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Flowers and Reproduction (Angiosperms) (Flower Structure and Cross…
Flowers and Reproduction (Angiosperms)
Asexual Reproduction
fragmentation
individual parts become self sufficient
Sexual Reproduction
flowers
produce the necessary reproductive cells and structures
The Plant Life Cycle
gametes=mammal or spores=plants
haploid sex cells
produced by meiosis
sperm (microgametes)
produced by males
egg (megagametes)
produced by females
zygote= sperm + egg
syngamy or fertilization
the fusion of gametes
sporophyte phase
a.k.a. sporophyte generation
diploid phase of plant life cycle
organs (located in the flowers)
capable of undergoing meiosis
produce spores
do not undergo syngamy
undergo mitosis
grows into new haploid plant (gametophyte)
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plant (-phyte)
gametes (gameto-)
alteration of generations
life cycle with two generations
sporophyte
gametophyte
gametophytes do not resemble sporophytes
alteration of heteromorphic generations
complex life cycle
3 distinct plants
1 sporophyte
2 gametophytes
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Flower Structure
basically a stem with leaf-like structures
never become woody
secondary growth does not occur
pedicel
a flowers stalk
receptacle
very end of axis
other flower parts are attached
four types of floral appendages:
sepals
lowermost and outermost appendage
modified leaves
enclose/ surround other flower parts
protect bud as it develops
calyx
all the sepals together
typically thickest, toughest, and waxiest flower part
petals
above the sepals on receptacle
"leaf-like"
contain pigments instead of chlorophyll
attract correct pollinators
distinct size, shape, color, and arrangement
corolla
all petals together
perianth
sepals and petals together
stamens
above the petals
technically not "male"
produce pollen
two parts:
filament
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anther
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androecium
all of the stamens together
carpels
constitute gynoecium
collective of parts that produce ovule
located highest level of receptacle
too few or zero carpels=imperfect flowers
too many carpels (fused)=pistil
three main parts:
1) stigma
catches pollen grains
which germinate producing a pollen tube
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2) style
elevates stigma to useful position
3) ovary
where megaspores are produced
placentae (singular, placenta)
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develops into the fruit
Fertilization (syngamy)
plasmogamy
fusion of protoplasts of the gametes
karyogamy
fusion of the nuclei
pollen tube grows downward
through style toward ovule
guided to ovule's micropyle
penetrates nucellus
reaches egg
integuments that surround nucellus
mature into seed coat (testa)
pollen tube tip bursts
two sperm released
1 sperm nucleus fuses with egg nucleus
diploid zygote
endosperm nucleus
2nd sperm undergoes karyogamy w/central cell
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double fertilization
both sperm nuclei undergo fusions
Embryo and Seed Development
endosperm nucleus proliferates
zygote also begins to grow
by both nuclear and cellular divisions
small cluster of cells
embryo proper
continue to divide mitotically
developing into embryo
first arranged in small sphere (globular stage)
two primordia grow into cotyledons
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embryo becomes elongate cyclinder (torpedo stage)
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vascular tissue differentiates
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suspensor
pushes embryo deep into endosperm
delicate
ephemeral (lasting for a short time)
crushed by later growth of embryo
Fruit Development
ovary matures into fruit
3 distinct layers during growth:
exocarp=outer layer (skin/peel)
mesocarp=middle layer (flesh)
endocarp=innermost layer (pit)
pericarp
entire fruit wall
Flower Structure and Cross-Pollination
Cross-Pollination
pollination of a carpel
by pollen from a different individual
Self-Pollination
pollination of a carpel
by pollen from
same flower
or another flower from same plant
Stamen and Style Maturation Times
self -fertilization prevented if:
anthers stigmas mature at different times
Stigma and Pollen Incompatibility
compatibility barriers
chemical reactions between pollen and carpels
prevent pollen growth
if incompatability proteins match
stigma and style block growth of pollen
Monoecious and Dioecious Species
stamens & carpels (essential organs)
produce critically important spores
imperfect flowers
lack either or both essential organs
perfect flower
has both essential organs
nonessential organs
sepals or petals
dioecy
(dioecious)species with individuals
produce only staminate flowers
produce carpellate flowers
extreme adaptation
ensures cross-pollination
monoecy
staminate flowers and carpellate flowers
located on same plant
monoecious species
Animal-Pollinated Flowers
adaptive mutations resulting in:
pigments
fragrances
sugar-rich secretions
probability of pollination improved
insect-flower association
120 million years ago
coevolution between insects and plants
actinomorphic
radially symmetrical
zygomorphic
billaterally symmetrical
Wind-Pollinated Flowers
adaptive mutations:
prevention of petal formation (energy saved)
reduced or absent sepals
ovaries need no special protection
large feathery stigmas (large number of pollen)
individuals producing thousands of small flowers
Ovary Position
ovary and ovules
must be protected from pollinators
adaptations that maximize seperation
long styles and stamen filaments
ovaries deep within flower
inferior ovary or other parts epigynous
base of stamens, petals, and sepals fuse
creating thick layer of protective tissues around ovaries
superior ovary or hypogynous parts
partially buried ovaries
half-inferior with perigynous flower parts
Inflorescences and Pollination
positoning of flowers important
position of flower relative to other flowers, leaves, and trunk
height from ground
open, uncluttered pollinator flight path
inflorescense
collective visual signal to pollinators
if many flowers are grouped together
two basic arrangements:
1) determinate inflorescences
2) indeterminate inflorescences
Fruit Types and Seed Dispersal
fruits are adaptations
protection
distribution of seeds
gravity
wind
water
animals
True Fruits and Accessory Fruits
"pericarp"
tissues of the fruit
regardless of origin
true fruit
fruits with only ovarian tissue
accessory fruit (or false fruit)
if any nonovarian tissue is present
simple fruit
fruit from single ovary or fused ovaries from one flower
aggregate fruit
separate carpels of one gynoecium fuse
multiple fruit
all individual fruits of an inflorescence fuse into one fruit
Classification of Fruit Types
several ways of grouping (classifying) fruits
dry
typically not eaten by
natural seed-distributing animals
dehiscent fruits
break open
release seeds
indehiscent fruits
do not break open to release seeds
fleshy
eaten
