Transcript 22.2 Reproduction in Flowering Plants

22.2 Reproduction in Flowering Plants
KEY CONCEPT
Reproduction of flowering plants takes place within
flowers.
22.2 Reproduction in Flowering Plants
Flowers contain reproductive organs protected by
specialized leaves.
• Sepals and petals are modified leaves.
– Sepals are outermost
layer that protects
developing flower
sepal
22.2 Reproduction in Flowering Plants
– Petals can help to attract animal pollinators
petal
22.2 Reproduction in Flowering Plants
• A stamen is the male structure of the flower.
stamen
filament
anther
– anther produces pollen grains
– filament supports the anther
22.2 Reproduction in Flowering Plants
• The innermost layer of a flower is the female carpel.
stigma
carpel
style
ovary
– stigma is sticky tip
– style is tube leading from stigma to ovary
– ovary produces female gametophyte
22.2 Reproduction in Flowering Plants
Flowering plants can be pollinated by wind or animals.
• Flowering plants pollinated when pollen grains land on
stigma.
• Wind pollinated flowers have small flowers and large
amounts of pollen.
22.2 Reproduction in Flowering Plants
• Animal pollinated flowers have larger flowers and less
pollen.
– many flowering plants pollinated by animal pollinators
pollen grains
– pollination occurs as animal feeds from flower to flower
– animal pollination more efficient than wind pollination
22.2 Reproduction in Flowering Plants
Fertilization takes place within the flower.
• Male gametophytes, or pollen grains, are produced in the
anthers.
– male spores produced in
anthers by meiosis
– each spore divides by
mitosis to form two
haploid cells
– two cells form a
pollen grain
single pollen grain
22.2 Reproduction in Flowering Plants
• One female gametophyte can form in each ovule of a
flower’s ovary.
– four female spores produced in ovule by meiosis
– one spore develops into female gametophyte
– female gametophyte contains seven cells
– one cell has two nuclei, or polar nuclei
– one cell will develop into an egg
22.2 Reproduction in Flowering Plants
• Pollination occurs when a pollen grain lands on a stigma.
pollen tube
sperm
stigma
– one cell from pollen grain forms pollen tube
– other cell forms two sperm that travel down tube
22.2 Reproduction in Flowering Plants
• Flowering plants go through the process of double
fertilization.
female
gametophyte
egg
sperm
polar nuclei
ovule
22.2 Reproduction in Flowering Plants
• Flowering plants go through the process of double
endosperm
fertilization.
– one sperm fertilizes
the egg
seed coat
– other sperm unites
with polar nuclei,
forming endosperm
– endosperm provides
food supply for
embryo
embryo
22.2 Reproduction in Flowering Plants
• Each ovule becomes a seed.
• The surrounding ovary grows into a fruit.
22.2 Reproduction in Flowering Plants
Animals, wind, and water can spread seeds.
• Seeds dispersed by animals can have nutritious fruits or
fruits that cling.
22.2 Reproduction in Flowering Plants
• Seeds dispersed by wind can have wing- or parachutelike fruits.
• Seeds dispersed by water can have fruits that float.
Cypselae
Double samaras
22.2 Reproduction in Flowering Plants
Seeds begin to grow when environmental conditions are
favorable.
• Seed dormancy is a state in which the embryo has stopped
growing.
– Dormancy may end
when conditions are
favorable.
– While dormant,
embryo can withstand
extreme conditions.
22.2 Reproduction in Flowering Plants
• Germination begins the growth of an embryo into a
seedling.
– water causes seed to swell and crack coat
– embryonic root, radicle, is first to emerge
– water activates enzymes that help send sugars to
embryo
22.2 Reproduction in Flowering Plants
• Germination begins the growth of an embryo into a
seedling.
– water causes seed to swell and crack coat
– embryonic root, radicle, is first to emerge
– water activates enzymes that help send sugars to
embryo
– embryonic shoot, plumule, emerges next
– leaves emerge last
22.2 Reproduction in Flowering Plants
• Once photosynthesis begins, the plant is called a seedling.
22.2 Reproduction in Flowering Plants
Plant hormones regulate plant functions.
• Hormones are chemical messengers.
– produced in one part of an organism
– stimulates or suppresses activity in another part
22.2 Reproduction in Flowering Plants
• Gibberellins are plant hormones that produce dramatic
increases in size.
– ending seed dormancy
– rapid growth of young
seedlings
– rapid growth of some
flower stalks
22.2 Reproduction in Flowering Plants
• Ethylene causes the ripening of fruits.
– some fruits picked before
they are ripe
– sprayed with ethylene to
ripen when reach
destination
22.2 Reproduction in Flowering Plants
• Cytokinins stimulate cytokinesis.
– final stage in cell division
– produced in growing roots, seeds, and fruits
– involved in growth of side branches
22.2 Reproduction in Flowering Plants
• Auxins lengthen plant cells in the growing tip.
– stimulates growth of
primary stem
– controls some forms of
tropism
• A tropism is the movement
of plant in response to an
environmental stimulus.
22.2 Reproduction in Flowering Plants
Went's Experiment Explore the steps involved in an
experiment performed by Dutch botanist Frits Went.
22.2 Reproduction in Flowering Plants
Plants can respond to light, touch, gravity, and seasonal
changes.
• Phototropism is the
tendency of a plant to
grow toward light.
– auxins build up on
shaded side of stem
– cells on shaded
side lengthen
– causes stem to
bend toward light
22.2 Reproduction in Flowering Plants
• Thigmotropism is a plant’s response to touchlike stimuli.
– climbing plants and vines
– plants that grow in direction of constant wind
Thigmotropism A
plant turns and
bends in response
to contact with an
object.
22.2 Reproduction in Flowering Plants
• Gravitropism is a plant’s response to Earth’s gravitational
pull.
– positive gravitropism is downward growth (roots)
– negative gravitropism is upward growth (shoots)
Gravitropism
Plant stems
grow upward,
against gravity.
22.2 Reproduction in Flowering Plants
• Photoperiodism is a response to the changing lengths of
day and night.
– triggers some plants to flower (see below)
– triggers fall colors/winter dormancy of deciduous trees
Photoperiodism
A plant moves
its leaves during
the day.