Bumper sticker of the day: "Consciousness: that annoying time between naps."


Review of Lecture 5: Scraping the sky: The Gymnosperms


1. Five phyla of gymnosperms: Ginkgophyta (1 species: Ginkgo biloba), Cycadophyta (9 genera, ca. 140 spp), Coniferophyta or Pinophyta (6 or 7 families, ca. 50 genera, ca. 500 spp.), Gnetophyta (3 genera -- Ephedra -- 40 spp, Gnetum -- 28 spp, Welwitschia -- 1 spp)

2. Life cycle of pine. Megagametogenesis: Megasporangium on scale of female cone produces Megaspore mother cell (diploid); Megaspore mother cell undergoes meiosis to produce four haploid Megaspores; three megaspores degenerate and the one remaining megaspore divides by mitosis to form the Megagametophyte -- nucellus, archegonium(s) with eggs, integument, micropyle. Microgametogenesis: Microsporangium on scale of male cone produces Microspore mother cell (diploid); Microspore mother cell undergoes meiosis to produce four haploid Microspores; each microspore divides by mitosis to form a vegetative (pollen tube) and generative cell; the microgametophyte is the pollen grain.

3. Pollination of pine is via wind dispersal of pollen. Pollen germinates to grow a pollen tube down through the female gametophyte tissue to the archegonium. Two sperm cells produced by each pollen grain, but only one is used for fertilization of the egg. Takes more than one year to complete the cycle from gamete formation to mature seed formation.

4. Nutrient reserve of the pine seed comes from the nucellus (tissue from megagametophyte).

5. Gymnosperms have most of the record holders in terms of age, size, and height.

6. Conifers adapted for dry and nutrient-poor environments -- leaves, roots, stems, etc.

7. Ecological and economic importance -- especially for the conifers.

8. Gnetophytes are the plants most closely-related to flowering plants (angiosperms).


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Last updated April 11, 1997.