Angiosperm Reproduction
& Biotechnology
Ch 38
Alternation of Generations (Revisited)

The life cycle of angiosperms and other plants are
characterized by an alternation of generations, in
which haploid (n) and diploid (2n) generations
take turns producing each other
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Diploid plant (sporophyte) produces haploid spores by
meiosis
These haploid spores divide by mitosis, producing
gametophytes
These small male and female haploid plants
(gametophytes) produce gametes
Gametes unite through fertilization, resulting in a
diploid zygote
The zygote divides by mitosis, producing the new
sporophyte
Alternation of Generations
A Review of Flower Structure
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Flowers are the
reproductive
structures of flowering
plants
Review: structure of
an idealized flower
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Male parts?
Female parts?
Flower Vocabulary

Complete vs. incomplete flowers
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Complete flowers = have all 4 floral parts (sepals,
petals, stamens, carpels)
Incomplete flowers = missing at least one floral
part
Perfect vs. imperfect flowers
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Perfect flowers have both stamens and carpels
Imperfect flowers are missing either stamens or
carpels
Flower Vocabulary

Monoecious vs. Dioecious Plants
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Plant species are monoecious (“one house”) if
the male and female parts are found on the
same individual plant
Plant species are dioecious (“two houses”) if
the male and female parts are found on
separate plants
Dioecious Plants
Pollination and Fertilization
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Pollination is the placing of pollen onto the stigma of a
carpel
Pollination is accomplished either by wind or by animals
A pollen grain absorbs moisture and produces a pollen tube
that extends down the style to the ovary
 The diploid microsporocytes (in sporangia of anther)
each undergo meiosis to produce 4 haploid microspores.
Each microspore undergoes mitosis and makes 2 cells:
tube nucleus (digs tube) and generative nucleus, both
contained in gametophyte. Generative nucleus mitosis
and makes 2 sperm nuclei.
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One sperm cell fertilizes the egg to form the (2n) zygote
The other sperm cell combines with the two polar bodies
to form a triploid (3n) nucleus. This cell will become the
endosperm, which serves as a food source to the
developing embryo
This process (double fertilization) ensures that the
endosperm (food source) will develop only in ovules where
the egg has been fertilized
Fertlization- Continued

Ovules are in ovary. Within ovule, large cell:
megasporocyte (2n). Undergoes meiosis and
makes 4 haploid megaspores, but 3 are small and
usually die (think polar bodies). Remaining
megaspore undergoes 3 mitotic divisions, but
instead of producing 8 haploid cells, there are 7
(one doesn’t undergo cytokinesis and keeps both
nuclei. Called polar nuclei). Polar nuclei unites
with 1 sperm nuclei/cell and becomes 3n
Endosperm (food). Another haploid cell unites
with the other sperm nuclei and becomes diploid
zygote. Mitosis follows and Seed then develops.
From Ovule to Seed
After double fertilization, the ovule will
develop into a seed
 The seed dehydrates as it nears the end of
its maturation
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The embryo and its food supply (cotyledons,
endosperm or both) are enclosed by a hard,
protective seed coat
Seed Structure- know?
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The radicle is the root
of the embryo and
where germination
begins
The part of the seed
below the point at
which the cotyledons
are attached is called
the hypocotyl
The portion of the
embryonic axis above
the cotyledons is the
epicotyl
Seed Structure-?
From Ovary to Fruit

After double fertilization, the ovary will
develop into a fruit enclosing the seed

The fruit protects the seeds inside and aids in
dispersal (by wind or animals)
Fruits

Simple Fruits
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Aggregate Fruit
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A fruit derived from a
single ovary
Can be fleshy (cherry) or
dry (soybean pod)
A fruit that results from a
single flower that has
several separate carpels
Blackberries, strawberries
Multiple Fruit
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Develops from a group of
separate flowers tightly
clustered together
Pineapple
Seed Dormancy
Seed dormancy means that a seed will not
germinate, even if sown in a favorable
place, until a specific environmental cue
causes them to break dormancy
 Seed dormancy increases the chances that
germination will occur at a time and place
most advantageous to the seedling

Stages of Seed Germination
(1)
(2)
(3)
(4)
The seed absorbs
water, causing it to
expand and rupture its
seed coat
The embryo resumes
growth, digesting the
storage materials of the
endosperm
The radicle (embryonic
root) emerges from the
germinating seed
The shoot tip breaks
through the soil surface
(if 2 leaves emerge:
dicot; 1 seed
leaf=monocot)
Stages of Seed Germination
Asexual Reproduction

When plant species
clone themselves by
asexual reproduction,
it’s known as
vegetative
reproduction
Asexual Reproduction

Fragmentation is the
separation of a parent
plant into parts that
re-form whole plants

This type of asexual
reproduction is used to
produce clones from
cuttings (common with
houseplants)
Plant Reproduction
Sexual
Asexual
(Vegetative Reproduction)
Flower  Seeds
Runners, bulbs, grafts, cuttings
vegetative (grass), fragmentation,
test-tube cloning
Genetic diversity
Clones
More complex & hazardous for
seedlings
Simpler (no pollinator needed)
Advantage in unstable
environments
Suited for stable environments
Asexual
reproduction in
aspen trees
Test-tube cloning
of carrots
Humans Modify Crops
Artificial selection of plants for
breeding
 Plant Biotechnology:
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Genetically modified organisms
Rice”: engineered to
produce beta-carotene (Vit. A)
 Bt corn: transgenic – expresses Bt
(bacteria) gene  produces
protein toxic to insects
 “Golden

Biofuels – reduce CO2 emissions
 Biodiesel:
vegetable oils
 Bioethanol: convert cellulose into
ethanol
Plant Biotechnology & Agriculture

Artificial Selection

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Favorable traits can be
selected for by using
selective breeding
tactics
Example: maize

Maize (corn ) has
been selectively bred
to contain higher levels
of protein for
consumption in
developing countries
Reducing World Hunger & Malnutrition
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800,000,000 people on Earth suffer from nutritional
deficiencies
40,000 people die each day of malnutrition
Increasing food production is an important part of
addressing this global issue
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There is a limited amount of land and water available for
farming
The best option is to increase the productivity of the land
currently being farmed
Developing transgenic plants that are resistant to herbicides
and repel insects without the use of pesticides and increasing
the nutritional quality of plants are possible with modern
biotechnology techniques
However, the use of biotechnology in the production of
genetically modified plants is controversial