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Chapter 9: Flowers and Reproduction - Coggle Diagram
Chapter 9: Flowers and Reproduction
Asexual Reproduction
fragmentation: most common asexual reproduction
in many cacti branches are poorly attached to trunk, encouraging fragmentation
large spreading/vining plant’s individual parts become self-sufficient by establishing adventitious roots
if middle portions of plant die ends separate & act as individuals
in some saxifrage/grass/pineapples plantlets formed where flowers would be expected
in willows/thistles adventitious shoot buds form roots & then grow into plants
may occur while parent plant is still alive, small cluster of trees might be one individual
look like small bulbs, called bulbils
Sexual Reproduction
Plant Life Cycle
all plants (trees,shrubs,herbs) in sporophyte phase
always diploid
have organs with cells capable of meiosis
results in haploid
spores
cannot undergo syngamy
each undergoes mitosis & grows into entire new haploid plant (
gametophyte
)
gametes are formed by haploid plants by mitosis
gametes undergo syngamy to form
zygote
, creates new diploid sporophyte
many plants
oogamous
have “male”
microgametophytes
form
microspores
have “female”
megagametophytes
form
megaspores
known as
heterospory
sperm produced by one type of individual, egg produced by another
aka sporophyte generation
when life cycle has 2 generations said to be
alternation of generations
gametophytes & sporophytes not similar, alternation of
heteromorphic generations
Flower Structure
pedicel:
flower stalk
receptacle:
end of axis, where flower parts attach
4 types of floral appendages
most flowers have all types,
complete flowers
some do not,
incomplete flowers
sepal
lowermost & outermost of floral appendages
modified leaves surround & enclose other flower parts as they mature
typically thickest/toughest/waxiest of flower parts
protect flower bud as it develops
all sepals together referred to as
calyx
petals
found on receptacle, make up the
corolla
sepals
&
petals
together make up
perianth
leaf-like, broad/flat/thin
but, contain pigments other than chlorophyll
have few/no fibers
tend to be thinner & more delicate
stamens
#essential organ
located above the petals
known collectively as
androecium
often referred to as “male” part of flower due to pollen production
technically untrue bc flower is part of sporophyte & only does not have a sex
2 parts
filament:
stalk
anther:
where pollen is actually produced
composed of diploid cells
4 long columns of tissue become distinct as they prepare for meiosis
called microspore mother cells or
microsporocytes
continue to enlarge & undergo meiosis each producing 4 microspores
microspores separate & form into
pollen
neighboring
tapetum
cells act as nurse cells
carpels:
constitute
gynoecium
located @ highest level on receptacle
#essential organ
3 main parts
stigma:
catches pollen grauns
style:
elevates stigma
ovary:
megaspores produced here
contained
placentae
which bear
ovules
ovule has central mass of parenchyma called
nucellus
Gametophytes
microgametophytes
develop from microspores
microspore nucleus divides mitotically producing large
vegetative cell
& small
generative cell
generative cell divides to form two sperm cells
microgametophyte consists of vegetative cell & sperm cells (
microgametes
)
walls form around nuclei & megaspore becomes megagametophyte with 7 cells, one binucleate
7 cells
1 large
central cell
w/ 2
polar nuclei
3 small
antipodal cells
1
egg apparatus
consisting of 2 synergids & egg (
megagamete
)
as pollen lands on stigma it produces
pollen tube
to penetrate stigma
grows downward & is nourished/protected by style tissue
sperm cells carried to ovule by tube
megagametophytes
develop from megaspore
multinucleate megagametophyte known as
embryo sac
nuclei migrate thru cytoplasm pulled by microtubules until 3 lie at each end & 2 in the center
Fertilization
involves 2 processes
plasmogamy:
fusion of protoplasts of gametes
karyogamy:
fusion of nuclei
pollen tube grows downward thru style towards ovule, guided to micropyle
penetrates nucellus & reaches egg apparatus, enters one synergid
pollen tube tip bursts releasing 2 sperm cells
1 sperm migrates thru synergid protoplasm towards egg
sperm cell’s plasma membrane breaks down & loses most of protoplasm
sperm nucleus enters egg, fuses with egg nucleus creating diploid zygote nucleus
in angiosperms only, 2nd sperm nucleus migrated to central cell to undergo
karyogamy
w/ both
polar nuclei
establishes large
endosperm nucleus
(
triploid
)
known as
double fertilization
Embryo and Seed Development
zygote begins to divide by nuclear & cellular division
grows into small cluster of cells, part becoming
embryo
the other becoming
suspensor
cells at one end of suspensor divide mitotically developing into embryo
first arranged as small sphere, known as
globular stage
in
torpedo stage
embryo is elongate cylinder
short axis is established
consists of
radicle
,
epicotyl
, &
hypocotyl
mature embryo becomes quiescent & partially dehydrates
funiculus may break leaving
hilum
scar
other end intimated 2 primordia that grow into
2 cotyledons
in basal angiosperms & eudicots
give embryo a heart shape, called
heart stage
dicots only
1
cotyledon primordia grows out
short stalk-like structure, pushes embryo deep into endosperm
co-enocytic
stage never occurs in embryo
in monocots:
during germination cotyledon acts as digestive/absorptive tissue
albuminous seed
in (most) eudicots:
cotyledons store nutrients used during & after germination
exalbuminous seed
Fruit Development
ovary matures into
fruit
3 layers distinct during growth
exocarp
outer layer (skin/peel)
mesocarp
middle layer (flesh)
endocarp
innermost layer (pit/stone)
entire fruit wall:
pericarp
#called pericarp regardless of origin of tissue
stigma, style, sepals, petals, & stamens wither away
Flower Structure & Cross-Pollination
Cross-Pollination
pollination of carpal by pollen from different individual
creates new combinations of genes
self-pollination:
pollination if carpal by pollen from same plant
#form of asexual reporduction
same as asexual reproduction
allows plant to propagate genes rather than lose them
Stamen & Style Maturation Times
anthers release pollen while stigma tissues still immature
anther at top of flower while stigma near base
when stigma & style mature may be no living pollen left
Stigma & Pollen Incompatibility
self-pollination inhibited by
compatibility barrier
one system as pollen tube grows stigma&style test proteins on tube’s surface
if protein produced by incompatible gene then stigma/style block growth
chemical reaction between pollen & carpels to prevent pollen growth
Monoecious& Dioecious Species
flowers lacking either/both stamens/carpels known as
imperfect flowers
stamen/carpels
essential organ
known as
perfect flower
if it has both
sepals/petals considered
nonessential organs
dioecy:
species with separate staminate/carpellate individuals
monoecy:
species with individuals having both staminate/carpellate
Animal-Pollinated Flowers
changed the pollination game
many plants/pollinators underwent
coevolution
plants became more distinct to ensure pollinators deposited pollen on correct species
actinomorphic:
radially symmetrical flowers
zygomorphic:
bilaterally symmetrical flowers
Wind-Pollinated Flowers
sepals often reduced/absent
zygomorphy provides no advantage
huge number of pollen needed to increase chances of success
Ovary Position
flower must protect ovules/ovary from pollinators
long styles/filaments adaptation to separate
inferior ovary:
ovary located below organs protected by thick layer of tissue
epigynous
flower parts
superior ovary:
ovary obviously other flower parts, no fusion
hypogynous
flower parts
half-inferior ovary:
partially buried ovary
perigynous
flower parts
Inflorescences & Pollination
Inflorescence:
many flowers grouped together
helps small flowers be seen
plant able to accurately control timing of initiation/maturation/opening of flowers
produces enough nectar to get pollinators to visit other plant
2 basic arrangements:
determinate inflorescence:
only has limited potential for growth bc apex is converted to flower
usually terminal flower opens first, then lower ones successively
indeterminate inflorescence:
lowest open first, new flowers still being insisted at apex
Fruit Types & Seed Dispersal
True Fruits & Accessory Fruits
pericarp
tissues of fruit regardless of origin
true fruit:
fruits containing only ovarian tissue
accessory fruit:
fruit w/ any nonovarian tissue present
also called
false fruit
, apples mainly composed of sepals&petals
simple fruit:
developed from single ovary/fused ovary if one flower
aggregate fruit:
separate carpels of one gynoecium fuse during development
multiple fruit:
in development all individual fruits of inflorescence fuse into one
Classification & Fruit Types
dry:
not one typically eaten by natural seed-distributing animals
fleshy:
usually eaten during natural seed distribution process
most fleshy fruits indehiscent
dehiscent fruits:
break open & release seeds
indehiscent fruits:
do not break open & release seeds
fruits/seeds carried by wind must be light
often have wings or parachutes
