Plant Reproduction: Structure, Cycle, and Propagation

1. Chapter 24:Plant Reproduction and response Sections 1-2

2. The Structure of Flowers • Reproductive structures made of specialized leaves

3. The Structure of Flowers • Sepals (outermost) enclose bud before it opens, protect flower during development • Petals just inside sepals – colors, shape, numbers attract pollinators

4. The Structure of Flowers • Stamens – male leaves • Stalk called filament • Anther at the end – produces pollen grains (male gametophyte • Carpels – female leaves – shelter female gametophytes and seeds • Broad base forms ovary, containing one or more ovules where female gametophytes produced • Narrow stalk called style with sticky stigma at the top to catch pollen • Sometimes called pistil

6. Angiosperm Life Cycle • Alternation of generations – male/female gametophytes live within sporophyte • Male gametophytes (pollen grains) develop within anthers • Meiosis produces 4 haploid cells, each undergoing mitosis to produce 2 haploid nuclei per pollen grain • Surrounded by thick wall for protection

7. Angiosperm Life Cycle • Female gametophytes develop within carpel • Ovules (future seeds) protected by ovary (future fruit) • Single diploid cell goes through meiosis to produce 4 haploid cells • 3 disintegrate, one undergoes mitosis to produce 8 nuclei • Surrounded my embryo sac – within ovule (female gametophyte) • Cell walls form around 6 of the nuclei

8. Angiosperm Life Cycle • Female gametophyte con’t • One nucleus is the nucleus of the egg • If fertilization occurs, egg with fuse with male gamete • Zygote grows into new sporophyte

9. Angiosperm Life Cycle • Most angiosperms pollinated by animals • Wind pollinated plants (oak trees) rely on good weather, lots of pollen • Animal pollinated plants have bright flowers, sweet nectar • Pollinator’s bodies adapted to reach nectar • Insect pollination a win-win

10. Angiosperm Life Cycle • If a pollen grain lands on the stigma of the same species, pollen tube begins to grow • One cell within pollen grain becomes pollen tube, the other divides into 2 sperm cells (“generative” cell) • Pollen tube grows into style to ovule

11. Angiosperm Life Cycle • Double fertilization takes place in embryo sac • One sperm nucleus fuses with egg nucleus, diploid zygote will grow into embryo • Other sperm nucleus fuses with 2 polar nuclei in embryo sac to form triploid cell (3n) • This grows into endosperm – nourishes seedling • Saves resources

13. Vegetative Reproduction • Asexual reproduction in flowering plants – produce identical offspring by mitosis • New plants can grow from roots, stems, leaves, plantlets (potatoes, strawberries, cacti) • Very quick, plants can take over favorable environments • No genetic recombination

14. Plant Propagation • Use cuttings - length of stem cut and planted in soil to encourage root formation • Use grafting - a piece of stem or a lateral bud is cut from the parent plant and attached to another plant

15. Seed and Fruit Development • The term “fruit” refers to a matured angiosperm ovary, usually containing seeds • Nutrients support development of growing embryo • Ovary wall thickens – can be fleshy, tough/dry

16. Seed Dispersal • Dispersal by animals through eating or carrying • Have tough coating and can pass through the digestive system, sprout in feces • Dry fruits catch on fur • Dispersal by wind/water • Lightweight fruits carried by wind (dandelion) or float (coconut)

17. Seed Dormancy and Germination • After they mature, some seeds remain dormant where the embryo is alive and not growing before they germinate • Germination is the resumption of growth • Affected by temperature, moisture

18. How Seeds Germinate • Before germination, seeds absorb water, tissues swell, seed coat cracks open • Young root emerges first, then the shoot • Cotyledons are the first leaves – store nutrients and transfer them to growing embryo • Monocots – leaf usually remains underground, shoot protected by sheath • Dicots – no sheath – end of shoot bends into a hook, straightens in sun

20. Advantages of Dormancy • Long distance dispersal • Germination only under ideal growth conditions