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24.5 plants.docx

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Wilfrid Laurier University
Tristan Long

24.5 Gymnosperms the first seed plants Gymnosperms (gymnos- naked, sperma- seed) - naked seeds - major changes in plants structures related to reproduction -important reproductive adaptations  pollen and pollination  ovule  seed 4 types of gymnosperms 1. conifers 2. cycads 3. ginkgoes Cool Cats Get Girls 4. gnetophytes 24.5a Major reproductive adaptations occurred as gymnosperms evolved - produce seeds that are exposed Ovules: Increased protection for Female gametophyte and Egg Two steps that would lead to the formation of a seed step 1 - spores are retained inside sporangia on the sporophyte step2 - megaspores = one per sporangium (4 produced by meiosis- 1 survies) heterosporous plant = gametophyte develops inside the megaspore wall and inside the megasporangium - no risks of predation - the egg developing inside the gametophyte = ovule [when fertilized= seed] - fertilized egg = embryo -> surrounded by protective layer = seed coat -- how can the sperm go through the layer of megasporangium? - a male structure will penetrate through the tissue and release sperm inside the female gametophyte Pollen: Eliminating the Need for Water in Reproduction Heterosporous plants -> microspore produces a male gametophyte ( in a microspore wall) - male gametophyte = pollen grain - transfer = pollination (via air or bodies of animal pollinators) - when in contact with female tissue = germinate= pollen tube - pollen tube -> a cell that grows through female gamtoyjhtis tissue and carries nonmotile sperm to the egg - no need of h20( exceptions - cycads, ginkgo) Seeds: protecting and nourishing plant embryos Seed =  ovule matures  pollen grain reaches and a sperm fertilizes the egg Three basic parts 1) Embryo sporophyte 2) Tissues surrounding the embryo - nourishes until it becomes established as a seedling with leaves and roots 3) Seed coat - a tough protective outer layer Advantages - shelters embryo from drought, cold - embryo can be transported far from its parents e.x ; ocean currents carry coconut seeds 24.5b Modern gymnosperms include conifers and a few other groups represented by relatively few species that tend to be restricted to certain climates Conifers are most common gymnosperms [Phylum Confirephyta] - 80% of all species ex pines, spruces, firs Characterisics - form woody cones - have needlike leaves  have thick cuticle  sunken stomata  fibrous epidermis  ALL THAT REDUCE WATER LOSS Gymnosperms produce Resins Resins- mix of organic compounds that are by products of metabolism - long resin ducts through the wood - used to fix violin bows - fossil resin -> amber Pine life cycle read page 568 Cyacds are restricted to warmer climates [phylum cydaphphyta] - flourished along with dinosaurs - tropics and subtropics - massive cone
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