BIO 200 Lecture Notes - Lecture 15: Ginkgo Biloba, Pollen Tube, Megaspore
27 Jun 2015
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Document Summary
Gymnosperms: gymnosperm life cycle is heterosporous, male sporangia. Scale from male cone produce microspore through meiosis. Male gametophyte (sperm) is inside pollen grain: female sporangia. Scale from female cone (ovary) contains ovules. Female gametophyte (embryo sac) created by megaspore through mitosis: sperm and egg unite to form seed. Conception can take up to 15 months: reduction of gametophytic phase, sporophyte (diploid) is the dominant form, gymnosperms have naked seeds (seeds are not always entirely enclosed by micropyle, four groups of gymnosperms, cycads, ginkgos, gnetophytes, conifers. Large: ancient, slow growing, resemble palm trees (different, grow up to 15 meters (50 feet) tall, cones may weigh up to 50 pounds. Ginkgos: no wild ginkgos, only extant species: gingko biloba. Last group with motile sperm: survived through rebreeding program, dioecious (males and females on separate plants) Gnetophytes: vessel cells (trachea, xylem and phloem, faster movement of nutrients, homoplasious with angiosperm vessel cells, contains three genera, gnetum, welwitschia.
