Transcript Lesson Overview

Lesson Overview
Reproduction in Flowering Plants
Lesson Overview
3.1 Reproduction in
Flowering Plants
Lesson Overview
Reproduction in Flowering Plants
THINK ABOUT IT
What makes a flower beautiful?
To a plant, the whole point of a flower is to bring gametes together for
reproduction and to protect the resulting zygote and embryo.
Lesson Overview
Reproduction in Flowering Plants
The Structure of Flowers
Flowers are reproductive organs that are composed of four different kinds
of specialized leaves: sepals, petals, stamens, and carpels.
This diagram shows the parts of a typical angiosperm flower.
Lesson Overview
Reproduction in Flowering Plants
Sepals and Petals
The outermost circle of floral parts contains the sepals.
Sepals enclose the bud before it opens, and they protect the flower
while it is developing.
Lesson Overview
Reproduction in Flowering Plants
Sepals and Petals
Petals, which are often brightly colored, are found just inside the sepals.
The colors, number, and shapes of such petals attract insects and other
pollinators to the flower.
Lesson Overview
Reproduction in Flowering Plants
Stamens
The stamens are the male parts of the flower—each stamen consists of
a stalk called a filament with an anther at its tip.
Anthers are the structures in which pollen grains—the male
gametophytes—are produced.
Lesson Overview
Reproduction in Flowering Plants
Carpels
The innermost floral parts are the carpels, which produce and shelter
the female gametophytes and, later, seeds.
Each carpel has a broad base forming an ovary, which contains one or
more ovules where female gametophytes are produced.
Lesson Overview
Reproduction in Flowering Plants
Carpels
The diameter of the carpel narrows into a stalk called the style. At the
top of the style is a sticky or feathery portion known as the stigma,
which is specialized to capture pollen.
Lesson Overview
Reproduction in Flowering Plants
Carpels
Botanists sometimes call a single carpel or several fused carpels a pistil.
Lesson Overview
Reproduction in Flowering Plants
Variety in Flowers
Flowers vary greatly in shape, color, and size.
Lesson Overview
Reproduction in Flowering Plants
Pollination
Pollination is the transfer of pollen to the female portions of the flower.
Some angiosperms are wind pollinated, but most are pollinated by
animals.
Because wind pollination is less efficient than animal pollination, windpollinated plants, such as oak trees, rely on favorable weather and
sheer numbers of pollen grains to get pollen from one plant to another.
Lesson Overview
Reproduction in Flowering Plants
Pollination
Animal-pollinated plants have a
variety of adaptations, such as
bright colors and sweet nectar,
to attract and reward animals.
Animals have evolved body
shapes that enable them to
reach nectar deep within
certain flowers.
Lesson Overview
Reproduction in Flowering Plants
Pollination
Insect pollination is beneficial to insects and other animals because it
provides a dependable source of food—pollen and nectar.
Plants benefit because the insects take the pollen directly from flower
to flower.
Insect pollination is more efficient than wind pollination, giving insectpollinated plants a greater chance of reproductive success.
Lesson Overview
Reproduction in Flowering Plants
Fertilization
If a pollen grain lands on the
stigma of a flower of the same
species, it begins to grow a
pollen tube.
Of the pollen grain’s two cells,
one cell—the “generative” cell—
divides and forms two sperm
cells. The other cell becomes the
pollen tube.
Lesson Overview
Reproduction in Flowering Plants
Fertilization
The pollen tube contains a tube
nucleus and the two sperm cells.
The pollen tube grows into the
style, where it eventually reaches
the ovary and enters an ovule.
Lesson Overview
Reproduction in Flowering Plants
Fertilization
Inside the embryo sac, two distinct fertilizations take place—a process
called double fertilization.
First, one of the sperm nuclei fuses with the egg nucleus to produce a
diploid zygote, which will grow into the new plant embryo.
Lesson Overview
Reproduction in Flowering Plants
Fertilization
Second, the other sperm nucleus fuses with two polar nuclei in the
embryo sac to form a triploid (3N) cell.
This cell will grow into a food-rich tissue known as endosperm, which
nourishes the seedling as it grows.
Lesson Overview
Reproduction in Flowering Plants
Fertilization
The endosperm and embryo of a corn seed are shown.
Lesson Overview
Reproduction in Flowering Plants
Fertilization
By using endosperm to store food, the flowering plant spends very little
in the way of food resources on producing seeds from ovules until
double fertilization has actually taken place.
The resources saved can be used to make many more seeds.