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Chapter 9: Flowers and Reproduction (Flower Structure and Cross…
Chapter 9: Flowers and Reproduction
Asexual Reproduction
fragmentation
large spreading or vining plant grows
7 meters in length
individual parts self sufficient
adventitious roots
modifications improve efficiency
cacti
branches poorly attatched and break off
broken parts form roots
saxifrage, grass, pineapple
plantlets formed where flowers expected
bulbis
willows, thistles
adventitious roots grow out while parent alive
Sexual Reproduction
The Plant Life Cycle
gametes
sperm
egg
together form fertilized egg
zygote
new diploid individual
resembles parents
sygamy or fertilization
two types
sperm cells
microgametes
microgametophytes
microspores
males
large eggs
megagametes
megametophytes
megaspores
females
one phase of life cycle
sporophyte phase
trees, shrubs, and herbs
always diploid
meiosis
haploid spores
#
mitosis
gametophyte
two generations
sporophyte and gametophyte
alteration of generations
heteromorphic
Flower Structure
complete flowers have 4 parts
Petals
sepals on the receptacle
make up corolla
sepals + petals=
perianth
leaf like
broad
flat
thin
more delicate
pigments than than chlorophyll
absorb ultraviolet lights
only insects can see
few to no fibers
attract the correct pollinators
use specific size, shape, color, arrangment
Stamens
above petals
male part of the plant
produce pollen
technically not male
part of sporophyte
produce spores
not gametes
two parts
filament
stalk
anther
pollen produced
composed of diploid cells
four columns of tissue
microspore mother cells
microsporocytes
enlarge, undergo mitosis
microspores
2 more items...
neighboring anther cells
tapetum
1 more item...
Carpels
constitute the gynoecium
located at the highest level on a receptacle
three main parts
stigma
catches pollen grains
style
elevates the stigma to useful position
ovary
megaspores produced here
fused together into single compound structure
pistil
inside ovary
placentae
regions of tissue
bears ovules
short stalk
funiculus
cariries water and nutrients from placenta to ovule
central mass
nucellus
megaspore mother cells or megasporocytes
develops into seed after fertilization
Sepals
lowermost and outermost floral appendage
modified leaves
surround and enclose flower parts as mature
thickest, toughest, waxiest
protect bud
sepals together
calyx
Pedicel
flower stalk
receptacle
flower parts attached
incomplete flowers
lack 1-4 basic floral appendages
Begonia
lack petals
have either stamens or carpels
Pigweed
all parts but petals
Gametophytes
#
mirogametophyte
developed from microspores
anginosperms
three cells located w/in original pollen wall nucleus migrates t side of pollen grains and lie next to wall
divides mitotically
vegetative cell
generative cell
two sperm cells
consists of vegetative cells and two sperm cells
full fledged plant
in 30% of angiosperms
formation of sperm cells occurs while pollen located in anther
pollen released from anther @ time generation cell has formed
majority angiosperms
pollen released from anther @ same time of generative cell has formed
sperm cells are not produced until after pollen carried to the sigma
germinates into the pollen tube
penetrates tissues of stigma
tube absorbs nutrients from stigma and grows downward from style to ovary
megagametophyte
within ovule
megaspore develops into megagametophyte
emryosac
multinucleate
three mitotic divisions
2,4,8 haploid nuclei in single cell
nuclei migrates through cytoplasm
pulled by microtubules
3 nuclei @ ends
two in center
walls form around nuclei
1 more item...
Fertilization
syngamy of sperm and egg
plasmogamy
fission of the protoplasts of gametes
karyogamy
#
fusion of the nuclei
pollen grows down through style
penetrates nucellus
reaches egg apparatus
enters one synergid
pollen tube tip bursts
releases sperm cells
one migrates through synergid to egg
sperm plasma membrane breaks down
3 more items...
angiosperms only second sperm nucleus release
2 more items...
Embryo and Seed Development
nucleus proliferates
zygote begins to grow
nuclear and cellular divisions
co-enocytic stage never occurs in embryo
zygote grows into snall cluster of cells
embryo proper
suspensor
short-stalk like structure
pushes embryo deep into endosperm
delicate and ephemeral in agiosperms
crushed by embryo growth
not easily detectable in mature seed
cells at one end continue dividing mitotically
develops into embryo
cells first arranged in small sphere
1 more item...
torpedo stage
1 more item...
end further from suspensor initiates two primordia
two cotledons
1 more item...
Fruit Development
ovule develops into seed
ovary matures into fruit
stigma and style usually wilt away
sepals, petals, stamens wither away
persist temporarily
three distinct layers during growth
exocarp
skin or peel
mesocarp
middle layer or flesh
endocarp
innermost layer
tough like stone or pit or thin
layers of fruit
#
pericarp
Flower Structure and Cross Pollination
Cross-Pollination
pollination of a carpel by pollen from diff individual
Self pollination
pollination of carpel by pollen from same flower or another on same plant
all alleles come from same parent
no possibility for new alleles
plant isolated by distance allows for set seed s and propagate its genes
genetic diversity
random mutations produce new versions of genes
allele
fitness
deleterious
sperm cells and egg cells from diff plants unite
new combinations of genes
few better adapted than parent
Stamen and Style Maturation Times
self fertilization in flowers that have stamens and carpels is prevented if anthers and stigmas mature @ diff times
anthers release pollen while stigma tissues are immature and unreceptive
style may not be elongated
stigmas may be near the base of the flower while anthers are @ top
elevated by elongated filaments
exposed pollen lives only briefly being susceptible to desiccation
in dry air
damage to DNA UV light
stigma and style mature
may be no living pollen left in the flower
pollination effected by younger flowers just opening anthers
not effective
Stigma and Pollen Incompatibility
compatibility barriers
inhibit self-pollination
chemical reactions between pollen and carpels prevent pollen growth
one incompatibility system
pollen tube grows
stigma and style test proteins on tubes surface
if protein produced by gene in carpel-bearing plant
stigma and style block growth of pollen tube
plant cannot pollinate itself
one system
critical proteins are deposited on outer surface of the developing pollen grain by anther tapetum
pollen tube and style involves haploid genome and diploid one
haploid pollen tube
diploid carpel
incompatibility genes blocks germination of pollen grain
second system
involves two diploid genomes (anther and carpel)
involves twice as many genes
has much greater probability of pollen rejection
self pollination is prevented
inbreeding relatives blocked
Monoecious and Dioecious Species
essential organs
latter two organs
produce critically important spores
if either organ is absent
flowers lack either or both essential organs
incomplete
imperfect flowers
has both organs
perfect flower
can lack sepals or petals or both
don't produce spores
nonessential organs
sexual reproduction is dramatically affected
dioecy
have individuals that produce only staminate flowers and others that produce only carpellate flowers
species is diecious
examples
marjiuana
dates
willows
papaya
four types of plants
microgametophytes
megagametophytes
staminate sporophytes
carpellate sporophytes
extreme adaptation that ensures cross pollination
#
monoecy
having staminate flowers located on the same plant as carpellate flowers
monoecious
examples
cattails
corn
Animal-Pollinated Flowers
dramatic impact of the evolution of flowering plants
increase probability of pollen grain reaching a stigma
association began 120 million years ago
coevolution
flowers adapted for visitation by particular insect, birds, bats
shape flower important
radically symmetrical
actinomorphic or regular
bilaterally symmetrical
zygomorphic flower
one orientation is comfortable for pollinator
allows pollen to attach to head
must prevent harm from animals
mutations prevent plants to make more effective deterrents
nectar robbing
both plant and animal benefit
Winded-Pollinated Flowers
adaptive modifications
attracting pollinators unneccesary
mutations prevent petal advantageous
sepals absent, ovaries need no protection
save energy
huge numbers of pollen grains must be produced
large feathery stigmas are adaptive
increase area that can catch pollen grains
plants grow in dense populations
Ovary Position
must be protected from pollinators
adaptations that maximize separation are long styles and stamen filaments
burry ovaries deep w/in flower
for protection
some species
primordia initiated @ receptacle apex
primordia crowd together and bases of petals, stamens, sepals fuse
create thick protective layer of tissue
inferior ovary
epigynous
superior ovary
hypogynous
partially buried ovaries
hal-inferior
perigynous flower parts
Inflorescences and Pollination
many flowers grouped together give off inflorescence
collective visual signal to pollinators
plant can control
timing of initiation
maturation
opening of the flowers
arrangments
determinate
linited potential for growth
apex is converted into flower
terminal flower opens first
lower ones open successively
indeterminate
lowest or outermost flowers open first
new flowers are being initiated at apex
Fruit Types and Seed Dispersal
True Fruits and Accessory Fruits
pericarp
tissues of fruit
ovary wall
inferior ovaries receptacle tissues or sepal, petal, stamen tissues
become involved in the fruit
true fruits
fruits contain only ovarian tissue
accessory fruit
false fruit
used if noovarian tissue present
apples
simple fruit
fruit develops from single ovary or fused ovaries of one flower
most common
aggregate fruit
separate carpels of one gynoecium fuse during development
multiple fruit
individual fruits of an inflorescence fuse into one fruit
ex: figs, pineapples, mulberries
Classification of Fruit Types
fleshy
berry
fleshy fruit w/3 layers
grape, tomato
pome
similar to berry
endocarp papery or leathery
apple
drupe
similar
endocarp hard, sclerenchymatous
peach, cherry, plum
pepo
fleshy fruit w/exocarp tough
hard rind
soft inner issues
pumpkin,squash, cantelope
hespermidium
exocarp leathery
citrius
dry
indehiscent fruits
since carpel
caryopsis
simple small
contain one seed
testa fuses withfruit wall during maturation
ex: grasses: wheat, corn, oats
samara
one-seeded fruit w/winglike outgrowths of the ovary wall
maples, adler, ash
achene
like a caryopsis
seed and fruit remain distinct
fruit wall thin and papery
sunflowers
compound gnoecium
nut
pericarp is hard at maturity
walnut
all but one ovule degenerates during development
single carpal
developing from a single carpellegume
fruit breaks open along both sides
beans, peas
follicle
breaks open only one side
columbine, milkweed
compound gnoecium
capsule
opens many ways
splitting along lines of fusion
hyperium
spiltting between lines of fusion
iris
splitting into top and bottom half
primose
opening by small pores
poppy
schizocarp
compound ovary breaks into individual carpels called mericarps
compound
aggregate fruits
carpels of flower not fused
grow together during maturation
rasberry
multiple fruit
all fruits of an inflorescence grow together during maturation
pineapple
agents of dispersal
animals
attached to animal
epizoochory
eaten by animal
endozoochory
birds
ornithochory
mammals
mammaliochory
bats
chiropterochory
ants
myrmecochory
wind
anemochory
water
hydochory
dispersed by the plant itself
autochory
