2 Adaptations of seed plants SeedsReduced gametophyte stageAlso seen in seedless vascularseed plants reduced to microscopic (spores develop in sporangia of sporophyte)HeterosporyMegaspores – make female gametophyteMicrosporangia – male gametophyteOvules = megaspore & integuments (protect)Pollen = micro (male gametophyte) & sporopollenin
7 Seed Double Fertilization Endosperm The union of two sperm cells with different nuclei of the embryo sac.EndospermFood storing tissue of the seed.
8 Seed to SeedlingImbibition is that state when the seed wakes up from dormancy and starts the intake of water.It causes the seed to expand and ruptures, releasing the shoot, the cotyledons and the stalk.It is the first sign of life after the dormant state.
9 Seed to Seedling http://students. usm. maine. edu/deidre
10 Spore survivalPrior to seeds: spore was the only protected stage for plants.Spore is single cellCould survive: cold hot dryCould be dispersed to another environment
14 Vascular Seed plants Gymnosperms: fir, pine Angiosperm: flowering plants
15 Pine tree The pine tree is the sporophyte (2N) Its sporangia are located on the pine coneHeterosporousSmall pollen cones: carried by wind and crittersLarge ovule conesEach tree has both types of cones
17 Angiosperm Flowering plants: vascular and seeds Most diverse and widespread plantsFlower: specialized for reproductionCarried by wind: like gymnospermCarried by insects: more directed pollinationFruit: protect seed and aid in dispersalFrom ovary. Ovary thickens after pollination.
18 Flower StructureFour main organs: sepals, petals, stamens, and carpelsStamens and carpels are reproductiveCarpel:Stigma: collects pollenStyle: to ovary with 1 or more ovulesovaryPistil: multiple fused carpelsStamen: filament, antherAnther: stalk where pollen madeSepals and petals: no repro organs
19 Gametophyte Development and Pollination Sporangia- structure onanther andovules where spores are producedPollen grains are made up of mature male gametophytes that are enclosed by a spore wallFound in the microsporangia, or pollen sacs
20 Hormones Auxin Stem elongation, root growth, develop fruit Cytokinins: affect, cell division, cell differentiation, and apical dominance.GibberellinsSeed and bud germinationAbscisic acidInhibit root growth, close stomataEthyleneFruit ripening
21 Mechanisms that Prevent Self-Fertilization Sexual reproduction ensures that there will be genetic diversity among offspring“Selfing” refers to self-fertilization in plantsEnsures that seed will develop
22 Pollination Vs. Fertilization Pollination is the transfer of pollen from anther to stigma (of other plant)Results in formation of a pollen tubePurpose is to grow down to ovary and release sperm within embryo sacThis fertilizes the eggEmbryo -> seed -> fruit containing seedThe fruit disperses seeds which germinate and develop into seedlings
23 Development Microsporocytes form four haploid microspores These develop into haploid male gametophytesThe microspore goes through mitosis and cytokinesisThis results in a generative cell and tube cell which make up the pollen grain
24 Megasporocyte grows resulting in four haploid megaspores May form a multicellular female gametophyteContains 3 cells: 1 egg and 2 synegridsSynegrids attract and guide pollen tubes to the embryo sacthere are also two nuclei at the other end of the cell that are not separate and share cytoplasm embryo sacsThese result in two integuments that form a seed
25 Ensuring that the egg and sperm cells come from different parents is a mechanism that inhibits self fertilizationDioecious plants cannot self fertilize because they have either staminate or carpellate flowers
26 Avoid self fertilization Flowers with functional stamen and carpels have organs that mature at different ratesAn animal pollinator would not transfer pollen from the anther to a stigma of the same flower
27 Self Incompatibility The ability of a plant to reject its own pollen Also, in some cases, the pollen of similar plantsIf pollen were to land on the stigma of a flower on the same plant a biochemical would prevent the pollen from developing and fertilizing an egg
28 Special Circumstances Plant breeders will hybridize different crop varieties to combine the best traits and to get sufficient resultsThis can result in inbreedingMay cause plants that are able to self fertilize to lose that characteristic.