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AEBI 210- Nov 16th.doc

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Biology (Agric & Envir Sc)
AEBI 210
Jaswinder Singh

Organisms 1- AEBI-210 001 November 16th, 2012 Evolution of Seeds and Pollen Seed Plants: All gymnosperms and angiosperms are seed plants Seed plants are heterosporic megaphylls which have microspores and megaspores A megaspore is contained within a nucellus (fleshy megasporangium) Megagametophytes are retained in the megaspore Have pollen which brings the male gamete to the female one Do not require water for fertilization to occur Seeds: The method of reproduction for most extant plants A seed has an embryo and food supply within a resistant coat A fertile nucellus envelope near integuments contains a megagametophtye The integuments develop into the seed coat Seed Evolution: Progymnosperms had wood and secondary phloem, but reproduced by free spores Embryo developed in the megagametophyte inside the megaspore An integument surrounds the megasporangium, but has a micropyle (small opening) The apex of the megasporangium was modified to receive pollen This new unit is called the ovule, which develops into the seed The female gametophyte is always protected by the sporangium Pollen: The male gametophyte has evolved into a 3 or 4 celled pollen grain Two sperm cells grow inside the pollen grain Pollen is carried to eggs by wind or insects, and grows into the ovule to fertilize it Gymnosperms: Coniferophyta -Needle-like leaves or scales -Have secondary growth -Xylem has only tracheids, but phloem has sieve cells and albuminou
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