Bài giảng Biology - Chapter 29: Plant Diversity I How Plants Colonized Land

Chapter 29Plant Diversity IHow Plants Colonized LandOverview: The Greening of EarthLooking at a lush landscapeIt is difficult to imagine the land without any plants or other organismsFigure 29.1For more than the first 3 billion years of Earth’s historyThe terrestrial surface was lifelessSince colonizing landPlants have diversified into roughly 290,000 living speciesConcept 29.1: Land plants evolved from green algaeResearchers have identified green algae called charophyceans as the closest relatives of land plantsMorphological and Biochemical EvidenceMany characteristics of land plantsAlso appear in a variety of algal cladesThere are four key traits that land plants share only with charophyceansRose-shaped complexes for cellulose synthesis30 nmFigure 29.2Peroxisome enzymesStructure of flagellated spermFormation of a phragmoplastGenetic EvidenceComparisons of both nuclear and chloroplast genesPoint to charophyceans as the closest living relatives of land plantsChara, a pond organism(a)10 mmColeochaete orbicularis, a disk-shaped charophycean (LM)(b)40 µmFigure 29.3a, bAdaptations Enabling the Move to LandIn charophyceansA layer of a durable polymer called sporopollenin prevents exposed zygotes from drying outThe accumulation of traits that facilitated survival on landMay have opened the way to its colonization by plantsConcept 29.2: Land plants possess a set of derived terrestrial adaptationsMany adaptationsEmerged after land plants diverged from their charophycean relativesDefining the Plant KingdomSystematistsAre currently debating the boundaries of the plant kingdomPlantaeStreptophytaViridiplantaeRed algaeChlorophytesCharophyceansEmbryophytesAncestral algaFigure 29.4Some biologists think that the plant kingdomShould be expanded to include some or all green algaeUntil this debate is resolvedThis textbook retains the embryophyte definition of kingdom PlantaeDerived Traits of PlantsFive key traits appear in nearly all land plants but are absent in the charophyceansApical meristemsAlternation of generationsWalled spores produced in sporangiaMulticellular gametangiaMulticellular dependent embryosAPICAL MERISTEMSApicalmeristemof shootDevelopingleaves100 µmApical meristems of plant shoots and roots. The light micrographs are longitudinal sections at the tips of a shoot and root.Apical meristemof rootRoot100 µmShootFigure 29.5Apical meristems and alternation of generationsHaploid multicellularorganism (gametophyte)MitosisMitosisGametesZygoteDiploid multicellularorganism (sporophyte)Alternation of generations: a generalized schemeMEIOSISFERTILIZATION2n2nnnnnnSporesMitosisALTERNATION OF GENERATIONSFigure 29.5Walled spores; multicellular gametangia; and multicellular, dependent embryosWALLED SPORES PRODUCED IN SPORANGIAMULTICELLULAR GAMETANGIAMULTICELLULAR, DEPENDENT EMBRYOSSporesSporangiumLongitudinal section ofSphagnum sporangium (LM)SporophyteGametophyteSporophyte and sporangium of Sphagnum (a moss)Female gametophyteArchegoniumwith eggAntheridiumwith spermMalegametophyteArchegonia and antheridia of Marchantia (a liverwort)EmbryoMaternal tissue2 µmWall ingrowthsPlacental transfer cell10 µmEmbryo and placental transfer cell of MarchantiaFigure 29.5Additional derived unitsSuch as a cuticle and secondary compounds, evolved in many plant speciesThe Origin and Diversification of PlantsFossil evidenceIndicates that plants were on land at least 475 million years agoFossilized spores and tissuesHave been extracted from 475-million-year-old rocksFossilized spores. Unlike the spores of most living plants, which are single grains, these spores found in Oman are in groups of four (left; one hidden) and two (right).(a)Fossilizedsporophyte tissue. The spores were embedded in tissue that appears to be from plants.(b)Figure 29.6 a, bWhatever the age of the first land plantsThose ancestral species gave rise to a vast diversity of modern plantsTable 29.1Land plants can be informally groupedBased on the presence or absence of vascular tissueAn overview of land plant evolutionBryophytes(nonvascular plants)Seedless vascular plantsSeed plantsVascular plantsLand plantsOrigin of seed plants(about 360 mya)Origin of vascular plants (about 420 mya)Origin of land plants(about 475 mya)Ancestralgreen algaCharophyceansLiverwortsHornwortsMossesLycophytes(club mosses, spike mosses, quillworts)Pterophyte (ferns, horsetails, whisk fern)GymnospermsAngiospermsFigure 29.7Concept 29.3: The life cycles of mosses and other bryophytes are dominated by the gametophyte stageBryophytes are represented today by three phyla of small herbaceous (nonwoody) plantsLiverworts, phylum HepatophytaHornworts, phylum AnthocerophytaMosses, phylum BryophytaDebate continues over the sequence of bryophyte evolutionMosses are most closely related to vascular plantsBryophyte GametophytesIn all three bryophyte phylaGametophytes are larger and longer-living than sporophytesThe life cycle of a mossMaturesporophytesYoungsporophyteMalegametophyteRaindropSpermKeyHaploid (n)Diploid (2n)AntheridiaFemalegametophyteEggArchegoniaFERTILIZATION(within archegonium)ZygoteArchegoniumEmbryoFemalegametophytesGametophoreFootCapsule(sporangium)SetaPeristomeSporesProtonemata“Bud”“Bud”MEIOSISSporangiumCalyptraCapsule with peristome (LM)RhizoidMaturesporophytes Spores develop intothreadlike protonemata.1 The haploidprotonemataproduce “buds”that grow intogametophytes.2 Most mosses have separatemale and female gametophytes,with antheridia and archegonia,respectively.3 A sperm swimsthrough a film ofmoisture to anarchegonium andfertilizes the egg.4 Meiosis occurs and haploidspores develop in the sporangiumof the sporophyte. When thesporangium lid pops off, theperistome “teeth” regulategradual release of the spores.8 The sporophyte grows along stalk, or seta, that emergesfrom the archegonium.6 The diploid zygotedevelops into a sporophyte embryo withinthe archegonium.5 Attached by its foot, thesporophyte remains nutritionallydependent on the gametophyte.7Figure 29.8Bryophyte gametophytesProduce flagellated sperm in antheridiaProduce ova in archegoniaGenerally form ground-hugging carpets and are at most only a few cells thickSome mossesHave conducting tissues in the center of their “stems” and may grow verticallyBryophyte SporophytesBryophyte sporophytesGrow out of archegoniaAre the smallest and simplest of all extant plant groupsConsist of a foot, a seta, and a sporangiumHornwort and moss sporophytesHave stomataBryophyte diversityLIVERWORTS (PHYLUM HEPATOPHYTA)HORNWORTS (PHYLUM ANTHOCEROPHYTA)MOSSES (PHYLUM BRYOPHYTA)Gametophore offemale gametophyteMarchantia polymorpha,a “thalloid” liverwortFootSporangiumSeta500 µmMarchantia sporophyte (LM)Plagiochiladeltoidea,a “leafy”liverwortAn Anthoceroshornwort speciesSporophyteGametophytePolytrichum commune,hairy-cap mossSporophyteGametophyteFigure 29.9“Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum canpreserve human or other animal bodies for thousands of years.Ecological and Economic Importance of MossesSphagnum, or “peat moss”Forms extensive deposits of partially decayed organic material known as peatPlays an important role in the Earth’s carbon cycleGametophyteSporangium attip of sporophyteLivingphoto-syntheticcellsDead water-storing cells100 µmCloseup of Sphagnum. Note the “leafy” gametophytes and their offspring, the sporophytes.(b)Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality.(c)Peat being harvested from a peat bog(a)Figure 29.10 a–d(d)Concept 29.4: Ferns and other seedless vascular plants formed the first forestsBryophytes and bryophyte-like plantsWere the prevalent vegetation during the first 100 million years of plant evolutionVascular plantsBegan to evolve during the Carboniferous periodOrigins and Traits of Vascular PlantsFossils of the forerunners of vascular plantsDate back about 420 million yearsThese early tiny plantsHad independent, branching sporophytesLacked other derived traits of vascular plantsFigure 29.11Life Cycles with Dominant SporophytesIn contrast with bryophytesSporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fernThe gametophytes are tiny plants that grow on or below the soil surfaceThe life cycle of a fern Fern sperm use flagellato swim from the antheridia to eggs in the archegonia.4 Sporangia release spores.Most fern species produce a singletype of spore that gives rise to abisexual gametophyte.1 The fern sporedevelops into a small,photosynthetic gametophyte.2 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanismspromote cross-fertilizationbetween gametophytes.3 On the undersideof the sporophyte‘sreproductive leavesare spots called sori.Each sorus is acluster of sporangia.6 A zygote develops into a newsporophyte, and the young plantgrows out from an archegoniumof its parent, the gametophyte.5MEIOSISSporangiumSporangiumMaturesporophyteNewsporophyteZygoteFERTILIZATIONArchegoniumEggHaploid (n)Diploid (2n)SporeYounggametophyteFiddleheadAntheridiumSpermGametophyteKeySorusFigure 29.12Transport in Xylem and PhloemVascular plants have two types of vascular tissueXylem and phloemXylemConducts most of the water and mineralsIncludes dead cells called tracheidsPhloemDistributes sugars, amino acids, and other organic productsConsists of living cellsEvolution of RootsRootsAre organs that anchor vascular plantsEnable vascular plants to absorb water and nutrients from the soilMay have evolved from subterranean stemsEvolution of LeavesLeavesAre organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesisLeaves are categorized by two typesMicrophylls, leaves with a single veinMegaphylls, leaves with a highly branched vascular systemAccording to one model of evolutionMicrophylls evolved first, as outgrowths of stemsVascular tissueMicrophylls, such as those of lycophytes, may have originated as small stem outgrowths supported by single, unbranched strands of vascular tissue. (a)Megaphylls, which have branched vascular systems, may have evolved by the fusion of branched stems.(b)Figure 29.13a, bSporophylls and Spore VariationsSporophyllsAre modified leaves with sporangiaMost seedless vascular plantsAre homosporous, producing one type of spore that develops into a bisexual gametophyteAll seed plants and some seedless vascular plantsAre heterosporous, having two types of spores that give rise to male and female gametophytesClassification of Seedless Vascular PlantsSeedless vascular plants form two phylaLycophyta, including club mosses, spike mosses, and quillwortsPterophyta, including ferns, horsetails, and whisk ferns and their relativesThe general groups of seedless vascular plantsLYCOPHYTES (PHYLUM LYCOPHYTA)PTEROPHYTES (PHYLUM PTEROPHYTA)WHISK FERNS AND RELATIVESHORSETAILSFERNSIsoetesgunnii,a quillwortSelaginella apoda,a spike mossDiphasiastrum tristachyum, a club mossStrobili(clusters ofsporophylls)Psilotumnudum,a whiskfernEquisetumarvense,fieldhorsetailVegetative stemStrobilus onfertile stemAthyrium filix-femina, lady fernFigure 29.14Phylum Lycophyta: Club Mosses, Spike Mosses, and QuillwortsModern species of lycophytesAre relics from a far more eminent pastAre small herbaceous plantsPhylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and RelativesFernsAre the most diverse seedless vascular plantsThe Significance of Seedless Vascular PlantsThe ancestors of modern lycophytes, horsetails, and fernsGrew to great heights during the Carboniferous, forming the first forestsFigure 29.15The growth of these early forestsMay have helped produce the major global cooling that characterized the end of the Carboniferous periodDecayed and eventually became coal