Hazel carpellate flower
(carpels / female sex organs only)
Adapted for wind pollination
Slide 15
Pollination by Bees
Common dandelion under
normal light
Common dandelion under
ultraviolet light
Color = visual cue / signal to attract pollinators
Slide 16
Pollination by Flies
Blowfly on carrion flower
Fly egg
Chemical signal: Odor attracts flies
Slide 17
Nectar = chemical attractant
Hummingbird drinking nectar of poro flower
Pollination by Birds
Slide 18
After landing on a receptive stigma, a pollen grain produces a pollen tube that extends between the cells of the style toward the ovary.
Double fertilization results from the discharge of two sperm from the pollen tube into the embryo sac in the ovule.
Sperm + egg = zygote 2n
Sperm + two polar nuclei = endosperm 3n
One sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid (3n) food-storing endosperm.
Slide 19
Stigma
Pollen tube
2 sperm
Style
Ovary
Ovule
Micropyle
Ovule
Polar nuclei
Egg
Synergid
2 sperm
Endosperm
nucleus (3n)
(2 polar nuclei
plus sperm)
Zygote (2n)
(egg plus sperm)
Egg
Pollen grain
Polar nuclei
Growth of the pollen tube
and
double fertilization
Slide 20
Growth of the Pollen Tube
Stigma
Pollen tube
2 sperm
Style
Ovary
Ovule
Micropyle
Egg
Pollen grain
Polar nuclei
Slide 21
Embryo Sac in the Ovule
Ovule
Polar nuclei
Egg
Synergid
2 sperm
Slide 22
Double Fertilization:
Endosperm
nucleus (3n)
(2 polar nuclei
plus sperm)
Zygote (2n)
(egg plus sperm)
Slide 23
After double fertilization, each ovule develops into a seed.
The ovary develops into a fruit enclosing the seed(s).
Slide 24
Endosperm development usually precedes embryo development.