UT Arlington BIOL BIOL 3427 - Gymnosperms (4 pages)

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This Lecture note describes the evolution of gymnosperms.

Lecture number:
Lecture Note
University of Texas at Arlington
Biol Biol 3427 - Plant Science
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BIOL 3427 1st Edition Lecture 14 Outline of Current Lecture II Prokaryotes III Viruses IV Fungi V Symbiotic relationships Current Lecture I Gymnosperms a Evolution of plants i Bryophytes ii Seedless vascular plants iii Seed plants 1 Gymnosperms 2 Angiosperms b Evolution of the seed i Why are seeds advantageous 1 Protects embryo 2 Stores food ii All seeds heterosporous iii Definition of seed 1 Fertilized mature ovule containing an embryo 2 Ovule a Nucellus megasporangium surrounded by 1 or 2 integuments with micropyle b Mature contains a megagametophte composed of archegonia and nutritive tissue c After fertilization integuments develop into seed coat d All seeds contain stored food iv Ovule evolution 7 events 1 Megaspore retained in megasporangium nucellus 2 Number of megaspore mother cells reduced to one 3 Only one of four megaspores survives 4 Megasporophyte highly reduced retained in megasporangium 5 Embryo young sporophyte develops within megasporophyte 6 Integument envelops megasporangium 7 Apex of megasporangium modified to receive pollen grains These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II III IV V VI Fossil record a Unclear exact order of events above b Oldest seeds from late Devonian 365 mya i Gradually integuments fused until only opening left at apex micropyle c Five phyla of seed plants with living representatives i Seed plants typically possess megaphylls 1 Coniferophyta 2 Cyadophyta 3 Ginkophyta a Gymnosperms b Naked seeds c 840 species ii Modified into needles or scales in some groups a Gnetophya gymnosperms b Antherophyta angiosperms covered seed 300 000 species d Progymnosperms i Not gymnosperms 1 Extinct group of seedless vascular plants 2 Ancestors of seed plants were similar to progymnosperms ii Late Paleozoic iii In between trimerophytes and seed plants 1 Spores 2 Bifacial vascular cambium a Secondary xylem similar to conifers b Secondary phloem 3 One group has eustele Extinct Gymnosperms a Pteridospermales seed ferns b Cordaitales Cordaites c Bennettitales cycadeoids Living Gymnosperms a Ovules and seeds exposed Female Gametophyte a Produces several archegonia i Results in polyembreyony more than one embryo per ovule Fertilization a Water not required b Pollination i Male gametophyte pollen grain transferred to female gametophyte via wind ii Pollen tube forms c No antheridia in seed plants VII VIII IX X XI XII XIII XIV XV XVI XVII Sperm differ among groups a Nonmotile in conifers and gnetophytes i Pollen tube conveys sperm to egg b Flagellated in cycads and Gingko i Pollen tube does not penetrate archegonium ii Pollen tube absorbs nutrients for production of sperm Phylum Coniferophyta a Most numerous most widespread most ecologically important gymnosperms b 70 genera 630 species c Late Carboniferous 300 mya d Leaves have many drought resistant characteristics Pines Pinus a 100 species b Dominate many areas of N America and Eurasia c Cultivated in Southern Hemisphere Unique leaf arrangement a Seedlings needlelike leaves single spirally arranged b In 1 2 years leaves in bundles fascicles of 1 8 Leaves adapted for low soil moisture a Thick cuticle b Hypodermis compactly arranged thick walled cells c Sunken stomata Xylem a Primarily tracheids Phloem a Primarily sieve cells Life cycle a Two years to complete Microsporangia and megasporangium a Borne on separate cones stroboli on same tree b Usually male on lower branches and female on upper Microsporangiate cones a Small 1 2 cm b Microsporocytes microspore mother cells c Meiosis in early spring i Produce four haploid microspores ii Each microspore becomes pollen grain immature iii Male gametophyte 2 prothalial cells 1 generative cell 1 tube cell Megasporangiate ovulate cones a Much larger more complex compound structure b Seed scale complex modified branch system i Coniferious scale with two ovules on upper surface ii Subtending sterile tract c Scales in spiral d Ovule i Megasporocyte within nucellus undergoes meiosis ii Only one of four megaspores is functional e Pollination i Occurs in spring 1 Takes two years to complete ii Scales on ovulate code widely separated iii Pollen grains land in pollination drops at the micropyle iv Pollen grain grows pollen tune into nucellus v Scales grow together to protect ovules vi Megaspore becomes megasporophyte 1 Very slow development 2 About 15 months after pollination archegonia formed XVIII Generative cell of pollen grain divides 12 months after pollination a 1 sterile cell b 1 spermatogeneous cell which then divides into two sperm cells c When sperm produces microgametophyte is mature

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