BIOL 2004 Lecture 8: Angiosperms

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2 integuments in angiosperms (only one in gymnosperm) Microphyle - gap between integument so pollen tube can go form through it. Synergids - sends signal so pollen tube knows where to grow to go toward the egg cell. Megaspore mother cell undergoes meiosis - forms 4 megaspores: three disintegrates to leave one functional megaspore, mitosis i - forms 2 nuclei, mitosis 2 - forms 4 nuclei, mitosis 3 - forms 8 nuclei. 3 on top, 3 on bottom, 2 in the center. When the mature megagametophyte is ready to be fertilized, the two nuclei in the center fuse into one: thus, the 7 celled, 8 nucleated structure. Integumented megasporangium: produces megaspore, megaspore produces a gametophyte, after fertilization, it houses and protects the embryo, and becomes a seed. Microspore mother cell/microsporocytes (diploid) undergo meiosis to produce microspores - 4 microspores: undergoes mitosis to produce pollen grain, tapetum is a cell layer within microsporocyte, tapetum undergoes apoptosis to release the spores.

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