Chapter 38 Plant Reproduction and Development

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Chapter 38 Plant Reproduction and
Development
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Flowers

• Sexual organs of Angiosperms.
• Develop from compressed shoots with four whorls
  of modified leaves.

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Flower Whorls

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

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Sepals

• Whorl of sterile leaf-like structures.
• May be brightly colored.
• Function
• Protect other flower parts.
• Attract pollinators.

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Petals

• Whorl of sterile flower parts.
• Often brightly colored.
• Function
• Attract pollinators.

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Stamens

• Male reproductive flower structure.
• Function
• Produce pollen (sperm).

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Stamen Structure

• Anther - pollen producing sac.
• Filament - stalk.

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Carpel

• Female reproductive flower structure.
• Also called pistil.
• Function
• Produce embryo sac (eggs).

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Carpel Structure

• Stigma receives the pollen.
• Style stalk.
• Ovary contains the ovules.

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Ovule

• A rudimentary seed before fertilization.

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Flowers

• Are highly variable in form, shape, and color.
• Not all flowers contain the same combination of
  whorls.

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Flower Variations

• Complete Flowers - have all four whorls.
• Incomplete Flowers less than all four whorls.

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Flower Variations

• Perfect Flowers - have stamens and carpels.
• Imperfect Flowers - have stamens or carpels.

Staminate Flower
Carpellate Flower
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Monoecious Plants

• Staminate and pistillate flowers are on the same
  plant.
• Ex corn
• Tassel staminate flowers
• Ears carpellate flowers

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Dioecious Plants

• Have staminate or pistillate flowers, but not
  both.
• Ex Holly, Ginkgo
• Comment - "Seedless" plants may be a staminate
  plant.
• Ex male Ginkgo

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Pollen Development

• Pollen is the male gametophyte.
• Starts with a 2N cell called a microsporocyte.

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Microsporocyte

• Undergoes meiosis and produces 4 Microspores
  (1N).
• Each Microspore undergoes mitosis and produces a
  pollen grain, which is the male gametophyte.

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Mature Pollen Grain

• Special cell wall.
• Tube Nucleus (cell).
• Generative Nucleus (cell) which will divide and
  produce two sperm nuclei.

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Homework

• Reading Chapters 37, 38
• Chapter 37 today
• Chapter 36 Wed. 4/9
• Chapter 38 - Friday
• Ts Lab data coming soon

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Embryo Sac Development

• The Embryo Sac is the female gametophyte.
• Starts with a megasporocyte (2N).

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Megasporocyte

• Undergoes meiosis and produces 4 Megaspores (1N).
• Three of the megaspores abort, leaving only one
  to develop into the embryo sac.

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Megaspore

• Undergoes three rounds of mitosis to produce a
  sac with 8 nuclei.
• The nuclei may wall off or may remain as part of
  a large cell.

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Embryo Sac

• 3 Antipodal cells.
• 2 Polar nuclei (1 cell)
• 2 Synergid cells
• 1 Egg cell

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Pollination

• The transfer of pollen from a stamen to the
  stigma.

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Pollen Vectors

• Bees Flies
• Butterflies Moths
• Birds Beetles
• Bats Wind

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Comment

• Movie bat pollination

• The flower is usually highly adapted to the
  pollen vector.
• Ex
• Colors
• Rewards
• Scents
• Shape

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Fertilization

• Movie

• The union of egg and sperm to produce a zygote
  (2N).

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Angiosperms

• Have double fertilization.
• 1. Egg sperm ? zygote
• 2. Polar nuclei sperm ? Endosperm

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Endosperm

• Is Triploid (3N) tissue that will be used as a
  nutrition source for the embryo.

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After Fertilization

• Zygote ? Embryo
• Ovule ? Seed
• Ovary ? Fruit

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Movie Seed Development
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Embryo Development

• Root/shoot polarity set with 1st cell division.
• Mature embryo has all three primary tissues,
  apical meristems etc.

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Endosperm

• Monocots - large tissue.
• Dicots - transfer the energy over to the embryo's
  two cotyledons.

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Seed Coat

• Formed from the integuments of the ovule.
• Hard layer to protect the seed.

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Fruit

• A mature ovary.
• Sometimes includes other plant parts.
• Ex apple

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Movie Fruit Development
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Fruit Functions

• Protect the seeds.
• Aid in seed dispersal.

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Fruit Types

• Fleshy soft ovary walls.
• Dry hard ovary walls.

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Fruit Types

• Simple Fruit from a single ovary.
• Ex Peach, Cherry
• Aggregate Fruit from a flower with multiple
  carpels.
• Ex Raspberry
• Multiple Fruit develops from several flowers
  into one structure.
• Ex Pineapple

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Seeds

• Contain a miniature plant.
• Main dispersal mechanism for plants.
• Embryo is often dormant when the seed is mature.

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Seed Dormancy

• When a seed is not actively growing.
• Used to increase the chances that the plant will
  develop when conditions are favorable.

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Seed Dormancy

• Usually controlled by plant hormones.
• May require changes in temperature, moisture,
  etc. before growth will continue.

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Imbibition

• The absorption of water by a seed.
• First step in seedling growth.
• Causes swelling which ruptures the seed coat.
• Starts metabolism to resume growth.

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Germination

• The continuation of growth of the plant within a
  seed.
• Root usually emerges first.
• Shoot tip must break through the soil surface.

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Role of Light

• Light is the usual clue that the shoot has broken
  above ground.
• Light causes many growth changes in the shoot
• Ex. Leaves to expand
• Stem elongation rate decreases

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Asexual Reproduction

• Offspring produced by mitosis.
• Also called cloning.

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Normal Method

• Fragmentation of the plant body so that new
  plants are formed.
• Ex Cuttings Grafting Offshoots

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High-Tech Methods

• Tissue Culture.

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Tissue Culture

• Clumps of cells grow into embryoids which can be
  used to regenerate whole plants.
• Often used in genetic engineering of plants.

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• Protoplast Fusion. A "naked" plant cell
  (no cell wall).
• Used to create new hybrids

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Plants

• Frequently use both sexual and asexual
  reproduction depending on the environment.
• Asexual - stable
• Sexual - unstable

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Plant Development

• Growth increase in size
• Development changes in body form and structure.

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Plant Problems

• Determining the direction of cell growth because
  of the cell wall.

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Control Mechanism

• Cytoskeleton determines the direction of cell
  expansion.
• Cellulose Microfibrils are arranged in parallel
  strips as guided by microtubules in the cell
  membrane.

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Cell Expansion

• Increase in cell size is usually caused by turgor
  pressure.
• Direction of cell increase is at right angles to
  the cellulose mircofibrils.

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Cell Differentiation

• Depends on the control of gene expression.
• (review previous chapters on this topic)

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Pattern Formation
Juvenile
Mature

• The development of specific structures in
  specific locations.
• Important in plants since cells dont usually
  migrate.

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Positional Information

• Gradients of chemicals that provide clues of
  position of cells to each other.
• Ex why some cells develop into shoots and others
  into roots.

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Organ-Identity Genes

• Genes for normal organ development.
• Used in positional information to determine which
  organ the cells should develop into.

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Example

• The combination of three genes that give rise to
  the flower parts.
• A ? sepals
• A B ? petals
• B C ? stamens
• C ? carpels

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Mutations

• Cause other floral parts to form in the flowers.
• (review Chapter 21).

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Summary

• Know the general structures of flowers.
• Know the general life cycle of flowers.
• Review the items on plant development.