plant_diversityII_web

plant_diversityII_web - 4 major events in plant evolution...

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4 major events in plant evolution... I. II. III. IV. Ordovician Silurian Devonian Cretaceous 475 mya 430 mya 360 mya 130 mya see Fig. 29.7
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One branch of the ferns developed primitive seeds and woody stems…Pteridosperms (seed ferns) late devonian/ carboniferous 370 mya
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Gymnosperms Cycad Transitional forms: woody, heterosporous, but lacking true seeds Progymnosperms (precursors to true seed plants) - present by late Devonian period
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Reproductive Adaptations of Seed Plants 1. Reduction of gametophyte retained in moist repro tissue of sporophyte generation (so not independent) • Zygotes developed into embryos packaged with a food supply within a protective seed coat. Can potentially survive long periods. • Seeds replaced spores as main means of dispersal. 3. Evolution of pollen . Plants no longer tied to water for fertilization. 2. Evolution of the seed (nutrition, protection from environment, dispersal)
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Reduction of Gametophyte Three variations on gametophyte/sporophyte relationships Fig. 30.1 6 th ed. Retention of gametophyte generation may afford protection from solar radiation-induced mutations of the genome (a diploid is tolerant of mutation), drought & additional environmental stresses
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Bryophytes and seedless vascular plants produce and release single-celled spores. • Seeds are more hardy because of their multicellular nature better protection from harsh environments more widespread dispersal of offspring. Seeds Seed = sporophyte embryo packaged with food in a protective coat. Recall:
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All seed plants are heterosporous - they possess two different kinds of sporangia, each producing a different type of spore. Recall: Megasporangia produce megaspores female (egg containing) gametophytes Microsporangia produce microspores male (sperm containing) gametophytes In seed plants, megaspores (feamle gametophytes) retained on the parent (sporophyte) – initially (until released with entire seed) (develop into pollen)
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Figure 30.3 From ovule to seed Megasporangium = Nucellus (a solid, fleshy structure) Integuments surround megasporangium & megaspore(s) Ovule (develops into female gametophyte) Pollen grain contains male gametophyte that develops a tube & discharges sperm.
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Bryophyta Anthocerophyta Hepatophyta Lycopodophyta Pterophyta Psilophyta* Sphenophyta* Ginkophyta Cycadophyta Coniferophyta Gnetophyta Anthophyta mosses hornworts liverworts club mossess ferns whisk ferns horsetails Ginkgo cycads conifers mormon tea & others flowering plants Kingdom Plantae Divisions = Phyla gymnosperms
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Gymnosperms - about 760 species worldwide
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