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Test 4 Guide Bio (98% on the test)

19 Pages

Biological Sciences
Course Code
BIOL 1002

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CHAPTER 44GAMETOPHYTE DEVELOPMENT IN FLOWERING PLANTSMALEThe gametophytes are haploid and develop within sporophyte flowers They are very small compared to the sporophyte and cannot live on their own Pollen male gametophyte develops within the pollen sacs of anthers 1 Microspore mother cell aka microsporocyte develops inside the pollen sacs2 Diploid microspore mother cells divide by meiosis to form 4 haploid microspores from each microspore mother cell3 Each microspore divides by mitosis to make an immature pollen grain containinga tube cell b generative cell inside the tube cell4 The generative cell goes through mitosis to form two sperm cells This is now the mature pollen grain see fig 445 Once the pollen matures the anther splits open and breezes carry away the pollen FEMALEEmbryo sac development see fig 447 Within the ovary of a carpel masses of cells differentiate into ovules The outer layers of the ovule are the integumentThe tissue of the ovule is diploidThe series of events leading to the female gametophyte are1 The megaspore mother cell aka megasporocyte develops within the ovule that is within the ovary of the carpel2 The megaspore mother cell divides by meiosis to form four haploid megaspores3 One of the four megaspores survives 4 The remaining one of the four goes through 3 rounds of mitosis producing eight haploid nuclei Plasma membranes and cells walls then form dividing the cytoplasm into the seven cells that make up the female gametophyte 5 There are 3 small cells at each end each with one nucleus and one large central cell with two nuclei The egg is one of the 3 cells at the lower end located near an opening in the integuments of the ovuleThe larger center cell becomes the primary endosperm cellPOLLINATION AND FERTILIZATION see fig 4481 Pollination starts when pollen leaves an anther and lands on a stigma The pollen absorbs water from the stigma 2 The tube cell breaks through the pollen coat and the pollen grain grows a tube down through the style towards the ovary It reaches the opening in the integuments of the ovule3 The pollen grain releases 2 sperm cells from the generative cell move down the tube to the ovary where a double fertilization occursDouble Fertilization One sperm fuses with the egg cell to form the diploid zygote The other sperm fuses with the polar nuclei in the primary endosperm cell making this triploid endosperm 3 sets of chromosomes tissueDEVELOPMENT OF SEEDS ANDS see fig 449The seed develops from the ovule1 The integuments become the seed coat2 The primary endosperm divides The daughter cells absorb nutrients from the parent plant forming a foodfilled endosperm acts as food for the new plant3 The zygote becomes the embryoThe walls of the ovary turn into the flesh of the fruitAs the seed grows the embryo differentiates into shoots and roots The shoot portion includes one or two cotyledons seed leaves see fig 4410 In dicots there are 2 cotyledons in the embryo and monocots have only 1 cotyledonIn the monocots the cotyledon is protected by a tough sheath called the coleoptile see fig 4411
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