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