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Unformatted text preview: Green Algae and Land Plants Homosporous and Heterosporous Plants Homosporous : produce a single type of spore that develops into a bisexual gametophyte that produces both gametes Homosporous and Heterosporous Plants Heterosporous : the production of two distinct types of spore-producing structures and two distinct types of spores, male and female Evolution of Pollen when pollen evolved, heterosporous plants lost their dependence on water for fertilization pollen grains tiny enough to be carried by wind or animals Seeds allow embryos to be dispersed to a new habitat, away from the parent plant are often dispersed by wind, water, or animals the evolution of heterospory, pollen, and seeds triggered a dramatic radiation of seed plants (about 290 mya) Seed Plants-gymnosperms and angiosperms - production of seeds and pollen grains- embryo develops within seed coat Heterospory in Gymnosperms Mature sporophyte (2 n ) Developing sporophyte Seed (disperses via wind or animals) Embryo (2 n ) Ovules (contain megasporangia) Ovulate cone Female gametophyte ( n ) Archegonia Eggs ( n ) Mother cel (2 n ) Pol en produces sperm Cones with microsporangia Microspore ( n ) forms pol en grain Pol en grain (male gametophyte Megasporangium Pol en grain Megaspore divides to form female gametophyte ( n ), which produces archegonia and eggs by mitosis. (Only one egg is fertilized and develops.) Note that the red dots here and elsewhere represent nuclei Pol en grains disperse via wind Four meiotic products; one is large and forms the megaspore ( n ) Three meiotic products die MEIOSIS MITOSIS PO LLIN AT IO N MEIOSIS MITOSIS FERTILIZATION Flowering plants - Angiosperms...
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