草履蟲 11

12 3 Major Groups of Protista: are without evolutionary contest Animal-like Heterophrophic protozoa Classified by locomotion Plant-like Autoprophic Cellulose cell walls Chloroplasts 2 groups: unicellular and multicellular Fungus-like Heteroprophic (some saprophytes; some parasities) Lack cell walls of chitin Slime molds and water molds have centrioles 12

13 Locomotion in Protozoa Pseudopods: Amoebas Ex. Amoeba Flagellates: one or more flagellum Ex. Giardia Cilia: short hair-like structures Ex. Paramecium Sporozoans: no locomotion; are all parasites Ex. Plasmodium 13

14 Protists Taxonomy Difficult to define due to vast differences in protists Very much in flux and an area of active research New classification scheme is based on that of the International Society of Protistologists doesn t utilize hierarchical ranks (class and order) 14

15 25.2 Supergroup Excavata: Primitive Eukaryotes 15

16 Supergroup Excavata: primitive eukaryotes Includes Fornicata, Parabasilia, and Euglenozoa Includes some of most primitive, or deeply branching eukaryotes most have a cytostome characterized by a suspension-feeding groove plays role in capturing particles from a feeding current 16

17 Microaerophilic protist epidemic diarrhea from contaminated water 1. Fornicata members are flagellated and lack mitochondria Giardia have mitosomes (mitochondria-like doublemembrane bounded organelles) Most are harmless symbionts with the following exceptions Giardia causes diarrhea Hexamida salmonis fish parasite H. meleagridis turkey pathogen 17

18 2. Parabasilia Most are flagellated endosymbionts of animals Lack a distinct cytosome, use phagocytosis to engulf food Two subgroups: Trichonymphida and Trichomonadida 18

19 2.1 Subgroup Trichonymphida Obligate mutuals of wood-eating insects such as termites Release cellulose for digesting May account for 1/3 biomass in termite Ecdysone hormone produced by host triggers sexual reproduction 19

20 2.2 Subgroup Trichomonadida Trichomonads do not required oxygen possess hydrogenosomes asexual reproduction only symbionts of digestive, reproductive, and respiratory traits of many vertebrates, including humans some strains are human pathogens 20

21 3. Euglenozoa 眼蟲門 Commonly found in fresh water 1/3 photoautotrophic, rest are chemoorganotrophs Euglena is the representative phototroph pellicle - proteinaceous strips, microtubules red eye spot (stigma) orients to light chlorophylls a and b, carotenoids contractile vacuole and flagella 21

Trypanosoma cruzi causes Chagas disease transmitted by kissing bugs causes damage

22 Trypanosomes Pathogenic Euglenozoa parasites of plants and animals leishmaniasis caused by members of genus Leishmania includes systemic and skin/membrane damage Trypanosoma cruzi causes Chagas disease transmitted by kissing bugs causes damage to nervous system T. gambiense and T. rhodesiense cause African sleeping sickness 22

23 Antigenic variation Trypanosomes thick glycoprotien layer coating cell wall surface which is changeable enables the parasite s escape from the host immune system no vaccines new drugs may target flagellar axonemal proteins important for division 23

24 25.3 Supergroup Amoebozoa includes protists with pseudopodia 24

netlike mesh Naked amoebae are surrounded only by a plasma membrane Testate amoebae plasma membrane

25 Supergroup Amoebozoa Amoeboid motility - use of pseudopodia for locomotion and feeding terms for shape of pseudopods lobopodia rounded Filopodia ( 絲狀偽足 ) long and narrow Reticulopodia ( 網狀偽足 ) form a netlike mesh Naked amoebae are surrounded only by a plasma membrane Testate amoebae plasma membrane covered by material made by amoebe or obtained from the environment Reproduce by binary or multiple fission 25

26 1. Tubulinea Members inhabit moist environments Free-living, endosymbiotic, commensal and parasitic forms Amoeba proteus present in this phylum commonly used in student laboratories 26

27 2. Entamoebida Lack mitochondria, hydrogenosomes may possess 20 mitochondrial proteins Entamoeba histolytica causes amoebic dysentery third leading cause of parasitic death worldwide acquired by consuming E. histolytica cysts may migrate to lungs, brain, liver, or skin 27

28 3. Eumycetozoa Slime Molds Have been classified as plants, animals, or fungi Monophyletic group Group includes myxogastria (the acellular slime mold) dictyostelia (the cellular slime mold) 28

29 3.1 Life Cycle Myxogastria (Acellular Slime Mold) Plasmodium lacks cell membrane contain up to 10,000 diving nuclei streaming masses of colorful protoplasm creep along in amoeboid fashion degrade rotting organic matter and feed by endocytosis develop fruiting bodies and resistant stalks spores germinate in good environments release haploid amoebaflagellate which fuse to form zygotes 29

30 Acellular Slime Mold 30

31 Strictly amoeboid 3.2 Dictyostelia (Cellular Slime Mold) Endocytosis to feed on bacteria and yeast Multicellularity in life cycle Pseudoplasmodium individual cells retain cell membrane move as mass starved cells release compounds detected by other cells which form aggregate around signaling cell cells pile on top, bottom cell forms stalk tip cells produce spores that germinate 31

32 Dictyostelia (Cellular Slime Mold) Some cells differentiate to resemble primitive immune cells Sentinel cells vanquish harmful bacteria These cells may patrol for pathogenic bacteria in slug Sexual reproduction involves formation of macrocysts Arise by a form of conjugation amoebae become enclosed in a wall of cellulose after conjugation, large amoeba cannibalizes remaining amoeba and matures into macrocyst diploid nucleus undergoes meiosis 32

33 33

34 25.4 Supergroup SAR 34

35 1. Rhizaria Includes Strameopila, Alveolata Amoeboid in morphology distinguished by fine pseudopodia (filopodia) - branched, simple, connected axopodia filopodia supported by microtubules protrude from the axoplast primarily used in feeding 35

36 1.1 Radiolaria Most have internal skeleton made of siliceous material Feed by endocytosis using mucous coated filopodia to entrap prey Sexual and asexual reproduction used 36

37 Called forams 1.2 Foraminifera ~20mm several centimeter size range Filopodia are arranged in branching network (reticulopodia) May harbor endosymbiotic algae contribute to foram nutrition Have characteristics tests arranged in multiple chambers that are sequentially added as organism grows 37

38 More about Forams Only eukaryote that can reduce nitrate to dinitrogen gas Complex life cycle sexual and asexual reproduction Found in marine and estuarine habitats Foram tests make up most modern-day chalk, limestone, and marble 38

39 Large group including 2. Alveolata Dinoflagellata (dinoflagellates) Ciliophora (ciliates) Apicomplexa (apicomplexans) 39

complex Trichocysts are defensive proteins Symbiotic forms

40 2.1 Dinoflagellates Large group found in marine plankton cause phosphorescence/toxic blooms in seawater Nutritionally complex Trichocysts are defensive proteins Symbiotic forms (zooxanthellae) live in association with reef building corals 40

41 2.2 Ciliophora Chemoorganotrophic Found in both benthic and planktonic communities in water and soil systems Use many cilia as locomotory and feeding organelles Reproduction asexual by transverse binary fission sexual by conjugation 41

42 Two nuclei micronucleus More about Ciliaphora diploid, normal somatic number of chromosomes divided by mitosis, gametes by meiosis sexual reproduction macronucleus is derived from micronuclei Polyploid; divides by elongating and constricting the proteins control normal cell functions 42

43 Conjugation in Paramecium caudatum 43

2.3 Apicomplexans Distinguished by the unipolar apical complex Parasitic with complex life cycles life cycle has both sexual and asexual phases clonal

44 2.3 Apicomplexans Distinguished by the unipolar apical complex Parasitic with complex life cycles life cycle has both sexual and asexual phases clonal and sexual stages are haploid, except for zygotes sporozoite is the motile, infective stage Most important member is Plasmodium, the cause of malaria 44

45 Plasmodium drives the TCA cycle in 2 directions 45

46 More about Apicomplexans Apicoplastids arose by endosymbiosis by cyanobacterium essential for viability not site of photosynthesis may be target for future drugs 46

47 3. Stramenopila Extremely diverse including diatoms, golden and brown algae, öomycetes, labyrinthulids and members of Hypochytriales found in marine plankton produce 40% to 50% of organic carbon in ocean Unifying feature is heterokont flagella 47

48 3.1 Diatoms Chlorophylls and accessory pigments Frustule two-piece cell wall of silica unique, beautiful patterns Asexual division hypotheca template forming epitheca Important in global carbon cycling marine planktonic diatoms produce 40 50% of organic ocean carbon 48

49 Gametic Life Cycle by Diatoms 49

50 3.2 Peronosporomycetes Egg fungi formerly called oomycetes are diploid and no chitin in cell wall Some grow in cottony masses on dead algae and animals Some parasites of fish gills Plant diseases include blue mold on tobacco and Irish potato blight 50

51 4. Haptophyta Planktonic photosynthetic protists such as Cocclithales Coccolithophores and the Foraminifera precipitate calcium carbonate in the open ocean for their ornate calcite scales called coccoliths has influence on Earth s carbon budget 51

52 5. Picozoa First cultivated in 2013: Picomonas judraskeda Isolated from marine coastal water; small in size (~2 x ~3 μm) 52

53 25.5 Supergroup Archaeplastida includes Green Algae 53

54 Supergroup Archaeplastida Includes organisms containing a photosynthetic plastid that arose through an ancient endosymbiosis with a cyanobacterium all higher plants and many algal species are included 54

55 Chloroplastida Chlorophytya (green algae) Phototrophs have chlorophylls a/b and carotenoids Many have cellulose cell walls Exhibit a diverse morphology 55

56 Chlamydomonas Member of subgroup Chlorophyta cells have a haploid nucleus, large chloroplast, conspicuous pyrenoid, and a stigma (eyespot) which plays a role in phototaxis osmoregulation controlled by two small contractile vacuoles at flagella base reproduces by sexual and asexual reproduction 56

57 The Structure and Life Cycle of Chlamydomonas 57

58 Prototheca moriformis A pathogenic chlorophyte Common in soil Causes protothecosis in humans and animals severe systemic infections in animals subcutaneous infection in humans 58

59 6/19/2018 Homework 1. Describe nutritional strategies used by protists. 2. Describe the reproduction modes of protists. 3. What are encystment and excystment? 4. Describe the modes of locomotion used by protists. 5. (Figure 25.8) How does a plasmodium differ from the pseudoplasmodium produced by cellular slime molds? 6. All apicomplexans are either intra- or intercellular parasites of animals. What is the apical complex seen in apicomplexans? Which stage would be most vulnerable to drug treatment in an effort to treat a human disease caused by an apicomplexan? 7. Explain the unique structural features of diatoms. How does their morphology play a role in the alternation between asexual and sexual reproduction? 59

BIOLOGY - CLUTCH CH.29 - PROTISTS.

BIOLOGY - CLUTCH CH.29 - PROTISTS. !! www.clutchprep.com Eukrayotic cells are large, have a nucleus, contain membrane-bound organelles, and use a cytoskeleton The nucleus is the synapomorphy that unifies eukaryotes Endosymbiotic theory