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Transcript
Plant Life Cycles Plant Evolution • Descendants from green algae (~450mya) – Contain cellulose in cell walls – Contain chlorophyll – Starch stored • Land Plants Must Overcome – Drying out – Gas exchange – Nutrient transport system – Support Land adaptations • Cuticle: Waxy coating prevents water loss • Stomata: pores that open/close to permit gas exchange • Roots & Stems: support • Vascular system: tissue that transports nutrients – Nutrients & water go up plant – Sugars go down the plant General Plant Life Cycle • Alternation of generations • Gametophyte (haploid) – Haploid spores created by meiosis – Gametophyte grows from spore – Gametophyte has sperm & egg cells General Plant Life Cycle • Sporophyte (diploid) – Diploid zygote created from sperm & egg – Zygote grows into a mature sporophyte – Sporophyte creates haploid spores by meiosis • Gametophyte grows from spore (cycle restarts) Mosses • Nonvascular, seedless • Grow low to ground to retain moisture • Lack true leaves – Leaf-like structures only 1 cell thick • Rhizoids anchor into soil • Early inhabitant of new ecosystems (succession) • Gametophyte phase – Dominant stage – Carpet of moss growing near ground • Female gametophyte: produces egg • Male gametophyte : produces sperm – Sperm swims through water to fertilize egg (zygote created) • Sporophyte phase – Sporophyte stalk grows up from the zygote – Sporangia contain haploid spores – Haploid spores land • Gametophyte stage restarts Moss Life Cycle Ferns • Seedless, vascular plants – Vascular: allows taller growth • Rhizoids: underground stems draw nutrients • Fronds: leaves uncurl – sporangia on underside Fern Life Cycle • Sporophyte phase – Dominant stage – Sporangia produces haploid spores – Spores released into air • Gametophyte phase – Spores land & grows into prothallus • Female gametophyte: produces egg • Male gametophyte : produces sperm – Sperm swims to egg – Zygote begins sporophyte stage Conifers • Seed advantages – Don’t depend on water – Protects & nourishes embryo – Allow plants to grow in new locations • Conifers: woody cone houses seeds – Male cones: produce pollen – Female cones: produce egg • Pines, redwoods, spruce, cedar Conifer Life Cycle • Sporophyte phase – Cones grow on mature tree – Female cones: contains megaspores (female gametophyte) – Male cones: contains microspores (male gametophyte) • Microspores released & stick to female cones • Pollen tube grows towards egg • Sperm travels down pollen tube (zygote/seed created) • Sporophyte stage restarts female male