Lecture_27_DulaiS09_PlantEvolution

Lecture_27_DulaiS09_PlantEvolution - Plant Evolution Bio...

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Plant Evolution Bio 001 Spring 2009
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The Plant Kingdom • Nearly all are multicelled • Vast majority are photoautotrophs – Energy from sun – Carbon dioxide from air – Minerals dissolved in water
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Setting the Stage for Plants • Earth’s atmosphere was originally oxygen free • Ultraviolet radiation bombarded the surface • Photosynthetic cells produced oxygen and allowed formation of a protective ozone layer
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Invading the Land • Cyanobacteria were probably the first to spread into and up freshwater streams • Later, green algae and fungi made the journey together • Every plant is descended from species of green algae
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Adaptations to Land • Root systems • Shoot systems • Vascular tissues • Waxy cuticle for water conservation
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Evolutionary Trend in Plant Life Cycles • Algae and bryophytes put most energy into making gametophytes • Land plants put energy into structures that produce spores and retain, nourish, and protect gametes
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Evolutionary Trend s p o r h y t e i m a n c ga oph por nc green algae bryophytes ferns gymnosperms angiosperms zygote only, no sporophyte
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Milestones in Plant Evolution charophytes bryophytes lycophytes horsetails ferns cycads ginkgos conifers gnetophytes flowering plants seed plants plants with true leaves vascular plants land plants (closely related groups)
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Pollen • Pollen grains are sperm-bearing male gametophytes that develop from microspores • Allows transfer of sperm to egg without water • Can drift on air currents, or be carried by pollinators
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Seeds • Ovules are female reproductive structures that become seeds • Consist of: – Female gametophyte with egg cell – Nutrient-rich tissue – Jacket of cell layers that will form seed coat
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Nonvascular Plants • Bryophytes • Include 24,000 species of: Liverworts Hornworts Mosses
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Bryophytes • Small, nonvascular, nonwooody • Gametophyte dominates life cycle;
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Lecture_27_DulaiS09_PlantEvolution - Plant Evolution Bio...

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