Sections 1-2
Sections 1-2
Reproductive structures made of specialized leaves
Sepals (outermost) enclose bud before it opens, protect flower during development
Petals just inside sepals – colors, shape, numbers attract pollinators
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
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
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
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
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
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
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
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
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
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
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)
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
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
Long distance dispersal
Germination only under ideal growth conditions