Chapter #43 – Plant
Reproduction
• 43.4 How Do Fruits and Seeds Develop?
• 43.5 How Do Seeds Germinate and Grow?
• 43.6 What Are Some Adaptations for Pollination and
Seed Dispersal?
Fruits and Seeds
• Get a paper ready
for thinking
questions to turn in
From Ovary to Fruit
• The ovary of the flower contains the ovules.
• As fertilized ovules develop into seeds, the
ovary wall develops into the fruit.
• In science, the term “fruit” refers to a mature,
ripened ovary that contains seeds.
Types of Dry Fruits
Capsule
(Poppy)
Legume
(Bean pod)
Silique
(Money Plant)
Achene
Follicle
(Columbine)
(Sunflower)
Nut
(Hazelnut)
Types of Fleshy
Fruits
Drupe
(Peach)
Berry
(Tomato)
Pome
(Apple)
Aggregate
(Strawberry)
Pepo
(Cucumber)
Multiple
(Pineapple)
Fruit Dispersal
• The form of the fruit gives clues about its
dispersal.
• Small, dry fruits with “wings” or “parachutes”
may be wind-dispersed. Fleshy fruits are often
animal dispersed. Explosive fruits can fling
seeds away. Floating fruits may be water
dispersed.
How are these Fruits
Dispersed?
Dandelion
Coconut
Maple
Cocklebur
Jewelweed
A Thinking Question?
• Why must fruits be dispersed away
from the parent plant?
Seeds
Seed Dormancy
• As seeds mature, they enter a period of
dormancy.
– Suspended growth and development.
– Lowered metabolic rate.
– Resistance to adverse environmental
conditions.
Seed Dormancy
• Conditions that break dormancy vary among plant
species.
– Some germinate as soon as the environment is
suitable (adequate moisture and temperature).
• Conditions that break dormancy vary among plant
species.
– Others have additional requirements:
• Initial drying (seeds within fleshy fruits)
• Exposure to prolonged cold (seeds of temperate and
arctic plants).
• Disruption of seed coat .
Seed Dormancy
• Seeds can remain dormant in the soil for long
periods of time. Dormancy ensures that seeds
only germinate when conditions are optimal.
• When we weed or cultivate a bare patch of
soil, the weeds that sprout up immediately
usually come from the “seed bank” already in
the soil.
Breaking Dormancy
• Seeds require moisture and the right
temperature to germinate.
• In addition, some seeds germinate only after
certain environmental signals:
• Drying
• Temperature (period of cold or heat)
• Disruption of the seed coat
? Thinking Question ?
• What could be the advantage of waiting for
each of these signals to germinate?
• Long period of cold
• High heat of a forest fire
• Drying out
• Disruption of the seed coat.
Monocot
Germination
• Monocot seeds
have one
cotyledon.
– Absorbs and
transfers most
nutrients
during seed
germination.
Dicot Germination
• Dicot seeds have two
cotyledons
– Absorb nutrients from
endosperm during
seed development and
store for future use.
– Transfer stored
nutrients to other parts
of embryo during seed
germination.
Seed Germination
• Emergence of the embryonic root is followed by
emergence of the embryonic shoot.
• Emerging roots and shoots must push through the soil
without abrading the apical meristems at their tips.
• Germination (resumption of growth) occurs when the
seed absorbs enough water to rupture the seed coat.
Cotyledons
• Food stored in the seed (as endosperm or within
cotyledons) provides the energy for sprouting.
• Cotyledons of dicots with
hypocotyl hooks are carried out of
the soil.
–
–
–
–
–
Remain below ground.
Digest endosperm and transfer nutrients to seedling.
Become photosynthetic.
Transfer stored nutrients and synthesized sugars to the seedling.
Wither and fall off when reserves have been consumed.
Coevolution
• 43.6 What Are some Adaptations for Pollination
and Seed Dispersal?
– Coevolution Matches Plants and Pollinators
– Fruits Help Disperse Seeds
Coevolution
• Some plants and pollinators have coevolved.
– Each acts as an agent of natural selection on the other.
• Animal-pollinated flowers must:
– Attract useful pollinators able to locate flowers and
extract pollen or nectar.
– Frustrate undesirable visitors who might eat nectar or
pollen without fertilizing the flower.
Coevolution
• Animal-pollinated flowers are grouped into
three categories based on how they attract
pollinators.
– Food
– Sex deceptions
– A nursery
Food
• Many animals forage
on flowers,
distributing pollen
from flower to flower
in the process.
• Examples: beetles,
bees, moths,
butterflies,
hummingbirds.
Food
• Bees are attracted by sweet odors and bright
colors.
• Bees do not see the same range of colors that
humans do.
• Bee-pollinated flowers are typically white, blue,
yellow, or orange, with markings that reflect UV
light pointing toward the center.
• Bee-pollinated flowers have structural adaptations to
ensure pollen transfer.
• When a bee visits a young plant, the stamens emerge
from a crevice between petals, brushing pollen onto her
back as her weight deflects the petals downward.
• In older flowers, the sticky stigma of the carpel
protrudes from the crevice, becoming pollinated by
pollen-coated, nectar-foraging bees.
Food
• Other adaptations for drawing
pollinators:
– Nectar-containing tubes to
accommodate the long tongues
of moths and butterflies
– Tubular flower shape to match
the long bills and tongues of
hummingbirds
– Flowers that heat up to
broadcast their scents
• Example: skunk cabbage
Sexual Deception
• Some plants capitalize on the
mating drive and behaviors of male
wasps.
• Example: some orchid flowers
mimic female wasps or bees in
scent and shape.
– The males attempt to copulate,
becoming covered with pollen in
the process.
– Pollen is transferred as they
repeat the process with other
orchids.
Nurseries
• Some insects fertilize a
flower and then lay their
eggs in the flower’s ovary.
• Example: yuccas and
yucca moths.
– A female moth collects
pollen from one flower and
transfers it to another,
smearing it over the stigma
and laying her eggs inside
the ovary.
– The developing seeds
provide nutrition for the
developing caterpillars.
Fruits Disperse Seeds
• Mechanisms to disperse seeds:
- Explosive fruits to eject seeds.
-
Light fruits with large wind-catching surfaces.
• Floating fruits for water dispersal.
• Clingy or tasty fruits that allow animal dispersal.
In Summary. . . .
• Plant Reproduction Structure and Functions
• Fruit and Seed Structure and Adaptations
• Coevolution