Bài giảng Biology - Chapter 28: Protists

Chapter 28ProtistsOverview: A World in a Drop of WaterEven a low-power microscopeCan reveal an astonishing menagerie of organisms in a drop of pond waterFigure 28.150 mThese amazing organismsBelong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protistsAdvances in eukaryotic systematicsHave caused the classification of protists to change significantlyConcept 28.1: Protists are an extremely diverse assortment of eukaryotesProtists are more diverse than all other eukaryotesAnd are no longer classified in a single kingdomMost protists are unicellularAnd some are colonial or multicellularProtists, the most nutritionally diverse of all eukaryotes, includePhotoautotrophs, which contain chloroplastsHeterotrophs, which absorb organic molecules or ingest larger food particlesMixotrophs, which combine photosynthesis and heterotrophic nutritionProtist habitats are also diverse in habitatAnd including freshwater and marine speciesFigure 28.2a–d100 m100 m4 cm500 mThe freshwater ciliate Stentor, a unicellular protozoan (LM)Ceratium tripos, a unicellular marine dinoflagellate (LM) Delesseria sanguinea, a multicellular marine red algaSpirogyra, a filamentous freshwater green alga (inset LM)(a)(b)(c)(d)Reproduction and life cyclesAre also highly varied among protists, with both sexual and asexual speciesA sample of protist diversityTable 28.1Endosymbiosis in Eukaryotic EvolutionThere is now considerable evidenceThat much of protist diversity has its origins in endosymbiosis The plastid-bearing lineage of protistsEvolved into red algae and green algaeOn several occasions during eukaryotic evolutionRed algae and green algae underwent secondary endosymbiosis, in which they themselves were ingestedCyanobacteriumHeterotrophiceukaryotePrimaryendosymbiosisRed algaeGreen algaeSecondaryendosymbiosisSecondaryendosymbiosisPlastidDinoflagellatesApicomplexansCiliatesStramenopilesEuglenidsChlorarachniophytesPlastidAlveolatesFigure 28.3Diversity of plastids produced by secondary endosymbiosisConcept 28.2: Diplomonads and parabasalids have modified mitochondriaA tentative phylogeny of eukaryotesDivides eukaryotes into many cladesFigure 28.4DiplomonadsParabasalidsKinetoplastidsEuglenidsDinoflagellatesApicomplexansCiliatesOomycetesDiatomsGolden algaeBrown algaeChlorarachniophytesForaminiferansRadiolariansGymnamoebasEntamoebasPlasmodial slime moldsCellular slime moldsFungiChoanoflagellatesMetazoansRed algaeChlorophytesCharophyceansPlantsAncestral eukaryoteChlorophytaPlantaeRhodophytaAnimaliaFungi(Opisthokonta)(Viridiplantae)DiplomonadidaParabasalaEuglenozoaAlveolataStramenopilaCercozoaRadiolariaAmoebozoaDiplomonads and parabasalidsAre adapted to anaerobic environmentsLack plastidsHave mitochondria that lack DNA, an electron transport chain, or citric-acid cycle enzymesDiplomonadsDiplomonadsHave two nuclei and multiple flagellaFigure 28.5a5 µm(a) Giardia intestinalis, a diplomonad (colorized SEM)ParabasalidsParabasalids include trichomonadsWhich move by means of flagella and an undulating part of the plasma membrane Figure 28.5b(b) Trichomonas vaginalis, a parabasalid (colorized SEM)FlagellaUndulating membrane5 µmConcept 28.3: Euglenozoans have flagella with a unique internal structureEuglenozoa is a diverse clade that includesPredatory heterotrophs, photosynthetic autotrophs, and pathogenic parasitesThe main feature that distinguishes protists in this cladeIs the presence of a spiral or crystalline rod of unknown function inside their flagellaFlagella0.2 µmCrystalline rodRing of microtubulesFigure 28.6KinetoplastidsKinetoplastidsHave a single, large mitochondrion that contains an organized mass of DNA called a kinetoplastInclude free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystemsThe parasitic kinetoplastid TrypanosomaCauses sleeping sickness in humansFigure 28.79 mEuglenidsEuglenidsHave one or two flagella that emerge from a pocket at one end of the cellStore the glucose polymer paramylonFigure 28.8Long flagellumShort flagellumNucleusPlasma membraneParamylon granuleChloroplastContractile vacuoleLight detector: swelling near thebase of the long flagellum; detectslight that is not blocked by theeyespot; as a result, Euglena movestoward light of appropriateintensity, an important adaptationthat enhances photosynthesisEyespot: pigmentedorganelle that functionsas a light shield, allowinglight from only a certaindirection to strike thelight detector Pellicle: protein bands beneaththe plasma membrane thatprovide strength and flexibility(Euglena lacks a cell wall)Euglena (LM)5 µmConcept 28.4: Alveolates have sacs beneath the plasma membraneMembers of the clade AlveolataHave membrane-bounded sacs (alveoli) just under the plasma membraneFigure 28.9FlagellumAlveoli0.2 µmDinoflagellatesDinoflagellatesAre a diverse group of aquatic photoautotrophs and heterotrophsAre abundant components of both marine and freshwater phytoplanktonEach has a characteristic shapeThat in many species is reinforced by internal plates of celluloseTwo flagellaMake them spin as they move through the waterFigure 28.103 µmFlagellaRapid growth of some dinoflagellatesIs responsible for causing “red tides,” which can be toxic to humansApicomplexansApicomplexansAre parasites of animals and some cause serious human diseasesAre so named because one end, the apex, contains a complex of organelles specialized for penetrating host cells and tissuesHave a nonphotosynthetic plastid, the apicoplastFigure 28.11Inside mosquitoInside humanSporozoites(n)OocystMEIOSISLiverLiver cellMerozoite(n)Red bloodcellsGametocytes(n)FERTILIZATIONGametesZygote(2n)KeyHaploid (n)Diploid (2n)MerozoiteRed blood cellApex0.5 µmMost apicomplexans have intricate life cycles With both sexual and asexual stages that often require two or more different host species for completion An infected Anopheles mosquito bites a person, injecting Plasmodium sporozoites in its saliva.1 The sporozoites enter the person’s liver cells. After several days, the sporozoites undergo multiple divisions and become merozoites, which use their apical complex to penetrate red blood cells (see TEM below).2 The merozoites divide asexually inside the red blood cells. At intervals of 48 or 72 hours (depending on the species), large numbers of merozoites break out of the blood cells, causing periodic chills and fever. Some of the merozoites infect new red blood cells.3 Some merozoites form gametocytes.4 Another Anopheles mosquitobites the infected person and picksup Plasmodium gametocytes alongwith blood.5 Gametes form from gametocytes.Fertilization occurs in the mosquito’sdigestive tract, and a zygote forms.The zygote is the only diploid stagein the life cycle.6An oocyst developsfrom the zygote in the wall of the mosquito’s gut. Theoocyst releases thousands of sporozoites, whichmigrate to the mosquito’ssalivary gland.7CiliatesCiliates, a large varied group of protistsAre named for their use of cilia to move and feedHave large macronuclei and small micronucleiThe micronucleiFunction during conjugation, a sexual process that produces genetic variationConjugation is separate from reproductionWhich generally occurs by binary fissionFigure 28.1250 µmThousands of cilia cover the surface of Paramecium.The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore.Paramecium, like other freshwater protists, constantly takes in waterby osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate excess water from radial canals and periodically expel it through the plasma membrane.Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell.Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis.Oral grooveCell mouthMicronucleusMacronucleusFEEDING, WASTE REMOVAL, AND WATER BALANCEExploring structure and function in a ciliateContractile VacuoleCONJUGATION AND REPRODUCTION872MICRONUCLEARFUSIONDiploidmicronucleusDiploidmicronucleusHaploidmicronucleusMEIOSISCompatiblematesKeyConjugationReproductionMacronucleusTwo cells of compatiblemating strains align sideby side and partially fuse.1Meiosis of micronuclei produces four haploidmicronuclei in each cell.23 Three micronuclei in each cell disintegrate. The remaining micro-nucleus in each cell divides by mitosis.The cells swap one micronucleus.4The cellsseparate.5Micronuclei fuse,forming a diploid micronucleus.6Three rounds of mitosis without cytokinesis produce eight micronuclei.7 The original macro-nucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei.8Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells.9Concept 28.5: Stramenopiles have “hairy” and smooth flagellaThe clade StramenopilaIncludes several groups of heterotrophs as well as certain groups of algaeMost stramenopilesHave a “hairy” flagellum paired with a “smooth” flagellumSmoothflagellumHairyflagellum5 µmFigure 28.13Oomycetes (Water Molds and Their Relatives)OomycetesInclude water molds, white rusts, and downy mildewsWere once considered fungi based on morphological studiesMost oomycetesAre decomposers or parasitesHave filaments (hyphae) that facilitate nutrient uptakeThe life cycle of a water moldFigure 28.14CystZoospore(2n)ASEXUALREPRODUCTIONZoosporangium(2n)Germ tubeZygotegerminationFERTILIZATIONSEXUALREPRODUCTIONZygotes(oospores)(2n)MEIOSISOogoniumEgg nucleus(n)Antheridialhypha withsperm nuclei(n)KeyHaploid (n)Diploid (2n) Encysted zoosporesland on a substrate andgerminate, growing intoa tufted body of hyphae.1 Several days later,the hyphae begin toform sexual structures.2 Meiosis produceseggs within oogonia(singular, oogonium).3 On separate branches of thesame or different individuals, meiosisproduces several haploid sperm nucleicontained within antheridial hyphae.4 Antheridial hyphae grow likehooks around the oogonium anddeposit their nuclei throughfertilization tubes that lead to theeggs. Following fertilization, thezygotes (oospores) may developresistant walls but are alsoprotected within the wall of theoogonium.5 A dormant periodfollows, during which theoogonium wall usuallydisintegrates.6 The zygotes germinateand form hyphae, and thecycle is completed.7 The endsof hyphaeform tubularzoosporangia.8 Each zoospor-angium producesabout 30biflagellatedzoosporesasexually.9The ecological impact of oomycetes can be significantPhytophthora infestans causes late blight of potatoesDiatomsDiatoms are unicellular algae With a unique two-part, glass-like wall of hydrated silica Figure 28.153 µmDiatoms are a major component of phytoplanktonAnd are highly diverseFigure 28.1650 µmAccumulations of fossilized diatom wallsCompose much of the sediments known as diatomaceous earthGolden AlgaeGolden algae, or chrysophytesAre named for their color, which results from their yellow and brown carotenoidsThe cells of golden algaeAre typically biflagellated, with both flagella attached near one end of the cellMost golden algae are unicellularBut some are colonialFigure 28.1725 µmBrown AlgaeBrown algae, or phaeophytesAre the largest and most complex algaeAre all multicellular, and most are marineBrown algaeInclude many of the species commonly called seaweedsSeaweedsHave the most complex multicellular anatomy of all algaeFigure 28.18BladeStipeHoldfastKelps, or giant seaweedsLive in deep parts of the oceanFigure 28.19Human Uses of SeaweedsMany seaweedsAre important commodities for humansAre harvested for foodFigure 28.20a–c(a) The seaweed is grown on nets in shallow coastal waters.(b) A worker spreadsthe harvested sea-weed on bambooscreens to dry.(c) Paper-thin, glossy sheetsof nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi.Alternation of GenerationsA variety of life cyclesHave evolved among the multicellular algaeThe most complex life cycles include an alternation of generationsThe alternation of multicellular haploid and diploid formsThe life cycle of the brown alga LaminariaFigure 28.21Sporophyte(2n)ZoosporesFemaleGametophytes(n)MEIOSISFERTILIZATIONDeveloping sporophyte Zygote(2n)Mature femalegametophyte(n)EggSpermMaleSporangiaKeyHaploid (n)Diploid (2n) The sporophytes of this seaweedare usually found in water just belowthe line of the lowest tides, attachedto rocks by branching holdfasts.1 In early spring, at the end ofthe main growing season, cells onthe surface of the blade developinto sporangia.2 Sporangia producezoospores by meiosis.3 The zoospores are allstructurally alike, butabout half of them developinto male gametophytesand half into femalegametophytes. Thegametophytes looknothing like the sporo-phytes, being short, branched filaments thatgrow on the surface ofsubtidal rocks.4 Male gametophytes release sperm, and female gametophytesproduce eggs, which remainattached to the female gameto-phyte. Eggs secrete a chemicalsignal that attracts sperm of thesame species, thereby increasingthe probability of fertilization inthe ocean.5 Sperm fertilizethe eggs.6 The zygotesgrow into newsporophytes,starting lifeattached tothe remains ofthe femalegametophyte.7Concept 28.6: Cercozoans and radiolarians have threadlike pseudopodiaA newly recognized clade, CercozoaContains a diversity of species that are among the organisms referred to as amoebasAmoebas were formerly defined as protistsThat move and feed by means of pseudopodiaCercozoans are distinguished from most other amoebasBy their threadlike pseudopodiaForaminiferans (Forams)Foraminiferans, or foramsAre named for their porous, generally multichambered shells, called testsFigure 28.2220 µmPseudopodia extend through the pores in the testForam tests in marine sedimentsForm an extensive fossil recordRadiolariansRadiolarians are marine protistsWhose tests are fused into one delicate piece, which is generally made of silicaThat phagocytose microorganisms with their pseudopodiaThe pseudopodia of radiolarians, known as axopodiaRadiate from the central bodyFigure 28.23200 µmAxopodiaConcept 28.7: Amoebozoans have lobe-shaped pseudopodiaAmoebozoansAre amoeba that have lobe-shaped, rather than threadlike, pseudopodiaInclude gymnamoebas, entamoebas, and slime moldsGymnamoebasGymnamoebasAre common unicellular amoebozoans in soil as well as freshwater and marine environmentsMost gymnamoebas are heterotrophicAnd actively seek and consume bacteria and other protistsFigure 28.24Pseudopodia40 µmEntamoebasEntamoebasAre parasites of vertebrates and some invertebratesEntamoeba histolyticaCauses amebic dysentery in humansSlime Molds Slime molds, or mycetozoansWere once thought to be fungiMolecular systematicsPlaces slime molds in the clade AmoebozoaPlasmodial Slime MoldsMany species of plasmodial slime moldsAre brightly pigmented, usually yellow or orangeFigure 28.254 cmAt one point in the life cycleThey form a mass called a plasmodium Figure 28.26FeedingplasmodiumMatureplasmodium(preparing to fruit)YoungsporangiumMaturesporangiumSpores(n)GerminatingsporeAmoeboid cells(n)Zygote(2n)1 mmKeyHaploid (n)Diploid (2n)MEIOSISSYNGAMYStalkFlagellated cells(n) The feeding stageis a multinucleateplasmodium that liveson organic refuse.1 The plasmodiumtakes a weblike form.2 The plasmodium erectsstalked fruiting bodies (sporangia)when conditions become harsh.3 Within the bulboustips of the sporangia,meiosis produces haploidspores.4 These cells areeither amoeboid orflagellated; the twoforms readily convertfrom one to the other.6 The cells unitein pairs (flagellatedwith flagellatedand amoeboid withamoeboid), formingdiploid zygotes.7 The resistant spores dispersethrough the air to new locationsand germinate, becoming activehaploid cells when conditionsare favorable.5The plasmodiumIs undivided by membranes and contains many diploid nucleiExtends pseudopodia through decomposing material, engulfing food by phagocytosisCellular Slime MoldsCellular slime molds form multicellular aggregatesIn which the cells remain separated by their membranesThe life cycle of Dictyostelium, a cellular slime moldSpores(n)EmergingamoebaSolitary amoebas(feeding stage)ASEXUALREPRODUCTIONFruitingbodiesAggregatedamoebasMigratingaggregateSYNGAMYMEIOSISSEXUALREPRODUCTIONZygote(2n)Amoebas600 µm200 µmKeyHaploid (n)Diploid (2n)Figure 28.27 In the feedingstage of the lifecycle, solitary haploidamoebas engulf bacteria.1 During sexual repro-duction, two haploidamoebas fuse andform a zygote.2 The zygotebecomes a giantcell (not shown)by consuminghaploid amoebas.After developing aresistant wall, thegiant cell undergoesmeiosis followed byseveral mitoticdivisions.3 The resistantwall ruptures,releasing newhaploid amoebas.4 When food is depleted,hundreds of amoebascongregate in response to achemical attractant and forma sluglike aggregate (photobelow left). Aggregateformation is the beginningof asexual reproduction.5The aggregate migrates for awhile and then stops. Some of the cells dry up after forming a stalk thatsupports an asexual fruiting body.6 Othercells crawlup the stalkand developinto spores.7 Sporesare released.8 In a favorableenvironment, amoebasemerge from the sporecoats and begin feeding.9Dictyostelium discoideumHas become an experimental model for studying the evolution of multicellularityConcept 28.8: Red algae and green algae are the closest relatives of land plantsOver a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiontAnd the photosynthetic descendants of this ancient protist evolved into red algae and green algaeRed AlgaeRed algae are reddish in colorDue to an accessory pigment call phycoerythrin, which masks the green of chlorophyllRed algae Are usually multicellular; the largest are seaweedsAre the most abundant large algae in coastal waters of the tropicsFigure 28.28a–c(a) Bonnemaisonia hamifera. This red alga has a filamentous form.Dulse (Palmaria palmata). This edible species has a “leafy” form.(b)A coralline alga. The cell walls ofcoralline algae are hardened by calcium carbonate. Some coralline algae aremembers of the biological communities around coral reefs.(c)Green AlgaeGreen algaeAre named for their grass-green chloroplastsAre divided into two main groups: chlorophytes and charophyceansAre closely related to land plantsMost chlorophytesLive in fresh water, although many are marineOther chlorophytesLive in damp soil, as symbionts in lichens, or in snowFigure 28.29Chlorophytes includeUnicellular, colonial, and multicellular formsVolvox, a colonial freshwater chlorophyte. The colony is a hollowball whose wall is composed of hundreds or thousands of biflagellated cells (see inset LM) embedded in a gelatinous matrix. The cells are usually connected by strands of cytoplasm;if isolated, these cells cannot reproduce. The large colonies seen here will eventually release the small “daughter” colonies within them (LM).(a)Caulerpa, an inter-tidal chlorophyte.The branched fila-ments lack cross-walls and thus are multi-nucleate. In effect,the thallus is onehuge “supercell.”(b)Ulva, or sea lettuce. This edible seaweed has a multicellular thallus differentiated into leaflike blades and a rootlike holdfast that anchors the alga against turbulent waves and tides.(c)20 µm50 µmFigure 28.30a–cFigure 28.31FlagellaCell wallNucleusRegionsof singlechloroplastZoosporesASEXUALREPRODUCTIONMature cell(n)SYNGAMYSEXUALREPRODUCTIONZygote(2n)MEIOSIS1 µmKeyHaploid (n)Diploid (2n)++++Most chlorophytes have complex life cyclesWith both sexual and asexual reproductive stages In Chlamydomonas,mature cells are haploid and contain a single cup-shaped chloroplast (see TEM at left).1 In response to ashortage of nutrients, dryingof the pond, or some otherstress, cells develop into gametes.2 Gametes of opposite mating types (designated + and –) pair off and cling together. Fusion of the gametes (syngamy) forms a diploid zygote.3 The zygote secretes a durable coat that protects the cell against harsh conditions.4 After a dormant period, meiosis produces four haploid individuals (two of each mating type) that emerge fromthe coat and develop into mature cells.5 When a mature cell repro-duces asexually, it resorbs its flagella and then undergoes two rounds of mitosis, forming four cells (more in some species).6 These daughter cells develop flagella and cell walls and then emerge as swimming zoospores from the wall of the parent cell that had enclosed them. The zoospores grow into mature haploid cells, completing the asexual life cycle.7