bio- chap 30-34

bio- chap 30-34 - Chapter 30 I. Overview of Reproductive...

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Chapter 30 I. Overview of Reproductive Adaptations of Seed Plants A. Gametophytes of seed plants became even more reduced than the gametophytes of seedless vascular plants 1. Gametophytes of seedless vascular plants develop in the soil as an independent generation 2. Minute gametophytes of seed plants are protected from desiccation by being retained w/in moist reproductive tissue of sporophyte generation 3. In seed plants all sporophyte embryos are dependent to some extent on tissues of maternal gametophyte B. In seed plants, the seed replaced the spore as the main means of dispersing offspring 1. Seed is a resistant structure that is multicellular and much more complex 2. Seed consists of a sporophyte embryo packaged along w/ a food supply w/in protective coat 3. All seed plants heterosporous-- two different types of sporangia that produce two types of spores: megasporangia (female gametophytes) & microsporangia (male gametophytes) 4. Nucellus: solid fleshy structure that constitutes the megasporangia 5. Integuments: additional layers of sporophyte tissues that envelop the megasporangia of seed plants 6. Ovule: whole structure (integuments, nucellus and megaspores), inside ovule female gametophyte develops C. Pollen became the vehicle for sperm cells in seed plants 1. Microspores develop into pollen grains which become male gametophytes of seed plants 2. Pollen grains, protected by tough sporopollenin-containing coats, can be carried away by wind or animals 3. When pollen grain lands on ovule, it elongates a tube that discharges one or more sperm into female gametophyte w/in ovule 4. Most common gymnosperms and all angiosperms, the sperm lacks flagella II. Gymnosperms A. The Mesozoic Era 1. Gymnosperms probably descended from progymnosperms, a group of Devonian plants 2. Adaptive radiation during Carboniferous and early and early Permian periods produced various divisions of gymnosperms B. The four divisions of extant gymnosperms are the cycads, the ginkgo, the gnetophytes, and the conifers 1. Cycads: division Cycadophyta, are not true palms, bear naked seeds on sporophylls (leaves specialized for reproduction) 2. Ginkgo: only extant species of division Ginkgophyta, fan-like leaves that turn gold and are deciduous in autumn 3. Gnetophyta: consists of three genera that are probably not closely
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related ( Weltwitschia, Gnetum, Ephedra ) 4. Conifers (Coniferophyta): reproductive structure is cone (cluster of scale like sporophylls) a. Includes pines, firs, spruces, larches, yews, junipers, cedars, cypresses b. dominate vast forested regions of Northern Hemisphere c. almost all evergreens (retain leaves throughout the year) d. among tallest, largest and oldest organisms on earth C. The life cycle of a pine demonstrates the key reproductive adaptations of seed plants 1. Pine tree is a sporophyte- sporangia located on scale like sporophylls (cones) 2. Conifers are heterosporous; male and female gametophytes develop from different types of spores produced by separate cones
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bio- chap 30-34 - Chapter 30 I. Overview of Reproductive...

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