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BIOL 1007February 11, 2019Lecture 10Plant Diversity II: The Evolution of Seed PlantsOverview: Transforming the WorldSeed plants became dominant producers in most terrestrial ecosystemsOriginated about 360 myaSeed:An embryo and nutrients surrounded by a protective coatoDomestication of seed plants had begun by 8,000 years ago and allowed for permanentsettlementsoAgricultural Revolution1. Reduced GametophytesGametophytesdevelop within walls of spores thatare retained within tissues of the parent sporophyte2. HeterosporySeed plants are heterosporous: This means that 2 types of spores areproduced by the sporophyte... ♀ & ♂Megasporangiaproducemegasporesthat give rise to female ♀gametophytesMicrosporangiaproducemicrosporesthat give rise to male ♂gametophytes3. Ovules and Production of EggsAn ovule:1.megasporangium2.megaspore3.one or moreprotective integumentsGymnosperm megaspores: one integumentAngiosperm megaspores: usually have two integuments4. Pollen and Production of Sperm
Microsporesdevelop intopollen grains, which contain the malegametophytesPollinationis the transfer of pollen to the part of a seed plantcontaining the ovulesPollen eliminates need for a film of water andCan be dispersed great distances byairoranimals (vectors)oIf a pollen grain germinates, it gives rise to a pollen tube thatdischarges sperm into the female gametophyte within the ovule5. Evolutionary Advantage of SeedsA seed develops from the whole ovuleA seed is asporophyte embryo, along with its food supply,packaged in a protective coatThey mayremain dormantfor days to years, until conditions arefavorable for germinationSeeds have a supply ofstored foodThey may betransported long distancesby wind or animalsSeed PlantsSeed plants can be divided into 2 clades1.GymnospermsExample, “evergreen” trees (Pine, etc)2.Angiosperms(aka flowering plants)Example, (sun-flowers, corn, maple trees)1. GymnospermsGymnosperms means “naked seeds”The seeds areexposed on sporophylls