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SEED PLANTS: SUBPHYLUM SPERMOSIDA Fig 22.5 pg 470 - members of Spermopsida produce seeds instead of spores - better dispersal - seed coat that surrounds developing embryo - embryo will grow for a while but will remain dormant until conditions are right for germination into new plant Diagram structure of a typical seed pg 470 A. FORMATION OF SEEDS fig 25.9 pg. 539 - seeds begin to develop once sperm fertilizes egg - zygote develops into embryo inside seed - cotyledon is seed that contains stored food for embryo once it germinates - structures of seeds are name according to their attachment to cotyledon(s) 1. epicotyl: part of seed that develops into stem - has apical meristem tissue 2. hypocotyls: structure beneath epicotyl - attached to radicle that will develop into primary root - has apical meristem tissue Diagram a typical seed in more detail pg 539 1 B. SEED DEVELOPMENT - begin to germinate once they absorb water - causes endosperm & cotyledon to swell & crack - radical emerges as primary root - some seeds develop instantly into plants; others enter dormancy when embryo is alive but not growing - dormancy allows seeds to be dispersed further from parent C. THE SPERMOPSIDA (SEED PLANTS) - members of Spermopsida are most successful & plants because: 1. Production of seeds: allows dispersal 2. Production of cones/flowers: attracts pollinators 3. Co-evolution with animals - key reproductive structures of spermopsida include: i) seeds ii) cones iii) flowers - Subphylum divided into: i) Gymnopserms ii) Angiosperms GYMNOSPERMS A. CONES Fig 22.7 pg 472 - gymnosperm = naked seed - specialized reproductive leaves called scales - several scales grouped to form male & female cones 1. pollen cones: produce male gametophytes called pollen 2. seed cones: produce female gametophytes called eggs - after fertilization in female cone seed develops on scales unprotected B. CLASSES three main classes 1. Cycadae: palm-tree like 2 2. Gingkoae: only one species, Gingko biloba 3. Coniferae: most abundant & widespread C. CONIFERS: THE EVERGREENS - very long, thin leaves called needles - fall off every fall or gradually every few years 1. Life Cycle - dominant sporophyte stage - microsporangia inside male pollen cones produce immature pollen grains - megasporangia inside female seed cones produce ovules (with eggs inside) - pollen grains released & land near ovule - pollen grain splits & grows a pollen tube that grows into ovary - inside pollen tube are two sperm nuclei (one will fertilize egg) - resulting zygote develops into embryo inside seed Diagram life cycle of typical conifer pg 534 3 ANGIOSPERMS (protected seed) A. FLOWERS Fig 25.4 pg 535, fig 25.5 pg 536 - flowers: mini-stems consisting of specialized leaves involved in reproduction though process called pollination 1. sterile leaves - sepals & petals don’t produce gametophytes a) sepals: outermost leaves, often green, resemble true leaves - protect flower bud while developing b) calyx: sepals & flower c) petals: second circle of leaves, brightly coloured - entire collection = corolla - attract insects & pollinators 2. Fertile leaves – stamen & carpels a) stamen: male part, long filament supports anther (where microsporangium produce microspores) b) carpel: female part, several fertile leaves that have rolled up to protect female gametophyte c) pistil: one or more carpels - ovary with several ovules, stalk called style, top of stalk is stigma Diagram a typical angiosperm flower pg 535 4 B. CLASSES - two subclasses - separated based on structure of seed 1. monocotyledenae – 1 cotyledon (seed leaf) 2. dicotyledenae- 2 cotyledons Characteristic Example Monocots Annuals: Tulips Veins in leaves Flower parts Vascular bundles in stems Vascular bundles in roots Growth of stems Parallel Multiples of 3 Scattered Dicots Woody trees: Deciduous trees Branched Multiples of 4 or 5 Ring Alternating xylem/phloem None Xylem forms X; phloem in between Yes C. LIFE CYCLE Fig 25.6 pg 537 1. Inside Ovary diploid megaspore mother cells produces 4 haploid cells (meiosis) *3 will die* remaining will undergo mitosis to produce 8 haploid nuclei 8 are enclosed within membrane called embryo sac 3 nuclei clump to form polar nuclei one of 3 will become egg other 2 lie on either side of egg nucleus remaining 3 die 2. Inside Anther diploid microspore mother cell produces 4 haploid microspores (meiosis) each becomes immature pollen grain 5 pollen grain lands on female gametophyte, nucleus divides (mitosis) produces 2 haploid nuclei one is tube nucleus which produces pollen tube then dies other is generative nucleus that divides (mitosis) produce 2 sperm cells pollen grains released when anther dries out 3. Pollination: transfer of pollen from anther to stigma; two types a. self-pollination: plant pollinates itself b. cross-pollination: plant pollinates another pollen grain on stigma grows pollen tube from tube nucleus generative nucleus divides to produce 2 sperm cells pollen tube extends towards embryo sac inside female double fertilization; one sperm fertilizes egg nucleus to form diploid zygote; other fertilizes two polar nuclei to form triploid endosperm endosperm provides food for embryo after fertilization, parts of ovule thicken to form seed ovary wall begins to form fruit that holds seeds fruit aids in dispersal by attracting insects & animals COEVOLUTION OF FLOWERING PLANTS & ANIMALS - particularly in angiosperms - animals are integral part of reproduction (& survival of plant species) - attract insects (instead of using wind), birds, & animals by producing flowers that produce liquid pollen; nectar - pollinators travel from one flower to next, carrying pollen = vector pollination - flower structure has evolved to target specific pollinators 6 e.g. colour, markings, odour, shape of flowing all ensure specific pollinators - production of fruit aids in dispersal - animals attracted to colour, odour, taste of fruit - eat fruit & seeds - seeds have tough seed coat out with wastes (natural fertilizer!) 7