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Bio2137-1.4.3 - 1.4.3 Conifers and their relatives The...

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1 1.4.3 Conifers and their relatives: The Gymnosperms Evolution 280 mybp in Permian period carboniferous ends with first great glaciations in north and south In north long cold winters with 6 months of frozen ground occur deserts expand into tropics and rainforests retreat into refugia Gymnosperms evolve: 1) Seeds = embryo (2n) + food reserve (n) that can survive long dry/ cold periods then grow. Gymnosperm = “Naked Seed” 2) Seed replaces spore as dispersal agent 3) Many other dry cold adaptations Changes in life cycle 1) Life cycle involves 2 gametophytes (mega and microgametophyte) which represent male and female 2) Seeds start as ovule which is the female gametophyte 3) In ovule, (mega) spores are not released and gametophyte is now carried by sporophyte (not a separate free living generation). 4) The male gametes are microspores aka “pollen”. Pollen is wind dispersed and resistant to drying. The need for water for fertilization is eliminated
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2 The ovule Extinct & intermediate groups Progymnosperms: radial growth but reproduction by spores Seed ferns Early gymnosperms of the carboniferous with large Fernlike leaves and reproduction by seed. Extinct by mesozoic. Four living divisions today: ginkgophyta, cycadophyta, gnetophyta, coniferophyta Progymnosperms: Intermediate between ferns and gymnosperms Reproduction by spores, but true radial growth
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3 Petrified forest Arizona Ginkgophyta Common 200-70 mybp but now a living fossil one existing species Ginkgo biloba , maidenhair tree
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