Plant Reproduction

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Plant Reproduction

• Creating the next generation

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W O R K T O G E T H E R

• 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.

4
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.

5
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.

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Plant Life Cycle
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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).

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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?

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Moss Life Cycle
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Fern Life Cycle
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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.

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Conifer life cycle
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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?

14
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 by Haploid gametophyte, by mitosis Diploid organism, by meiosis
Spores made by Diploid sporophyte, by meiosis No spores
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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.

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A diploid sporophyte produces haploid spores.
Which process did it use?

1. Meiosis
2. Mitosis

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A haploid gametophyte produces

1. Diploid spores
2. Haploid spores
3. Diploid gametes
4. Haploid gametes

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Flowers
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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?

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Flower Parts
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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.

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Imperfect flowers
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Angiosperm Life Cycle
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Gametogenesis Male
25
Gametogenesis Female
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Double Fertilization
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The male structures of a flower are the

1. Petals
2. Sepals
3. Carpels
4. Stamens

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A flower is perfect if it has

1. Anthers and carpels
2. Petals and sepals
3. Petals and carpels
4. Sepals and stamens

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The two sperm from the pollen help give rise to

1. Petals and sepals
2. Stamens and pistils
3. Endosperm and embryo
4. Gametes and spores

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Fruits
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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.

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Flower to Fruit
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Types of dry fruits
Capsule (Poppy)
Legume (Bean pod)
Achene (Sunflower)
Follicle (Columbine)
Silique (Money Plant)
Nut (Hazelnut)
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Types of fleshy fruits
Drupe (Peach)
Pome (Apple)
Pepo (Cucumber)
Aggregate (Strawberry)
Multiple (Pineapple)
Berry (Tomato)
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Seeds arise directly from

1. Ovaries
2. Ovules
3. Pollen grains
4. Anthers

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Seeds
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Ovule to seed
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Seed Anatomy
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Seed anatomy
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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.

41
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

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Seed Germination
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Cotyledons are

1. Embryonic leaves
2. Structures that contain food for the embryo
3. Embryonic plants
4. The seed coat

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W O R K T O G E T H E R

• 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.