Download Ch_38 plant reproduction

Chapter 38.
Plant Reproduction
AP Biology
2005-2006
Animal vs. Plant life cycle
Animal
Plant
multicellular
2n
multicellular
sporophyte
2n
gametes
1n
unicellular
gametes
1n
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spores
2n
multicellular
gametophyte
1n
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alternation of generations
Alternation of generations
diploid
haploid
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Alternation of generations
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Alternation of generations
 Fern sporophyte

leafy plant you are familiar with
 Fern spores

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haploid cells that will sprout into
gametophyte
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Alternation of generations
 Fern gametophyte

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small diploid plant which produces
gametes
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Alternation of generations
 Archegonium
female gamete-producing structure
 produces a single egg cell in a
vase-shaped organ

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Alternation of generations
 Antheridia
male gamete-producing structure
 produces many sperm cells that are
released to the environment

flagella =
swimming sperm
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Evolutionary trends
 Alternation of generations

dominant haploid plant
 bryophytes - mosses

dominant diploid plant
 pteridophytes - ferns
 gymnosperm - conifers
 angiosperm - flowering plants
 Evolutionary advantage?

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reduction of gametophyte protects delicate
egg & embryo in protective sporophyte
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Moss sporophytes
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Reduction of gametophyte
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Gametophytes of seed plants
Gymnosperm
Angiosperm
 male gametophyte
 male gametophyte

pollen in male cone
 female gametophyte

develops in female
cone
 seed

naked in cone

 female gametophyte

develops in ovaries
of flower
 seed


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pollen in anthers of
flower
protected in ovary
ovary wall can
develop into fruit
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Gymnosperm life cycle
female
gametophyte
in cone
male
gametophyte
in pollen
sporophyte
in seed
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Angiosperm life cycle
male
gametophyte
in pollen
female
gametophyte
in ovary
sporophyte
in seed
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Flowers
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2005-2006
Flower
 Modified shoot
with 4 rings of
modified leaves
sepals
 petals
 stamens

 male

carpals
 female
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pistil
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Male & female parts of flower
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Parts of flower
 Male
stamens = male reproductive organs
 stamens have stalks (filament) &
terminal anthers which carry pollen
sacs
 pollen sacs produce pollen
 pollen grain = gametophyte

 sperm-producing structure
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2005-2006
Parts of flower
 Female
carpels = female reproductive organs
 ovary at the base
 slender neck = style
 within the ovary are 1 or more ovules
 within ovules are embryo sacs
 female gametophyte = embryo sac

 egg-producing structure
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Fertilization
 Pollination


pollen released from anthers is carried by wind
or animals to land on stigma
pollen grain produces a pollen tube
 pollen tube grows down style into ovary &
discharges 2 sperm into the embryo sac
 1 sperm fertilizes egg = zygote
 zygote develops into embryo


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ovule develops into a seed
ovary develops into a fruit containing
1 or more seeds
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Preventing self-pollination
 Various mechanisms
 stamens & carpels may mature at different times
 arranged so that animal pollinator won’t transfer
pollen from anthers to stigma of same flower
 biochemical self-incompatibility = block pollen
tube growth
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2005-2006
Preventing self-fertilization
 This model involves the “S” allele

Pollen (male) with same allele cannot
germinate on stigma (female)
 Matching alleles interact & inhibit RNA
production
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Biochemical mechanism
 Preventing self-fertilization

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pollen produces signal → receptor → kinase →
signal transduction path → effector protein
produced → block pollen tube growth
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Fertilization in flowering plants
 Double fertilization

2 sperm from pollen
 1 sperm fertilizes
egg = diploid zygote
 1 sperm fuses with
2 polar nuclei to
form 3n endosperm
 endosperm = food
tissue in seed
 coconut milk
 grains
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Pollen tube growth
 grow down style to ovule
 path for sperm nuclei
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Fertilization in flowering plants
 Development of the new sporophyte
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Plant embryo
endosperm
seed coat
cotyledons
ovary wall
embryo
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Seed Anatomy
 Sporophyte in seed

Sets stage for
structure of plant
 Roots
 Shoots
 Leaves
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Germination
 How does the dicot differ from the
monocot?
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Mobilization of nutrients
 Seed germination




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1. seed imbibes water
2. gibberellin release signals aleurone layer
3. amylase is released which hydrolyzes starch
4. sugar is absorbed by embryo
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Fruit
 Fruit is a mature ovary



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seeds develop from ovules
wall of ovary thickens to form fruit
fruits protect dormant seeds &
aid in their dispersal
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Fruit development
 Pea (legume)
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Fruit development
 Peach (stone fruit or drupe)

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1 flower : 1 carpel : 1 ovary : 1 seed
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Fruit development
 Apple (pome fruit)

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1 flower : 5 carpels : many ovaries :
many seeds
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Fruit development
 Citrus fruit (berry)

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1 flower : many carpels : many ovaries :
many seeds
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Fruit development
 Raspberry (aggregate fruit)
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1 flower : many ovaries : many seeds
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Reproduction in angiosperm
 Sporophyte plant produces unique
reproductive structure = the flower

male gametophyte = pollen grain
 develop within anthers of flower

female gametophyte = embryo sac
 develop within ovaries of flower


pollination by wind or animals brings pollen
grain to female gametophyte
fertilization takes place within ovary
 double fertilization = embryo & endosperm

seeds contain sporophyte embryo
 development of seeds in ovary
 ovary develops into fruit around the seed
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Coevolution of plants & animals
 Angiosperms & animals have shaped
one another’s evolution
 Natural selection reinforced the
interactions
because they
improved the
reproductive
success of
both partners
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Seed dispersal
 Plants produce enormous numbers of seeds to
compensate for low survival rate
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a lot of genetic variation for natural selection to screen
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