Transcript Chapter 24: Plant Reproduction and response

Sections 1-2
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Reproductive structures made of specialized
leaves
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Sepals (outermost) enclose bud before it opens,
protect flower during development
Petals just inside sepals – colors, shape,
numbers attract pollinators
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Stamens – male leaves
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Stalk called filament
Anther at the end – produces pollen grains (male
gametophyte
Carpels – female leaves – shelter female
gametophytes and seeds
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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
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Alternation of generations – male/female
gametophytes live within sporophyte
Male gametophytes (pollen grains) develop
within anthers
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Meiosis produces 4 haploid cells, each undergoing
mitosis to produce 2 haploid nuclei per pollen grain
Surrounded by thick wall for protection
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Female gametophytes develop within carpel
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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
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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
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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
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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
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Double fertilization takes place in embryo sac
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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
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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
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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
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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
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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
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Dispersal by wind/water
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Lightweight fruits carried by wind (dandelion) or
float (coconut)
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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
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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
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Long distance dispersal
Germination only under ideal growth
conditions