23.1 introduction to plant...
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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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