Bài giảng Biology - Chapter 30: Plant Diversity II: The Evolution of Seed Plants

Chapter 30Plant Diversity II: The Evolution of Seed PlantsOverview: Feeding the WorldSeeds changed the course of plant evolutionEnabling their bearers to become the dominant producers in most terrestrial ecosystemsFigure 30.1Concept 30.1: The reduced gametophytes of seed plants are protected in ovules and pollen grainsIn addition to seeds, the following are common to all seed plantsReduced gametophytesHeterosporyOvulesPollenAdvantages of Reduced GametophytesThe gametophytes of seed plantsDevelop within the walls of spores retained within tissues of the parent sporophyteGametophyte/sporophyte relationshipsFigure 30.2a–cSporophyte dependent on gametophyte (mosses and other bryophytes).(a)Large sporophyte and small, independent gametophyte (ferns and other seedless vascular plants).(b)Microscopic femalegametophytes (n) inovulate cones(dependent) Sporophyte (2n),the flowering plant(independent)Microscopic malegametophytes (n)inside these partsof flowers(dependent)Microscopic malegametophytes (n)in pollen cones(dependent) Sporophyte (2n)(independent)Microscopic femalegametophytes (n)inside these partsof flowers(dependent)Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms).(c)Gametophyte(n)Gametophyte(n)Sporophyte(2n)Sporophyte(2n)Heterospory: The Rule Among Seed PlantsSeed plants evolved from plants that had megasporangiaWhich produce megaspores that give rise to female gametophytesSeed plants evolved from plants that had microsporangiaWhich produce microspores that give rise to male gametophytes Ovules and Production of EggsAn ovule consists ofA megasporangium, megaspore, and protective integumentsFigure 30.3a(a) Unfertilized ovule. In this sectional view through the ovule of a pine (a gymnosperm), a fleshy megasporangium is surrounded by a protective layer of tissue called an integument. (Angiosperms have two integuments.)IntegumentSpore wallMegasporangium(2n)Megaspore (n)Pollen and Production of SpermMicrospores develop into pollen grainsWhich contain the male gametophytes of plantsPollinationIs the transfer of pollen to the part of a seed plant containing the ovulesIf a pollen grain germinatesIt gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovuleFigure 30.3b(b) Fertilized ovule. A megaspore develops into a multicellular female gametophyte. The micropyle,the only opening through the integument, allowsentry of a pollen grain. The pollen grain contains amale gametophyte, which develops a pollen tubethat discharges sperm.Spore wallMale gametophyte(within germinatingpollen grain) (n)Femalegametophyte (n)Egg nucleus (n)Dischargedsperm nucleus (n)Pollen grain (n)MicropylePollen, which can be dispersed by air or animals Eliminated the water requirement for fertilizationThe Evolutionary Advantage of SeedsA seed Develops from the whole ovuleIs a sporophyte embryo, along with its food supply, packaged in a protective coatFigure 30.3cGymnosperm seed. Fertilization initiatesthe transformation of the ovule into a seed,which consists of a sporophyte embryo, a food supply, and a protective seed coat derived from the integument.(c)Seed coat(derived fromIntegument)Food supply(femalegametophytetissue) (n)Embryo (2n)(new sporophyte)Concept 30.2: Gymnosperms bear “naked” seeds, typically on conesAmong the gymnosperms are many well-known conifersOr cone-bearing trees, including pine, fir, and redwoodThe gymnosperms include four plant phylaCycadophytaGingkophytaGnetophytaConiferophyta Exploring Gymnosperm DiversityFigure 30.4Gnetum Ephedra Ovulate conesWelwitschia PHYLUM GNETOPHYTAPHYLUM CYCADOPHYTAPHYLUM GINKGOPHYTACycas revolutaExploring Gymnosperm DiversityFigure 30.4Douglas fir PacificyewCommon juniperWollemia pineBristlecone pineSequoiaPHYLUM CYCADOPHYTAGymnosperm EvolutionFossil evidence reveals that by the late DevonianSome plants, called progymnosperms, had begun to acquire some adaptations that characterize seed plantsFigure 30.5Gymnosperms appear early in the fossil record And dominated the Mesozoic terrestrial ecosystemsLiving seed plantsCan be divided into two groups: gymnosperms and angiospermsA Closer Look at the Life Cycle of a PineKey features of the gymnosperm life cycle includeDominance of the sporophyte generation, the pine treeThe development of seeds from fertilized ovulesThe role of pollen in transferring sperm to ovulesFigure 30.6OvuleMegasporocyte (2n)IntegumentLongitudinalsection ofovulate coneOvulateconePollenconeMaturesporophyte(2n)Longitudinalsection ofpollen coneMicrosporocytes(2n)Pollengrains (n)(containing malegametophytes)MEIOSISMicropyleGerminatingpollen grainMegasporangiumMEIOSISSporophyllMicrosporangiumSurvivingmegaspore (n)Germinatingpollen grainArchegoniumIntegumentEgg (n)FemalegametophyteGerminatingpollen grain (n)Dischargedsperm nucleus (n)PollentubeEgg nucleus (n)FERTILIZATIONSeed coat(derived fromparentsporophyte) (2n)Food reserves(gametophytetissue) (n)Embryo(new sporophyte)(2n)Seeds on surfaceof ovulate scaleSeedlingKeyDiploid (2n)Haploid (n)The life cycle of a pine A pollen cone contains many microsporangia held in sporophylls. Each microsporangium contains microsporocytes (microspore mothercells). These undergo meiosis, giving rise tohaploid microspores that develop into pollen grains.3 In mostconifer species,each tree hasboth ovulateand pollencones.1 A pollen grainenters throughthe micropyleand germinates,forming a pollentube that slowlydigeststhrough themegasporangium.4 While thepollen tubedevelops, themegasporocyte(megasporemother cell)undergoes meiosis,producing fourhaploid cells. Onesurvives as amegaspore. 5 The female gametophytedevelops within the megasporeand contains two or threearchegonia, each with an egg.6 By the time the eggs are mature,two sperm cells have developed in thepollen tube, which extends to thefemale gametophyte. Fertilization occurswhen sperm and egg nuclei unite.7 Fertilization usually occurs more than a year after pollination. All eggs may be fertilized, but usually only one zygote develops into an embryo. The ovule becomes a seed, consisting of an embryo, food supply, and seed coat.8 An ovulate cone scale has twoovules, each containing a mega-sporangium. Only one ovule is shown.2Concept 30.3: The reproductive adaptations of angiosperms include flowers and fruitsAngiospermsAre commonly known as flowering plantsAre seed plants that produce the reproductive structures called flowers and fruitsAre the most widespread and diverse of all plantsCharacteristics of AngiospermsThe key adaptations in the evolution of angiospermsAre flowers and fruitsFlowersThe flowerIs an angiosperm structure specialized for sexual reproductionA flower is a specialized shoot with modified leavesSepals, which enclose the flower Petals, which are brightly colored and attract pollinatorsStamens, which produce pollenCarpels, which produce ovulesFigure 30.7AntherFilamentStigmaStyleOvaryCarpelPetalReceptacleOvuleSepalStamenFruitsFruitsTypically consist of a mature ovary Figure 30.8a–e(b) Ruby grapefruit, a fleshy fruitwith a hard outer layer andsoft inner layer of pericarp(a) Tomato, a fleshy fruit withsoft outer and inner layersof pericarp(c) Nectarine, a fleshyfruit with a soft outerlayer and hard innerlayer (pit) of pericarp(e) Walnut, a dry fruit that remains closed at maturity(d) Milkweed, a dry fruit thatsplits open at maturityCan be carried by wind, water, or animals to new locations, enhancing seed dispersalFigure 30.9a–cWings enable maple fruits to be easily carried by the wind.(a)Seeds within berries and other edible fruits are often dispersed in animal feces.(b)The barbs of cockleburs facilitate seed dispersal by allowing the fruits to “hitchhike” on animals.(c)The Angiosperm Life CycleIn the angiosperm life cycleDouble fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovuleOne sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the female gametophyte and initiates development of food-storing endospermThe endospermNourishes the developing embryoThe life cycle of an angiospermFigure 30.10KeyMature flower onsporophyte plant(2n)Ovule withmegasporangium (2n)Female gametophyte(embryo sac)Nucleus ofdevelopingendosperm (3n)Dischargedsperm nuclei (n)PollentubeMale gametophyte(in pollen grain)PollentubeSpermSurvivingmegaspore(n)Microspore (n)Generative cellTube cellStigmaOvaryMEIOSISMEIOSISMegasporangium(n)PollengrainsEggNucleus (n)Zygote (2n)Antipodal cellsPolar nucleiSynergidsEgg (n)Embryo (2n)Endosperm(foodSupply) (3n)Seed coat (2n)SeedFERTILIZATIONHaploid (n)Diploid (2n)AntherSperm(n)PollentubeStyleMicrosporangiumMicrosporocytes (2n)GerminatingSeed Anthers contain microsporangia.Each microsporangium contains micro-sporocytes (microspore mother cells) thatdivide by meiosis, producing microspores.1 Microspores formpollen grains (containingmale gametophytes). Thegenerative cell will divideto form two sperm. Thetube cell will produce thepollen tube.2 In the megasporangiumof each ovule, themegasporocyte divides bymeiosis and produces fourmegaspores. The survivingmegaspore in each ovuleforms a female gametophyte(embryo sac).3 After pollina-tion, eventuallytwo sperm nucleiare discharged ineach ovule.4 Double fertilization occurs. One spermfertilizes the egg, forming a zygote. Theother sperm combines with the two polarnuclei to form the nucleus of the endosperm,which is triploid in this example.5 The zygotedevelops into anembryo that ispackaged alongwith food into aseed. (The fruittissues surround-ing the seed arenot shown).6 When a seedgerminates, theembryo developsinto a maturesporophyte.7Angiosperm EvolutionClarifying the origin and diversification of angiospermsPoses fascinating challenges to evolutionary biologistsAngiosperms originated at least 140 million years agoAnd during the late Mesozoic, the major branches of the clade diverged from their common ancestorFossil AngiospermsPrimitive fossils of 125-million-year-old angiospermsDisplay both derived and primitive traitsFigure 30.11a, bCarpelStamenArchaefructus sinensis, a 125-million-year-old fossil.(a)Artist’s reconstruction of Archaefructus sinensis(b)5 cmAn “Evo-Devo” Hypothesis of Flower OriginsIn hypothesizing how pollen-producing and ovule-producing structures were combined into a single flowerScientist Michael Frohlich proposed that the ancestor of angiosperms had separate pollen-producing and ovule-producing structuresAngiosperm DiversityThe two main groups of angiospermsAre monocots and eudicotsBasal angiospermsAre less derived and include the flowering plants belonging to the oldest lineagesMagnoliidsShare some traits with basal angiosperms but are more closely related to monocots and eudicotsExploring Angiosperm DiversityFigure 30.12Amborella trichopodaWater lily (Nymphaea “Rene Gerard”)Star anise (Illicium floridanum)BASAL ANGIOSPERMSHYPOTHETICAL TREE OF FLOWERING PLANTSMAGNOLIIDSAmborellaWater liliesStar aniseand relativesMagnoliidsMonocotsEudicotsSouthern magnolia (Magnoliagrandiflora)Exploring Angiosperm DiversityFigure 30.12Orchid(Lemboglossumfossii)MonocotCharacteristicsEmbryosLeafvenationStemsRootsPollenFlowersPollen grain withone openingRoot systemUsually fibrous(no main root)Vascular tissuescatteredVeins usuallyparallelOne cotyledonTwo cotyledonsVeins usuallynetlikeVascular tissueusually arrangedin ringTaproot (main root)usually presentPollen grain withthree openingsZucchini(CucurbitaPepo), female(left) andmale flowersPea (Lathyrus nervosus,Lord Anson’sblue pea), a legumeDog rose (Rosa canina), a wild rosePygmy date palm (Phoenix roebelenii)Lily (Lilium“Enchant-ment”)Barley (Hordeum vulgare), a grassAntherStigmaCaliforniapoppy(Eschscholziacalifornica)Pyrenean oak(Quercuspyrenaica)Floral organsusually inmultiples of threeFloral organs usuallyin multiples offour or fiveFilamentOvaryEudicotCharacteristicsMONOCOTSEUDICOTSEvolutionary Links Between Angiosperms and AnimalsPollination of flowers by animals and transport of seeds by animalsAre two important relationships in terrestrial ecosystemsFigure 30.13a–c(a) A flower pollinated by honeybees. This honeybee is harvesting pollen and nectar (a sugary solution secreted by flower glands) from a Scottish broom flower. The flower has a tripping mechanism that arches the stamens over the beeand dusts it with pollen, some ofwhich will rub off onto the stigmaof the next flower the bee visits.(c) A flower pollinated by nocturnal animals. Some angiosperms, such as this cactus, depend mainly on nocturnal pollinators, including bats. Common adaptations of such plants include large, light-colored, highly fragrant flowers that nighttime pollinators can locate.(b) A flower pollinated by hummingbirds.The long, thin beak and tongue of this rufous hummingbird enable the animal to probe flowers that secrete nectar deep within floral tubes. Before the hummer leaves, anthers will dust its beak and head feathers with pollen. Many flowers that are pollinated by birds are red or pink, colors to which bird eyes are especially sensitive.Concept 30.4: Human welfare depends greatly on seed plantsNo group is more important to human survival than seed plantsProducts from Seed PlantsHumans depend on seed plants forFoodWoodMany medicinesTable 30.1Threats to Plant DiversityDestruction of habitatIs causing extinction of many plant species and the animal species they support