16Embryo Sac Development The Embryo Sac is the female gametophyte.Starts with a megasporocyte (2N).MegasporocyteUndergoes meiosis and produces 4 Megaspores (1N).Three of the megaspores abort, leaving only one to develop into the embryo sac.
17MegasporeUndergoes three rounds of mitosis to produce a “sac” with 8 nuclei.The nuclei may wall off or may remain as part of a large cell.Embryo Sac3 Antipodal cells.2 Polar nuclei (1 cell)2 Synergid cells1 Egg cell
25Embryo Development Root/shoot polarity set with 1st cell division. Mature embryo has all three primary tissues, apical meristems etc.EndospermMonocots - large tissue.Dicots - transfer the energy over to the embryo's two cotyledons.
26Seed Coat Formed from the integuments of the ovule. Hard layer to protect the seed.FruitA mature ovary.Sometimes includes other plant parts.Ex: apple
28Fruit Functions Protect the seeds. Aid in seed dispersal. Fruit Types Fleshy: soft ovary walls.Dry: hard ovary walls.
29Fruit Types Simple Fruit: from a single ovary. Ex: Peach, CherryAggregate Fruit: from a flower with multiple carpels.Ex: RaspberryMultiple Fruit: develops from several flowers into one structure.Ex: Pineapple
31Seeds Contain a miniature plant. Main dispersal mechanism for plants. Embryo is often “dormant” when the seed is mature.
32Seed Dormancy When a seed is not actively growing. Used to increase the chances that the plant will develop when conditions are favorable.Usually controlled by plant hormones.May require changes in temperature, moisture, etc. before growth will continue.
33Imbibition The absorption of water by a seed. First step in seedling growth.Causes “swelling” which ruptures the seed coat.Starts metabolism to resume growth.
34Germination The continuation of growth of the plant within a seed. Root usually emerges first.Shoot tip must break through the soil surface.
35Role of LightLight is the usual clue that the shoot has broken above ground.Light causes many growth changes in the shootEx. Leaves to expandStem elongation rate decreases
36Asexual Reproduction Offspring produced by mitosis. Also called “cloning”.
37Normal MethodFragmentation of the plant body so that new plants are formed.Ex: Cuttings Grafting Offshoots
38High-Tech Methods Tissue Culture. Clumps of cells grow into embryoids which can be used to regenerate whole plants.Often used in genetic engineering of plants.
39Protoplast Fusion. A "naked" plant cell (no cell wall). Used to create new hybrids
40PlantsFrequently use both sexual and asexual reproduction depending on the environment.Asexual - stableSexual - unstable
41Plant Development Growth: increase in size Development: changes in body form and structure.Plant ProblemsDetermining the direction of cell growth because of the cell wall.
42Control MechanismCytoskeleton: determines the direction of cell expansion.Cellulose Microfibrils: are arranged in parallel strips as guided by microtubules in the cell membrane.