Lesson Overview
Reproduction in Flowering Plants
Lesson Overview
24.1 Reproduction in
Flowering Plants
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
The Angiosperm Life Cycle
Angiosperms have a life cycle that shows an alternation of
generations between a diploid sporophyte phase and a
haploid gametophyte stage.
Male and female gametophytes live within the tissues of the
sporophyte.
Lesson Overview
Reproduction in Flowering Plants
Development of Male Gametophytes
The male gametophytes—the pollen grains—develop inside
anthers.
First, meiosis produces four haploid spore cells.
Lesson Overview
Reproduction in Flowering Plants
Development of Male Gametophytes
Each spore undergoes one mitotic division to produce the
two haploid nuclei of a single pollen grain.
The two nuclei are surrounded by a thick wall that protects
the male gametophyte.
Lesson Overview
Reproduction in Flowering Plants
Development of Female Gametophytes
Female gametophytes develop inside each carpel of a
flower.
The ovules—the future seeds—are enveloped in a
protective ovary—the future fruit.
Lesson Overview
Reproduction in Flowering Plants
Development of Female Gametophytes
A single diploid cell goes through meiosis to produce four
haploid cells, three of which disintegrate.
Lesson Overview
Reproduction in Flowering Plants
Development of Female Gametophytes
The remaining cell undergoes mitosis, producing eight
nuclei. These eight nuclei and the surrounding membrane
are called the embryo sac.
The embryo sac, contained within the ovule, makes up the
female gametophyte of a flowering plant.
Lesson Overview
Reproduction in Flowering Plants
Development of Female Gametophytes
Cell walls form around six of the eight nuclei.
One of the eight nuclei, near the base of the gametophyte,
is the nucleus of the egg—the female gamete.
If fertilization takes place, this egg cell will fuse with the
male gamete to become the zygote that grows into a new
sporophyte plant.
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, wind-pollinated
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
Pollination
Reproduction in Flowering Plants
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 insect-pollinated 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
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.
Lesson Overview
Reproduction in Flowering Plants
Vegetative Reproduction
Many flowering plants can reproduce asexually. This
process, known as vegetative reproduction, enables a
single plant to produce offspring genetically identical to
itself by mitosis. It does not require gametes, flowers, or
fertilization.
This process takes place naturally in many plants.
Lesson Overview
Reproduction in Flowering Plants
Types of Vegetative Reproduction
New plants may grow from roots,
leaves, stems, or plantlets.
A potato is an underground stem
that can grow whole new plants
from buds, called “eyes.”
Because vegetative reproduction
does not involve pollination or
seed formation, a single plant can
reproduce quickly.
Lesson Overview
Reproduction in Flowering Plants
Types of Vegetative Reproduction
Asexual reproduction allows a single plant to produce
genetically identical offspring, enabling well-adapted
individuals to rapidly fill a favorable environment.
One drawback of asexual reproduction is that it does not
produce new combinations of genetic traits, which may be
valuable if conditions in the physical environment change.
Lesson Overview
Reproduction in Flowering Plants
Plant Propagation
To propagate plants with desirable characteristics,
horticulturists use cuttings or grafting (shown) to make
many identical copies of a plant or to produce offspring
from seedless plants.
Lesson Overview
Reproduction in Flowering Plants
Plant Propagation
One of the simplest ways to
reproduce plants vegetatively is by
cuttings.
A grower cuts from the plant a
length of stem that includes a
number of buds containing
meristem tissue.
That stem is then partially buried
in soil or in a special mixture of
nutrients that encourages root
formation.
Lesson Overview
Reproduction in Flowering Plants
Plant Propagation
Grafting is a method of
propagation used to reproduce
seedless plants and varieties
of woody plants that cannot be
propagated from cuttings.
To graft, a piece of stem or a
lateral bud is cut from the
parent plant and attached to
another plant, as shown.
Lesson Overview
Reproduction in Flowering Plants
Plant Propagation
Grafting works only when the two plants are closely
related, such as when a bud from a lemon tree is grafted
onto an orange tree.
Grafting usually works best when plants are dormant,
which allows the wounds created by the cut to heal before
new growth starts.