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Unformatted text preview: Plant Reproduction and Development March 14, 2007 to March 26, 2007 • Alternation of generations o All plants have distinct haploid and diploid stages during their life cycles In other words, plants alternate between n and 2 n generations o Alternating generations are physically separate in many plants like ferns • Sporophyte generation o Diploid stage o Produced by fertilization when a haploid sperm and haploid egg merge o Sporophyte undergoes meiosis and gives rise to specialized haploid spores This begins the gametophyte generation Spores are NOT gametes; they are just haploids • “All gametes are haploids, but not all haploids are gametes” They will grow into a haploid plant • Gametophyte generation o Haploid stage Each contains one of each basic chromosome o Spores divide to give rise to male and female gametophytes o Spores produce gametes via mitosis o Male and female gametes then join in fertilization to yield a sporophyte • Diagram of the cycle: • Condition of alternation of generation in angiosperms o Gametophyte develops in sporophyte tissue Hence, the stages occur together on a single plant o Basic terms of angiosperms Floral organs • Sepals-modified leaves at the base of flower petals • Petals-brightly colored for pollination • Stamen-where the male gametophyte (pollen) develops • Carpals-where the female gametophyte develops • Both the stamen and the carpals carry the gametophyte generation Complete versus incomplete flowers • Complete-flowers that contain all four flower organs • Incomplete-flowers missing one or more of the four flower organs Perfect versus imperfect flowers • Perfect-flowers with both stamens and carpals o Has male and female gametophytes • Imperfect-flowers with either stamens or carpals Monoecy versus dioecy 1 • Refers to the whole plant, not just a single flower • Monoecious-has both staminate and carpallate flowers o Thus, flowers can be imperfect or perfect • Doescious-has either staminate or carpallate flowers o Thus, flowers can only be imperfect • Gametophyte development in angiosperms o Male gametophyte (pollen) Microsporocytes (cells) are present in the sporangia • Micro-small like pollen • Sporo-part of the diploid generation • Cyte-cells • Microsporocytes are small diploid cells • Sporangia-sac that houses spores after meiosis Microsporocytes undergo meiosis to form pollen grains • Results in four haploid microspores o These cells are the gametophyte generation o Each is a single cell at the start of gametophyte generation Each cell/haploid microspore divides by one round of mitosis • Analogous to the growth phase of gametophytes • Results in four pollen grains for each original pollen grain each with o Generative cell Divides to produce a sperm like all other plants o Tube cell Grows pollen tube o Female gametocyte (embryo sac) One megasporocyte in each sporangium • Mega-big • Sporo-sporocyte...
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This note was uploaded on 04/17/2008 for the course BIOSC 0160 taught by Professor Bledsoe during the Spring '08 term at Pittsburgh.
- Spring '08