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Biology
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24-2 Seed Development
and Germination
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Seed and Fruit Development
Seed and Fruit Development
As angiosperm seeds mature, the ovary
walls thicken to form a fruit that enclosesthe developing seeds.
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Seed and Fruit Development
A fruit is a ripened ovary that contains angiosperm
seeds.
As seeds mature, the ovary walls thicken to form a
fruit that encloses the developing seeds.
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Seed Dispersal
How are seeds dispersed?
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24-2 Seed Development and
Germination
Copyright Pearson Prentice Hall
Seed Dispersal
Seed Dispersal
Seeds are dispersed by animals, wind, and
water.
Seeds dispersed by animals are typically
contained in fleshy, nutritious fruits.
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Seed Dispersal
Seeds of many plants are eaten by animals.
These seeds are covered with tough coatings that
protect them from digestive chemicals, allowing them
to pass through an animals digestive system
unharmed.
The seeds then sprout in the feces eliminated from
the animal.
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Seed Dispersal
Seeds dispersed by wind or water are
typically lightweight, allowing them tobe carried in the air or to float on the
surface of the water.
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Seed Dispersal
Some seeds are encased in winglike structures that
spin and twirl, helping them glide from their parent
plants.
A coconut is buoyant enough to float in seawater
within its protective coating for many weeks.
Tumbleweed plants break off at their roots and
scatter their seeds as they are blown by the wind.
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Seed Dormancy
Seed Dormancy
Many seeds will not grow when they first mature.
These seeds enter a period ofdormancy, during
which the embryo is alive but not growing.
The length of dormancy varies in different plant
species.
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Seed Dormancy
What factors influence the dormancy and
germination of seeds?
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Seed Dormancy
Environmental factors such as
temperature and moisture can cause a
seed to end dormancy and germinate.
Seed dormancy can be adaptive in several
ways:
allows for long-distance dispersal allows seeds to germinate under ideal
growth conditions
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Seed Germination
Seed Germination
Seed germination is the early growth stage of the
plant embryo.
When seeds germinate, they absorb water whichcauses food-storing tissues to swell and crack
open the seed coat.
The young root grows through the cracked seedcoat.
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Seed Germination
In most monocots, the single cotyledon remains
underground.
The growing shoot emerges while protected by a
sheath.
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Seed Germination
Corn (monocot)
Young
shoot
Germinating
seedPrimary
root
Foliage
leaves
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Seed Germination
In dicots, germination takes place in one of two ways.
In some species, the cotyledons emerge aboveground, protecting the stem and first foliage
leaves.
In other species, the cotyledons stayunderground and provide a food source for the
growing seedling.
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Seed Germination
Cotyledons
Bean (dicot)
Germinatingseed
Primary
root
Young
shoot Cotyledons
Seed coat
Foliage
leaves
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24-2
http://localhost/var/www/apps/conversion/tmp/scratch_2/Resources/ch24_sectn02_quiz.qtbhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Resources/ch24_sectn02_quiz.qtbhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Resources/ch24_sectn02_quiz.qtb7/30/2019 Chapter24 Section02 Edit
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24-2
A germinating corn seedling has
a. a single cotyledon, which remains belowground.
b. two cotyledons, which push above ground.
c. a single cotyledon, which pushes aboveground.
d. two cotyledons, which remain below
ground.
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24-2
Angiosperm fruits develop from
a. the ovary wall of the flower.
b. seed endosperm.
c. swollen sepals of the flower.
d. flower stamens.
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24-2
An example of a seed that is transported by
water is a
a. coconut.
b. tumbleweed.c. blackberry.
d. maple seed.
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24-2
The seeds of many plants that form fruits are
dispersed mainly by
a. animals.
b. water.c. wind.
d. the plant itself.
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24-2
An environmental condition that can cause the
activation of a dormant seed is
a. a sharp drop in temperature.
b. the heat from a forest fire.c. an extended drought.
d. falling from a great height.
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