Chapter 39 Reproduction in plants Most flowering plants display sexual reproduction Two gametes fuse to produce offspring with a unique combination of genes They undergo  Alternation of Generations Two multicellular life cycle stages diploid Spore producing sporophyte produces spores by meiosis a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores. haploid Gamete producing gametophyte produces gametes by mitosis a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth. Egg is Female Sperm is Male Evolutionary Trends in the Plant Kingdom Sporophyte has become larger, more complex Flowering plants Sporophyte independent  Dependent gametophyte is only a few cells contained within flowers Gametophyte has become smaller, less complex Moss Sporophytes small and dependent on gametohyte (Dominant form) Female 7 cells Male 2-3 cells Flower and Sexual Cycle Flowers ONLY in angiosperms All sizes, shapes, colors, and aromas Essential process of Sexual reproduction occurs within flowers Meiosis/cytokenesis reduces chromosome number Syngamy (fertilization) restores chromosome number "Ideal" Flower Uses highly modified leaves arranged in whorls (circular) at the tip of a highly modified stem A flower is a highly modified determinate (short term) shoot system Pedical, receptical, 4 sets of highly modified leaves are all 2N and part of the sporophyte generation Pollen (sperm) and eggs of embryo sac are part of the 1N generation Pedical flower stalk Recepticle tip of modified stem with 4 whorls attached Sexual Cycle Male Pollen formation occurs within the anther of stamen Anther Bilobed with 2 pollen chambers per lobe 2N microspore mother cell meiosis/cytokenesis 4 1N microspores Each: mitosis/cytokenesis unequal and incomplete 1N Generating cell 1N Tubecell Male Gametophyte Pollination Transfer of pollen from the anther to the stigma Self-pollination Transfer with the same flower or between flowers on the same plant   Cross-Pollination Transfer between  flowers of other plants Pollinating Agents Mechanisms utilized for transfer of pollen Wind small/lightweight pollen Water Transfer with a few aquatic plants Animals Majority of plants Utilized as a "trick and reward" system nectar, colors, and aromas to attract animals Female Ovule Development Ovule future seed Enclosed within the ovary of pistol  (carpel) One to many ovules per ovary ovary will become fruit Ovule attached to central axis or to wall of hollow fruit always enclosed angiosperms within ovule is 1 large 2N cell megaspore mother cell 2N megaspore mother cell meisos/sytokenesis 4 1N Megaspores 3 degrade 2N Functional megaspore Series of 3 mitosis/cytokenesis cycles Incomplete and unqueal 7-celled embryo sac 8 nuclei Female gametophyte   1N Functional megaspore 3 mitosis/cytokenesis divisions One cell with 1 nucleus becomes 8 nuclei but only 7 cells Embryo sac 8 nuclei, 7 cell structure female gametophyte 3 antipodal cells (1N) opposite end from micropyle 1 central cell with 2 large 1N polar nuclei 2 Synergids (1N) Micropyle end on outside 1 egg (1N) Middle at micropyle end Syngamy (fused gametes) 1N egg + 1N sperm = 2N zygote (single fertilized egg) Pollen grain germination tube cells form pollen tube (delivers sperm) generative cell divides by mitosis/cytokenesis to produce 2 sperm Pollen tube enters micropyle digests tube cell nucleus Pollen tube enters one synergid releases it's content (sperm) synergid ruptures mycropyle closes   "Double fertilization" (double fusion) 1N egg +1N sperm = 2N zygote 1N sperm +2 1N polar nuclei = 3N primary endosperm cell   Post fertilization with ovule 2N zygote grows by mitosis/cytokenesis into 2N multicellular embryo 3N primary endosperm cell grows by mitosis/cytokenesis into 3N multicellular endosperm nutrient tissue for embryo   Ovule/ovary with 2N zygote  mature/enlarges with sugars/H2O into a fruit (mature ovary) with enclosed seeds (mature ovules) Seed dispersal (seeds enclosed withing a fruit) agents wind water animals - majority Seed germination Seed with 2N embryo enters period of dormancy dormancy broken by a combination of internal (hormones) and external factors (environmental) radical (first root) emerges and grows down shoot emerges and grows up