Chapter 24: Plant Reproduction and response Sections 1-2

The Structure of Flowers Reproductive structures made of specialized leaves

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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