Life Cycle1 - Vascular plants show a progression of...

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Life Cycles Animal life cycles have meiosis followed immediately by gametogenesis. Gametes are produced directly by meiosis. Male gametes are sperm. Female gametes are eggs or ova. The plant life cycle has mitosis occurring in spores , produced by meiosis, that germinate into the gametophyte phase. Gametophyte size ranges from three cells (in pollen ) to several million (in a "lower plant" such as moss). Alternation of generations occurs in plants, where the sporophyte phase is succeeded by the gametophyte phase. The sporophyte phase produces spores by meiosis within a sporangium . The gametophyte phase produces gametes by mitosis within an antheridium (producing sperm) and/or archegonium (producing eggs). Within the plant kingdom the dominance of phases varies. Nonvascular plants , the mosses and liverworts, have the gametophyte phase dominant.
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Unformatted text preview: Vascular plants show a progression of increasing sporophyte dominance from the ferns and "fern allies" to angiosperms. Angiosperms Flowering plants, the angiosperms , were the last of the seed plant groups to evolve, appearing over 100 million years ago during the middle of the Age of Dinosaurs (late Jurassic ). All flowering plants produce flowers and if they are sexually reproductive, they produce a diploid zygote and triploid endosperm . Whence came the angiosperms? This was Darwin's "abominable mystery". Clearly angiosperms are descended from some group of Mesozoic-aged gymnosperm seed plant. ...but which one? The classical view of flowering plant evolution suggests early angiosperms were evergreen trees that produced large Magnolia-like flowers....
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