chapter 38: plant reproduction and development
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Chapter 38: Plant Reproduction and Development. Flowers. Sexual organs of Angiosperms. Develop from compressed shoots with four whorls of modified leaves. Flower Whorls 1. Sepals 2. Petals 3. Stamens 4. Carpels. Sepals. Whorl of sterile leaf-like structures. May be brightly colored. - PowerPoint PPT PresentationTRANSCRIPT
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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.
Flower Whorls1. Sepals2. Petals3. Stamens4. 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). Carpel Structure
Stigma – receives the pollen. Style – stalk. Ovary – contains the ovules.
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. Perfect Flowers - have stamens and carpels. Imperfect Flowers - have stamens or carpels.
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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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Embryo Sac Development The Embryo Sac is the female gametophyte. Starts with a megasporocyte (2N). 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. 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. Pollen Vectors
Bees Flies Butterflies Moths Birds Beetles Bats Wind
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Comment The flower is usually highly
adapted to the pollen vector. Ex:
Colors Rewards Scents Shape
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Fertilization
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
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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Embryo Development Root/shoot polarity set with 1st cell division. Mature embryo has all three primary tissues,
apical meristems etc. 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. Fruit
A mature ovary. Sometimes includes other plant parts. Ex: apple
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Fruit Functions Protect the seeds. Aid in seed dispersal.
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. 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. 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. 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 The development of specific
structures in specific locations.
Important in plants since cells don’t usually migrate.
Juvenile Mature
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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.