Lesson 6 notes - Lesson 6 Unique Features of Reproduction in Angiosperms Structure and Evolution of flowers Flowers evolved in angiosperms Morphology o

Lesson 6 notes - Lesson 6 Unique Features of Reproduction...

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Lesson 6: Unique Features of Reproduction in Angiosperms Structure and Evolution of flowers Flowers evolved in angiosperms Morphology o Complete flower – has all four whirls o Incomplete flower – lacks one or more whirls These 4 distinct whirls of parts are characteristic of most modern day angiosperm o All stems = androecium all stamens which are male structures of a flower, most stamens have a stalk or filament and an anther which houses the microspore mother cells o All carpels = gynoecium female parts of the flower, consists of one or more carpels Ovary of carpel – contains ovules Slender neck of carpel – style which has a pollen receptive stigma at the tip o All petals = corolla primarily functions to attract pollinators o All sepals = calyx outermost whirl of flower parts, protects flower bud Floral modifications are often result of natural selection acting on traits that enhance pollination Floral organs are thought to have evolved from leaves Trends in Floral specialization/symmetry Major trends in floral evolution have lead to a wide diversity of flowering plants Fusion of flower parts that were once separate Reduction in numbers of flower parts Radial symmetry Bilateral symmetry more advanced than radial Gamete production Alternation of generations – angiosperms have this life cycle, feature of all plants Flower is part of sporophyte generation Gametophytes are very small and contained within sporophyte o Diploid and haploid generations o Pollen grains Microgametophytes – male gametophytes are the pollen grains o Embryo sac Megagametophytes – female gametophytes Inside the anther are pollen sacs with microspore mother cells that undergo meiosis to produce microspores Microspores through mitosis and wall differentiation become pollen
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The pollen consists of two cells – the tub cell grows a pollen tube and the generative cell divide to form two sperm Formation of an embryo sac has significant differences from formation of pollen Inside ovule is the megaspore mother cell that goes through meiosis to produce four megaspores Mitosis results in production of microspore and megaspore Three of four megaspores disintegrate, the remaining megaspore undergoes mitotic divisions to produce a seven-celled, eight-nucleic embryo sac which is the megagametophyte Gametophytes Through mitotic divisions, the megaspore develops into the embryo sac Embryo sac o 8 nuclei o 7 cells o Precise positions of nuclei and cells o
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  • Spring '08
  • GEORGESIMMONS
  • Biology, Pollination, Pollen, embryo sac

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