Plant Reproduction
Creating the next generation
W
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• Is a seed alive? Is a fruit alive? Answer
as completely as you can on your own
paper. (Hang on to your paper until the
end of class.)
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Asexual Reproduction
• Asexual reproduction is natural “cloning.”
Parts of the plant, such as leaves or
stems, produce roots and become an
independent plant.
• List some benefits and some drawbacks
to asexual reproduction.
Sexual Reproduction
• Sexual reproduction requires fusion of
male cells in the pollen grain with female
cells in the ovule.
• List some advantages and drawbacks to
sexual reproduction.
Terms to know:
• Haploid: having a single set of
chromosomes in each cell.
• Diploid: having two sets of
chromosomes in each cell.
• Mitosis: cell division, which produces
two genetically identical cells.
• Meiosis: reduction division, which
produces four haploid reproductive cells.
Plant Life Cycle
Alternation of Generations
• Plants have a double life cycle with two
distinct forms:
• Sporophyte: diploid, produce haploid
spores by meiosis (reduction division).
• Gametophyte: haploid, produce
gametes by mitosis (simple cell
division).
Non-flowering plants
• Mosses, ferns, and related plants have
motile, swimming sperm.
• What kind of environmental conditions
would be required for reproduction in
these plants?
• What kinds of limits does external
reproduction impose on these plants?
Moss Life Cycle
Fern Life Cycle
Conifers
• Conifers (also non-flowering plants) have
reduced gametophytes.
• Male gametophyte is contained in a dry
pollen grain.
• Female gametophyte is a few cells
inside of the structures that become
the seed.
Conifer life cycle
Conifer pollination
• Conifers are wind-pollinated plants.
• Chance allows some pollen to land on
the scales of female cones.
• Pollen germinates, grows a pollen tube
into the egg to allow sperm to fertilize the
egg.
• What are some advantages and
disadvantages to wind pollination?
Animals vs. Plants
Plant Reproduction Animal Reproduction
Life cycle
Alternation of
generations
No alternation of
generations
Gametes
Haploid gametes
Haploid gametes
Spores
Haploid spores
No spores
Gametes made Haploid gametophyte,
by
by mitosis
Spores made
by
Diploid sporophyte, by
meiosis
Diploid organism, by
meiosis
No spores
Meiosis produces cells that
have:
1. Twice the number of
chromosomes as the
original cell.
2. The same number of
chromosomes as the
original cell.
3. Half the number of
chromosomes as the
original cell.
33%
1
33%
2
33%
3
A diploid sporophyte produces haploid
spores. Which process did it use?
50%
50%
1. Meiosis
2. Mitosis
1
2
A haploid gametophyte produces:
25%
1.
2.
3.
4.
25%
25%
25%
Diploid spores
Haploid spores
Diploid gametes
Haploid gametes
1
2
3
4
Flowers
Pollen go-betweens
• Showy flowers are the result of selection
for more efficient pollination strategies.
• Flower parts are modified leaves. Those
that were brightly colored attracted
insects in search of pollen.
• Why would insects search for pollen?
What other rewards do flowers offer?
• What are advantages and disadvantages
to relying on insects as pollinators?
Flower Parts
Incomplete flowers
• Flowers are complete if they have all
parts, and perfect if they have both male
and female parts.
• Grass flowers: incomplete, usually
imperfect (separate male and female
flowers)
• A tulip is complete (though the sepals
are the same color as the petals) and
perfect.
Imperfect flowers
Angiosperm Life Cycle
Gametogenesis: Male
Gametogenesis: Female
Double Fertilization
The male structures of a flower
are the:
25%
1.
2.
3.
4.
25%
25%
25%
Petals
Sepals
Carpels
Stamens
1
2
3
4
A flower is perfect if it has:
25%
1.
2.
3.
4.
25%
25%
25%
Anthers and carpels
Petals and sepals
Petals and carpels
Sepals and stamens
1
2
3
4
The two sperm from the pollen help give
rise to:
25%
25%
25%
25%
1. Petals and sepals
2. Stamens and pistils
3. Endosperm and
embryo
4. Gametes and spores
1
2
3
4
Fruits
From ovary to fruit
• The ovary of the flower contains the
ovules.
• As fertilized ovules develop into seeds,
the ovary wall develops into the fruit.
• In science, the term “fruit” refers to a
mature ovary that contains seeds.
Flower to Fruit
Types of dry fruits
Capsule
(Poppy)
Legume
(Bean pod)
Silique
(Money Plant)
Follicle
(Columbine)
Achene
(Sunflower)
Nut
(Hazelnut)
Types of fleshy fruits
Drupe
(Peach)
Berry
(Tomato)
Pome
(Apple)
Pepo
(Cucumber)
Aggregate
(Strawberry)
Multiple
(Pineapple)
Seeds arise directly from:
25%
1.
2.
3.
4.
25%
25%
25%
Ovaries
Ovules
Pollen grains
Anthers
1
2
3
4
Seeds
Ovule to seed
Seed Anatomy
Seed anatomy
Seed dormancy
• Seeds can remain dormant in the soil for
long periods of time. Dormancy helps
ensure that seeds only germinate when
conditions are right.
• When we weed or cultivate a bare patch
of soil, the weeds that sprout up
immediately usually come from the “seed
bank” already in the soil.
Breaking dormancy
• Seeds require moisture and the right
temperature to germinate.
• In addition, some seeds germinate only
after certain environmental signals:
• Drying
• Temperature (period of cold or heat)
• Disruption of the seed coat
Seed Germination
Cotyledons are:
25%
25%
25%
25%
1. Embryonic leaves
2. Structures that
contain food for the
embryo
3. Embryonic plants
4. The seed coat
1
2
3
4
W
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• Use what you have learned about plant
life cycles to explain why most mosses
and ferns live in moist environments, but
flowering plants can live just about
anywhere.
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