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Plant Reproduction Alternation of Generations Mosses - gametophyte is the dominant form of the plant Ferns, gymnosperms and angiosperms - sporophyte is the dominant form of the plant Sexual reproduction in angiosperms Flower parts sepals - outer whorl or ring protect the other parts of the developing flower petals - next whorl animal pollinated plants have brightly colored petals wind pollinated plants usually have small or absent sepals/petals Stamens - next whorl; male reproductive structures consist of: -anther (produce microspores that develop into pollen grains) -filament (supports the anther) Carpels - innermost whorl; female reproductive structures pistil (one or more fused carpels) -ovary - enlarged base of pistil -style - stalklike -stigma -top, sticky or with hairs to trap pollen grains Gametophytes develop within the reproductive structures -female gametophyte (embryo sacs) form within the ovary of the pistil Megasporangium surrounded by two integuments, each with a micropyle -contains a megaspore mother cell, which undergoes mitosis to produce four haploid megaspores -one megaspore undergoes three mitotic divisions, which produces a cell with eight haploid nuclei -one nuclei from each end (pole) migrate to center and become polar nuclei -one cell nearest to micropyle enlarges and become the egg -two cells on either side of egg help attract pollen tube toward the egg -the integuments and embryo sac are now a mature ovule, which may develop into a seed -male gametophyte (pollen grains) form within the anthers of the stamens An anther contains four microsporangia (pollen sacs) -microspore mother cells each produce four haploid microspores -each microspore undergoes mitosis to produce two haploid cells that do not separate (pollen grain) -the larger of the two cells is the tube cell (forms pollen tube) - the smaller of the two cells is the generative cell, which will divide by mitosis to form two sperm Pollination -occurs when pollen grains are transferred from an anther to a stigma -self-pollination - involves one flower, flowers on the same plant, or flowers from two genetically identical plants -cross-pollination - involves two genetically different plants -self-pollinated due to structure of flower -pollen dispersed by water -pollen dispersed by air (wind) *depends on: release of large amounts of pollen ample air circulation proximity of plants to which pollen is transferred dry weather -pollinated by animals -have bright flowers, distinctive odors, nectar (sugar solution) -pollinators include bats, bees, beetles, moths, butterflies, mosquitoes, monkeys, and hummingbirds Fertilization -union of haploid gametes resulting in diploid zygote -a pollen grain must land on a stigma, absorb moisture, and germinate (form a pollen tube) -pollen tube grow through stigma and style toward the ovary -enter ovule in ovary through micropyle -two sperm travel through pollen tube and reach the egg -double fertilization is unique to angiosperms *one sperm fuses with the egg to form diploid zygote *one sperm fuses with two polar nuclei, and then eventually develops into endosperm (provides nourishment for the embryo) Dispersal of fruits and seeds Fruits and seeds are dispersed by: -animals (carried or eaten) -wind (tiny or with “parachutes”) -water (contain air chamber) -forcible discharge (pod dries and breaks open) -gravity Fruit types A fruit is a mature ovary. Fruits protect seeds, aid in their dispersal, and delay sprouting of seeds. Classified based on: -how many pistils or flowers form the fruit -whether the fruit is dry or fleshy p. 619 Table 30-1 Structure of seeds A seed is a plant embryo surrounded by a protective coat called the seed coat. Seed structure differs between monocots, dicots, and gymnosperms. -dicot - two cotyledons which store nutrients (no endosperm) *plumule - shoot tip with embryonic leaves *epicotyl - between plumule and cotyledons *hypocotyl - cotyledons to radicle *radicle - embryonic root -monocot - one cotyledon and endosperm *absorbs nutrients from endosperm -gymnosperm - sporophyte embryo with needle-like cotyledons, surrounded by the tissue of the female gametophyte which functions as a source of nutrients for the embryo Seed germination A seed will not germinate (sprout) until it is exposed to certain environmental conditions. Many seeds experience dormancy (a state of reduced metabolism; growth and development do not occur). Conditions needed for germination: -water - softens seed coat, activates enzymes that convert starch in cotyledons into simple sugars -oxygen - needed for cellular respiration -light - some seeds need light -temperature - within a certain range -extreme conditions - pass through digestive system of animal Corn (monocot) 1. Appearance of radicle 2. Shoot begins to grow -cotyledon remains underground Bean (dicot) 1. Appearance of radicle 2. Hypocotyl curves and becomes hook-shaped 3. Hypocotyl straightens after it breaks through the soil 4. Embryonic leaves unfold (cotyledons shrink and fall off) Asexual Reproduction Production of individual without union of gametes -clones -vegetative reproduction (leaves, stems, roots) - table 30-2 p. 623 Propagation by humans Cuttings -roots form from a piece of stem, or shoots form on a piece of root (houseplants, ornamental trees and shrubs, some fruit crops) Layering -roots form on stems where they make contact with the soil (raspberries) Grafting -joining of two or more plant parts to form a single plant -bud or small stem of one plant is attached to the roots or stem of a second plant (vascular cambiums must be aligned) -commercial fruit and nut trees, many ornamental trees and shrubs Tissue culture -production of new plants from pieces of tissue placed on a sterile nutrient medium -commercial production of orchids, houseplants, cut flowers, fruit plants, and ornamental trees, shrubs, and nonwoody plants