BSC_2011Ch29Seeds - BSC 2011 Dr Presley Chapter 29...

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BSC 2011 Chapter 29 Dr. Presley Sadava9th Ch 29 1 of 10 THE EVOLUTION OF SEED PLANTS SEED PLANTS - dominant plant form on Earth today, many arose in Carboniferous period - seed survival and germination have been important factors for success - Judean date seed over 2,000 years old was germinated in 2005 and continues to grow and thrive—the oldest seed ever germinated. - include gymnosperms (cone-bearing plants) and angiosperms (flowering plants) REPRODUCTIVE ADAPTATIONS of seed plants - gametophytes are more reduced and protected by moist sporophyte tissue - attached and nutritionally dependent on the sporophyte *provides shelter from UV induced mutations and desiccation Review Figure 29.3, p. 610 - seeds = embryo with food reserve covered by seed coat (from integuments) *provide greater embryo protection from desiccation and predators *resting or dormant stage of embryonic growth (viable) *function: greater range of plant dispersal - contents represent 3 generations in plant life cycle a. seed coat – integuments of diploid parent generation b. food reserve – is or develops from the haploid megagametophyte tissue (replaced in angiosperms by endosperm) c. embryo – is the new sporophyte generation after fertilization and growth - heterosporous seed plants - megasporangium - undergoes meiosis, produces 4 megaspores, only one megaspore survives, **megaspore is never shed develops into female gametophyte produces the egg fertilization occurs producing the diploid zygote b embryo surrounded by sterile protective tissue that forms the integuments that later becomes the seed coat provides food for developing embryo in ovule seed develops - microsporangium - cells under go meiosis, produce many microspores each microspore divides to produce bi-celled pollen grain the male gametophytes = pollen grains ** replaces flagellated sperm (except in few gymnosperms) - fertilization now independent from requirement for water - pollen grains distributed by wind, insect, other animals = pollination - cell wall contains sporopollenin , chemically resistant protection - pollen tube elongates and digests its way to egg for fertilization - seed is the end product (ripened ovule) - embryo may become dormant within the seed - secondary growth – production of thickened woody stems, secondary xylem
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BSC 2011 Chapter 29 Dr. Presley Sadava9th Ch 29 2 of 10 GYMNOSPERMS – naked seeds cycads , ginkgo , gnetales , conifers 4 phyla: Cycadophyta, Ginkgophyta, Gnetophyta, Coniferophyta - see text diagram on p. 612 Mesozoic era was the age of gymnosperms, earlier than flowering plants once were the dominant plants on Earth, now still dominant in northern parts of Northern Hemisphere and at high altitudes extensive secondary growth - stems and roots grow larger in diameter over time produce “ naked seeds ” for dispersal - lack enclosure (ovaries) in which seeds could develop tracheids of xylem for water transport and support (except: Gnetales which have vessel cells ) specialized leaves (sporophylls) bear sporangia
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This note was uploaded on 06/06/2011 for the course BSC 2011 taught by Professor Presley during the Spring '11 term at FAU.

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BSC_2011Ch29Seeds - BSC 2011 Dr Presley Chapter 29...

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