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chapter 36 Reproduction in Flowering Plants

chapter 36 Reproduction in Flowering Plants - Reproduction...

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Reproduction in Flowering Plants · Angiosperms have about 300,000 species and are the largest, most successful living group of plants · Sexual reproduction includes meiosis which produces gametes , union of gametes is called fertilization The Flowering Plant Life Cycle · Undergo alternation of generations , the gametophyte gives rise to gametes by mitosis and the fusion of gametes ( fertilization ) gives rise to sporophyte generation which produces haploid spores by meiosis · Cues from the environment interact with plant hormones to signal when reproduction should start · Arabidopsis used as model organism to study · Flowering Locus C (FLC) gene codes for transcription factor that represses flowering · Flowering Locus D (FLD) gene codes for protein that removes acetyl groups from histones in the chromatin where the FLC gene is located, represses transcription factor so that the shoot apical meristem undergoes transition from vegetative growth to reproductive growth · Order of whorls from inner flower: sepals à petals à stamens à carpels · Receptacle- tip of the stalk enlarges to form this where some or all of the flower parts are borne · Sepals- protect the flower, all are carpels · Petals- attract pollinators, all are corolla · Stamens- male reproductive organs · Filament- thin stalk · Anther- sac like structure where pollen grains form o Generative cell- divides mitotically to form 2 nonflagellate male gametes ( sperm cells ) o Tube cell- produces pollen tube where sperm cell travels to reach the ovule · Carpels- female reproductive organs · Ovules- can develop into seeds · Pistil- female part of the flower o Stigma- pollen grains land “sticky stigma” o Style- neck like structure through which the pollen tube grows “stylish style” o Ovary- jug like structure with one or more ovules that can become a fruit · Each ovule has a diploid megasporocyte, undergoes meiosis to produce 4 haploid megaspores · 3 disintegrate and one divides mitotically to produce a multicellular female gametophyte ( embryo sac ) usually has 7 cells with 8 haploid nuclei o 6 cells (including gamete) have one nucleus while one has 2 polar nuclei , egg and polar nuclei are involved in fertilization · Pollen sacs contain diploid microsporocytes, each of which undergoes meiosis to produce 4 haploid cells called microspores, divide mitotically to produce immature male gametophyte (pollen grain) which has 2 cells, tube cell and generative cell · Becomes mature when generative cell divides to form 2 nonmotile sperm cells Pollination
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· Pollination- transfer of pollen grains from anther to the stigma · Can be self-pollinated or cross-pollinated , cross has a genetic advantage · Plants have defenses against self-pollination which can cause inbreeding- mating of genetically similar individuals · Some only have a male or female type · Some are both but the reproductive structures open at alternative times · Promote outcrossing (outbreeding) mating of dissimilar individuals ·
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chapter 36 Reproduction in Flowering Plants - Reproduction...

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