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23.1IntroductiontoPlantReproductionVegetativeReproduction

§ Theplantsthatresultfromvegetativereproductionareclonesoftheoriginalplantbecausetheirgeneticmakeupsareidenticaltotheoriginalplant.

AdvantagesofVegetativeReproduction

§ Itisfastertogrownewplantsthanfromasporeoraseed.§ Theresultantplantsaremoreuniformintheircharacteristics.§ Theonlywaytoproducesomefruitsthatdonotproduceseeds

NaturalVegetativeReproduction

§ Whenconditionsaredry,somemossesdryout,breakapart,andarescatteredbythewind.

§ Whenconditionsimprove,someofthesepiecesareabletoresumegrowthinanewlocation.

HumansUseVegetativeReproduction

§ Farmers,horticulturists,andscientistscanusebuds,leaves,stems,orrootpiecesfromcertainplantstogrownewplants.

§ Afewcellsofplanttissuecanbeplacedonnutrientagarinsterileconditionstoproducehundredsofidenticalplants.

AlternationofGenerations

§ Thelifecycleofmostplantsincludesadiploid(2n)sporophytestageandahaploid(n)gametophytestage.

§ Thegametophytestageproducesgametes—eggandsperm.

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§ Innonvascularplants,thespermmusthaveasmallamountofwatertogettotheegg.§ Invascularplants,thespermmaybecarriedbythewind,oranothervectorsuchasan

insect.§ Fertilizationoftheeggbythespermformsacell

thatisthefirstcellofthesporophytestage.§ MossReproductionandLifeCycle§ Thelifecycleofthemossesbeginswiththe

dominantstage,thegametophyte.§ Therearebothmaleandfemaleformsofthe

gametophyte.§ Eggsareproducedinthefemalestructure,called

thearchegonium.§ Spermareproducedinthemalestructure,called

theantheridium.§ Spermrequirewatertoswimtotheegg.§ Thechemicalthatallowsspermtofindtheeggischemotaxis.§ Thematuresporophyteconsistsofastalkthatgrowsinthegametophytestage.§ Atthetipofthestalkisacapsulewhereupto50millionsporesmayformbymeiosis.§ Thesporesproduceaprotonemathatcandevelopintothegametophyteplantandstart

anewcycle.

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FernReproductionandLifeCycle

§ Anotherlifecyclethathasalternationofgenerationsandproducessporesisthatofthefern.

§ Sporesareproducedfromthesori,ontheundersideofafrond.

§ Ifafernsporelandsondamp,richsoil,itcangrowandformatiny,heart-shapedgametophytecalledaprothallus.

§ Fertilizationproducesasporophytethatgrowsfromtheprothallus.

§ Theyoungsporophytedevelopsintoafrondtostartthecycleoveragain.

ConiferReproductionandLifeCycle

§ Conifersareheterosporus—theyproducetwotypesofsporesthatdevelopintomaleandfemalegroups.

FemaleCones

§ Atthebaseofeachscaleonafemaleconearetwoovules.§ Eachovulehasamegasporangiumthatproducesmegaspores.§ Oneofthemegasporesdevelopsintothefemalegametophyte.

MaleCones

§ Eachscaleonthemaleconecontainshundredsofsporangia.§ Thesporangiaproducemicrospores,whichproducethemalegametophyte,orpollen

grain. Pollination

§ Pollinationoccurswhenthepollengrainfromonespeciesofaplantlandsonthefemalereproductivestructureofaplantofthesamespecies.

§ Thepollengrainistrappedinastickysubstancecalledthepollendropwhichislocatednearthemicropyle.

SeedDevelopment

§ Seeddevelopmentwithintheconemaytakeaslongasthreeyears.§ Theseedembryowillusethecotyledonsforphotosynthesisuponsprouting.

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