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npsABB7 - Seed plants and the seed habit la n d p la n ts v...

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1 Charophycean ancestor Charophyceans Bryophytes Pteridophytes Gymnosperms Angiosperms (mosses, etc.) (ferns, etc.) (conifers, etc.) (flowering plants) Seed plants and the ‘seed habit’ seed plants vascular plants land plants Reproduction by flowers Dispersal by seeds Presence of vascular tissue Basic land plant attributes Trends in plant complexity: Bryophytes Bryophytes have the gametophyte as the ‘dominant’ generation: Diploid Haploid fertilization mitosis sporophyte meiosis spores protonemata young gametophytes mitosis mitosis sperm in antheridium egg in archegonium Trends in plant complexity: Bryophytes Bryophytes have the gametophyte as the ‘dominant’ generation: Diploid Haploid young gametophytes mitosis Alternation of generations Independent and dominant gametophytes Dependent sporophytes Trends in plant complexity: Pteridophytes Diploid sporophyte dominates the life cycle: Diploid Haploid spore young gametophyte gametophyte archegonia antheridia young sporophyte sori sporangium mature sporophyte meiosis mitosis
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2 Trends in plant complexity: Pteridophytes Diploid sporophyte dominates the life cycle: Diploid Haploid gametophyte young sporophyte mature sporophyte Alternation of generations Independent and dominant sporophyte Independent and transient gametophyte Seed plants and the ‘seed habit’ To review: Pteridophytes (at least, ferns) have several advances over Bryophytes: vascular tissue , allowing increasing specialization of organs, and much greater size true leaves , including branched vascular systems Like many Bryophytes, Pteridophytes can disperse widely via tough, walled spores -- but these are unicellular and lack significant nutrient stores. Pteridophytes remain dependent on liquid water for reproduction, restricting their range of habitats to fairly moist areas (at least seasonally moist) Seed plants and the ‘seed habit’ SEED PLANTS became enormously successful in land habitats because of two evolutionary advances over Pteridophytes: • A tough-walled male gametophyte -- POLLEN -- that can disperse widely without liquid water Propagation via complex multicellular SEEDS that have protective coverings and significant stored nutrients to assist early growth of the embryo and young plant • Seeds may also contain external ‘food’ to entice animals to move them around (‘fruits’) • As part of these functional advances: even more reduction of gametophyte generation Seed plants and the ‘seed habit’ Reduction of gametophyte generation Bryophytes Pteridophytes Seed plants Sporophyte dependent on gametophyte ( gametophyte dominant) Large sporophyte, small but independent gametophyte Gametophyte small and dependent on sporophyte ( sporophyte dominant) gametophyte sporophtye spores gametophyte sporophtye spores gametophyte sporophtye Diploid sporophyte (2N) Haploid gametophyte (N)
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3 Seed plants and the ‘seed habit’ integuments Nucellus ( megasporangium) megaspore micropyle Unfertilized ovule All seed plants are heterosporous: they produce
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