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Sections 1-2.  Reproductive structures made of specialized leaves.

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Presentation on theme: "Sections 1-2.  Reproductive structures made of specialized leaves."— Presentation transcript:

1 Sections 1-2

2  Reproductive structures made of specialized leaves

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

4  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  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  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  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  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  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  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  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  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  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  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  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  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  Long distance dispersal  Germination only under ideal growth conditions

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